Rarity and diversity in Amazonian forest trees

Threat of extinction has two components. The first is the intrinsic vulnerability of a population to disturbance; and the second comprises changes in the environment that send a population into decline. These components are related because vulnerability can be assessed properly only with respect to specific threats. Nonetheless, many ecologists and conservation biologists believe that certain properties of populations make them generally vulnerable to a variety of disturbances and perturbations. One property is population size, specifically the rarity of a species. Abundance, ecological breadth and geographic distribution vary greatly among species, even among close relatives 1 Gaston K.J. Rarity. Chapman & Hall, 1994 Crossref Google Scholar , 2 Brown J.H. Macroecology. University of Chicago Press, 1995 Google Scholar . The causes of this variation are poorly understood, although, for some taxa in some regions, distribution and abundance have a historical dimension 3 Ricklefs R.E. Bermingham E. Taxon cycles in the Lesser Antillean avifauna. Ostrich. 1999; 70: 49-59 Crossref Scopus (72) Google Scholar .