The concept of biodiversity. Local and global trends in biodiversity.…

The idea

Biodiversity encompasses the variety of life at genetic, species, and ecosystem levels. You must understand both global trends, such as the rapid decline of tropical biomes, and local trends, like the loss of specific native flora in a UK woodland. The causes of this decline are multifaceted, including habitat destruction, climate change, pollution, and invasive species. You need to quantify the rates of decline, recognising that current extinction rates are estimated to be hundreds of times higher than the natural background rate, indicating a potential sixth mass extinction. Finally, evaluate the impacts of this loss, ranging from the collapse of local food webs and reduced ecosystem resilience to global consequences like compromised food security and the loss of potential medicinal resources.

What earns the marks

• Define biodiversity comprehensively, including genetic, species, and ecosystem diversity.
• Contrast global biodiversity trends, such as widespread tropical deforestation, with local trends, such as changes in a specific nature reserve.
• Identify and explain the primary anthropogenic causes of biodiversity loss, such as land-use change, overexploitation, and climate change.
• Provide evidence for the rates of declining biodiversity, comparing current extinction rates to historical background rates.
• Assess the ecological and human impacts of declining biodiversity, including loss of ecosystem services and reduced ecological resilience.

Common mistakes and how to put them right

• Defining biodiversity solely as the number of different species.

  Put it right: Broaden the definition to include genetic diversity within species and the variety of ecosystems.

• Confusing local and global trends or providing only global examples.

  Put it right: Ensure you have distinct examples for both scales, such as global coral reef bleaching versus local hedgerow removal.

• Discussing causes of decline without referencing the rate of change.

  Put it right: Explicitly mention the accelerated speed of current biodiversity loss compared to natural evolutionary timescales.

Exam tips

• Use specific indices, such as the Living Planet Index, to provide concrete evidence when discussing global rates and trends of biodiversity decline.
• Link the causes of biodiversity loss directly to their impacts; for example, explain how agricultural runoff causes eutrophication, leading to local fish mortality.
• When discussing impacts, categorise them into ecological impacts, like food web collapse, and anthropogenic impacts, like loss of economic resources, to demonstrate breadth of knowledge.