Threats to Biodiversity (HL IB ESS OLD COURSE - IGNORE)

Threats to Biodiversity

• Biodiversity is crucial for ecosystem stability, resilience and functioning

  • However, biodiversity is being negatively affected by both direct and indirect human influences

Direct threats

• Overharvesting:

  • Harvesting of species at a rate faster than their natural reproduction, leading to population decline

    • For example, overfishing of Atlantic cod in the North Sea, leading to population collapse

    • Many tropical rainforests are also under threat from overexploitation

    • They have major ecological and economic value

    • The trees are being cut down and harvested at a rate much faster than reforestation takes place

  • Continued overexploitation of a species can drive it to become extinct

• Poaching:

  • Illegal hunting or capturing of wildlife, often for trade or consumption

    • For example, poaching of African elephants for their tusks, leading to a decline in elephant populations

  • If too many individuals within a species are killed then the population will become so small that it is no longer able to survive and the species may go extinct

• Illegal pet trade:

  • Trafficking of live animals for the exotic pet market

Indirect threats

• Habitat loss:

  • Destruction or fragmentation of natural habitats due to human activities such as deforestation, urbanisation, or agricultural expansion

    • For example, clearing of rainforests in the Amazon for cattle ranching

  • Causes of aquatic habitat loss include: destructive fishing techniques, dredging of wetlands, damage from ships, tourism and pollution

  • Causes of terrestrial habitat loss include: inland dams, deforestation, desertification, agriculture and pollution

  • When a species’ habitat is destroyed or degraded, they no longer have the support systems and resources they need to survive

• Climate change:

  • The change in global climate patterns due to greenhouse gas emissions, leading to habitat disruption, shifts in species distributions and increased frequency of extreme weather events

    • For example, melting of polar ice caps, threatening species like polar bears

• Pollution:

  • Introduction of harmful substances or contaminants into the environment, including air, water and soil pollution

    • For example, plastic pollution in oceans, endangering marine species

• Invasive alien species:

  • Non-native species introduced into an ecosystem that disrupt native species and ecosystems

    • For example, Japanese knotweed in the UK, which outcompetes native plants and causes damage to buildings

  • When humans travel between countries and continents, they often exchange (either intentionally or unintentionally) animal and plant species between their home country and the foreign country

    • These non-native species can be highly problematic as they often have no natural competitors, predators or pathogens that help limit population growth

    • Without these natural population checks, non-native species can massively increase in number

    • The large numbers of non-native species can negatively affect the native species through factors such as competition and disease

Combined impacts

• Most ecosystems face multiple human impacts simultaneously

  • This leads to cumulative effects

  • This is when negative effects are amplified when different threats act together, reducing ecosystem resilience

    • For example, in a coral reef ecosystem, overfishing by human populations weakens the resilience of the coral reef to coral bleaching caused by climate change, making ecosystem collapse more likely