next up previous
Next: Rates of extinction Up: Patterns of biological extinction Previous: Background extinction


The causes of extinction

The causes of extinction are (mostly) fairly obvious, and my first set of notes touched on one of the largest ones all ready--habitat destruction and conversion. But let's spend a little time reminding ourselves what the causes of extinction are, because knowing those causes helps us better to understand their consequences.


Table 1: Proportion of old-growth forest remaining in selected temperate forest countries (from Table 11.2-6 [17]).
Country/Region % of old growth forest
USA 15
    Washington & Oregon 13
Canada 52
    British Columbia 40
Europe  
    Western Europe 1
    Scotland 1
    Sweden 1
    Finland 2
    Norway 3
Oceania  
    New Zealand 25
    Australia 5-21
Asia  
    China 1


Wilcove, Rothstein, Dubow, Phillips, and Losos [19] surveyed recovery plans for species listed under the United States Endangered Species Act and categorized the threats they identified into one of five categories: habitat degradation/loss, alien species, pollution, overexploitation, and disease. Table 2 shows the percentage of listed species for which each of these five factors was mentioned as a cause contributing to endangerment.7


Table 2: Causes of endangerment mentioned in species recovery plans [19].
  All Vertebrates Invertebrates Plants
Cause $(n=1880)$ $(n=494)$ $(n=331)$ $(n=1055)$
Habitat degradation 85% 92% 87% 81%
Alien species 49% 47% 27% 57%
Pollution 24% 46% 45% 7%
Overexploitation 17% 27% 23% 10%
Disease 3% 11% 0% 1%


In short, many species are going extinct now to reasons related to human activities. We are responsible for the elevated rates of extinction, but they don't tell us how many species are going extinct.


next up previous
Next: Rates of extinction Up: Patterns of biological extinction Previous: Background extinction
Kent Holsinger 2013-08-29