Shore fishes and biogeographic subdivisions of the Tropical Eastern Pacific

We examined the geographic distributions of 1135 species of resident shore fishes to assess biogeographic subdivision of the Tropical Eastern Pacific (TEP), which stretches from the Gulf of California to northern Peru. Using hierarchical clustering refined by Analysis of Similarity (ANOSIM), we determined geographic groupings in the distributions of the entire fauna, of regional endemics and of 3 functional (habitat) groups of species. We also examined the distributions of local endemics throughout the TEP and how differences in faunal size versus faunal composition among sites contribute to the subdivision pattern. Our results indicate that: (1) the continental coast contains 2 provinces, the Cortez (Gulf of California and lower Pacific Baja) and the Panamic (southward), each of which has a peak in abundance of local endemics and of overall species richness; (2) the northern and southern boundaries of the TEP are located near Magdalena Bay on Baja California (similar to 25 degrees N) and the southern shore of the Gulf of Guayaquil (similar to 4 degrees S), respectively; and (3) the 5 oceanic islands/archipelagos collectively represent a third, Ocean Island Province. Relative to mainland areas, the fauna of the ocean islands is smaller, has a different functional-group composition, and includes more transpacific species and more highly localized endemics. The 3-province pattern probably developed in response to the formation of the Gulf of California, the rise of the Isthmus of Panama, immigration from the north, south and west to the TEP, and differing environmental conditions between and within provinces. In contrast, barriers to dispersal within this geographically simple region are weak and likely had much less influence.