Health and environment
Health and environment

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Health and environment

4 Changes in relative abundance of species

4.1 Human predation and extinctions

There are a number of ways in which humans have altered ecosystems, that have led to the decline of particular species. We will leave to one side any major interference such as felling forests to provide land for agricultural and urban development, and instead begin by looking at examples where we have eroded or eradicated stocks of particular species. This has notably been a consequence of the over-exploitation of food species (prey items). Predators do not normally eliminate their prey (see Figure 4), but the use of sophisticated tools, such as guns and fishing gear, has led to our being over-successful as hunters. The disappearance of the dodo must surely be the best-known example, but it is not an isolated occurrence. Table 2 shows some other vertebrate extinctions that correlate with human activity. This table gives a selection of species only. For example, around 100 species of bird are known to have become extinct since 1600.

Table 2 Some vertebrate extinctions.

Species Former distribution Last recorded in wild Probable cause of extinction
Birds
dodo Mauritius c. 1680 hunting
great auk North Atlantic 1844 hunting by sailors
passenger pigeon North America 1889 hunting and habitat destruction
pink-headed duck Bengal 1936 hunting
Mammals
auroch Europe 1627 hunting and habitat destruction
Caribbean monk seal Caribbean c. 1960 hunting
Steller's sea cow North Pacific 1768 hunting
Tasmanian wolf Tasmania 1900s hunted as a ‘pest’
Fish
harelip sucker rivers of North America 1893 fishing and habitat destruction
blue pike Great Lakes, North America 1970 over-fishing, pollution, predation by introduced fish species
Reptile
St Croix racer St Croix, US Virgin Isles 1900s
SK220_2

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