The phylogenetic Janzen-Connell effect can explain multiple macroecological and macroevolutionary patterns

Abstract

The classical Janzen-Connell (J-C) hypothesis states that species-specific natural enemies induce local-density dependence which explains high diversity observed in tropical tree communities. Recent studies have extended the hypothesis to include the fact that these natural enemies often attack phylogenetically related species as well, which reduces diversity and hence the explanatory power of the hypothesis. However, these studies consider ecological time scales at which the phylogenetic relatedness between species is constant, and thus ignore that at evolutionary time scales the population dynamics change the phylogeny. We use a spatially explicit eco-evolutionary model of the interplay between the dynamics of the phylogeny and the species abundances to study the predictions for common macroevolutionary and macroecological patterns. We confirm that hyperdiversity can be maintained by the J-C effect but the phylogenetic relatedness effect weakens the rarity advantage, reducing diversity. Incorporating protracted speciation further improves the result. Our model predicts a triphasic species-area relationship at much shorter time scales than in neutral scenarios. The species-abundance distribution can have one or two modes depending on the dispersal distance. Phylogenetic trees show diversification slowdowns and imbalance, consistent with empirical patterns. We study a new pattern of phylogenetic relatedness through space and find that small dispersal distance causes clusters of species with large phylogenetic distance to the community while large dispersal distance makes species distribute uniformly. As an illustration of how our models predictions can be compared to empirical data we study macroecological and phylogenetic patterns of the Barro Colorado Island (BCI) tree community. We conclude that the spatially explicit eco-evolutionary phylogenetic J-C effect can explain commonly observed macroevolutionary and macroecological patterns, providing an alternative way, while the traditional methods are prone, to demonstrate the role of J-C effect on species community assembly.