HOW DO FOOD WEBS FALL APART - A STUDY OF CHANGES IN TROPHIC STRUCTURE DURING RELAXATION ON HABITAT FRAGMENTS

The distribution of vertebrate and plant species among different trophic categories (their trophic distribution) varies very little between different-sized fragments of formerly-continuous habitat. If these fragments plausibly represent different stages in relaxation, then 1) there is no tendency for any of the trophic categories to lose species proportionally faster than any of the others, and 2) species in different trophic categories do not go extinct and colonize independently of one another. Rather, 3) extinctions and/or colonizations in different trophic categories depend on one another in such a way that the same trophic distribution persists on a given fragment while the total number of species declines. This pattern contrasts with earlier evidence that species at higher trophic levels have higher probabilities of extinction. It also contrasts with observed changes in trophic structure during recolonization. This latter difference suggests a potentially important disanalogy between community assembly and community ''disassembly''.