Nested subsets and partition patterns in ant assemblages (Hymenoptera,Formicidae) of Colombian dry forest fragments

摘要

We analyzed the conservation status of ant assemblages in seven dry forest fragments located in the Cauca River valley in southwestern Colombia, by means of nested subsets techniques which are applicable in situations where a fragmented landscape can be compared with an archipelago. Ant communities were intensively sampled between 1993 and 1995 in all forests as well as in their surrounding matrices (i.e.. neighboring agricultural lands). From 123 ant species found, 63 species were captured only in the forest habitat and 60 ant species in both forests and matrices ("habitat generalist"). No significant species-area relation was found. Monte Carlo simulations and N index showed a significant nesting for "habitat generalist" ant species. The opposite was true for the ant species limited to forests: we found a pattern of' extreme non-nestedness (i.e., the opposite of nestedness pattern). which cannot be explained in terms of random effects. This led us to amplify the nested subsets analysis by the concept of "partition pattern" which describes a scheme, where species found on one island of an archipelago are not likely to be found on any other one. The relevance of partition identification in conservation biology is obvious: in a partitioned archipelago, it is essential to protect all component islands. Each one possesses a fauna not repeated in the whole archipelago. Destroying this fauna means extinguishing it in the whole archipelago.