Biodiversity through time

• Millions of species have already been discovered, named and described, but many more remain undiscovered.

• Fossil evidence suggests there are more species alive now than at any time in the past.

• Exam link: current biodiversity is very high, but it is now threatened by the sixth mass extinction.

• NOS point: classification can vary; “splitters” recognize more species, while “lumpers” group more organisms together.

• This means measured biodiversity can depend partly on how species are classified.

Anthropogenic species extinction

• Focus on human-caused extinction, not the natural causes of earlier mass extinctions.

• The current crisis is the sixth mass extinction and is anthropogenic.

• Learn extinction as a consequence of human activity such as overhunting, habitat destruction, pollution, and introduced species/disease.

• Required case-study examples named in the syllabus:

  • North Island giant moa (Dinornis novaezealandiae) = loss of terrestrial megafauna.

  • Caribbean monk seal (Neomonachus tropicalis) = loss of a marine species.

  • One local/extinct familiar species may also be used by teachers.

• In longer responses, always connect the extinction to a specific human driver.

This image shows the Caribbean monk seal, one of the syllabus extinction examples. It is useful for linking anthropogenic extinction to the loss of marine biodiversity. Source

This image shows the North Island giant moa, the syllabus example of extinct terrestrial megafauna. Use it to remember that humans have caused major biodiversity loss on land as well as at sea. Source

Ecosystem loss

• Study only directly or indirectly anthropogenic causes of ecosystem loss.

• Key idea: losing an ecosystem removes habitat, disrupts food webs, reduces species richness, and often lowers genetic diversity too.

• Named syllabus case study: loss of mixed dipterocarp forest in Southeast Asia.

• Common human causes include:

  • deforestation

  • clearance for agriculture

  • urbanization

  • resource extraction

  • fragmentation of habitats

• Exam tip: distinguish species extinction from ecosystem loss, but explain how they are strongly linked.

These images show mixed dipterocarp forest, the named Southeast Asian ecosystem case study in the syllabus. They are useful for linking deforestation and habitat clearance to large-scale ecosystem loss. Source

Evidence for a biodiversity crisis

• Evidence should come from reliable surveys across a wide range of habitats.

• Surveys must be repeated over time to show changes in:

  • species richness = number of species present

  • species evenness = how evenly individuals are distributed among species

• A single survey shows a snapshot; repeated surveys show change.

• Evidence can come from expert scientists and also citizen scientists, but methods must be checked carefully.

• NOS point: evidence should ideally come from published, peer-reviewed sources with a method that can be evaluated.

• Exam tip: if asked why evidence is convincing, mention repetition, large sample range, published methodology, and changes in richness/evenness.

This page summarizes major global evidence for a modern biodiversity crisis. It is useful for remembering that the crisis is supported by large-scale international assessments, not isolated observations. Source

Causes of the current biodiversity crisis

• Human population growth is the overarching cause because it increases pressure on land, water, food, energy, and natural resources.

• You must know the named direct causes:

  • hunting and other forms of over-exploitation

  • urbanization

  • deforestation

  • clearance of land for agriculture

  • loss of natural habitat

  • pollution

  • spread of pests, diseases, and invasive alien species through global transport

• Best exam approach: explain the crisis as human population growth driving multiple direct pressures.

• Do not treat the causes as isolated; many act together.

Conservation strategies: why multiple approaches are needed

• No single conservation strategy is sufficient.

• Different species and habitats need different measures.

• Required approaches:

  • In situ conservation = conserving species in their natural habitats.

  • Nature reserve management = active protection/monitoring of important habitats.

  • Rewilding = restoring natural processes and species interactions.

  • Reclamation of degraded ecosystems = repairing damaged habitats.

  • Ex situ conservation = conservation outside natural habitats, such as zoos and botanic gardens.

  • Storage of germ plasm in seed banks or tissue banks.

• High-mark point: compare in situ vs ex situ.

  • In situ keeps organisms in normal ecological interactions and preserves habitat.

  • Ex situ is useful when wild populations are extremely small or habitats are no longer safe.

• Seed banks/tissue banks help preserve genetic diversity for future restoration and breeding programmes.

This image represents ex situ conservation through germ plasm storage. It is useful for remembering how seed banks preserve plant genetic diversity even when wild populations are threatened. Source

EDGE of Existence and conservation prioritization

• EDGE stands for Evolutionarily Distinct and Globally Endangered.

• The idea is to prioritize species that are:

  • highly endangered, and

  • evolutionarily unique with few close relatives.

• Rationale: if an EDGE species goes extinct, a large amount of unique evolutionary history is lost.

• This helps conservationists decide where limited funding and effort may have the greatest long-term value.

• Exam tip: this is about prioritization, not saying other species do not matter.

• NOS point: conservation priorities involve ethical, environmental, political, social, cultural, and economic debates.

Exam links and common mistakes

• Be able to separate species extinction, ecosystem loss, biodiversity crisis evidence, causes, and conservation responses.

• Do not define biodiversity only as number of species; include genetic and ecosystem diversity too.

• Do not say one method alone solves biodiversity loss; the syllabus explicitly says several approaches are needed.

• When using evidence, mention repeated surveys, species richness, and species evenness.

• When discussing causes, include human population growth as the overarching cause plus named direct causes.

• When discussing conservation, use precise vocabulary: in situ, ex situ, rewilding, germ plasm, seed bank, tissue bank, nature reserve management.