Reproductive Success of Natterjack Toads Bufo calamita in Two Contrasting Habitats

Abstract

(1) Adult natterjack population density and toadlet production per 100 m2 of breeding water were substantially higher (5-fold and 2-9-fold, respectively) on a eutrophic (dune) habitat than on an oligotrophic (heathland) study site. (2) Key factors in mortality during development were desiccation of shallow, natural dune slacks and saltmarsh pools and predation of tadpoles by invertebrates in all pool types. Developmental failure of spawn was caused primarily by Saprolegnia infestation at low temperatures or by low pH (< 6). (3) Metamorphic success was correlated with high tadpole growth rates. These rates were determined primarily by temperature and food supply, and the latter was a function of water chemistry. Tadpoles grew faster in the more eutrophic pools, though low pH (< 6) reduced growth rates irrespective of food supply. (4) Major predators of natterjack larvae were dytiscid water beetles; others of significance included Notonecta species, Odonata larvae and the newt Triturus cristatus (Linnaeus). (5) Toadlet production varied inversely with respect to numbers of invertebrate predators in the breeding pools, and these in turn varied as a function of pond permanence. Deeper artificial pools exhibited lower tadpole mortality from desiccation but correspondingly higher mortality from invertebrate predation.