Ecological niche segregation within a community of sympatric dolphins around a tropical island

Investigating ecological segregation among organisms of a given community is challenging, especially when these organisms share similar patterns of distribution, and similar size and morphology. Around the island of Mayotte, a diversified community of at least 4 sympatric delphinids is present year round within a very restricted range: the Indo-Pacific bottlenose dolphin Tursiops aduncus, the spinner dolphin Stenella longirostris, the pantropical spotted dolphin S. attenuata, and the melon-headed whale Peponocephala electra. In addition, the Fraser's dolphin Lagenodelphis hosei makes temporary incursions into peri-insular waters as well. This study aims to assess niche segregation among this tropical dolphin community. We hypothesized that each species occupies its own distinct niche defined by the following axes: habitat, resources and time. We analysed habitat in relation to physiography, behavioural budgets and C and N stable isotope values from skin and blubber samples for each species. The results highlighted that habitat and behavioural budgets were relatively distinct among species, with few exceptions. However, in those species living on the outer reef slope where habitat and behaviour were not well discriminated, stable isotope analyses confirmed that species have different trophic levels (mostly reflected through delta N-15 values) or foraging habitat (mostly reflected through delta C-13 values). This study confirms that the use of multiple methodologies (habitat, behaviour and feeding ecology studies) help in discerning ecological niche segregation, especially when examining closely related species within a common restricted range.