EDEXCEL GEOGRAPHY A2: Biodiversity Under Threat

Revision cards of biodiversity under threat

~ Defining Biodiversity

~ Threats to Biodiversity

~ Managing Biodiversity

  • Created by: Chloe
  • Created on: 19-01-12 12:18


Biodiversity: Ecologists define as the totality of genes, species and ecosystems in a given area.

Genetic Diverstiy: range of genes found within a particular species. Often determines the degree of resisitance to pests and diseases. Genetic erosion and Genetic pollution found in agro-systems - narrowing of genetic base and general weakening of plant resistance to disease and climate change. Like to have an impact on future global food security.

Species Diversity: Variety of plant and animal species present in an ecosystem. Needed to enable the ecosystem to carry out its functions e.g. carbon cycling, with max efficiency. helps an ecosystem cope with climate change. Removing species from various trophic levels (various parts of the food chain) can have a huge impact on biodiversity & ecosystem functions. Endemism is especially important.

Ecosystem Diversity: number of different ecosystems in a given area. Partly controlled by physical conditions, partically climate, geology, relef & soils. People modifying this is a threat. High biodiversity ecosystems - coral reefs and rainforests.

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Global and continental factors:

  • Size of an area - biodiversity increases with area. large continuous biomes support a wider range of species and extensive boundaries encourage migration. 'size matters'. Only with comparable with similar ecosystems. E.g. polar habitat contains fewer species than a smaller area of rainforest.
  • History and age - biodiversity greater in oldest & least disturbed ecosystems.
  • Isolation - Geographical isolation reducews the number of species but encourages endemism e.g. Galapagos Islands.
  • Altitudinal Range - Large altitudinal range means a cross-section of different climates. More climatic zones - more diverse the habitats. Same with ocean depths. (CLIMATE CHANGE?)

Regional factors:

  • Productivity - Most significant. High temperatures & humidity levels, rich supplies of nutrients & light for photosynthesis. Lack of annual seasons all encourage high primary productivity. e.g. rainforests & coral reefs. Factors limiting growth reduce range and numbers of species.
  • Habitat Architechure - High primary productivity encourages development & ecological niches.
  • Habitat Heterogeneity - Varied physical environment harbour biodiversity - wider range of habitats for a larger variety of species.
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Local Factors:

  • Succession - Biodiversity increases as species establish themselves, interact and subtly alter the environment. e.g. in a sand dune or pond.
  • Interaction Between Species - Competition which may drive certain species to extinction - e.g. when exotic species are introduces.
  • Disturbance - Major environmental disasters e.g. fires, flooding & storms can destroy biodiversity.
  • Dispersal and Colonisation - Individual species' dispersal & colonisation rates have an impact on biodiversity. High rates of efficiency enhance biodiversity.

Human Factors:

  • Undisturbed ecosystems provide a greater range of ecological niches and therefore higher levels of biodiversity.
  • Human factors - Good in terms of conservation. Bad in terms of exploitation/degrading of ecosystems.
  • Level of protection/management, poverty level, direct actions exploiting flora & fauna, hunting, fishing, over-harvesting, clearance for agriculture leading to deforestation, growth of human population, rate of development & local ecosystem factors.
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Direct drivers of change: Local land use, species introduction or removal, technology adaptation & use, external inputs (e.g. fertiliser use, pest control & irrigation), harvest & resource consumption, natural physical & biological drivers e.g. evolution, volcanoes

Indirect drivers of change: Demographic, economic (globalisation, trade, market & policy framework), science & technology, cultural & religious (e.g. beliefs, consumption choices), climate change.

Can cause biodiversity loss OR gain

The Global Distribution of Biodiversity

  • Biodiversity strongly correlated with latitude. Higher levels generally in tropical countries.
  • These are nearly all developing countries with less resources to support sophisticated conservation strategies.
  • Gradual decrease in biodiversity towards higher latitudes.
  • Spatial pattern because of presence or absence of limiting factors controlling primary productivity.
  • Anomalies - 'continental island' of Australia which has high levels of endemism.
  • Brazil - country with most biodiversity. 55,000 species of flowering plant, 1,635 species of bird & nearly 400 species of mammal. Contains Amazonian (largest rainforest in world) - highest biodiversity 
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Hotspots are areas of high biodiversity. They contain a huge number of species & a large percentage that are endemic. They cover less than 2% of the Earths surface, yet they contain 44% of the world's plant species & 35% of its animal species. Hotspots mostly in tropical areas, especially rainforests - many in LDCs where main threat is poverty.

  • Continental hotspots: richest in terms of biodiversity. e.g. Cape floral region in South Africa 
  • Large Island (or continental island) hotspots: harbour diverse and distinctive species
  • Small Island Hotspots: low in species number, but contain a high proportion of endemics. Species on these islands are susceptible to extinction due to small populations, physical disturbances, human exploration and vulnerability to alien species.
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