Hybrid niche-neutral models outperform an otherwise equivalent neutral model for fitting coral reef data.

Niche theory and neutral theory are two major developments aiming at explaining patterns of biodiversity observed in nature. Both theories have been found relevant either separately or simultaneously in some real communities, and it has been theoretically demonstrated that they can produce similar species abundance distributions. However, it remains controversial whether the two theories can produce similar patterns via different mechanisms, or can interact to jointly produce the observed diversity patterns, or whether the patterns generated by the neutral model are robust to niche structure. Here we show that, although the neutral model proposed for spatially discrete communities remains robust to strong niche structure for high-diversity communities, the inclusion of more realistic niche differentiation modes greatly improves the goodness of fit to Indo-Pacific coral reefs. Actually, the multiple discrete communities' neutral model, due to its underestimation of the number or abundance of common species, fails to capture the combination of many rare species and a few highly abundant species that characterize the Indo-Pacific coral reef communities. By incorporating niche structure into the multiple discrete communities' model, the hybrid niche-neutral models can successfully reproduce both the species-based and individual-based abundance distribution patterns observed in the coral reefs. We proposed that both niche theory and neutral theory may be involved in explaining the structure of such communities. Our results also suggest a negative relationship between per capita birth to death ratio and immigration among different guilds of coral species, which clearly deserves further investigation.