A4.2 Conservation of biodiversity

Conservation of biodiversity connects biodiversity measurement, human-driven losses, ecosystem evidence, and targeted conservation strategies for protecting species, communities, and evolutionary history.

Learning objectives

A4.2.1Biodiversity definition• Biodiversity is the variety of life in its forms, levels, and combinations• It includes ecosystem, species, and genetic diversity• Species diversity depends on richness and evenness; Simpson's reciprocal index compares communities A4.2.2Current vs. past biodiversity• About 9 million species are estimated, with many still undescribed• Fossils and radiometric dating give incomplete evidence of past biodiversity• Current species diversity may be higher than in the past, but fossil gaps make this uncertain A4.2.3Anthropogenic species extinction• Human activity is driving a sixth mass extinction• Hunting, habitat change, and resource use caused extinctions such as North Island giant moa• Caribbean monk seal loss shows how removing a top predator can alter food webs A4.2.4Ecosystem loss causes• Ecosystem loss is mainly caused by anthropogenic disturbance and habitat conversion• Mixed dipterocarp forests in Borneo are lost through logging and oil palm plantations• Great Barrier Reef loss is linked to climate, pollution, fishing, and other human pressures A4.2.5Evidence for biodiversity crisis• IPBES reports and repeated biodiversity surveys provide evidence of crisis• Richness, evenness, and Simpson's reciprocal index can compare disturbed and undisturbed habitats• Peer-reviewed studies and citizen science both contribute data, with reliability checks needed A4.2.6Causes of biodiversity crisis• Human population growth increases demand for food, housing, energy, and land• Major drivers include overexploitation, urbanization, deforestation, agriculture, mining, and pollution• Invasive species such as lionfish and water hyacinth can outcompete or disrupt native species A4.2.7Conservation approaches• Conservation needs multiple approaches because species and threats differ• In situ conservation uses protected areas, reserve design, corridors, active management, and rewilding• Ex situ conservation uses zoos, captive breeding, botanic gardens, seed banks, and tissue banks A4.2.8EDGE of Existence programme• EDGE prioritizes evolutionarily distinct and globally endangered species• It combines phylogenetic uniqueness with IUCN extinction risk• The goal is to prevent disproportionate loss of evolutionary history

Biodiversity is the variety of life at genetic, species and ecosystem levels. A community can have the same richness as another yet lower diversity if one species dominates.

Two beetle communities have equal species richness but different evenness; the more even community has greater species diversity.

$D = \frac{N(N-1)}{\sum n(n-1)}$

N is the total number of organisms and n is the number in each species. For comparable samples, a larger D indicates greater species diversity.

Present biodiversity is estimated from field surveys, species records and DNA-based discovery. Past biodiversity is reconstructed from fossils placed in dated geological contexts.

Parallel evidence pathways show field sampling, records and DNA barcoding for living species, and fossils, strata and radiometric dates for past diversity; both contain sampling gaps.

Claim	Main evidence	Main limit
about 9 million living species	sampled habitats, described species and extrapolation	many habitats and species remain unsampled or undescribed
change in diversity through geological time	fossils, stratigraphy and radiometric dating	fossilisation and discovery are selective and incomplete

Human activity can raise mortality, remove habitat and shrink populations until recovery is impossible. Small fragmented populations also face inbreeding, genetic drift and chance events.

Two causal chains link hunting and habitat clearance to moa extinction, and hunting plus overfishing to Caribbean monk seal extinction.

Case	Human pressure	Population effect	Wider effect
North Island giant moa	hunting and forest clearance	mortality rose while habitat fell	extinction
Caribbean monk seal	hunting and depletion of food by fishing	a small population could not recover	extinction and loss of a top predator

Ecosystem loss includes conversion, degradation and fragmentation. These change habitat structure and abiotic conditions, disrupt interactions and nutrient cycling, and reduce resilience.

Borneo rainforest pressures and Great Barrier Reef pressures lead to loss of terrestrial and marine community structure.

Ecosystem	Pressures	Biological pathway
Borneo mixed dipterocarp forest	logging, fire and oil-palm conversion	canopy and habitat loss → fragmentation → decline of forest communities
Great Barrier Reef	warming, falling pH, runoff and fishing	coral stress and mortality → habitat loss → reef-community decline

A biodiversity crisis is supported by consistent declines across repeated, comparable measurements, not by one low count.

Set a baseline with defined sites, season, method and sampling effort.
Repeat the same protocol and control changes in detectability.
Track richness, evenness, abundance and, where suitable, Simpson reciprocal index.
Compare independent datasets and syntheses such as IPBES reports.

Evidence source	Strength	Reliability check
peer-reviewed study	detailed methods and scrutiny	sampling design, replication and uncertainty
citizen science	wide spatial and temporal coverage	training, validation and correction for reporting bias

Population size and consumption create pressure through land, food, energy and material demand. Biodiversity changes through the biological mechanism of each driver.

Driver	Biological mechanism	Useful response to monitor
habitat conversion and urbanisation	habitat area and connectivity fall	range, occupancy and fragment connectivity
overexploitation	mortality exceeds recruitment	abundance, age structure and harvest rate
pollution and climate change	survival, reproduction or species interactions change	reproductive success, mortality and distribution
introduced invasive species	competition, predation, disease or habitat change	native abundance and invader spread

An alien species occurs outside its natural range through human activity. It is invasive when it spreads and causes ecological or economic harm; alien does not automatically mean invasive.

Conservation works when the intervention removes or reduces the diagnosed threat and protects a viable population, habitat or ecological process.

Reserve-design comparisons show the effects of size, edge shape, isolation and habitat corridors on conservation value.

Approach	Best suited to	Examples	Key condition
in situ	protecting species in functioning habitat	reserves, corridors, rewilding	threats must be controlled in the habitat
ex situ	preventing immediate loss or preserving genetic material	captive breeding, zoos, botanic gardens, seed and tissue banks	genetic diversity and suitable release habitat must be maintained

diagnose threat → select action at the same scale → set a measurable biological target → monitor → adapt management

EDGE combines Evolutionary Distinctiveness (ED) with Global Endangerment (GE). ED measures how isolated a species is on the tree of life; GE reflects IUCN extinction risk.

A phylogenetic branch and endangerment gauge combine to place a highly distinct, highly threatened frog in the high-EDGE region.

High ED + high GE → high EDGE priority. Protecting such a species avoids losing a disproportionately large amount of evolutionary history.

EDGE is a prioritisation tool, not the whole conservation plan: feasibility, ecosystem role, cost and the causes of decline still shape the intervention.

Focus	Measure the state or trend	Diagnose the driver	Match the action	Monitor recovery
genetic diversity	allelic variation, heterozygosity, population size	isolation, bottleneck or inbreeding	reconnect populations or manage breeding	genetic diversity and effective population size
species diversity	richness, evenness, abundance, extinction risk	exploitation, invasive species or habitat change	protect, control threats, breed or reintroduce	abundance, recruitment and distribution
ecosystem diversity/function	habitat extent, condition and process indicators	conversion, fragmentation, pollution or climate stress	protect, restore and reconnect habitat	structure, processes and resilience

Define the level → establish a comparable trend → identify the causal driver → choose an action at the same scale → test whether biological recovery follows.

No single index or intervention is sufficient: species counts can miss evenness, genetic erosion and ecosystem dysfunction, while a reserve can fail without connectivity, enforcement or threat removal.

4 marks

Entire communities need to be conserved in order to preserve biodiversity. Suggest different quantitative methods to measure changes in biodiversity in a community over time.

1 mark

The North Island giant moa (Dinornis novaezealandiae) went extinct some time between the arrival of humans in New Zealand and the 1800s.

What do scientists believe to be the cause of this extinction?

1 mark

The satellite images show changes in the area covered by forest, much of which is mixed dipterocarp forest, on the island of Borneo in Southeast Asia.

Which human activities are most likely to have caused the changes shown in the map?

3 marks

List human actions that could threaten populations of insect pollinators such as bees.

4 marks

Discuss in situ and ex situ conservation of endangered species.

2 marks

Outline the importance of the EDGE of Existence programme.

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A4.2 Conservation of biodiversity

Learning objectives

Biodiversity Exists at Three Linked Levels

Present and Past Biodiversity Need Different Evidence

Trace Human Pressure to Extinction through Populations

Ecosystem Loss Breaks Structure and Process

A Biodiversity Crisis Is a Trend, Not One Snapshot

Human Demand Acts through Several Biological Drivers

Conservation Must Match the Threat and the Scale

EDGE Prioritizes Unique Evolutionary History at Risk

Summary: Turn Biodiversity Evidence into Action

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