17. Behavior and Ecology of Endangered Species Living Together: Long-Term Monitoring of Resident Sympatric Dolphin Populations

Sympatric species may exploit the same resources, potentially acting as competitors when resources are limited. For cetaceans, ecological separation between sympatric species is based on differences in diet and habitat use. The fransiscana dolphin Pontoporia blainvillei (Pontoporiidae) and the Guiana dolphin Sotalia guianesis (Delphinidae) live in sympatry along the southern and southeastern Brazilian coast, but Babitonga Bay is the only estuarine region in which these species occur throughout the year and live in direct sympatry. Twenty years of data on these populations give some indication of how this ecologically similar species share the same habitat. That coexistence is facilitated through differences in diet, distribution, and habitat use patterns. The Guiana dolphin is probably dominant in the niche partitioning system in Babitonga Bay. This fact, combined with small franciscana population size, makes the latter highly vulnerable to local extinction.