Extinction Risk
  •   Many species are currently on the brink of extinction due to increasing human activity; this is particularly well-documented in the well-studied groups of birds, mammals, and amphibians.

  •   Island species have had a higher rate of extinction than mainland species, due to small populations sizes and less previous exposure to humans and mainland species. Among aquatic species, freshwater species apparently have a higher extinction rate than marine species.

  •   Current rates of extinction are between 100 and 1000 times greater than background extinction levels. More than 99% of modern species extinctions are attributable to human activity.

  •   The island biogeography model is used to predict the numbers of species that will persist in new protected areas and the numbers that will go extinct elsewhere due to habitat destruction and other human activities.

  •   Those species that are most vulnerable to extinction have particular features, including a narrow range, one or only a few populations, small population size, declining population size, and economic value to humans, which leads to overexploitation.

  • Small populations are vulnerable to further declines in size and eventual extinction due to genetic, demographic, and environmental factors, including those that are stochastic (randomly occurring). Intensive management of small populations may be required to prevent their extinction. Effective population size measures the number of breeding individuals, which is likely smaller than the total population and is affected by sex ratios, age structure, and other issues.

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