The island of Mo’orea in French Polynesiafunctions as a model system to study the biologicaland ecological concept of niche differentiation,whereby two or more species are forced into differenthabitats so as to avoid competition with each other.In the waters surrounding this island, two speciesof sea urchin within the genus Echinometra livein distinctly different habitats. Previous studiesdocument Echinometra sp. A located exclusivelyon the fringing reef and Echinometra mathaeilocated exclusively on the barrier reef. This studyinvestigated three short-term factors (availablespace, nutrient supply, and predation) that mightbe influencing this spatial distribution. None ofthese factors appear to be causing the separation ofE. sp. A and E. mathaei. In fact, they all support thedistributional findings of this study that showednon-mutually exclusive distribution data on the tworeef types.
