No abstract

among islands and regions using nested, mixed-model ANOVA. We screened several potential estimators to find that the Chao 1 procedure provided the most stable values for local species richness. This estimator is the sum of the observed number of species and the quotient a 2 /2b, where a and b equal the number of species represented by one and two colonies, respectively.To analyse the local-regional species richness relationship in each habitat, we used a simple linear regression of the mean local richness per site in a region against habitatspecific regional richness. Linearity is supported by these and supplemental regressions using: (1) log-transformed richness data; (2) local richness standardized to 100 or more colonies per sample 18 ; and (3) the two alternative measures of local species diversity, Fisher's alpha and the Chao 1 estimator of local richness.

Slowing rates of global biodiversity loss requires preventing species extinctions. Here we pinpoint centers of imminent extinction, where highly threatened species are confined to single sites. Within five globally assessed taxa (i.e., mammals, birds, selected reptiles, amphibians, and conifers), we find 794 such species, three times the number recorded as having gone extinct since 1500. These species occur in 595 sites, concentrated in tropical forests, on islands, and in mountainous areas. Their taxonomic and geographical distribution differs significantly from that of historical extinctions, indicating an expansion of the current extinction episode beyond sensitive species and places toward the planet's most biodiverse mainland regions. Only one-third of the sites are legally protected, and most are surrounded by intense human development. These sites represent clear opportunities for urgent conservation action to prevent species loss.biodiversity ͉ conservation ͉ protected area ͉ threatened species