Long-term management of a natterjack toad (Bufo calamita) population in southern Britain

Abstract

Abstract We have investigated the dynamics of an isolated population of natterjack toads (Bufo calamita) over the period 1972-1991. During this time the habitat was manipulated by clearance of scrub woodland and by creation and restoration of ponds. The adult toad population increased at least threefold during the study, with a nadir in the late 1970s and a maximum in the late 1980s. Female population size, as judged by spawn string counts, varied according to metamorphic success rates three years previously. Ponds suitable for natterjack breeding on chemical and topographical grounds nevertheless varied both in their attractiveness to natterjacks and in their success rates in sustaining larvae through to metamorphosis; those desiccating at intermediate times were more successful than highly ephemeral or longer-lasting water bodies. Artificial eutrophication of one naturally acid pond by addition of Ca((OH)2 increased its attractiveness to natterjacks for several years but did not sustain high levels of toadlet production. Female natterjacks survived up to twice as long as the oldest males, a difference possibly attributable to selective predation by the snake Natrix natrix. Invertebrates, especially beetles (Coleoptera) and ants (Hymenoptera) were the primary food of both natterjacks and sympatric common toads (B. bufo) at the study site. Addition of fish (Leuciscus idus) to breeding pools reduced numbers of predatory invertebrates and increased toadlet production in two separate experiments. Optimal terrestrial habitat for natterjacks was sustained only for 2-3 years after scrub clearance, after which seral succession rendered it unsuitable.