Factors Affecting Population Densities of Adult Natterjack Toads Bufo calamita in Britain

Abstract

The population densities of adult natterjack toads (Bufo calamita, Laurenti) were found to vary over an order of magnitude between different localities for this species in Britain. Adult toad population density correlated positively with average toadlet production over the previous decade at each site. Average toadlet production in turn correlated with breeding pond density at natterjack sites and the adult toad population size at one study site increased subsequent to an artificial increase of pond density. Toadlet production within particular ponds was positively correlated with spawn deposition rate and there was no evidence of density-dependent regulation of toadlet production in two natterjack breeding ponds studied over several years. The proportion of breeding seasons in which greater than the median number of toadlets was produced per hectare of total natterjack habitat was positively correlated with pond density at natterjack sites. Taken together, these data suggest that adult natterjack population density is primarily regulated by the average rate of metamorphic success at a site, and this in turn is dependent upon stochastic rather than density-dependent processes operating at the level of the breeding ponds.