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|
|great auk||North Atlantic||1844||hunting by sailors|
|passenger pigeon||North America||1889||hunting and habitat destruction|
|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’|
|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|
|St Croix racer||St Croix, US Virgin Isles||1900s|