A latitudinal diversity gradient of shallow-water gorgonians (Cnidaria: Octocorallia: Alcyonacea) along the Tropical Eastern Pacific Ocean: testing for underlying mechanisms

摘要

One of the most pervasive patterns leading the distribution of life on Earth is the latitudinal diversity gradient (LDG). Considering its generality, understanding its main causes is critical to predicting climatically driven biodiversity loss. Here, we analyzed the LDG pattern in gorgonians (Octocorallia: Alcyonacea) in the Tropical Eastern Pacific Ocean (TEP), where they form a widespread, species-rich, and ecologically important group of marine benthic organisms. We compiled a database of the geographic occurrence of shallow-water (< 40 m depth) gorgonians with a range extent restricted to the TEP, in order to evaluate the shape of their LDG and to test different hypotheses that could explain these patterns (Rapoport's and mid-domain effects), as well as the possible underlying mechanisms (source-sink dynamics and climatic variability hypothesis). The species richness showed a peak at 7-10 degrees N with > 60 spp., declining toward the north and south. The gorgonians exhibit an increase of their distribution ranges at higher latitudes, supporting predictions of Rapoport's effect, an effect rarely found in TEP marine faunas. This pattern is likely the result of a decrease of gorgonian temperature tolerances at lower latitudes. We highlight the existence of at least four gorgonian assemblages within the TEP exhibiting distinctive temperature adaptations, and a strong change in species composition with latitude. Our results indicate that sea temperature is an important factor shaping the distribution of gorgonians in the TEP, as in several other marine taxa.