Proc. 4th Int. Symp., Bonn Bonn zool. Monogr. 46 (2000) Rheinwald, G. (ed.), In: Isolated Vertebrate Communities in the Tropics pp. 9-24.   Analyzing species composition in fragments B.D. Patterson & W. Atmar Abstract : Fragmented systems tend to exhibit distinctive patterns of species richness and species composition. Because local extinctions on fragments are no longer balanced by immigration from surrounding areas, their species-area relationships characteristically exhibit high slopes. Small fragments often support many fewer species than an equivalent area of contiguous habitat. In addition, fragments often support “nested subsets” of species, where the species comprising smaller local assemblages constitute a proper or included subset of the species in richer ones. Nestedness appears most prevalent and most strongly developed in fragmented systems, where species composition has been sculpted by local extinction. However, this structure also characterizes other kinds of ecological systems. Extinction, colonization, disturbance, habitat distribution, hierarchical niche relationships, and passive sampling may all shape local assemblages into nested patterns. Although nested structure per se can tell us little about the processes that produced it, the ordering of species and sites in a nested matrix can tell us a great deal about possible causation. Characteristics of species or sites that correlate strongly with these vectors become plausible contributors to the nested structure shown by the system as a whole. Key words : Biogeography, extinction, habitat fragments, nested subsets, species composition (259K)