INTERSPECIFIC COMPETITION BETWEENBUFOLARVAE UNDER CONDITIONS OF COMMUNITY TRANSITION

Abstract

Progressive stabilization (“fixation”) of a sand dune system by vegetational succession has allowed one anuran species (Bufo bufo) to encroach and breed in areas formerly the sole preserve of another (B. calamita). We investigated interactions and the potential for competition between larvae of these two species under conditions of community transition. Survival, growth rates, and spatial and feeding niche overlaps of larvae as well as abundance of the unicellular microorganism Prototheca richardsi (a mediator of interference competition between tadpoles) were measured in three duplicated sets of ponds in the same habitat. One set was used by B. bufo only, one by B. calamita only, and one by both species. B. bufo larvae survived and grew as well, or better, in mixed-species ponds as they did when alone. By contrast, B. calamita larvae grew more slowly, suffered higher premetamorphic mortality, and emerged as smaller toadlets in mixed-species ponds, compared with single-species ponds. B. calamita changed its spatial niche in mixed-species ponds much more markedly than did B. bufo, but spatial and feeding niche overlaps remained high. P. richardsi was rare in guts and feces of larvae in single-species ponds, but it occurred in large numbers in guts and feces of larvae from mixed-species ponds. The data indicate that B. bufo is a superior competitor to B. calamita and that both resource and interference competition may occur between the two species in this transitional situation.