Using data for 25,780 species categorized on the International Union for Conservation of Nature Red List, we present an assessment of the status of the world’s vertebrates. One-fifth of species are classified as Threatened, and we show that this figure is increasing: On average, 52 species of mammals, birds, and amphibians move one category closer to extinction each year. However, this overall pattern conceals the impact of conservation successes, and we show that the rate of deterioration would have been at least one-fifth again as much in the absence of these. Nonetheless, current conservation efforts remain insufficient to offset the main drivers of biodiversity loss in these groups: agricultural expansion, logging, overexploitation, and invasive alien species

2016-12-23T18:52:10

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No abstract

We have used computer simulations to determine the sampling distributions of four indices of overlap or similarity: the coefficient of community, Morisita's index, Horn's information theory index, and Euclidean distance. Estimates of overlap were systematically biased downward when sample size was small and when expected values were close to 1. The standard deviations of samples of indices were greatest when expected values were intermediate between 0 and 1, and sample sizes were small. In studies having sample sizes of 25, 50, or 100, one could expect the standard error of an estimated index of similarity to fall between 0.05 and 0.10, provided that samples were truly drawn from homogeneous populations. We suggest that simulations be used to estimate confidence limits on similarity and overlap indices where hypothesis testing is required. In addition, efforts should be made to develop indices of overlap for which statistical measures of dispersion and bias can be derived analytically.