THE BREEDING SYSTEM OF PUPFISH, CYPRINODON-PECOSENSIS - EFFECTS OF DENSITY AND INTERSPECIFIC INTERACTIONS WITH THE KILLIFISH, FUNDULUS-ZEBRINUS

The relative importance of intraspecific competition and interspecific competition with killifish on the breeding activities of territorial male pupfish was investigated in two populations. Compared to Lake Francis, pupfish densities in Mirror Lake were higher, individuals were larger, and intraspecific aggression was more important than interspecific interactions with killifish. Killifish had little impact on the activity budgets of territorial male pupfish, but were excluded from favored breeding habitats. The opposite pattern was observed in Lake Francis. Killifish were numerically dominant as well as relatively larger than pupfish, and they interfered with the breeding activities of territorial males. In Lake Francis most of the agonistic activities of territorial male pupfish were directed toward killifish. Asymmetries in the interactions between pupfish and killifish in the two lakes also were reflected in qualitative and quantitative differences in the breeding activities of pupfish. In Mirror Lake the frequency of agonistic and breeding behaviors increased over the breeding season, but in Lake Francis they decreased. The underlying factors responsible for the observed competitive asymmetries between the species in the two habitats are not known. However, the higher salinity tolerances of pupfish may, in part, have accounted for both their numerical dominance and their size-advantage over killifish in the more saline environment of Mirror Lake. Physiological and ecological factors may thus play an important role in the outcome of competitive asymmetries between species.