THE BASIS OF NICHE SEPARATION DURING TERRESTRIAL LIFE BETWEEN 2 SPECIES OF TOAD (BUFO-BUFO AND BUFO-CALAMITA) - COMPETITION OR SPECIALIZATION

Two congeneric anurans with highly overlapping geographical ranges, Bu fo bufo and B. calamita, were investigated with respect to isolating m echanisms during the terrestrial phase of life in the three habitat ty pes in which both species occur in Britain. Marked spatial niche separ ations were observed in all three habitats (coastal dunes, upper saltm arshes and lowland heaths). B. bufo was associated with complex, dense vegetation structures and had a relatively wide niche, while B. calam ita had a narrower niche and occurred mostly on open, poorly-vegetated ground. Food niche overlap was high at all three study sites. Animals translocated into atypical habitats returned to their preferred type whenever possible, and suffered increased mortality or loss of conditi on if prevented from doing so. B. calamita operated at significantly h igher body temperatures (by an average of 1.4-degrees-C) than B. bufo when hunting at night. Experiments in outdoor vivaria indicated that B . calamita survived in open habitats because individuals escaped desic cation in daytime by burrowing into the substrate, whereas B. bufo lac ked this behaviour and perished on the inhospitable surface. By contra st, B. calamita individuals lost mass and became hyperactive in densel y-vegetated conditions because their hunting efficiency was selectivel y reduced relative to that of B. bufo. Taken together, the data indica ted that spatial niche separation between these species during the ter restrial phase of life was dictated primarily by behavioural and physi ological factors, and not by competition.