Reproductive Ecology of Bombina variegata: Habitat Use

Abstract

Reproduction in variable habitats is characterized by uncertainty and requires selection of suitable conditions. Environmental variability may be temporal, spatial, or both. The same site may differ in its suitability for reproduction at different times within a reproductive period, and several associated sites may differ at any one time (Stearns, 1992). The appropriate response to temporal variability depends on the predictability of the environment. In periodically changing habitats, reproduction at predictably successful times is the normal case, whereas in an unpredictable and changing habitat, assessing and reacting to rapidly changing conditions may be essential. Anurans spawning in rain-filled ponds of unpredictable duration may be expected to synchronize their spawning with rainfall, reproduce more than once per season in favorable years and skip reproduction in unfavorable years (see Barandun and Reyer, 1997a, 1997b; Barandun et al., 1997; and references therein). The response to spatial variability is more complex. In patchily distributed breeding sites, there are three possibilities: (1) individuals can return to their natal site throughout their life, provided the site persists over sufficient time; (2) they can disperse to new sites as juveniles and thereafter remain sedentary as adults; and (3) they can remain nomadic and search for new sites throughout their lives. Dispersal is a common phenomenon among all groups of organisms (Hanski and Gilpin, 1991) and can lead to genetic exchange among populations, colonization of new habitats, and recolonization after local extinction (Greenwood, 1982; Hansson, 1991). When a local population is saturated, dispersal can be favored even when there is only a small chance for individuals to become established in another population (Hansson, 1991). Dispersal does not exclude the possibility that some individuals may return to their natal sites. Whether sexually mature individuals exhibit site fidelity depends on the scale of environmental variability and life expectancy. When reproduction is likely to be successful at the same site throughout an individual's life, site fidelity may be the best choice. Several species of anurans breeding in stable and permanent ponds seem to choose this strategy (Heusser, 1960; Berven and Grudzien, 1990; Reading et al., 1991). Dispersal to new sites will be favored when the suitability of the habitat changes quickly or is unpredictable. Ovipositing in different ponds also spreads the risk of reproductive loss (Kaplan and Cooper, 1984). Empirical data, however, are scarce for anurans, mostly because of methodological constraints. Juvenile dispersal seems to be widespread, but adult dispersal and spawn distribution is poorly documented (Merrell, 1970; Daugherty and Sheldon, 1982; Reading et al., 1991). Bombina variegata uses various ponds for reproduction, most of them temporary (Bauer, 1987). We studied a population in a habitat with a variety of different temporary ponds, where pond conditions change unpredictably within and among years, mainly due to climatic conditions and human activities (Barandun and Reyer, 1997a). The question was whether individuals spawn in a single pond or spread the risk of reproductive failure, mainly due to desiccation (Barandun and Reyer, 1997b), by ovipositing in different ponds within a breeding season.