Real-world examples
Named cases you can use in an answer, each under the syllabus point it illustrates and linked to the lesson it comes from.
1 Foundation
1.1 Perspectives
1.1.6Worldviews are the lenses shared by groups of people through which they perceive, make sense of and act within their environment. They shape people’s values and perspectives through culture, philosophy, ideology, religion and politics.
Aboriginal Australians' traditional fire (cultural burning) management and indigenous Amazonian agroforestry view humans as part of nature with a responsibility to maintain ecological balance rather than to control resources.
Shows how culture and belief systems shape an environmental worldview in which humans are interdependent with, not separate from, nature.
Australia Environmental worldviews
1.1.8Environmental perspectives (worldviews) can be classified into the broad categories of technocentric, anthropocentric and ecocentric.
New Zealand granted legal personhood to the Whanganui River in 2017, giving the river its own legal rights and guardians, a policy that treats ecosystem health as intrinsically valuable rather than a resource for human use.
Demonstrates an ecocentric worldview by prioritising the rights of nature over economic growth or human expansion.
Whanganui River, New Zealand Environmental worldviewsProposed stratospheric sulfur-aerosol injection and ocean iron fertilisation are geoengineering schemes intended to cool the planet and boost carbon absorption through large-scale technological intervention in the climate system.
Shows a technocentric worldview built on confidence that human ingenuity and engineering can solve environmental problems.
1.2 Systems
1.2.4Flows are processes that may be either transfers or transformations.
Inside Biosphere 2 the crew lost about seven tonnes of oxygen, with levels falling from 21% to 14.2%, because excess soil compost was decomposed by microbes that consumed O₂ and released CO₂, which was then chemically transformed as it reacted into the concrete of the structure.
Shows a transformation (change of form) as decomposition converts organic carbon and O₂ into CO₂ which is then fixed into concrete, altering the system's atmospheric balance.
Biosphere 2, Oracle, Arizona, USA Systems and systems diagrams
1.2.5Systems can be open or closed.
Biosphere 2, a three-acre sealed glass-and-steel structure in Arizona, housed eight people for two years (1991–1993) as a materially closed but energetically open system: no matter entered or left, but solar energy passed through, mirroring how Earth's biosphere operates.
Demonstrates the definition of a closed system as one that exchanges energy but not matter with its surroundings, at an engineered whole-system scale.
Biosphere 2, Oracle, Arizona, USA Systems and systems diagramsThe global hydrological cycle behaves as a closed system: solar energy enters and heat is radiated back to space, but the total mass of water stays essentially constant, simply cycling between oceans, atmosphere, ice caps and groundwater without meaningful exchange with space.
Contrasts a closed system (energy in/out, matter conserved) with an open drainage basin, clarifying the matter-versus-energy distinction at planetary scale.
1.2.8Negative feedback loops occur when the output of a process inhibits or reverses the operation of the same process in such a way as to reduce change. They are stabilising as they counteract deviation.
Lovelock and Watson's Daisyworld model shows black and white daisies self-regulating a planet's temperature: as the star warms, heat-absorbing black daisies decline and reflective white daisies spread, cooling the surface and holding global temperature near an optimum despite changing solar output.
Demonstrates how negative feedback from the biota maintains a planet in stable equilibrium, in contrast to a lifeless world.
The lynx and snowshoe hare population cycle in the boreal forests of Canada: when hares are abundant lynx numbers rise, increased predation crashes the hare population, lynx then starve and decline, allowing hares to recover — producing regular oscillations around a long-term equilibrium.
Demonstrates how predator-prey negative feedback counteracts deviation to maintain a steady-state equilibrium over time.
Canada Feedback loops
1.2.9As an open system, an ecosystem will normally exist in a stable equilibrium, either in a steady-state equilibrium or in one developing over time (for example, succession), and will be maintained by stabilising negative feedback loops.
The reintroduction of grey wolves to Yellowstone National Park in 1995 triggered a trophic cascade: wolves reduced elk browsing, allowing willows and aspen to recover, which stabilised riverbanks and changed river courses, shifting the ecosystem toward a new, more resilient equilibrium.
Shows how feedback following a species reintroduction can move a system into an alternative stable state.
Yellowstone National Park, USA Feedback loops
1.2.10Positive feedback loops occur when a disturbance leads to an amplification of that disturbance, destabilizing the system and driving it away from its equilibrium.
Forest removal and erosion: clearing forest exposes soil to erosion that strips organic matter and nutrients, leaving fewer plants to anchor the soil, which in turn accelerates further erosion — a harmful, self-amplifying positive feedback that degrades the ecosystem.
Demonstrates a destabilising positive feedback driving a system away from equilibrium toward a degraded new state.
The ice-albedo feedback: as Arctic sea ice melts, dark ocean replaces reflective white ice, lowering albedo so more solar radiation is absorbed, which warms the region and melts still more ice — an amplifying loop that can drive the climate towards a tipping point.
Shows positive feedback causing exponential deviation from equilibrium that can push the system past a tipping point into a new state.
Arctic Ocean Feedback loops
1.2.13A model is a simplified representation of reality; it can be used to understand how a system works and to predict how it will respond to change.
James Lovelock's Gaia hypothesis, named in 1965 with novelist William Golding, models Earth as a self-regulating system in which ocean algae emit gases that seed reflective clouds (keeping Earth ~10°C cooler) and made ten predictions that later came true.
Shows how a systems model can be used to make testable predictions about the outcome of events, such as biologically mediated temperature regulation.
1.2.14Simplification of a model involves approximation and, therefore, loss of accuracy.
The Anthropocene Working Group proposed sediment from Crawford Lake, Ontario — a meromictic lake ~270 m across and 23 m deep with undisturbed annual layers recording a ~1950 plutonium spike from hydrogen-bomb tests — as the 'golden spike', but the International Commission on Stratigraphy rejected it in 2023 as too brief (under 70 years) to model in geologic time.
Demonstrates that models of a system have limitations: stratigraphic tools built for deep time struggle to represent recent, rapid human impact.
Crawford Lake, Ontario, Canada Systems and systems diagrams
1.2.17Diversity and the size of storages within systems can contribute to their resilience and affect their speed of response to change (time lags).
Pacific Northwest old-growth forests store 400–1,200 tonnes of carbon per hectare, and this large nutrient and biomass store is released slowly during drought years, allowing trees to survive months without rainfall.
Quantifies how a large storage creates a delayed, buffered output that sustains system function through periods of low input.
Pacific Northwest, USA System resilienceThe Pacific Ocean's massive thermal mass takes decades to centuries for deep water temperatures to change significantly, so El Niño/La Niña cycles reveal a large time lag between climate forcing and ocean response, unlike small lakes that shift temperature rapidly with weather.
Demonstrates how a large storage introduces a long time lag between inputs and outputs, buffering the system against rapid change.
Pacific Ocean System resilience
1.3 Sustainability
1.3.1Sustainability is a measure of the extent to which practices allow for the long-term viability of a system. It is generally used to refer to the responsible maintenance of socio-ecological systems such that there is no diminishment of conditions for future generations.
The 2014 Lake Erie cyanobacterial bloom, driven largely by agricultural phosphorus and nitrogen runoff, produced the toxin microcystin that shut off drinking water for around 500,000 people in Toledo, Ohio for three days.
Demonstrates how an imbalance between nutrient inputs and a system's outputs pushes eutrophication past a tipping point, undermining sustainability.
Lake Erie, USA System resilienceThe Irish Potato Famine (1845–1852) struck because a single potato variety, the Lumper, was grown across Ireland, so late blight wiped out the entire crop and caused mass starvation, whereas Peru's cultivation of over 3,000 potato varieties buffers against any single disease.
Shows how low genetic diversity destroys resilience while high diversity maintains a stable relationship between food inputs and outputs.
Ireland System resilience
1.3.8Common indicators of economic development, such as gross domestic product (GDP), neglect the value of natural systems and may lead to unsustainable development.
GDP excludes environmental costs such as pollution and unpaid work, prompting the Green GDP concept that subtracts the value of environmental degradation from GDP so that a country with heavily polluting factories records a lower Green GDP.
Shows how conventional economic indicators fail to capture the poorly understood links between Earth systems and economic activity, requiring adjusted metrics.
1.3.13The concept of ecological footprints can be used to measure sustainability. If these footprints are greater than the area or resources available to the population, this indicates unsustainability.
A single BLT sandwich carries an embedded footprint of ~800 g CO₂ equivalent — the fertiliser for the bread and especially the four strips of bacon dominate — so eating one daily for a year equals the emissions of driving a car from New York to Chicago.
Demonstrates how the resources and waste absorption behind everyday consumption accumulate, making an ecological footprint concrete at the individual scale.
Amsterdam became the first city to downscale the Doughnut Economics model in 2020 (with Circle Economy), adopting it to guide its ambition of becoming a fully circular city by 2050 and to account for its overseas impacts, such as on garment workers in Bangladesh.
Shows a more-developed city acting to bring its consumption back within planetary boundaries, as required of high-income nations with the greatest obligation to transform.
Amsterdam, Netherlands ModelsCalifornia's Central Valley almond groves are flood-irrigated several times each season, giving high water footprints of ~1 gallon per almond, ~5 gallons per walnut, ~14 per orange and up to 60 gallons per avocado, in a state where ~80% of US water use goes to agriculture.
Shows how the land and water required to supply a population's food is measurable and location-specific, a core component of the ecological footprint.
Central Valley, California, USA Measuring sustainabilityCosta Rica launched the 'Regenerate Costa Rica' initiative using the Doughnut Economics framework, aiming to become one of the world's first regenerative nations.
Shows a national-scale attempt to redesign the economy to operate within Earth-system capacity through regenerative and distributive design.
Costa Rica Models
1.3.14The carbon footprint measures the amount of greenhouse gases (GHGs) produced, measured in carbon dioxide equivalents (in tonnes). The water footprint measures water use (in cubic metres per year).
StatisticPer-capita CO₂ production emissions vary starkly: the USA emits ~16.1 tonnes per person per year, China ~7.1 tonnes, the UK ~5.5 tonnes, the DR Congo only ~0.03 tonnes, and oil-and-gas-rich Qatar ~38.6 tonnes.
Quantifies how unevenly humanity draws down the atmosphere's carbon-absorbing capacity, showing that climate debt is driven overwhelmingly by wealthy, high-consumption nations.
1.3.15Biocapacity is the capacity of a given biologically productive area to generate an ongoing supply of renewable resources and to absorb its resulting wastes.
The ecological footprint, measured in global hectares per person, reveals ecological overshoot when a region's footprint exceeds its available biocapacity, meaning resources are consumed faster than ecosystems can regenerate them.
Quantifies how Earth's finite biocapacity imposes measurable limits on resource use and flags unsustainable consumption.
1.3.17There are a range of frameworks and models that support our understanding of sustainability, each with uses and limitations.
Kate Raworth's Doughnut Economics model (first published 2012) frames a 'safe and just space for humanity' between a social foundation (based on the social SDGs) and an ecological ceiling (based on the nine planetary boundaries), redefining sustainability as thriving in balance rather than endless GDP growth.
Demonstrates an alternative interpretation of sustainability that integrates both social justice and ecological limits, contrasting with growth-based definitions.
The 2025 Planetary Health Check by the Potsdam Institute's Planetary Boundary Science Lab reported that seven of the nine planetary boundaries have now been breached, with ocean acidification the latest as surface ocean pH has fallen ~0.1 units (a 30–40% rise in acidity) since the industrial era.
Provides a science-based interpretation of sustainability as staying within quantified Earth-system limits, and quantifies the extent of overshoot.
Potsdam, Germany Models
1.3.18The UN Sustainable Development Goals (SDGs) are a set of social and environmental goals and targets to guide action on sustainability and environmental justice.
In 2015 UN member states adopted the 2030 Agenda's 17 Sustainable Development Goals with 169 targets; at the 2023 halfway point only 15% of targets were on track and over a third had stagnated or regressed, with more than 780 million people facing chronic hunger.
Demonstrates the SDG framework as a concrete global sustainability agenda while quantifying its limited progress against both social foundation and planetary-boundary targets.
1.3.19The planetary boundaries model describes the nine processes and systems that have regulated the stability and resilience of the Earth system in the Holocene epoch. The model also identifies the limits of human disturbance to those systems, and proposes that crossing those limits increases the risk of abrupt and irreversible changes to Earth systems.
IKEA, in partnership with WWF, sources acacia timber from FSC-certified plantations grown with smallholder farmers to allow forest regeneration and support local communities.
Illustrates operating within the land-system-change and biosphere-integrity boundaries by managing a renewable resource at its replacement rate.
1.3.20The doughnut economics model is a framework for creating a regenerative and distributive economy in order to meet the needs of all people within the means of the planet.
MUD Jeans in Amsterdam leases jeans rather than selling them, returning worn pairs to be shredded and remanufactured into new denim in Prato, Italy; the EU circular-economy package projected 2 million new jobs and €600 billion in business savings.
Shows how the doughnut model's economic redesign can decouple prosperity from resource depletion while staying within planetary limits and meeting social needs.
Amsterdam, Netherlands SustainabilitySouth Africa's 1996 Constitution was the first in the world to explicitly recognise the right to a healthy environment as a basic human right, implemented via the National Environmental Management Act (NEMA), which mandates public participation and environmental impact assessments before development is approved.
Demonstrates how legal structures deliver social-foundation goals such as equity, health and political voice by empowering communities to hold polluters accountable.
South Africa Sustainability
2 Ecology
2.1 Individuals, populations, communities, and ecosystems
2.1.2An individual organism is a member of a species.
A zebra and a horse can interbreed to produce a zebroid, but the zebroid is sterile and cannot itself reproduce, so zebra and horse are not the same species under the fertile-offspring definition.
Demonstrates the biological species concept by showing that producing offspring is insufficient — fertility of the offspring is the decisive criterion for species membership.
2.1.3Classification of organisms allows for efficient identification and prediction of characteristics.
Carl Linnaeus (Swedish botanist, b. 1707) devised binomial nomenclature and the taxa kingdom–phylum–class–order–family–genus–species in Systema Naturae, cataloguing roughly 7,700 plants and 4,400 animals using morphology-based homologous traits.
Shows how a standardised hierarchical classification system enables efficient identification and prediction of shared characteristics across the ~2 million known species.
Uppsala University, Sweden IndividualsThe domestic cat is classified Animalia > Chordata > Mammalia > Carnivora > Felidae > Felis > catus, with each rank defined by predictive traits (vertebral column, lactation and three ear bones, retractable claws), giving the binomial Felis catus.
Demonstrates how following an organism down the taxonomic hierarchy allows prediction of characteristics and reveals it is more closely related to a cow than a chicken.
2.1.4Taxonomists use a variety of tools to identify an organism.
Modern taxonomists use genetic testing (e.g. RNA polymerase similarity showing Archaea are more closely related to Eukarya than to Bacteria) alongside Linnaeus's morphology-based methods, and this molecular evidence largely agrees with classifications based on structure and form.
Shows the variety of tools taxonomists deploy, contrasting traditional morphological keys with genetic analysis that resolved the three-domain system.
2.1.5A population is a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.
Humpback whales are divided into 14 distinct population segments worldwide, of which four are classified as endangered, illustrating spatially separated groups of the same species.
Demonstrates that a species can comprise multiple distinct populations defined by area and interbreeding.
2.1.8A niche describes the particular set of abiotic and biotic conditions and resources upon which an organism or a population depends.
In European deciduous forests the Great Spotted Woodpecker (Dendrocopos major) deep-excavates wood-boring beetle larvae from main trunks (2–10 cm depth, foraging upward), while the Eurasian Nuthatch (Sitta europaea) gleans the surface (0–2 cm) foraging headfirst downward and caches seeds, partitioning the same trees to reduce interspecific competition.
Shows how two species occupy distinct niches through different foraging depths, techniques and diets despite sharing habitat.
2.1.9Populations interact in ecosystems by herbivory, predation, parasitism, mutualism, disease and competition, with ecological, behavioural and evolutionary consequences.
In British deciduous forests, introduced grey squirrels outcompete native red squirrels, leading to competitive exclusion and local extinction of red squirrels, with niche partitioning only where coexistence occurs.
Shows interspecific competition producing competitive exclusion and evolutionary/behavioural consequences like niche differentiation.
United Kingdom PopulationsWhite-nose syndrome, a fungal disease (*Pseudogymnoascus destructans*), has caused population crashes of over 90% mortality in North American bat populations, driving some colonies to local extinction and disrupting ecosystem services such as insect control.
Demonstrates disease as a population interaction with dramatic density-dependent mortality and cascading ecological consequences.
North America Populations
2.1.10Carrying capacity is the maximum size of a population determined by competition for limited resources.
On St. Matthew Island the reindeer population overshot carrying capacity because a 2–3 year time lag masked lichen depletion; overgrazing reduced future carrying capacity so slowly-regenerating lichen could never again support even a small herd.
Shows how competition for a single limiting resource (lichen) sets carrying capacity and how overshoot permanently degrades it.
St. Matthew Island, Alaska, USA Population Size
2.1.11Population size is regulated by density-dependent factors and negative feedback mechanisms.
On St. Matthew Island the 1963–64 crash was driven by density-dependent starvation: at peak density (18.1 reindeer per km²) the depleted lichen could not feed the herd, causing mass die-off evidenced by bone marrow depletion and declining body weights.
Demonstrates a density-dependent factor (food scarcity intensifying with density) driving negative feedback on population size.
St. Matthew Island, Alaska, USA Population Size
2.1.12Population growth can either be exponential or limited by carrying capacity.
In 1944 the US Coast Guard introduced 29 reindeer to St. Matthew Island (332 km²) in the Bering Sea, Alaska; with abundant lichen and no predators the herd irrupted to about 6,000 by 1963, overgrazed the lichen mat from 100 mm to under 25 mm, then crashed to just 42 animals after the severe winter of 1963–64 and went extinct by the 1980s.
Demonstrates a J-curve exponential growth followed by overshoot and crash rather than an S-curve stabilising at carrying capacity.
St. Matthew Island, Alaska, USA Population Size
2.1.15Population abundance can be estimated using random sampling, systematic sampling or transect sampling.
A transect laid at 1 m intervals away from a field gate showed daisy density per m² rising with distance from the gate, attributed to reduced trampling (a biotic factor) further from the entrance.
Demonstrates transect sampling revealing how abundance changes along an environmental gradient caused by a specific pressure.
2.1.16Random quadrat sampling can be used to estimate population size for non-mobile organisms.
Dr Acton measured a field as ~620 m², used a random number generator to place a 1 m² quadrat at 10 coordinates, counted Bellis perennis (daisies) to find a mean of 7 per m², then multiplied by 620 to estimate a total population of 4,340 daisies.
Shows random quadrat sampling used to estimate the population size of a non-mobile organism by scaling mean density up to total area.
2.1.17Capture–mark–release–recapture and the Lincoln index can be used to estimate population size for mobile organisms.
In an ant colony study, researchers vacuumed and counted 300 surface foragers, marked them with fluorescent printer's ink diluted in ether, then 24 hours later recaptured 300 ants of which ~150 (50%) were marked, giving a Lincoln index estimate of (300×300)/150 ≈ 600 foragers.
Demonstrates capture-mark-release-recapture and the Lincoln index applied to a real mobile-organism population, showing both the marking method and the (M×N)/R calculation.
2.1.21Sustainability is a natural property of ecosystems.
StudyA 2024 PLOS Climate study of California kelp (1910–2016) found central California, where ~3,000 southern sea otters survived, expanded its kelp canopy and withstood the same disease, heatwave and El Niño that collapsed northern California, with otter density the strongest predictor of kelp change.
Demonstrates that intact keystone predation and functional redundancy confer the resilience that sustains an ecosystem through disturbance.
Central California coast, USA Communities and ecosystems
2.1.22Human activity can lead to tipping points in ecosystem stability.
Northern California's kelp forests lost over 95% of canopy across ~350 km of coast (2013–2025) after sea star wasting disease killed sunflower sea stars and the 2014–2016 'blob' marine heatwave and El Niño raised sea temperatures 2–3°C, letting purple urchins explode with no otters (extirpated in the 1800s fur trade) to check them.
Shows how loss of a keystone predator plus climatic stress pushed a resilient system past a tipping point into a near-irreversible urchin-barren state.
Mendocino County, California, USA Communities and ecosystems
2.1.23Keystone species have a role in the sustainability of ecosystems.
Sea otters are a keystone species in California's bull kelp forests: a single otter eats ~25% of its body weight (up to 15 lb) daily in sea urchins, and this top-down control of urchin grazers allows kelp forests supporting over 1,000 species to persist rather than collapse into urchin barrens.
Demonstrates how a species of low abundance exerts disproportionately large control over ecosystem structure and biodiversity via a trophic cascade.
Monterey Bay, California, USA Communities and ecosystems
2.1.24The planetary boundaries model indicates that changes to biosphere integrity have passed a critical threshold.
StatisticThe planetary boundaries model shows biosphere integrity has crossed a critical threshold, with current extinction rates running at 100–1000 times the natural background rate.
Quantifies the degree to which the biosphere-integrity boundary has been transgressed in the planetary boundaries framework.
2.1.25To avoid critical tipping points, loss of biosphere integrity needs to be reversed.
The River Otter Beaver Trial in Devon, England found that reintroducing beavers raised plant species richness by 28% and bird species by 26%, and tripled fish populations in some areas, while Scottish beaver populations now support over 30 specialist wetland plant species.
Shows how restoring a keystone ecosystem engineer reverses biodiversity loss and rebuilds biosphere integrity across multiple niches.
River Otter, Devon, England Communities and ecosystems
2.1.26There are advantages of using a method of classification that illustrates evolutionary relationships in a clade.HL
Cladistic analysis places crocodiles closer to birds than to lizards or snakes, uniting them as archosaurs sharing four-chambered hearts, nest-building and vocalisation, and reveals the traditional class 'Reptilia' to be paraphyletic because it excludes birds.
Shows how clade-based classification uncovers true evolutionary relationships and corrects misleading paraphyletic groupings.
2.1.27There are difficulties in classifying organisms into the traditional hierarchy of taxa.HL
The giant panda's 'thumb' looks like a human thumb but is actually a modified wrist (sesamoid) bone that evolved independently, and polar and brown bears interbreed to produce fertile 'pizzly'/'grolar' hybrids, showing gene flow across supposedly distinct species.
Illustrates how analogous traits and interbreeding make discrete traditional taxonomic boundaries difficult to define.
2.1.28The niche of a species can be defined as fundamental or realized.HL
Joseph Connell's 1961 study on Scottish rocky shores showed that Chthamalus stellatus has a fundamental niche spanning the upper and middle intertidal zones, but is competitively excluded from the middle zone by Semibalanus balanoides, restricting its realised niche to the upper zone; when Connell experimentally removed Semibalanus, Chthamalus colonised the middle zone.
Demonstrates experimentally that a species' realised niche is narrower than its fundamental niche due to competitive exclusion.
2.1.30Knowledge of species’ classifications, niche requirements and life cycles help us to understand the extent of human impacts upon them.HL
In the Netherlands, winter moth (Operophtera brumata) caterpillars evolved to hatch as oak buds burst, and great tits (Parus major) time breeding to peak caterpillar abundance; warming springs advance bud burst while great tit cues (day length) stay fixed, creating a phenological mismatch that reduces chick survival.
Shows how knowledge of synchronised life cycles reveals climate-change-driven phenological mismatch cascading through trophic levels.
Pied flycatchers (Ficedula hypoleuca) leave West African wintering grounds on a photoperiod cue that has not changed, yet spring caterpillar peaks in European breeding woodlands have shifted earlier with warming, so birds arrive too late for peak food, causing population declines across parts of Europe.
Demonstrates that species locked into fixed photoperiod cues cannot adjust migration timing to human-caused warming, exposing them to mismatch impacts.
2.2 Energy and biomass in ecosystems
2.2.1Ecosystems are sustained by supplies of energy and matter.
Coral reef ecosystems are sustained by dual inputs: solar energy captured by photosynthesising zooxanthellae living inside coral polyps, and matter delivered by ocean currents (dissolved nitrates, phosphates and minerals for skeleton formation), supporting biodiversity from plankton up to apex reef sharks — blocking the light or halting the nutrient flow degrades the whole system.
Shows how continuous, separate supplies of both energy and matter are jointly required to sustain a real ecosystem.
Great Barrier Reef, Australia EnergyOn Bear Island (Bjørnøya), Norway, at 74°N, Charles Elton conducted one of the first systematic food-web studies in 1921, mapping an Arctic community that links terrestrial, freshwater and marine subsystems — e.g. phytoplankton → zooplankton → Arctic cod → ringed seal → polar bear.
Shows how an ecosystem is sustained by energy and matter flowing through interconnected trophic relationships across sub-systems.
Bear Island (Bjørnøya), Norway Biomass and food websThe California kelp forest is sustained by giant kelp (Macrocystis pyrifera) with a net primary productivity of ~5,000 g dry mass m⁻² yr⁻¹, one of the highest on Earth, which feeds urchins, otters and detritus-based food chains alike.
Shows how a supply of energy captured by producers underpins an entire ecosystem and all its consumer pathways.
California kelp forest, USA Energy flows
2.2.6Cellular respiration releases energy from glucose by converting it into a chemical form that can easily be used in carrying out active processes within living cells.
A sprinting cheetah's muscle cells rapidly break down glucose via cellular respiration, converting stored chemical energy into ATP to power the active process of muscle contraction during the chase.
Shows respiration converting glucose into an immediately usable chemical form (ATP) to drive an active life process.
2.2.7Some of the chemical energy released during cellular respiration is transformed into heat.
In cellular respiration only about 38–40% of glucose's chemical energy is captured as usable ATP while the remaining ~60–62% is transformed into heat, which is why an exercising human gets hot and loses roughly 2,000–2,500 kcal of heat energy daily that must be replaced by eating.
Quantifies the fraction of respiratory energy converted irreversibly to heat and links it to daily food requirements.
Southern sea otters (Enhydra lutris nereis) lack blubber and have a field metabolic rate of ~687 kJ kg⁻¹ day⁻¹ (2–3× that of similar-sized land mammals), consuming 25% of their body mass daily so that most assimilated energy is lost as heat maintaining body temperature in cold water, giving an ecological efficiency of only ~5% from urchins to otters.
Demonstrates how chemical energy from respiration is transformed into heat, and why endotherms in cold environments show especially low ecological efficiency.
California kelp forest, USA Energy flowsStudyThe stick-insect and cabbage-white caterpillar (Pieris brassicae) experiments show consumers lose far more assimilated biomass to respiration than producers, because mobile animals expend energy on locomotion, foraging and (in homeotherms) maintaining body temperature.
Demonstrates that chemical energy released in respiration is transformed into heat, explaining high respiratory losses in consumers.
2.2.8The second law of thermodynamics states that energy transformations in ecosystems are inefficient.
An oak woodland receives 7,000,000 kJ/m²/yr of solar radiation but fixes only 42,000 kJ as GPP; of the 16,800 kJ NPP, just 1,680 kJ (10%) passes to herbivores and 168 kJ (10%) to primary carnivores, with ~89% of NPP passing to decomposers and most energy lost as heat.
Quantifies the inefficiency of energy transformations, giving ~10% trophic transfer efficiency and <1% photosynthetic efficiency.
In a North Atlantic marine ecosystem the pyramid of biomass is inverted — zooplankton (21.0 g m⁻²) exceeds phytoplankton (4.0 g m⁻²) — because fast-reproducing phytoplankton are grazed almost as fast as they grow, yet the corresponding pyramid of energy remains upright.
Counter-example showing biomass pyramids can invert while energy pyramids cannot, reinforcing the second law's constraint on energy flow.
North Atlantic Ocean Biomass and food websStudyIn a stick-insect feeding experiment, ten insects fed privet leaves assimilated 2.4 g (gross productivity) but gained only 0.3 g biomass, meaning 2.1 g — about 87.5% — was lost to cellular respiration.
Quantifies the inefficiency of energy transformation predicted by the second law, with most assimilated energy lost rather than stored as biomass.
In an African grassland food chain, grass captures ~10,000 kJ of solar energy, a zebra eating the grass obtains ~1,000 kJ (10%), and a lion eating the zebra obtains only ~100 kJ (10% again), with the rest lost as respiratory heat — explaining why vast grassland areas support only a few lions and why food chains rarely exceed four or five levels.
Demonstrates how repeated ~90% energy losses per transfer limit food-chain length and predator abundance.
In the California giant kelp (Macrocystis pyrifera) forest food chain, energy flow falls from 50,000 kJ m⁻² yr⁻¹ in kelp to 4,000 kJ m⁻² yr⁻¹ in purple sea urchins (Strongylocentrotus purpuratus) to just 200 kJ m⁻² yr⁻¹ in southern sea otters (Enhydra lutris nereis), giving an overall efficiency of only 0.4% from producer to secondary consumer.
Quantifies the second law's inefficiency of energy transfer with real trophic-level energy values, showing losses well below and above the 10% approximation.
California kelp forest, USA Energy flows
2.2.18Pollutants that are non-biodegradable, such as polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT) and mercury, cause changes to ecosystems through the processes of bioaccumulation and biomagnification.
The Minamata Bay disaster (Japan, discovered 1956): the Chisso Corporation discharged mercury-laden wastewater which bacteria converted to methylmercury; it biomagnified from 0.000003 ppm in seawater to ~200 ppm in fish-eating birds (a ~67-million-fold increase), causing over 1,500 deaths and thousands of cases of severe neurological damage in people who ate contaminated fish.
Demonstrates how a non-biodegradable, lipophilic pollutant (mercury) bioaccumulates in fatty tissue and biomagnifies up the food chain to devastate top predators including humans.
Minamata, Japan Pollutants, Bioaccumulation and Biomagnification
2.2.19Non-biodegradable pollutants are absorbed within microplastics, which increases their transmission in the food chain.
The Great Pacific Garbage Patch, the largest of five oceanic gyres concentrating plastic debris, contains areas where microplastics outnumber plankton in surface samples; hydrophobic PCBs and DDT bind to their large surface areas, so filter feeders ingest plastic-borne pollutants at the base of the food chain.
Demonstrates how microplastics act as vectors concentrating non-biodegradable pollutants and transmitting them into food chains while disrupting energy transfer at low trophic levels.
Great Pacific Garbage Patch Pollutants, Bioaccumulation and Biomagnification
2.2.20Human activities, such as burning fossil fuels, deforestation, urbanization and agriculture, have impacts on flows of energy and transfers of matter in ecosystems.
Between 1988 and 2008, deforestation in the Brazilian Amazon ran at 10,000–30,000 km² per year (65–70% driven by cattle ranching), releasing carbon from a biome storing roughly 150–200 billion tonnes of carbon in its biomass.
Shows how deforestation removes producers, disrupts food webs and releases stored carbon, altering energy flows and matter transfer while creating a climate feedback loop.
Amazon Rainforest, Brazil Pollutants, Bioaccumulation and BiomagnificationIowa (USA) has converted over 85% of its land to corn and soybean monoculture using ~30 million kg of nitrogen fertiliser annually, whose runoff feeds a Gulf of Mexico dead zone covering up to 22,000 km² each summer.
Demonstrates how agriculture simplifies food webs, removes matter via harvest, and links terrestrial nutrient loading to eutrophication and disrupted energy flow in a distant aquatic ecosystem.
2.2.23Primary productivity is the rate of production of biomass using an external energy source and inorganic sources of carbon and other elements.HL
At deep-ocean hydrothermal vents (2000–4000 m depth), first discovered in 1977, chemoautotrophic bacteria oxidise inorganic hydrogen sulphide to fix carbon, powering an entire ecosystem including giant tube worms (Riftia pachyptila) with no reliance on sunlight.
Shows primary productivity driven by an external chemical energy source rather than light, using inorganic carbon and chemosynthesis.
2.2.26Maximum sustainable yields (MSYs) are the net primary or net secondary productivity of a system.HL
The Grand Banks cod fishery off Newfoundland, Canada collapsed in 1992 after annual catches (e.g. 0.8 million tonnes in 1970) repeatedly exceeded the maximum sustainable yield, crashing estimated cod biomass from 1.6 million tonnes in 1960 to under 0.1 million tonnes, triggering a moratorium that still restricts the fishery over 30 years later.
Demonstrates that harvesting Atlantic cod (Gadus morhua) above the net secondary productivity (MSY) depletes the stock and causes population collapse.
Grand Banks, Newfoundland, Canada Productivity, Sustainable Yields and Thermodynamics
2.2.27Sustainable yields are higher for lower trophic levels.HL
In a simplified agricultural food chain, crop plants receiving 10,000 kJ pass 1,000 kJ to cattle and only 100 kJ to humans, so eating crops directly gives people ten times more energy than eating beef.
Quantifies why sustainable yields are higher at lower trophic levels, making plant-based diets more sustainable than meat-based ones.
2.2.28Ecological efficiency is the percentage of energy received by one trophic level that is passed on to the next level.HL
In the kelp forest case study, ecological efficiency from producers to secondary consumers was only ~0.4%, and sea otters showed unusually low efficiency (~5%) because their high metabolic rate diverts much assimilated energy to heat.
Shows that real ecological efficiencies deviate widely from the 10% rule, with high-metabolism endotherms passing on very little energy.
2.3 Biogeochemical cycles
2.3.1Biogeochemical cycles ensure chemical elements continue to be available to living organisms.
In the global carbon cycle photosynthesis removes about 120 GtC/year from the 800 GtC atmospheric store while respiration and decomposition return about 60 GtC/year, keeping carbon continuously available to organisms with an atmospheric residence time of only 3-5 years.
Quantifies the biogeochemical fluxes that recycle carbon and keep it available to living organisms.
2.3.7Fossil fuels are stores of carbon with unlimited residence times. They were formed when ecosystems acted as carbon sinks in past eras and become carbon sources when burned.
The global fossil fuel pool holds about 10,000 GtC accumulated over hundreds of millions of years, yet humans are releasing roughly 9 GtC per year, converting stores with effectively unlimited residence times into a rapid carbon source.
Quantifies how ancient carbon sinks with near-infinite residence times become sources when burned, releasing millions of years of stored carbon in decades.
2.3.8Agricultural systems can act as carbon stores, sources and sinks, depending on the techniques used.
Draining and repeatedly ploughing a wetland for arable land exposes its organic matter to oxygen, accelerating decomposition and oxidation so the soil switches from a carbon store to a source, whereas no-till farming, cover crops and crop rotation keep soils acting as stores or sinks.
Demonstrates how agricultural technique choice determines whether a soil system is a carbon store, sink or source.
2.3.9Carbon dioxide is absorbed into the oceans by dissolving and is released as a gas when it comes out of a solution.
Ocean-atmosphere exchange moves roughly 90 GtC in each direction annually, but the oceans currently take up a net ~2.5 GtC per year, acting as a carbon sink even though this is far less than the 9+ GtC/year humans emit.
Quantifies bidirectional dissolving and out-gassing of CO2 and shows the ocean's net uptake is limited relative to emissions.
2.3.10Increases in concentrations of dissolved carbon dioxide cause ocean acidification, harming marine animals.
Ocean surface pH has fallen from about 8.2 in pre-industrial times to roughly 8.1 today; because pH is logarithmic this represents a ~26% increase in acidity, reducing calcification in molluscs and corals such as the Great Barrier Reef, which is experiencing bleaching and reduced calcification rates.
Quantifies how rising dissolved CO2 lowers ocean pH and demonstrates the concrete harm to calcium-carbonate-forming marine animals.
Great Barrier Reef, Australia A Tour of the Carbon Cycle
2.3.11Measures are required to alleviate the effects of human activities on the carbon cycle.
IPCC-style carbon budget figures show anthropogenic emissions of 9.4 GtC/year from fossil fuels plus 1.6 GtC/year from land-use change, against natural sinks of only 3.4 GtC/year (land) and 2.5 GtC/year (ocean), leaving a net ~4 GtC/year accumulating in the atmosphere.
Quantifies why sources exceed sinks and justifies mitigation measures targeting emission reduction over sink enhancement.
2.3.14In past geological eras, organic matter from partially decomposed plants became fossilized in coal, and partially decomposed marine organisms became fossilized in oil and natural gas held in porous rocks.HL
Coal formation peaked during the Carboniferous period (~360–300 million years ago), when vast swamp forests of ferns, horsetails and early trees near the equator died in waterlogged, anaerobic conditions and were buried and compressed over tens of millions of years.
Demonstrates that coal derives from partially decomposed plant matter fossilized under specific geological-era conditions, as required by the syllabus point.
Oil and natural gas formed mainly during the Jurassic (201–145 mya) and Cretaceous (145–66 mya) periods, when warm climates, high CO₂ and extensive shallow seas produced enormous plankton productivity; dead marine algae and zooplankton sank, were buried, and were transformed by heat and pressure into oil and gas held in porous rocks.
Shows that oil and gas originate from marine organisms fossilized in porous rock during specific eras of high productivity, illustrating the syllabus point in detail.
2.3.16Methane has a residence time of about 10 years in the atmosphere and is eventually oxidized to carbon dioxide.HL
Methane has an atmospheric residence time of only about 10 years before being oxidized to CO₂, yet it has roughly 80× the warming potential of CO₂ over a 20-year period, meaning cuts to methane emissions can deliver rapid climate benefits.
Quantifies methane's short residence time and its oxidation fate, showing why potency and residence time must be considered together.
2.3.19Denitrification only happens in anaerobic conditions, such as soils that are waterlogged.HL
The Flow Country of Caithness and Sutherland, northern Scotland, is Europe's largest blanket bog (~4,000 km²) whose waterlogged, acidic, anaerobic peat soils cause denitrification and leaching to strip available nitrogen, so insectivorous sundews (Drosera rotundifolia) trap and digest insects to obtain nitrogen instead.
Demonstrates how anaerobic waterlogged soils drive denitrification/leaching and create nitrogen-poor conditions favouring insectivorous plants.
Flow Country, Scotland The Nitrogen Cycle: From Bacteria to Planetary Boundaries
2.3.20Plants cannot fix nitrogen so atmospheric dinitrogen is unavailable to them unless they form mutualistic associations with nitrogen-fixing bacteria.HL
Brazil, the world's largest soybean producer, has farmers inoculate seeds with Bradyrhizobium japonicum so the legume–bacteria mutualism fixes atmospheric N₂ into ammonia, saving the sector billions of dollars annually in synthetic fertiliser costs (Embrapa).
Shows the agricultural significance and competitive advantage of the legume–Rhizobium mutualism as a route for plants to access unavailable atmospheric nitrogen.
2.3.22Human activities such as deforestation, agriculture, aquaculture and urbanization change the nitrogen cycle.HL
Synthetic nitrogen fertiliser on intensive maize in the US Corn Belt (Iowa, Illinois, Indiana) generates nitrate run-off carried down the Mississippi, feeding the Gulf of Mexico 'dead zone', a hypoxic area of roughly 15,000 km² and one of the world's largest cases of eutrophication.
Quantifies how agricultural nitrogen inputs alter the nitrogen cycle and produce large-scale downstream eutrophication.
Gulf of Mexico dead zone The Nitrogen Cycle: From Bacteria to Planetary Boundaries
2.3.23The Haber process is an industrial process that produces ammonia from nitrogen and hydrogen for use as fertilizer.HL
The Haber-Bosch process, developed by Fritz Haber in 1909 and scaled by Carl Bosch for BASF, produces ammonia from N₂ and H₂, now sustaining roughly half the world's food production while consuming about 1–2% of global energy, almost entirely from fossil fuels.
Shows both the advantage (feeding half the world) and disadvantage (fossil-fuel dependence and emissions) of industrial ammonia production for fertiliser.
2.3.24Increases in nitrates in the biosphere from human activities have led to the planetary boundary for the nitrogen cycle being crossed, making irreversible changes to Earth systems likely.HL
The Baltic Sea, bordered by nine countries, is one of the most eutrophied seas in the world because agricultural nitrogen run-off from all of them has caused severe oxygen depletion, illustrating the consequences of exceeding the proposed 62 Tg N yr⁻¹ nitrogen planetary boundary.
Demonstrates the transboundary eutrophication that results from crossing the nitrogen planetary boundary driven by fertiliser use.
2.3.25Global collaboration is needed to address the uncontrolled use of nitrogen in industrial and agricultural processes and bring the nitrogen cycle back within planetary boundaries.HL
Sri Lanka's 2021 abrupt ban on synthetic fertiliser imports, intended to force a switch to fully organic farming, collapsed rice and tea yields because there was no phased transition or alternative nitrogen source.
Counter-example showing that reducing inorganic fertiliser dependence requires careful, phased global collaboration rather than abrupt bans.
2.4 Climate and biomes
2.4.2A biome is a group of comparable ecosystems that have developed in similar climatic conditions, wherever they occur.
Tropical rainforests in the Amazon Basin, the Congo Basin and Southeast Asia share recognisable structural features (tall canopy, dense undergrowth, high diversity) despite containing entirely different species, because similar climatic conditions produce convergent structures.
Shows the defining 'wherever they occur' idea that comparable climates produce parallel ecosystem features across continents.
Congo Basin Biomes: Characteristics, Distribution and Change
2.4.5The tricellular model of atmospheric circulation explains the behaviour of atmospheric systems and the distribution of precipitation and temperature at different latitudes. It also explains how these factors influence the structure and relative productivity of different terrestrial biomes.
The Sahara (≈25°N), Arabian (≈25°N) and Australian (≈25°S) deserts all sit at roughly 30° latitude because dry, cool air descends there as the poleward limb of the Hadley cell, creating a permanent zone of high pressure and arid, low-productivity conditions.
Demonstrates how the descending arm of the Hadley cell produces high-pressure arid biomes at a predictable latitude in both hemispheres.
Sahara Desert Climate, Atmospheric Circulation and Biome DistributionWestern Europe, including the UK (≈45°–60°N), experiences frequent rainfall and variable weather because it lies in the Ferrel cell where warm subtropical air rises over cold polar air at ≈60°, cooling and condensing to produce the moderate precipitation that supports temperate forest.
Shows how the rising air and polar front of the Ferrel cell generate the mid-latitude precipitation and variable weather characteristic of temperate biomes.
United Kingdom Climate, Atmospheric Circulation and Biome Distribution
2.4.6The oceans absorb solar radiation and ocean currents distribute the resulting heat around the world.
London (51°N) averages about 5°C in January while Calgary, Canada (51°N) averages about −7°C, because the Gulf Stream and its extension the North Atlantic Drift carry warm water from the Gulf of Mexico across the Atlantic, warming the westerly winds that reach western Europe.
Quantifies how a warm ocean current redistributes tropical heat to give two locations at the same latitude very different climates.
The Humboldt Current brings cold water northward along the west coast of South America, cooling the adjacent coast and contributing to the aridity of the Atacama region.
Shows how a cold current transports polar water towards the equator and shapes the climate and biomes of nearby land masses.
Humboldt Current, west coast of South America Climate, Atmospheric Circulation and Biome Distribution
2.4.7Global warming is leading to changing climates and shifts in biomes.
Along the Dalton Highway ~232 miles north of Fairbanks, Alaska, researchers study the boreal-tundra treeline, the largest ecosystem transition on Earth; Arctic warming is occurring ~6 times faster than at the equator, but although spruce may advance north the tundra extends to the Arctic Ocean and has nowhere to retreat.
Demonstrates poleward biome shift under global warming and why the tundra is squeezed with nowhere to migrate.
Dalton Highway, Alaska, USA Biomes: Characteristics, Distribution and ChangeCanada's boreal forest, part of the largest relatively untouched forest on Earth (1.9 billion hectares globally, supporting 3.7 million people), is contracting at its southern margin as milder winters and hotter summers cause drought stress, stomatal closure and mountain pine beetle outbreaks, while expanding at its northern margin into Arctic tundra.
Shows a biome being squeezed from both margins simultaneously, illustrating that biome shifts are not smooth migrations.
2.4.8There are three general patterns of climate types that are connected to biome types.HL
London (maritime temperate) has a January average of around 5°C while Calgary (continental temperate) at the same latitude averages around -10°C, showing how proximity to the ocean, not latitude, determines the temperate subdivision and biome potential.
Demonstrates the distinction between maritime and continental subdivisions of the temperate climate type at equal latitude.
Calgary, Canada Climate Types, ENSO and Tropical Cyclones
2.4.9The biome predicted by any given temperature and rainfall pattern may not develop in an area because of secondary influences or human interventions.HL
Nairobi, Kenya, sits at just 1°S latitude but at an altitude of 1,795 m, so the environmental lapse rate (~6.5°C per 1,000 m) cools it enough that it does not develop the tropical rainforest predicted by its equatorial latitude.
Demonstrates how a secondary influence (altitude) overrides the biome predicted by latitude-based temperature and rainfall.
Nairobi, Kenya Climate Types, ENSO and Tropical CyclonesThe Atacama Desert in Chile receives under 15 mm of precipitation per year despite lying on the Pacific coast, because the rain shadow of the Andes and the cold Humboldt Current suppress moisture and rainfall.
Shows two secondary influences (rain shadow and cold ocean current) preventing the moister biome expected at a coastal location.
Atacama Desert, Chile Climate Types, ENSO and Tropical Cyclones
2.4.10The El Niño Southern Oscillation (ENSO) cycle is the fluctuation in wind and sea surface temperatures that characterizes conditions in the tropical Pacific Ocean. The two opposite and extreme states are El Niño and La Niña, with transitional and neutral states between the extremes.HL
The catastrophic 1972-73 El Nino decimated Peru's anchoveta population, killed millions of seabirds and crashed Peru's export economy, illustrating the irregular and severe extremes of the ENSO cycle.
Shows the extreme El Nino state of the ENSO cycle and the unpredictability of event intensity over decades.
2.4.11El Niño is due to a weakening or reversal of the normal east–west (Walker) circulation, which increases surface stratification and decreases upwelling of cold, nutrient-rich water near the coast of north-western South America. La Niña is due to a strengthening of the Walker circulation and reversal of other effects of El Niño.HL
During the 2023-24 El Nino, one of the five strongest on record with eastern Pacific SSTs ~2.0°C above average, Peru cancelled the June 2023 anchoveta fishing season because collapsed upwelling drove fish below 100 m, cutting fishmeal production 28% and raising global feed prices since Peru supplies ~20% of world fishmeal.
Quantifies how weakened Walker circulation suppresses upwelling off Peru and collapses marine productivity with global economic knock-on effects.
2.4.13Rises in ocean temperatures resulting from global warming are increasing the intensity and frequency of hurricanes and typhoons because warmer water and air have more energy.HL
Hurricane Milton (October 2024) intensified from tropical storm to Category 5 in ~24 hours over a Gulf of Mexico that Climate Central found 400-800 times more likely to be so warm due to climate change; World Weather Attribution concluded that without warming it would have made landfall as Category 2 rather than 3, with rainfall 20-30% higher.
Provides attribution-study evidence linking elevated ocean temperatures to rapid intensification and greater cyclone severity.
Gulf of Mexico Climate Types, ENSO and Tropical Cyclones
2.5 Zonation, succession and change in ecosystems
2.5.1Zonation refers to changes in community along an environmental gradient.
At Studland Bay, Dorset, walking inland from the shore produces clear sand dune zonation: marram grass peaks (~63% cover) around 20 m from the sea while heather only appears from 40 m and dominates (100% cover) at 60–70 m, as salt spray falls and soil depth and humus rise.
Shows community changing along a distance-from-sea environmental gradient, with species replacing one another as abiotic conditions shift.
Studland Bay, Dorset, England Zonation and Succession
2.5.2Transects can be used to measure biotic and abiotic factors along an environmental gradient in order to determine the variables that affect the distribution of species.
Students at Studland Beach laid three parallel transects at 90° to the sea, sampling 1 m² quadrats at 10 m intervals to record percentage cover of marram grass and heather alongside slope angle, revealing that the two species barely overlap and are separated along the gradient.
Demonstrates transect methodology (parallel replicates, regular quadrats, biotic and abiotic factors) used to determine variables affecting species distribution.
Studland Bay, Dorset, England Zonation and Succession
2.5.3Succession is the replacement of one community by another in an area over time due to changes in biotic and abiotic variables.
Surtsey, a ~1 km² volcanic island off southern Iceland formed by eruptions in 1963–67, shows primary succession on bare rock (lithosere): first insects arrived in 1964, mosses and lichens as pioneers, the first willow shrub in 1999, and by 2008 it had 69 vascular plant species (versus 460 on mainland Iceland), with 2–5 new species arriving each year.
Quantifies primary succession from a documented start date, showing pioneer colonisation of newly formed substratum and slow community development due to isolation.
Surtsey, Iceland Zonation and SuccessionThe Studland Bay dune psammosere progresses over ~400+ years from foredunes (sea rocket, pH 8.5) through mobile and fixed dunes to climax oak-ash woodland (>40% humus, pH 4.5), so walking the 2.5 km inland from the 16th-century oldest dunes is effectively walking forward through time.
Demonstrates succession as temporal replacement of communities, with the spatial dune sequence mirroring change over centuries.
Studland Bay, Dorset, England Zonation and Succession
2.5.4Each seral community (sere) in a succession causes changes in environmental conditions that allow the next community to replace it through competition until a stable climax community is reached.
In the Studland Bay psammosere, marram grass traps sand and adds leaf-litter organic matter, raising humus and lowering soil pH from ~8.0 to 6.5, so that red fescue and heather eventually outcompete the marram, which itself requires sand burial to thrive — each sere engineering its own replacement.
Shows a seral community modifying abiotic conditions (pH, humus) so the next community can outcompete and replace it, the core mechanism of succession.
Studland Bay, Dorset, England Zonation and Succession
2.5.6Secondary successions happen on bare soil where there has been a pre-existing community, such as a field where agriculture has ceased or a forest after an intense firestorm.
The Broadbalk Wilderness at Rothamsted Research, Hertfordshire, England, is one of the world's longest-running ecological experiments: a section of the Broadbalk wheat field abandoned in the 1880s underwent unmanaged secondary succession, progressing through annual weeds, perennial grasses, hawthorn and blackthorn scrub, and by the present day a closed-canopy mixed deciduous woodland of oak, ash and sycamore after roughly 140 years.
Demonstrates secondary succession on pre-existing soil with a seed bank following the cessation of agriculture, reaching woodland in about 100 years.
Rothamsted Research, Harpenden, Hertfordshire, England Secondary Succession, Changes During Succession and Resilience
2.5.7Energy flow, productivity, species diversity, soil depth and nutrient cycling change over time during succession.
Along a sand-dune succession transect, the strandline pioneer stage supports only 2–3 species while the dune heath supports dozens of plant species plus associated animals, and soil humus rises from near zero to over 40%, showing species diversity and soil depth both increase through the seres.
Quantifies the systematic rise in species diversity and soil organic matter across successional stages.
At Broadbalk Wilderness the deepening leaf litter and steadily rising soil organic carbon since 1881, alongside the shift from short simple food chains to a branched woodland food web, provides direct long-term evidence that soil depth, nutrient cycling and energy-flow complexity increase during succession.
Quantifies how soil depth, nutrient cycling and energy flow change over time using a documented 140-year dataset.
Rothamsted Research, Harpenden, Hertfordshire, England Secondary Succession, Changes During Succession and Resilience
2.5.8An ecosystem's capacity to tolerate disturbances and maintain equilibrium depends on its diversity and resilience.
Sustained trampling on the sand dunes at Studland Bay, Dorset, destroys marram grass and exposes bare sand, resetting succession and creating a plagioclimax; because the pioneer community has low diversity and small biomass storage it is pushed toward a tipping point, unlike a resilient climax oak woodland.
Shows how low diversity and small storage reduce resilience, and how human interference (trampling) diverts succession to a plagioclimax.
Studland Bay, Dorset, England Secondary Succession, Changes During Succession and ResilienceThe displacement of diverse North American prairie ecosystems with monoculture crops drastically reduces species diversity and the size of biomass and nutrient storages, simplifying food webs and lowering the ecosystem's resilience to disturbance.
Demonstrates how human activity reduces diversity and storage, thereby lowering resilience and moving a system closer to tipping points.
Great Plains, North America Secondary Succession, Changes During Succession and Resilience
2.5.9The type of community that develops in a succession is influenced by climatic factors, the properties of the local bedrock and soil, geomorphology, together with fire and weather-related events that can occur. There can also be top-down influences from primary consumers or higher trophic levels.HL
The Flow Country of Caithness and Sutherland, Scotland, is one of the world's largest blanket bogs (~4,000 km²) where flat topography, impermeable bedrock and high rainfall keep soils waterlogged; Sphagnum moss, cotton grass and sundews dominate instead of the forest predicted by latitude, because anaerobic conditions halt decomposition and tree establishment.
Shows how geomorphology and poor drainage arrest succession at a bog seral stage rather than forest.
Flow Country, Caithness and Sutherland, Scotland Factors Influencing Succession, Productivity and PlagioclimaxThe serpentine soils of the Troodos Mountains, Cyprus, form from ultra-basic oceanic crust that weathers to soils very high in nickel and chromium but low in calcium and potassium; instead of the Mediterranean woodland predicted by climate, only sparse endemic metallophyte plants grow, halting succession by soil chemistry.
Demonstrates how bedrock and extreme soil chemistry override climate to determine the community that develops.
Troodos Mountains, Cyprus Factors Influencing Succession, Productivity and Plagioclimax
2.5.12The concept of a climax community has been challenged, and there is uncertainty over what ecosystems would develop naturally were there no human influences.HL
Frans Vera's wood-pasture hypothesis proposes that post-glacial Europe was a shifting mosaic of woodland, scrub and grassland maintained by large herbivores such as aurochs, wild horses and European bison, rather than the closed-canopy forest of the traditional monoclimax view; early Holocene pollen and open-habitat beetle fossils are cited as support, though the evidence remains contested.
Demonstrates how the single-climax concept is challenged and uncertainty over the 'natural' human-free ecosystem.
2.5.13Human activity can divert and change the progression of succession leading to a plagioclimax.HL
The open heather moorland of the Scottish Highlands is a plagioclimax: wolves and lynx were extirpated centuries ago, and combined with sheep grazing and deer-stalking management this prevented regeneration of the native Caledonian pine forest, until rewilding by Trees for Life in Glen Affric let Scots pine, birch and rowan recover.
Shows how removing top carnivores plus human grazing diverts succession into a maintained plagioclimax that recovers when pressure is removed.
Glen Affric, Scotland Factors Influencing Succession, Productivity and Plagioclimax
3 Biodiversity and conservation
3.1 Biodiversity and evolution
3.1.1Biodiversity is the total diversity of living systems and it exists at several levels.
The Swiss National Park in the Engadin (170 km², founded 1914) spans 1,400 m to 3,174 m, creating distinct habitats—coniferous forest (28%), alpine grassland (21%) and high alpine rock/scree (51%)—that support 36 mammal species, ~100 bird species and over 650 vascular plant species.
Demonstrates how a steep altitudinal gradient generates high habitat diversity, one of the three levels of biodiversity.
Swiss National Park, Engadin, Switzerland Biodiversity and ResilienceThe Tasmanian devil (Sarcophilus harrisii) has extremely low genetic diversity from historical population bottlenecks, leaving it vulnerable to devil facial tumour disease (DFTD); with immune systems unable to recognise the transmissible cancer as foreign due to similar MHC genes, the population has declined over 85% since 1996.
Shows genetic diversity as a distinct level of biodiversity and the consequences of its loss within a population.
Tasmania, Australia Biodiversity and Resilience
3.1.2The components of diversity contribute to the resilience of ecological systems.
In Lake Geneva each quagga mussel filters up to 2 litres of water per day, feeding on phytoplankton at the base of the food chain; the resulting phytoplankton decline cuts food for zooplankton and fish, threatening the livelihoods of roughly 120 professional fishers on the lake.
Shows how loss/replacement of species propagates up the food chain, affecting ecosystem functioning and human livelihoods.
Lake Geneva, Switzerland Human Impact on Biodiversity and Invasive Alien SpeciesQuagga mussels (Dreissena rostriformis bugensis), native to the Ponto-Caspian Black Sea region, were found in Lake Geneva by 2016 and by 2024 made up 100% of mussel samples at densities over 35,000 per m², driving native snails, shrimps and mussels to local extinction through competitive exclusion for space and food on the lake bed.
Demonstrates competitive exclusion — one of the three biodiversity-reduction mechanisms — with quantified colonisation of a named local ecosystem.
Lake Geneva, Switzerland Human Impact on Biodiversity and Invasive Alien SpeciesThe reintroduction of wolves to Yellowstone in the 1990s triggered a trophic cascade that restored ecosystem function, whereas the historical loss of wolves from European forests let deer populations explode, reducing tree regeneration and simplifying the ecosystem.
Shows how species diversity and a keystone predator maintain complex food webs and ecosystem resilience.
Yellowstone National Park, USA Biodiversity and ResilienceWild banana populations with high genetic diversity resist Panama disease TR4, which devastates genetically uniform commercial Cavendish plantations where every plant shares the same disease susceptibility.
Demonstrates how genetic diversity confers resilience while genetic uniformity leads to collapse under a single pathogen.
3.1.3Biodiversity arises from evolutionary processes.
Italian wall lizards (Podarcis sicula) introduced to Pod Mrčaru, Croatia in 1971 evolved over ~36 years (~30 generations) a plant-based diet (up to 60% plant matter), larger heads with stronger bite force, and novel cecal valves in the gut compared to the source population on Pod Kopište.
Demonstrates evolution as cumulative, heritable change in a population's characteristics observable over a short timescale.
Pod Mrčaru, Croatia Biodiversity and Resilience
3.1.4Natural selection is the mechanism driving evolutionary change.
The European robin (Erithacus rubecula), a year-round woodland resident, faces harsh winters with reduced invertebrate food; individuals with higher metabolic efficiency and greater fat-storage capacity survive to breed in spring and pass these heritable traits on, increasing their frequency over generations.
Illustrates natural selection as a continuous mechanism acting on heritable variation through seasonal selection pressures.
3.1.5Evolution by natural selection involves variation, overproduction, competition for limited resources, and differences in adaptation that affect rates of survival and reproduction.
A single pedunculate oak (Quercus robur) can produce over 70,000 acorns in a mast year, yet an ancient woodland may hold only a few hundred mature oaks — most seeds are lost to herbivory, competition and shading, while seedlings germinating in canopy gaps receive more light and are more likely to survive.
Quantifies overproduction and demonstrates competition for limited resources and differential survival driving natural selection.
European great tits (Parus major) that time their egg-laying to coincide with the ~2–3 week spring peak in canopy caterpillar abundance raise more surviving chicks, and populations have shifted laying dates earlier within a few decades in response to warming springs.
Shows heritable variation, competition and differential reproductive success producing measurable evolutionary change over just decades.
3.1.6Speciation is the generation of new species through evolution.
Four similar leaf warblers — chiffchaff (Phylloscopus collybita), willow warbler (P. trochilus), wood warbler (P. sibilatrix) and garden warbler (Sylvia borin) — coexist in a single European woodland by partitioning niches through feeding height, food source and nest location, having diverged from common ancestors after Pleistocene isolation.
Shows how repeated speciation and adaptation from ancestral populations generates biodiversity and niche partitioning within one habitat.
The Eurasian treecreeper (Certhia familiaris) and short-toed treecreeper (Certhia brachydactyla) diverged when Pleistocene ice sheets (2.6 million–11,700 years ago) fragmented European woodland into isolated refugia in Iberia, Italy and the Balkans; adapting separately, the populations could no longer interbreed when woodlands reconnected.
Demonstrates allopatric speciation via geographic isolation, divergent selection and resulting reproductive isolation.
Iberian Peninsula Natural Selection
3.1.8Simpson's reciprocal index is used to provide a quantitative measure of species diversity, allowing different ecosystems to be compared and for change in a specific ecosystem over time to be monitored.
On a rewilded estate in the Scottish Highlands, ground beetle (Carabidae) communities were compared using pitfall traps: after 15 years of rewilding (sheep removed, birch and Scots pine regenerating) Site 1 gave a Simpson's reciprocal index of D = 5.28, while the still-grazed Site 2, dominated by 45 Nebria brevicollis out of 60 individuals, gave only D = 1.74 — despite both sites having identical richness (5 species) and total individuals (60).
Demonstrates how Simpson's reciprocal index quantifies diversity and detects change from a management intervention when richness alone stays constant, using a valid same-organism, same-ecosystem, same-method comparison.
Scottish Highlands, Scotland Species diversity
3.1.9Knowledge of global and regional biodiversity is needed for the development of effective management strategies to conserve biodiversity.
Dr Erpur Snær Hansen of the South Iceland Nature Research Centre conducts a twice-yearly 'puffin rally', travelling over 3,100 miles to about 700 marked burrows across 12 colonies with plumbing cameras; this government-linked systematic monitoring revealed Iceland's puffin decline since the early 2000s, linked to falling sand eel numbers and rising sea surface temperatures.
Demonstrates why systematic professional monitoring, alongside citizen science, provides the long-term trend data needed for effective conservation strategies.
Iceland Species diversityIceland's Puffling Patrol on Heimaey in the Westman Islands is a citizen-science programme where local children and families collect, weigh, log and release disoriented Atlantic puffin chicks each August–September, feeding standardised data into GBIF (the Global Biodiversity Information Facility) for use by researchers.
Shows how citizen science following a standardised protocol gathers regional biodiversity knowledge that aggregates into global databases underpinning conservation management.
Heimaey, Westman Islands, Iceland Species diversity
3.1.10Mutation and sexual reproduction increase genetic diversity.HL
Eastern tree frogs (Hyla orientalis) in Ukraine's Chernobyl Exclusion Zone are, per 2022 research, significantly darker than frogs in uncontaminated areas nearby; pre-existing melanin-producing alleles gave protection against elevated radiation after the 1986 disaster, so darker frogs were selected over ~14 generations.
Demonstrates how mutation first generates genetic variation (dark-pigment alleles) which natural selection then amplifies once the environment changes.
Chernobyl Exclusion Zone, Ukraine Reproductive Isolation and Biodiversity Hotspots
3.1.11Reproductive isolation can be achieved by geographical separation or, for populations living in the same area, by ecological or behavioural differences.HL
Bonobos (Pan paniscus) and common chimpanzees (Pan troglodytes) diverged from one ancestral population ~1.5–2 million years ago when the Congo River became too deep and wide to cross; chimps north of the river evolved male-dominant, aggressive, tool-using societies while bonobos south of it (lacking gorilla competitors) became female-dominant and less aggressive.
Shows speciation by geographical separation, with a physical barrier splitting a gene pool and different selective pressures driving divergence.
Congo River Reproductive Isolation and Biodiversity HotspotsThe apple maggot fly (Rhagoletis pomonella) began, from the mid-1800s in North America, laying eggs on introduced apples rather than native hawthorn; because flies mate on their host fruit and apples and hawthorn ripen at different times, the two 'host races' rarely interbreed and now differ in emergence timing and genetic markers.
Demonstrates behavioural (sympatric) reproductive isolation without a geographical barrier — 'speciation in progress' within a few hundred generations.
North America Reproductive Isolation and Biodiversity Hotspots
3.1.12Biodiversity is spread unevenly across the planet, and certain areas contain a particularly large proportion of species, especially species that are rare and endangered.HL
Socotra, an Indian Ocean island ~380 km south of Arabia isolated from Africa ~6 million years ago, has ~37% endemic plant species, including the dragon blood tree (Dracaena cinnabari) and the cucumber tree (Dendrosicyos socotranus), the only tree-form cucumber on Earth; it became a UNESCO World Heritage Site in 2008.
Shows how long island isolation concentrates rare endemic species, illustrating the uneven, vulnerable distribution of biodiversity.
Socotra, Yemen Reproductive Isolation and Biodiversity HotspotsThe Mediterranean Basin, one of 36 recognised biodiversity hotspots, holds over 25,000 plant species (~13,000 endemic) adapted to hot dry summers and mild wet winters (maquis and garrigue), yet millennia of agriculture, urbanisation, tourism and fire have destroyed most of its original habitat.
Demonstrates a non-tropical hotspot meeting both criteria (high endemism plus severe habitat loss), showing hotspots are not only tropical rainforests.
Mediterranean Basin Reproductive Isolation and Biodiversity Hotspots
3.1.13Human activities have impacted the selective forces acting on species within ecosystems, resulting in evolutionary change in these species.HL
European great tits (Parus major) have evolved earlier egg-laying dates as climate warming shifts the caterpillar peak earlier; populations that cannot keep pace suffer a phenological mismatch where chicks hatch after peak food, reducing breeding success.
Shows how climate change from burning fossil fuels alters the selective advantage of a trait (laying date), driving evolutionary change dependent on a population's genetic diversity.
Europe Humans and SelectionIn Gorongosa National Park, Mozambique, ivory poaching during the civil war (1977–1992) killed ~90% of elephants (from ~2,500 to ~200); tuskless females rose from ~18.5% before the war to ~51% of survivors, and ~33% of the next generation, a genetic shift confirmed by Campbell-Staton et al. (Science, 2021).
Demonstrates how a human activity (poaching) unintentionally altered the selective force on a population, causing rapid, measurable, heritable evolutionary change — human-altered natural selection, not artificial selection.
Gorongosa National Park, Mozambique Humans and Selection
3.1.14Artificial selection reduces genetic diversity and, consequently, species resilience.HL
The Cavendish banana, which dominates global trade, is propagated vegetatively as genetic clones with essentially zero genetic diversity and no resistance to the spreading fungus Tropical Race 4 (Fusarium oxysporum); it replaced the Gros Michel variety, itself wiped out by Panama disease in the 1950s for the same reason.
Demonstrates how artificial selection for uniformity eliminates genetic variation, leaving no material for selection to act upon and creating extreme vulnerability (loss of resilience) to disease.
3.1.15Earth history extends over a period of 4.5 billion years. Processes that occur over an extended timescale have led to the evolution of life on Earth.HL
The limestone peaks of the Jura mountains near Ferney-Voltaire, such as La Dôle (1,677 m), contain marine fossils (ammonites, belemnites, corals, sea urchins) deposited on the floor of the warm shallow Tethys Sea around 150 million years ago during the Jurassic, before being uplifted 1.7 km by the collision of the African and Eurasian plates.
Shows how fossils and the geological record work together to reveal both the evolution of life and the movement of environments over deep time.
La Dôle, Jura, France Deep Time and the Anthropocene
3.1.16Earth history is divided up into geological epochs according to the fossil record.HL
The Cretaceous–Palaeogene (K–Pg) boundary at 66 million years ago is marked worldwide in rocks by the sudden disappearance of non-avian dinosaurs and ammonites together with a chemical signal from a large meteorite impact, and is formally defined by the International Commission on Stratigraphy.
Demonstrates how an epoch/period boundary is read from a globally synchronous change in the fossil record rather than assigned arbitrarily.
3.1.17Mass extinctions are followed by rapid rates of speciation due to increased niche availability.HL
Ammonites, shelled cephalopods related to modern squid, adaptively radiated into thousands of species after surviving three mass extinctions (Late Devonian, Permian–Triassic, Triassic–Jurassic) before going completely extinct at the K–Pg boundary 66 Ma, after which niches were filled by radiating bony fish.
Illustrates repeated rapid speciation into vacant niches following mass extinctions, plus eventual extinction, within a single well-documented lineage.
The Permian–Triassic 'Great Dying' at ~252 Ma, caused by super-volcanic eruption and resulting climatic change, killed ~96% of species — the largest extinction in Earth's history — after which surviving lineages radiated into vacant niches.
Quantifies the scale of a mass extinction and its abiotic cause, and shows the vacated niches that drive subsequent adaptive radiation.
3.1.18The Anthropocene is a proposed geological epoch characterized by rapid environmental change and species extinction due to human activity.HL
The 2024 proposal to formalise the Anthropocene used a 1950s start with the 1964 Carbon-14 peak as its golden spike, preserved in the annual varves of Crawford Lake, Ontario, but the Subcommission on Quaternary Stratigraphy voted against it in March 2024, leaving the Anthropocene a proposed epoch.
Demonstrates the golden-spike concept and the contested, unresolved status of the proposed Anthropocene epoch.
Crawford Lake, Ontario, Canada Deep Time and the Anthropocene
3.1.19Human impacts are having a planetary effect, which will be detectable in the geological record.HL
Plastiglomerate — fragments of plastic fused with natural rock, first documented on beaches in Hawaii — is a novel human-made mineral-like material with no pre-industrial precedent that will persist in the far-future rock record.
Provides a concrete example of novel minerals as a permanent planetary-scale human signal in the geological record.
Kamilo Beach, Hawaii, USA Deep Time and the Anthropocene
3.2 Human impact on biodiversity
3.2.3Invasive alien species can reduce local biodiversity by competing for limited resources, predation and introduction of diseases or parasites.
In Lake Geneva quagga mussel filtering makes water clearer and lets light penetrate deeper, while climate change has stopped seasonal lake mixing since 2012, warming deep water and raising the risk of toxic blue-green algal blooms — a combined impact far greater than either stressor acting alone.
Quantifies the amplification effect where climate change and an invasive species interact to reduce resilience beyond the sum of their parts.
Lake Geneva, Switzerland Human Impact on Biodiversity and Invasive Alien SpeciesIn Lake Geneva quagga mussels clogged the deep-water cooling pipes of the Swiss Federal Technology Institute of Lausanne (EPFL), cutting heat-exchanger efficiency by a third, and prompting plans for a new closed-loop cooling system beginning in 2027 since eradication is impossible.
Shows why adaptation rather than eradication is the only management option once an invader is established, illustrating persistent multi-impact stress.
EPFL, Lausanne, Switzerland Human Impact on Biodiversity and Invasive Alien Species
3.2.6Investigate three different named species: a species that has become extinct due to human activity; a species that is critically endangered; and a species whose conservation status has been improved by intervention.
Steller's sea cow (Hydrodamalis gigas), an 8–9 m sirenian discovered in 1741 around the Commander Islands, was hunted to extinction by Russian fur traders for meat and hide within just 27 years (by 1768) — the first historical extinction of a marine mammal caused by humans; its small remnant population (~1,500), tameness and shallow-water habitat made it defenceless.
Demonstrates a species driven extinct by human overharvesting, with cascading effects on kelp-forest food webs and no conservation attempted.
Commander Islands, Russia The IUCN Red List and the Tragedy of the CommonsThe vaquita (Phocoena sinus), the world's smallest porpoise, is Critically Endangered with fewer than 10 individuals remaining in the upper Gulf of California; its decline is driven not by hunting but by bycatch in illegal gillnets set for totoaba fish, whose swim bladders sell for thousands of dollars per kg, despite a 2005 refuge, a 2017 gillnet ban and support from WWF and Sea Shepherd.
Shows a critically endangered species whose decline continues despite well-funded intervention because economic incentives behind the threat remain unaddressed.
Upper Gulf of California, Mexico The IUCN Red List and the Tragedy of the Commons
3.2.7The tragedy of the commons describes possible outcomes of the shared unrestricted use of a resource, with implications for sustainability and the impacts on biodiversity.
The Baltic Sea, bordered by nine countries, now holds the world's largest human-caused dead zone at almost 70,000 km² (about 1.5 times the area of Denmark) after agricultural nitrogen and phosphorus runoff drove eutrophication; despite the Helsinki Convention (HELCOM) cutting nitrogen inputs ~20% and phosphorus ~40% since the 1980s peak, levels remain roughly double those of the early 1900s.
Shows the tragedy of the commons through contamination of a shared resource, where each nation gains from farming but shares the collective cost of biodiversity loss.
The Grand Banks cod fishery off Newfoundland, once among the world's most productive, collapsed after 1950s industrialised trawling by multiple nations acting in self-interest under weak international regulation; Canada imposed a moratorium in 1992, costing over 35,000 jobs, and after 30+ years cod have still not recovered because shrimp and snow crab occupied the vacant niche.
Quantifies the tragedy of the commons through overharvesting of an unowned shared fishery leading to catastrophic, possibly irreversible, ecosystem collapse.
Grand Banks, Newfoundland, Canada The IUCN Red List and the Tragedy of the Commons
3.2.8Biodiversity hotspots are under threat from habitat destruction, which could lead to a significant loss of biological diversity, especially in tropical biomes.HL
The Boma-Badingilo KBA illustrates the wealth-biodiversity mismatch: South Sudan has per-capita GDP under US$500 and, after civil war (2013–2018), depends almost entirely on a single NGO (African Parks, 10-year agreement signed 2022), and the 2024 survey found hippos, elephants and warthogs had collapsed over 40 years due to bushmeat hunting where enforcement was absent.
Demonstrates how tropical biodiversity concentrated in low-income countries lacks the governance, funding and security capacity to prevent habitat and population loss.
Boma National Park, South Sudan Hotspots, KBAs and the Conservation Conflict
3.2.9Key areas that should be prioritized for biodiversity conservation have been identified on the basis of the international importance of their species and habitats.HL
The Aeolian Archipelago off Sicily (~115 km²) holds the entire global population of the Critically Endangered Aeolian wall lizard (Podarcis raffonei), roughly 2,000 individuals in an area of occupancy under two hectares, qualifying as a KBA under criterion A (threatened biodiversity) and B (geographically restricted biodiversity).
Shows that KBA prioritisation applies at tiny scale in a temperate high-income biome, based on international importance of a microendemic species rather than megafauna spectacle.
Aeolian Islands, Italy Hotspots, KBAs and the Conservation ConflictThe Boma-Badingilo-Gambella landscape (~122,000 km² across eastern South Sudan and western Ethiopia) hosts the largest land mammal migration on Earth: a 2024 African Parks aerial survey confirmed ~6 million migrating antelope, including ~5 million white-eared kob, and it qualifies as a KBA under criterion D (biological processes), C (ecological integrity) and A (threatened species such as the endemic Nile lechwe).
Demonstrates how a specific site is prioritised as globally important on the basis of a globally significant life-cycle stage (migration) meeting formal KBA criteria.
Boma National Park, South Sudan Hotspots, KBAs and the Conservation Conflict
3.2.10In KBAs, there is conflict between exploitation, sustainable development and conservation.HL
At COP30 in Belém (November 2025), Brazil launched the Tropical Forest Forever Facility (TFFF), under which consumer countries pay tropical governments to keep forests standing with at least 20% going to indigenous and local communities; over US$6.7 billion had been pledged by the summit's end.
Shows an attempted resolution to the exploitation-versus-conservation conflict by realigning who pays, addressing the justice dimension of protecting hotspots in lower-income countries.
Belém, Brazil Hotspots, KBAs and the Conservation ConflictThe Brazilian Cerrado, a biodiversity hotspot holding ~5% of global biodiversity, has lost over 55% of its native vegetation (~650,000 ha in 2024 alone) as soy occupies ~75% of cropland; Brazil's Forest Code requires retaining only 20–35% of native vegetation there (vs 80% in the Amazon), and the 2006 Soy Moratorium excluded the Cerrado, displacing ~16% of avoided Amazon deforestation into the savanna.
Quantifies the three-way conflict between profitable legal soy/cattle exploitation, water/climate-based sustainable development needs, and conservation of KBAs meeting criteria A and B.
Cerrado, Brazil Hotspots, KBAs and the Conservation Conflict
3.2.11Traditional indigenous approaches to land management can be seen as more sustainable but are facing challenges of population growth, economic development, climate change and a lack of governmental support and protection.HL
Sámi reindeer herding across Sápmi (northern Norway, Sweden, Finland and Russia's Kola Peninsula) is an extensive, low-input system managed collectively through the siida, but faces external threats such as climate-driven 'rain-on-snow' events that ice over lichen pastures and internal threats such as motorisation (snowmobiles, GPS) and young people leaving for salaried urban work.
Demonstrates a named sustainable Indigenous practice and the syllabus distinction between threats from outside and from within.
3.2.12Environmental justice must be considered when undertaking conservation efforts to address biodiversity loss.HL
At the Fosen wind farm in central Norway, the Norwegian Supreme Court ruled unanimously in 2021 that the Storheia and Roan licences were invalid because the turbines violated Sámi herders' cultural rights under Article 27 of the ICCPR, yet the turbines kept operating and only 2023–24 settlements left them standing in exchange for compensation — an example of 'green colonialism'.
Demonstrates the gap between legal rights and environmental justice when 'green' projects dispossess a biodiversity-rich Indigenous community.
Fosen, Norway Indigenous Land, Justice and Biosphere IntegrityThe Swiss National Park, founded in 1914 in the Engadine valley of Graubünden and classified under the strict IUCN category Ia, banned all traditional uses (grazing, hunting, fishing, mowing, wood-cutting) on land leased from local communes, making it a textbook European case of fortress conservation.
Shows conservation overriding traditional land use, illustrating the environmental-justice tension even without forced relocation of Indigenous people.
Swiss National Park, Engadine, Graubünden, Switzerland Indigenous Land, Justice and Biosphere Integrity
3.2.13The planetary boundary \"loss of biosphere integrity\" indicates that species extinctions have already crossed a critical threshold.HL
The planetary boundaries framework developed by Johan Rockström, Will Steffen and colleagues at the Stockholm Resilience Centre identifies nine Earth-system processes; its 2023 update placed 'loss of biosphere integrity' firmly in the high-risk zone, with extinction rates (its genetic-diversity component) estimated at tens to hundreds of times the natural background rate against a proposed safe boundary of ~10 extinctions per million species per year.
Quantifies how the biosphere-integrity boundary has been crossed and shows the distinction between its genetic-diversity and functional-integrity components.
Stockholm Resilience Centre, Stockholm, Sweden Indigenous Land, Justice and Biosphere Integrity
3.3 Conservation and regeneration
3.3.1Arguments for species and habitat preservation can be based on aesthetic, ecological, economic, ethical and social justifications.
In South Sudan the elephant population has fallen to about 5% of the ~133,500 estimated in the early 1970s; in Badingilo National Park the last bull elephant, so isolated it moved with a herd of giraffes, was killed by suspected poachers at the end of 2025, and one hunter said he killed an elephant out of hunger for $50 per tusk.
Shows how ecological (keystone role), ethical and social justifications collide with extreme poverty, undermining preservation arguments in practice.
Badingilo National Park, South Sudan Why and How We ConserveIn Zimbabwe about 60,000 of the country's ~100,000 elephants pass through Hwange National Park in the dry season (roughly double the region's carrying capacity), where safari tourism is a major income source yet Fransica Sibanda's husband was trampled to death near their home — the same elephants generating economic value and social/human cost.
Demonstrates how one species can simultaneously carry economic (ecotourism) and social (well-being, livelihoods) justifications that conflict in local context.
Hwange National Park, Zimbabwe Why and How We Conserve
3.3.2Species-based conservation tends to involve ex situ strategies, and habitat-based conservation tends to involve in situ strategies.
CITES listed African elephants under Appendix I in 1989, effectively banning international commercial ivory trade after catastrophic 1970s–80s declines; enforcement varies by country and southern African states like Zimbabwe and Botswana repeatedly push at CoP meetings to sell ivory stockpiles or downlist to Appendix II.
Illustrates ex situ, species-based conservation through international trade regulation and its dependence on national enforcement.
The Conservatoire et Jardin botaniques de Genève seed bank, established 1999 in Chambésy, is Switzerland's only wild-flora seed bank, holding over 600 species (~30% of Switzerland's threatened flora, 57% of Geneva canton's) dried to ~5% moisture and stored at -20°C for reintroduction projects.
Shows ex situ, species-based conservation preserving genetic material outside natural habitat as an insurance policy against wild extinction.
Conservatoire et Jardin botaniques de Genève, Chambésy, Switzerland Why and How We Conserve
3.3.3Sometimes a mixed conservation approach is adopted, where both habitat and particular species are considered.
The giant panda combines ex situ conservation at the Chengdu Research Base (founded 1987, ~240 ha, 9 million+ visitors in 2019) with the in situ Giant Panda National Park created in 2021 (27,134 km²), which reconnects habitats for ~1,900 wild pandas; as a flagship species (WWF logo since 1961) it provides an 'umbrella effect' protecting 8,000+ other species, though leopards, wolves and wild dogs in the region have declined.
Demonstrates a mixed approach using a flagship species to justify protecting intact habitat, including its trade-offs.
Giant Panda National Park, Sichuan, China Why and How We Conserve
3.3.4The Convention on Biological Diversity (CBD) is a UN treaty addressing both species-based and habitat-based conservation.
The Convention on Biological Diversity, established at the 1992 Rio Earth Summit and in force from 1994, is a legally binding UN treaty requiring national biodiversity strategies covering both species and habitat; its 2010 Nagoya Protocol ensures fair and equitable sharing of benefits from genetic resources with countries of origin.
Shows a UN treaty addressing both species-based and habitat-based conservation plus benefit-sharing, broader than trade-focused CITES.
Rio de Janeiro, Brazil Why and How We Conserve
3.3.5Habitat conservation strategies protect species by conservation of their natural environment. This may require protection of wild areas or active management.
La Grande Cariçaie, Switzerland's largest lakeside wetland (>3,000 ha along 40 km of Lake Neuchâtel's south shore, ~800 plant and 10,000 animal species), was created accidentally by the First Jura Waters Correction (1868–1889) lowering the lake by 2.7 m; the Second Correction (1962–1973) then removed the seasonal flooding that kept it open, so since 1982 it requires rotational mechanical mowing on a 3–4 year cycle and Highland cattle grazing to stop alder, willow and buckthorn succeeding it to woodland.
Demonstrates active management to hold a habitat at a seral stage, and shows how surrounding engineering, farmland runoff and invasive Louisiana crayfish create the pressures conservation must balance.
La Grande Cariçaie, Lake Neuchâtel, Switzerland Habitat Conservation and Reserve DesignSanctuary Mountain Maungatautari (3,400 ha, Waikato, New Zealand) is the world's largest fenced ecosanctuary, enclosed by a 47 km Xcluder pest-proof fence (2004–2006) with a curved anti-climb hood and buried mesh skirt; after aerial brodifacoum drops eradicated 14 mammal species, natives like kiwi, takahē, tuatara and (in 2023) four kākāpō were reintroduced, though mice could not be eradicated and some kākāpō climbed out over fallen trees.
Shows pest-exclusion fencing as an active management strategy in a country whose birds evolved without mammalian predators, illustrating both its power and its 'ecological island' limitations.
Sanctuary Mountain Maungatautari, Waikato, New Zealand Habitat Conservation and Reserve Design
3.3.6Effective conservation of biodiversity in nature reserves and national parks depends on an understanding of the biology of target species and on the effect of the size and shape of conservation areas.
StudyA study of European protected areas by Lurgi (2025, Swansea University) found that reserves and national parks do increase species richness and support larger predators, but they do not consistently preserve ecological interactions such as food-chain length and food-web complexity, with remoteness, habitat diversity, human pressure and surrounding agricultural land all affecting how well food webs were maintained.
Provides evidence that reserve design factors (surrounding land use, edge effects, connectivity) determine effectiveness beyond mere species counts, adding critical depth to conservation-area evaluation.
The Yasuní Biosphere Reserve in the Ecuadorian Amazon uses the UNESCO three-zone model — a ~10,000 km² national park core (protected 1979, biosphere reserve 1989), a buffer including the Tagaeri-Taromenane Intangible Zone for uncontacted peoples, and a transition zone of Kichwa and Waorani communities — protecting record biodiversity (~1,300 tree, 150 amphibian, 170 mammal species) despite sitting on 1.7 billion barrels of oil (~40% of Ecuador's reserves) drilled since 2016.
Demonstrates the core/buffer/transition zonation model applied to a globally significant biodiversity site and the human-impact conflict (oil extraction, 2023 anti-drilling referendum) it must manage.
Yasuní National Park, Ecuador Habitat Conservation and Reserve Design
3.3.7Natural processes in ecosystems can be regenerated by rewilding.
At Hinewai Reserve (~1,250 ha) on Banks Peninsula, New Zealand, botanist Hugh Wilson from 1987 stopped fighting invasive gorse (Ulex europaeus) on former sheep pasture, using it as a nitrogen-rich nurse crop under which native broadleaf forest regenerated with no replanting, herbicide or intervention.
Demonstrates rewilding through minimisation of human influence and cessation of agriculture, showing natural succession can regenerate forest when active management ceases.
Hinewai Reserve, Banks Peninsula, New Zealand Rewilding, Regeneration and Conservation ChoicesOn Chris Jones's organic beef farm in Cornwall, Eurasian beavers (Castor fiber) reintroduced in 2017 expanded a pond by two-thirds and built leaky dams, and University of Cambridge scientists measured an 80% reduction in nitrates in water leaving the beaver wetland, alongside larger fish and returning otters and invertebrates.
Shows how reintroducing a keystone ecosystem engineer regenerates natural hydrological and water-quality processes even on a small farm in a populated landscape.
Cornwall, England Rewilding, Regeneration and Conservation Choices
3.3.8Conservation and regeneration measures can be used to reverse the decline in biodiversity to ensure a safe operating space for humanity within the biodiversity planetary boundary.
After being hunted to extinction in Britain ~400 years ago, the Eurasian beaver's return culminated in the UK government's 2025 decision to licence wild releases (first at Purbeck Heath, Dorset), requiring each release to have a beaver management plan with mitigations, linked to the international 30 by 30 target to protect 30% of land and water by 2030.
Illustrates how national legislation and international targets combine as regeneration measures to reverse biodiversity decline within the planetary boundary.
Purbeck Heath, Dorset, England Rewilding, Regeneration and Conservation ChoicesThe Eurasian beaver, hunted to extinction in Switzerland by ~1820, was reintroduced from 1956 by naturalist Maurice Blanchet and artist Robert Hainard using French beavers, so that several thousand now live across Switzerland including in the Rhône, Arve and Versoix rivers in canton Geneva.
Shows a successful long-term national regeneration measure re-establishing a locally extinct keystone species, with the 70-year head start over the UK highlighting the role of success factors.
Versoix, Geneva, Switzerland Rewilding, Regeneration and Conservation Choices
3.3.9Environmental perspectives and value systems can impact the choice of conservation strategies selected by a society.
In the UK beaver debate, ecocentric voices like Derek Gow argued beavers intrinsically belong in British rivers, anthropocentric water companies backed them for cheaper flood and pollution control, while some dairy farmers and landowners lobbied against releases over flooded fields and felled trees, resolved by a technocentric licensing system with chicken-wire tree guards and German-style trap-and-relocate schemes.
Demonstrates how ecocentric, anthropocentric and technocentric value systems produce conflicting conservation preferences over a single species, resolved through compromise.
United Kingdom Rewilding, Regeneration and Conservation ChoicesMaungatautari ecosanctuary in New Zealand uses high-tech pest-exclusion fencing (a technocentric strategy) to protect a wild forest that is then largely left to run itself (an ecocentric goal), showing a single project spanning the EVS spectrum.
Shows how a real conservation project blends technocentric intervention with ecocentric non-intervention, reflecting mixed underlying values.
Maungatautari, New Zealand Rewilding, Regeneration and Conservation Choices
3.3.10Success in conserving and restoring biodiversity by international, governmental and non-governmental organizations depends on their use of media, speed of response, diplomatic constraints, financial resources and political influence.HL
Swiss NGOs Pro Natura and WWF Switzerland, despite far smaller budgets than the state, used direct democracy by gathering 65,000 signatures to trigger the 2020 wolf referendum, ran media campaigns, and challenged individual culls in court to halt some shooting orders.
Illustrates how NGOs compensate for weak financial resources by leveraging political influence, media and legal challenge to shape conservation outcomes.
The 1979 Bern Convention (Council of Europe, 49 member states) listed the wolf as 'strictly protected', but only in December 2024 did its Standing Committee — acting on an EU proposal and needing a two-thirds majority — vote to downgrade the wolf to merely 'protected', effective March 2025, with the Czech Republic, Monaco and the UK opting out; Switzerland's own bid for the downgrade in 2022 had failed.
Shows how an IGO's political influence is constrained by diplomatic negotiation and slow speed of response — change took years while wolf numbers shifted rapidly on the ground.
Strasbourg, France The return of the wolf: judging conservation success
3.3.11Positive feedback loops that enhance biodiversity and promote ecosystem equilibrium can be triggered by rewilding and habitat restoration efforts.HL
Along Knepp's restored River Adur, Eurasian beaver (Castor fiber) held in an enclosure dammed the flow and created wetland that supports more aquatic plants and prey, and dragonfly and damselfly abundance rose by around +871% between 2005 and 2025.
Quantifies a rewilding-triggered positive feedback loop in which beaver-created wetland reinforces the conditions supporting more wetland species.
River Adur, West Sussex, England Rewilding Knepp: tipping points, trade-offs and tourismAt Knepp Estate, West Sussex, grazing and trampling by free-roaming herbivores let thorny scrub such as blackthorn and hawthorn establish, which shelters oak seedlings from browsing ('the thorn is the mother of the oak'); more trees and scrub support more insects, birds and seed dispersal, which builds still more scrub — a self-reinforcing loop.
Demonstrates how rewilding triggers a positive feedback loop through food-web interactions that amplifies biodiversity past a threshold into a new wood-pasture stable state.
Knepp Estate, West Sussex, England Rewilding Knepp: tipping points, trade-offs and tourism
3.3.12Rewilding projects have both benefits and limitations.HL
In Gorongosa National Park, Mozambique (4,067 km²), civil war left only ~7,000 large animals by 1994, but the Gorongosa Restoration Project begun in 2008 lifted this to over 100,000 by a 2022 aerial survey, with waterbuck rising from under 500 to over 55,000 and lions from ~15 to over 100 — though rising elephant numbers now damage crops on surrounding farms.
Illustrates the benefits of restocking wildlife in a rewilding project alongside the limitation of rising human-wildlife conflict as populations recover.
Gorongosa National Park, Mozambique Rewilding Knepp: tipping points, trade-offs and tourismKnepp took 1,400 hectares of loss-making arable and dairy farmland out of food production from 2001; its twenty-year review reported breeding birds up around +900% and nightingale singing males rising from 9 to 62 (1999–2025), but the estate has no apex predators (no wolves or lynx) so cattle, ponies, pigs and deer must be controlled by culling, and it depends on stewardship grants and private income.
Shows both the biodiversity/ecosystem-service benefits and the limitations (culling need, funding dependence, lost food production) at the heart of the food-versus-rewilding land-use tension.
Knepp Estate, West Sussex, England Rewilding Knepp: tipping points, trade-offs and tourism
3.3.13The success of conservation or regeneration measures needs to be assessed.HL
In Switzerland's 27 September 2020 referendum on a revised Hunting Act to make wolves easier to shoot, 51.9% voted no (keeping strict protection), but rural Alpine cantons voted heavily for easier culling (~69% in favour in Valais and Uri, 67% in Graubünden) while urban cantons opposed it (only ~37% in favour in Geneva and Basel-City), against a backdrop of ~1,480 farm animals killed by wolves in 2022.
Quantifies Level 2 (community reception) — a measure popular nationally is rejected by the rural communities that bear its costs, so acceptance is uneven.
Valais, Switzerland The return of the wolf: judging conservation successThe gray wolf recolonised Switzerland naturally, with a single male (M1) crossing from the Italian Apennine population into Valais in 1995; the first pack formed at Calanda in 2012, and by the 2025/26 KORA monitoring year there were 43 confirmed packs with 148 cubs, against habitat capacity of 50–100 packs.
Demonstrates Level 1 (outcome) success — a native apex predator absent for a century is now established and breeding — while distinguishing natural recolonisation from reintroduction.
Calanda, Graubünden, Switzerland The return of the wolf: judging conservation success
3.3.14Ecotourism can increase interdependence of local communities and increase biodiversity by generating income and providing funds for protecting areas, but there can also be negative societal and ecological impacts.HL
Gorongosa National Park's 'community-based capitalism' model uses donor funding plus profits from tourism, aviation and agriculture to pay for rangers and restocking, and in 2025 employed 1,894 people (99% Mozambican), including paying farmers to grow coffee on Mount Gorongosa to restore the rainforest feeding the park's rivers.
Shows in a named protected area how tourism income funds biodiversity protection and ties local livelihoods to conservation, while remaining vulnerable to donor withdrawal and long-haul-flight emissions.
Gorongosa National Park, Mozambique Rewilding Knepp: tipping points, trade-offs and tourismKnepp's nature-tourism business — guided wildlife safaris, camping and glamping, and pasture-fed wild-range meat — turns over roughly £800,000 a year, funding the rewilding and reducing reliance on grants while bringing trade to nearby pubs, shops and B&Bs, though it risks disturbing wildlife, causing trampling and over-dependence on visitor income.
Demonstrates how ecotourism income funds area protection and builds local interdependence while also carrying ecological and societal downsides.
Knepp Estate, West Sussex, England Rewilding Knepp: tipping points, trade-offs and tourism
4 Water
4.1 Water systems
4.1.1Movements of water in the hydrosphere are driven by solar radiation and gravity.
On the Mer de Glace glacier in the French Alps, solar radiation drives summer meltwater into the Arve and Rhône and winter sublimation off the ice, while gravity drives the ice downhill at ~75 m/year; since 1850 it has retreated ~2.5 km and thinned ~200 m, forcing repeated relocation of access from the 1909 Montenvers station.
Shows both drivers of the hydrosphere at one site — solar-driven melting and sublimation versus gravity-driven ice and meltwater flow — with outputs now exceeding inputs.
Mer de Glace, France Water Systems
4.1.5Human activities, such as agriculture, deforestation and urbanization, can alter these flows and stores.
During the Valencia DANA of 29 October 2024, over 490 mm of rain fell in 8 hours onto a heavily sealed and deforested floodplain, so infiltration dropped near zero and run-off surged; the barranco del Poyo rose to a peak discharge of ~2,300 m³/s in under two hours, producing flash floods that killed over 230 people, Spain's deadliest in modern history.
Shows how urbanisation reduces infiltration and evapotranspiration while increasing surface run-off, converting rainfall into a rapid, deadly flood peak.
Valencia, Spain Water SystemsIntensive irrigated agriculture (sugar beet, apples, wheat, grapes) in the catchment of Lake Urmia, north-western Iran, involving over 50 dams and more than 88,000 wells, cut river streamflow and depleted groundwater so severely that by 2015 the lake had lost about 88% of its surface area and 95% of its volume, leaving a 5,000 km² salt desert whose dust storms harm about 6 million people.
Demonstrates how agricultural diversion of inflows and groundwater abstraction shrinks a surface freshwater store and reduces streamflow and groundwater flows.
Lake Urmia, Iran Water Systems
4.1.6The steady state of any water body can be demonstrated through flow diagrams of inputs and outputs.
Lake Geneva (Lac Léman) holds ~89 km³ of freshwater and stays roughly in steady state with annual inputs and outputs both around 7.1 km³/year (Rhône inflow 5.7, outflow 6.6, evaporation 0.4, abstraction 0.1), supplying drinking water to about 1 million people.
Quantifies steady state as balanced inputs and outputs in a real water budget, letting sustainable abstraction limits be calculated.
Lake Geneva Water SystemsThe freshwater aquifer beside the Salar de Atacama in northern Chile receives ~180 million m³/year of Andean recharge against outputs of ~165 million m³/year (120 seepage to flamingo wetlands and Atacameño farms, 30 evaporation, 15 town abstraction), so a lithium mining request for an extra 40 million m³/year would push outputs above inputs and deplete the store.
Shows how a flow diagram of inputs and outputs sets the maximum sustainable harvest and reveals when abstraction breaches steady state.
Salar de Atacama, Chile Water Systems
4.2 Water access, use and security
4.2.2Social, cultural, economic and political factors all have an impact on the availability of, and equitable access to, the freshwater required for human well-being.
During Cape Town's 2015–2018 drought, dam levels fell to ~23% of capacity and authorities imposed a 50 L/person/day limit and rising block tariffs; wealthy suburbs drilled private boreholes while ~20% of residents in informal settlements shared communal taps, and agricultural water rights were cut by 60% amid rivalry between city and national government and the legacy of apartheid-era infrastructure.
Demonstrates how social, cultural, economic and political factors together produced deeply unequal water access within one city.
Cape Town, South Africa Water Security and Scarcity
4.2.4Water supplies can be increased by constructing dams, reservoirs, rainwater catchment systems, desalination plants and enhancement of natural wetlands.
In Morocco's semi-arid Aït Baamrane region, the NGO Dar Si Hmad runs the world's largest fog-harvesting project, with ~1,700 m² of mesh nets on Mount Boutmezguida collecting on average ~35,000 litres per day and piping water to over 1,000 people across ~16 villages, cutting women's daily water-collection time from around 3 hours.
Shows a low-energy rainwater/fog catchment system delivering village-scale supply where fog is reliable but not at city scale.
Aït Baamrane, Morocco Water Security and ScarcityThe Grand Ethiopian Renaissance Dam on the Blue Nile, inaugurated in 2025 with a ~74 km³ reservoir and ~5,150 MW capacity (costing ~US$5 billion), more than doubles Ethiopia's electricity but is fiercely opposed by Egypt, which draws ~97% of its freshwater from the Nile, and displaced 5,000–20,000 people.
Shows how dams and reservoirs increase supply while creating evaporation losses, displacement and international disputes.
Grand Ethiopian Renaissance Dam, Ethiopia Water Security and Scarcity
4.2.5Water scarcity refers to the limited availability of water to human societies.
Haiti receives around 1,400 mm of rain a year yet roughly 70% of its population lacks safely managed drinking water and two-thirds lack basic sanitation, because political instability and disasters such as the 2010 earthquake left treatment plants, pipes and sewage systems under-built.
Shows economic water scarcity, where abundant rainfall exists but weak infrastructure and governance prevent safe delivery.
Jordan is one of the most water-scarce countries on Earth: in 2021 each Jordanian had only ~61 m³ of renewable freshwater per year (against the 500 m³ absolute-scarcity threshold), its Jordan and Yarmouk river flows are shared with Syria and Israel, and about half of households receive piped water only once a week despite near-universal connection.
Demonstrates physical water scarcity where extensive infrastructure cannot compensate for a genuine climatic and geographic lack of water.
Jordan Water Security and Scarcity
4.2.6Water conservation techniques can be applied at a domestic level.
Chennai's "Day Zero" arrived in June 2019 when all four city reservoirs ran dry and families queued for 25 L of water per day, prompting mandatory dual plumbing for grey-water reuse in many new buildings.
Illustrates rationing and grey-water recycling as domestic conservation responses forced by acute urban scarcity.
Chennai, India Water Conservation StrategiesUnder NSW's BASIX scheme all new Australian homes since 2004 must meet water-saving targets, usually via rainwater tanks, and ~26% of Australian households now have a tank (rising to ~50% in Adelaide).
Shows regulation-led domestic rainwater harvesting scaled through building codes.
New South Wales, Australia Water Conservation Strategies
4.2.7Water conservation strategies can be applied at an industrial level in food production systems.
India championed the 2023 UN International Year of Millets, expanding drought-resistant crops such as pearl millet, ragi and sorghum (viable on ~350 mm rainfall/year versus ~1,200 mm for rice) to 13.7 million ha by 2024, and highlighting that 1 kg of beef needs ~15,000 L of water against ~1,800 L for wheat.
Shows drought-resistant crops and diet as low-infrastructure industrial strategies that cut agricultural water demand.
Sundrop Farms at Port Augusta, South Australia is a 20 ha greenhouse using solar-desalinated seawater to grow ~17,000 tonnes of tomatoes per year with no fresh water and no fossil fuels, built for ~A$200 million.
Demonstrates a capital-intensive greenhouse system that eliminates freshwater use in industrial food production.
Port Augusta, South Australia Water Conservation Strategies
4.2.8Mitigation strategies exist to address water scarcity.
Australia's national response to Millennium Drought scarcity combined near-universal metering with volumetric pricing, Melbourne's Stage 3a rationing (April 2007–April 2010) which nearly halved per-capita use from ~458 L/day in 1996 to 236 L/day in 2011, compulsory dual-flush toilets (all new toilets since 1993, saving ~32,000 L/household/year), and A$13 billion of Murray-Darling drip/sprinkler conversion saving ~700 GL/year by 2024.
Demonstrates how a high-income country combines domestic and industrial techniques into a coherent national mitigation strategy against drought-driven scarcity.
Australia Water Conservation StrategiesIndia's response to physical and economic water scarcity blends traditional and regulatory measures: Tamil Nadu made rainwater harvesting compulsory for all buildings in 2003 (~5 million homes retrofitted in three years, raising Chennai's water table by up to 50%), Bengaluru's 2024 rationing banned drinking water for car washes and construction with ₹5,000 fines, and the PMKSY scheme put ~8 million ha under subsidised drip/sprinkler irrigation by 2024.
Shows a middle-income country's subsidy-led national mitigation strategy drawing on both domestic and agricultural techniques to address recurrent scarcity.
4.3 Aquatic food production systems
4.3.2Humans consume organisms from freshwater and marine environments.
Lake Geneva perch (Perca fluviatilis), served as filets de perche, is the region's signature dish, but while the lake yields only ~400 tonnes a year, lakeside restaurants sell ~7,300 tonnes annually — the rest imported frozen (mainly from Estonia), and a 2017 Swiss investigation found 6 of 20 restaurants falsely claiming imported perch were locally caught.
Demonstrates a local freshwater species consumed by humans and quantifies how demand outstrips local stocks even before global trade.
Lake Geneva From plankton to plateThe Atlantic salmon (Salmo salar) is an anadromous high-trophic-level predator whose wild populations have collapsed across most of its North Atlantic range, so that most salmon eaten globally is now farmed, with Norway the world's largest producer followed by Chile, Scotland, the Faroe Islands and Canada.
Shows a globally significant food species and links its high trophic level to the energetic inefficiency of producing it as food.
Norway From plankton to plate
4.3.4The increasing global demand for seafood has encouraged use of unsustainable harvesting practices and overexploitation.
In the Baltic Sea WWF and Healthy Seas estimate several hundred tonnes of fishing gear are lost each year, and recovery dives off the German and Polish coasts have pulled up Soviet-era nets some still actively catching cod, demonstrating how ghost gear kills marine life for decades.
Shows ghost fishing as an unsustainable method causing prolonged mortality because synthetic gear does not biodegrade.
Baltic Sea From plankton to plateThe Dogger Bank in the North Sea is one of the most intensively bottom-trawled seabeds in the world with largely degraded seafloor habitats; the UK banned bottom trawling across four offshore Marine Protected Areas including it in 2022, though enforcement remains a challenge.
Illustrates bottom trawling as a destructive unsustainable method and the gap between banning and enforcing.
Dogger Bank, North Sea From plankton to plate
4.3.5Overexploitation has led to the collapse of fisheries.
The Monterey Pacific sardine recovered through the 1990s but collapsed a second time, falling ~97% after 2006, prompting regulators to close the fishery from 2015, again because fishing had been allowed to continue too far into a known decline.
Shows that repeated overexploitation during natural declines reproduces collapse even after an apparent recovery.
Monterey Bay, California, USA Collapse, limits and warming watersThe Pacific sardine (Sardinops sagax) fishery off Monterey Bay, California — once the largest in the western hemisphere at ~700,000 tonnes/year in the 1930s–40s — collapsed after its 1946 peak, falling ~90% in five years (from ~234,000 to ~24,000 tonnes) because the fleet kept fishing hard through a natural, temperature-linked decline; a ban ran 1967–1986 and the stock never fully recovered.
Demonstrates how overexploitation combined with a natural downturn drives a fishery to a collapse from which the commercial stock cannot recover.
Monterey Bay, California, USA Collapse, limits and warming waters
4.3.6The maximum sustainable yield (MSY) is the highest possible annual catch that can be sustained over time, so it should be used to set caps on fishing quotas.
The Monterey sardine fleet illustrates fishing well to the right of the MSY peak: because fleet capacity far exceeded the effort needed to fish at MSY, boats kept working while the stock was already falling, pushing catch onto the downhill side of the yield–effort curve rather than staying at the sustainable maximum.
Demonstrates the syllabus point that real fisheries often fish at far higher effort than the MSY, running the stock down.
Monterey Bay, California, USA Collapse, limits and warming waters
4.3.7Climate change and ocean acidification are having impacts on ecosystems and may cause collapse of some populations in freshwater or marine ecosystems.
Australia's Great Barrier Reef, the world's largest reef system, has suffered repeated mass coral bleaching as ocean temperatures rise, with corals expelling their symbiotic algae and dying, threatening the thousands of species dependent on living coral.
Shows warming waters causing marine ecosystem stress and potential collapse that fishing quotas cannot address.
Great Barrier Reef, Australia Collapse, limits and warming watersLake Geneva (Léman) has failed to mix fully since the cold winter of 2012 because milder winters leave surface water too warm to sink, and monitoring by CIPEL and EPFL shows deep-water oxygen has fallen ~90% in ten years, below the level most aquatic life needs.
Demonstrates climate warming stressing a freshwater ecosystem via reduced deep mixing and deoxygenation, disrupting the food web.
Lake Geneva Collapse, limits and warming waters
4.3.8Unsustainable exploitation of freshwater and marine ecosystems can be mitigated through policy legislation addressing the fishing industry and changes in consumer behaviour.
Sustainable seafood certification schemes shift consumer demand: the Marine Stewardship Council (MSC) blue label certifies wild-caught fish, the Aquaculture Stewardship Council (ASC) certifies farmed fish, and the Marine Conservation Society Good Fish Guide advises shoppers, so producers gain a reason to fish and farm more sustainably even though labelling bans nothing.
Illustrates individual-level mitigation through consumer behaviour and food labelling working via demand rather than legal prohibition.
4.3.9Marine protected areas (MPAs) can be used to support aquatic food chains and maintain sustainable yields.
In 2014 the ~280 km² South Arran Marine Protected Area was designated around Lamlash Bay, with scallop dredging banned from 2016; surveys show adult scallop density falls with distance from the boundary, a spillover sign the benefit reaches surrounding fished waters, while recovering seagrass, kelp and maerl now shelter juvenile fish including young cod.
Shows how a protected area seeds and supplies the wider sea via spillover and nursery habitat, maintaining sustainable yield beyond the reserve boundary.
South Arran Marine Protected Area, Scotland Rules, reserves and fish farmsScotland's first no-take zone was created in Lamlash Bay, Isle of Arran, in 2008 (about 2.67 km²) after over ten years of campaigning by COAST; University of York surveys found king scallop density rose from about 6 to about 23 per 100 m² between 2010 and 2019, and legal-sized lobsters became around four times more abundant and larger than in nearby fished areas.
Quantifies how protecting one patch of sea allows adults to grow larger and denser, demonstrating the recovery mechanism behind MPAs.
Lamlash Bay, Isle of Arran, Scotland Rules, reserves and fish farms
4.3.10Aquaculture is the farming of aquatic organisms, including fish, molluscs, crustaceans and aquatic plants. The industry is expanding to increase food supplies and support economic development, but there are associated environmental impacts.
Scotland is the world's third largest producer of farmed Atlantic salmon (after Norway and Chile), producing around 163,000 tonnes in 2016 with a target of 300,000–400,000 tonnes by 2030; open net sea cages cause seabed dead zones from waste feed and faeces, copper anti-fouling toxicity, antibiotic and sea-lice pesticide pollution, sea lice spread to wild salmon, and escapees that cause genetic introgression in wild stocks.
Demonstrates aquaculture's role in expanding food supply and economic development alongside a full range of named environmental impacts.
West coast lochs, Scotland Rules, reserves and fish farmsTo control sea lice without relying only on chemicals, Scottish salmon farms have placed cleaner fish (wrasse and lumpfish) in cages since the 1990s to eat lice off the salmon, but large numbers of cleaner fish die in the cages, demand has pressured wild wrasse stocks, and in 2025 one of the biggest producers stopped using lumpfish.
Shows a named management technique (biological control) that reduces one impact while creating new problems, allowing evaluation.
Scotland Rules, reserves and fish farms
4.4 Water pollution
4.4.1Water pollution has multiple sources and has major impacts on marine and freshwater systems.
The 2022 River Oder fish kill on the Poland–Germany border: salty waste water from upstream mines and industry, combined with low water levels and high summer temperatures, triggered a bloom of toxic golden alga (Prymnesium parvum) whose toxins attacked fish gills, killing around 250 tonnes of fish over hundreds of kilometres; the two nations ran a joint investigation, restricted salty discharges and set new salinity limits.
Demonstrates how a diffuse industrial pollution source interacts with climate conditions to cause a major freshwater impact and how transboundary management responds.
River Oder, Poland/Germany border Water Pollution and Water QualityThe Lonza chemical plant at Visp, Valais discharged around 50 tonnes of mercury into a canal on the river Rhône between 1930 and 1976; the contamination was only discovered by chance in 2010 and clean-up continues today.
Shows how an identifiable point-source industrial effluent can persist in sediments and soil for decades, making pollution long-lasting and hard to remediate.
Visp, Valais, Switzerland Water Pollution and Water Quality
4.4.2Plastic debris is accumulating in marine environments. Management is needed to remove plastics from the supply chain and to clear up existing pollution.
EPFL researchers towed a manta trawl across Lake Geneva and found microplastics in every beach sample, dominated by tiny polystyrene beads, at levels comparable to parts of the ocean, with the river Rhône carrying the plastic onward towards the Mediterranean.
Shows that plastic accumulation is not just marine — ~80% of ocean plastic originates on land, so lakes and rivers are the source of the problem.
Lake Geneva, Switzerland Water Pollution and Water QualityThe Great Pacific Garbage Patch in the North Pacific is the best-known accumulation of floating plastic trapped in the calm centre of one of the five great ocean gyres, where wind- and Earth-spin-driven currents concentrate debris that persists as plastic for decades.
Demonstrates how ocean gyre circulation concentrates persistent plastic debris, the mechanism behind marine plastic accumulation.
Great Pacific Garbage Patch, North Pacific Ocean Water Pollution and Water Quality
4.4.5Eutrophication occurs when lakes, estuaries and coastal waters receive inputs of mineral nutrients, especially nitrates and phosphates, often causing excessive growth of phytoplankton.
Lake Geneva's decline from the 1950s was driven by phosphate from washing powders, sewage and farm run-off, with total phosphorus peaking near 90 µg/L in 1979 — far above the healthy 10–15 µg/L target — triggering thick blooms because phosphate is the limiting nutrient in most fresh water.
Shows that adding the limiting nutrient (phosphate) from detergents, sewage and fertilisers causes the excessive phytoplankton growth described in the point.
Lake Geneva The lake that turned green
4.4.6Eutrophication leads to a sequence of impacts and changes to the aquatic system.
Brittany's green tides show the eutrophication sequence on a coast: living *Ulva* seaweed is harmless, but when piled a metre thick on beaches it decomposes under a dry crust in airless conditions, and this rotting step releases poisonous hydrogen sulphide.
Shows the decomposition step of the impact sequence is where harm arises, not the growth of algae itself.
Brittany, France The lake that turned green
4.4.7Eutrophication can substantially impact ecosystem services.
Brittany's *marées vertes* (green tides): rivers carry nitrate — over 90% from agriculture per the French Court of Auditors — into shallow sandy Atlantic bays where *Ulva* sea lettuce grows a metre thick, then rots to release toxic hydrogen sulphide that has killed animals including a horse and been linked to human deaths, closing beaches and harming fisheries.
Quantifies how coastal eutrophication simultaneously damages fisheries, recreation, aesthetics and health services.
Brittany, France The lake that turned green
4.4.8Eutrophication can be addressed at three different levels of management.
Lake Geneva (Lac Léman), source of drinking water for over 600,000 people, was badly eutrophic after 1950s phosphate inputs pushed total phosphorus to a peak of ~90 µg/L in 1979; a Franco-Swiss commission (CIPEL, 1963) drove recovery via Switzerland's 1986 laundry-detergent phosphate ban, upgraded phosphorus-stripping sewage works and reduced farm phosphate, bringing total phosphorus down to 15.6 µg/L by the 2025 report with far fewer blooms.
Demonstrates all three management levels (change activity, reduce release, clean up) working together to reverse eutrophication, quantified by the fall from 90 to 15.6 µg/L.
Lake Geneva The lake that turned green