Endemism in historical biogeography and conservation biology: concepts and implications

Endemism is often misinterpreted as referring to narrow distributions (range restriction). In fact, a taxon is said to be endemic to an area if it lives there and nowhere else. The expression “endemic area” is used to identify the geographical area to which a taxon is native, whereas “area of endemism” indicates an area characterized by the overlapping distributions of two or more taxa. Among the methods used to identify areas of endemism, the optimality criterion seems to be more efficient than Parsimony Analysis of Endemism (PAE), although PAE may be useful to disclose hierarchical relationships among areas of endemism. PAE remains the best explored method and may represent a useful benchmark for testing other approaches. Recently proposed approaches, such as the analysis of nested areas of endemism, networks and neighborjoining, are promising, but need to be more widely tested. All these methods attempt to identify biogeographically homogeneous sets of areas characterized by shared species, without any attempt to evaluate their relative importance for conservation purposes. Analyses based on weighted endemism methods identify areas of endemism according to specie distributional rarity and phylogenetic position, being thus appropriate for conservation purposes. The proportion of endemic species to the total number of species living a given area is the most frequently used measure to rank areas according to their relative endemism. However, proportions obscure differences in raw numbers that can be important in conservation biology. Because the number of (endemic) species tends to increase with area, some authors proposed to model the endemics-area relationship and to consider the areas displaced above the fitting curve (i.e. those having a positive residual) as hotspots. However, the use of residuals may lead to areas being identified as hotspots for almost every size class of richness. Thus, it is important to evaluate the ability of the hotspots recovered by these procedures to really conserve total (endemic) species diversity.