RARITY IN NEOTROPICAL FOREST MAMMALS REVISITED

The identification of rare species is an important goal in conservatio n biology. Recent attempts to classify rare species have emphasized di chotomies in such characteristics as local population density, area of distribution, and degree of ecological specialization. In particular, Arita et al. (1990) dichotomized 100 Neotropical forest mammals accor ding to local population density and area of distribution Among these species of mammals, mean body mass was significantly associated with l ocal population density and area of distribution. We argue that the ef fects of body mass should be removed before species are classified wit h respect to rarity. We re-evaluated the data on Neotropical mammal sp ecies, using regression analyses to remove the effects of body mass on population density and area of distribution, followed by analysis of residuals. This new method resulted in substantial changes in the dich otomous classification of rare species. We combined the analysis of re gression residuals with a ranking procedure that assumed that local po pulation density and area of distribution were equally important in th eir effects on rarity. The new ranking technique produced another diff erent classification of the rarity of the Neotropical forest mammal sp ecies A graphical analysis showed that ranked species differed substan tially in their degree of rarity, and in the importance of local popul ation density, area of distribution, or both, to their degree of rarit y. The ranking method allows the species of greatest concern to be sin gled out it can be modified to include additional variables such as ni che breadth, and it should be helpful for making conservation decision s.