Temporary ponds as amphibian habitats

1. Temporary ponds provide rich but unpredictable habitats for amphibians. Frogs, toads and newts have life cycles which are geared to the filling and drying-up of temporary ponds, and have evolved strategies for dealing with desiccation and short-term changes in pond quality. 2. Plasticity in development allows frogs and toads to adjust the rate of larval development according to the risk of pond desiccation. This may be achieved by increasing behavioural thermoregulation so that body temperature is raised in warm, shallow water. 3. As a pond dries up, increased crowding between amphibian larvae may result in increased competition, growth inhibition, and cannibalism. Large larvae may therefore survive at the expense of small larvae, but this may increase the chance of some reproductive success within the population as a whole. Conflicting selection pressures may maintain different breeding strategies within the same population. 4. Despite high fecundity, repeated breeding by adults, and developmental plasticity and cannibalism in larvae, many larval populations still suffer catastrophic mortality each year. Providing catastrophes do not occur more often than once per generation, the population may still persist. Should extinction occur at one pond, immigration of juveniles or adults from a neighbouring pond may ensure population continuity. Networks of ponds are therefore essential to maintain viable, self-adjusting metapopulations into the long-term. (C) 1997 John Wiley & Sons, Ltd.