The Janzen-Connell (J-C) hypothesis states that species-specific natural enemies (pathogens, predators) induce local-density dependence which explains high diversity observed in tropical tree communities. However, these natural enemies often attack phylogenetically related species as well. Here, we use a spatially explicit model in which the continuously changing phylogeny and abundances affect recruitment to study the predictions for common diversity and phylogenetic patterns. The species-area relationship is triphasic, while the species-abundance distribution has a rare species mode (neutral scenario), a two modes (large dispersal distance) or a single interior mode (small dispersal distance). Small dispersal distance forms clusters of species with large phylogenetic distance to the community while large dispersal distance makes species distribute uniformly. Phylogenetic trees show diversification slowdowns and imbalance, consistent with empirical patterns. However, the phylogenetic relatedness effect reduces diversity. We conclude that the spatially explicit phylogenetic J-C effect explains commonly observed diversity and phylogenetic patterns.

Models of trait evolution usually assume that abiotic factors pull species toward an optimal trait value, whereas competitive interactions drive the trait values apart. However, these models do not consider population dynamics and dynamics of the trait variance and they oversimplify competition. Here we develop a coherent trait evolution model, with abundance-dependent competitive interactions, against a macroevolutionary background encoded in a phylogenetic tree. We use Approximate Bayesian Computation to fit the model to baleen whale body sizes and compare it to a model without population dynamics and a model where competition depends on the total metabolic rate of the competitors. All models suggest that baleen whales undergo weak environmental attraction and strong competition. However, they differ in their predictions of the abundance distribution. Data on abundance distriubutions, therefore, allow us to distinguish the models from one another, and infer the nature of competitive interactions.

The Janzen-Connell (J-C) hypothesis states that species-specific natural enemies (pathogens, predators) induce local-density dependence which explains high diversity observed in tropical tree communities. However, these natural enemies often attack phylogenetically related species as well. Here, we use a spatially explicit model to study the predictions of a phylogenetic J-C effect for common diversity patterns. The species-area relationship is triphasic, while the species-abundance distribution has a rare species mode (neutral scenario), a two modes (large dispersal distance) or a single interior mode (small dispersal distance). Small dispersal distance forms clusters of species with large phylogenetic distance to the community while large dispersal distance makes species distribute uniformly. Phylogenetic trees show diversification slowdowns and imbalance, consistent with empirical patterns. However, the phylogenetic relatedness effect reduces diversity. We conclude that the spatially explicit phylogenetic J-C effect explains commonly observed diversity patterns, but hyperdiversity only results when the natural enemies are extremely species-specific.