Biodiversity and human population

• Human population density is closely linked with loss of natural habitat for wildlife - the loss tends to be highest where population density is highest.
  
  
• A study of population density and habitat loss showed that out of 50 non-desert countries in Asia and Africa, the top 10, ranked in terms of population density, had lost an average of 79 per cent of their original wildlife habitat. Their average population density was 2,687 persons per square kilometre. The 10 countries with lowest population density had lost an average of only 47 per cent of their wildlife habitat - and their average population density was only 95 persons per square kilometre.
  

  Asian Three-striped Box Turtle (Cuora trifasciata) is one of the most Critically Endangered freshwater turtles in Asia.
  © Kurt A. Buhlmann/IUCN
  
  
  
  

• Loss of diversity of species does not proceed as rapidly as loss of habitat - the two are linked by the species-area formula, based on studies of the number of species found in habitats of varying sizes. Roughly speaking, the number of species declines as the fourth root of the decline in area, though this varies depending on local conditions. This means, for example, that a loss of half of the habitat could still leave over 80 per cent of the species surviving, and half the species would still survive even after 93 per cent of the original habitat had been lost.
  

• Fragmentation of habitats such as rainforest can have a much bigger effect than the simple loss of area would suggest. A loss of half the area, for example, could create a scatter of fragmented patches, each one of which is only a fraction of the size of the original.
  

• A study of biodiversity data from 102 countries found a significant link between population density and the percentage of local bird and plant species that were under threat. In the 51 countries where population density was higher (averaging 168 persons per square kilometre) an average of 5.1 per cent of bird species and 3.7 per cent of plant species were threatened. In the 51 countries where population density was lower (averaging 22 people per square kilometre) only 2.7 per cent of bird species and 1.8 per cent of plants were threatened.
  

• Present population density, of course, is the outcome of past population growth. Slower population growth now will mean lower population density in the future - and hence less deforestation, less loss of wildlife habitat, and fewer threats to biodiversity.

Sources:

Conservation International: Biodiversity

Paul Harrison, The Third Revolution, Penguin Books, London, 1993.

Richard Cincotta and Robert Engelman, Nature's Place, Population Action International, Washington, 2000.

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