Professor National Autonomous University of Mexico, Mexico
Abstract: Clusters of species with similar niches or traits have been observed in communities, but the mechanisms behind this pattern are still unclear. The emergent neutrality model suggests that species with similar niches and competitive ability may self-organize into clusters. Under emergent neutrality species may coexist within groups because of similarities in their niche and fitness while coexistence between groups may be possible due to niche differences. Even though there has been theoretical support for this model, it has been suggested that other niche dimensions, or hidden niches, may actually be responsible for stabilizing coexistence within clusters. Another less explored alternative is that clustering may also occur through alliances of species that facilitate each other either directly or indirectly. We tested whether clustering in communities occurs through emergent neutrality, hidden niches or facilitation. We used 14 years of field data to parameterize population-growth models that consider interspecific interactions for 35 species. We then simulated the expected community dynamics under different scenarios of species interactions to disentangle the mechanisms behind clustering. We did not find support for emergent neutrality but rather hidden niches. We found that interspecific competition was weaker within rather than between clusters, suggesting that differences in unmeasured niche axes stabilize coexistence within clusters. We also found that indirect facilitation promoted species alliances in clusters whose members suppressed common competitors in other clusters. These species alliances seem to arise more easily when within cluster competition is weak.
