Understanding how evolutionary relatedness affects stable coexistence of species has been a long-standing question in ecology. Coexistence is though to be unstable between close relatives because of high niche similarity. Related species may also be synchronic (have similar demographic responses over time) affecting fluctuation-dependent mechanisms: storage effect should destabilize coexistence of synchronic species, and relative non-linearity should be stronger due to increased fluctuations in competition.
To test these hypotheses, we used invasion analysis based on a model parameterized for 19 plant species from a semiarid grassland. We analyzed how pairwise competition, synchronicity and the ingredients of the storage effect depend on phylogenetic relatedness. We also assessed the effects of phylogenetic distance between species on each of the coexistence mechanisms considering pairs of species and also when multiple species are interacting. Finally, we analyzed how synchronicity affects coexistence by simulating communities in which all the species have identical or very different responses to environmental fluctuations.
Results/Conclusions
We found that stabilization through fluctuation-independent niche differentiation was stronger between distant relatives as a result of weaker competition. Synchronicity was higher between close relatives, having the expected negative effects on the contribution of storage effect to coexistence. Relative non-linearity was strong at both ends of the phylogenetic relatedness gradient but not in the middle. This may be the result of different non-linear responses between distant relatives and stronger fluctuations in competition due to synchronicity between closer relatives. The effect of phylogenetic distance on coexistence was almost negligible when pairwise species were analyzed, in accordance with previous research. However, phylogeny became more important as more species interacted, suggesting that evolutionary relatedness may be decisive in species-rich communities.