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.

SpeciesFormer distributionLast recorded in wildProbable cause of extinction
Birds
dodoMauritiusc. 1680hunting
great aukNorth Atlantic1844hunting by sailors
passenger pigeonNorth America1889hunting and habitat destruction
pink-headed duckBengal1936hunting
Mammals
aurochEurope1627hunting and habitat destruction
Caribbean monk sealCaribbeanc. 1960hunting
Steller's sea cowNorth Pacific1768hunting
Tasmanian wolfTasmania1900shunted as a ‘pest’
Fish
harelip suckerrivers of North America1893fishing and habitat destruction
blue pikeGreat Lakes, North America1970over-fishing, pollution, predation by introduced fish species
Reptile
St Croix racerSt Croix, US Virgin Isles1900s
SK220_2

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