Impact of Evolutionary Relatedness on Species Diversification: A New Birth-Death Model

Abstract

AbstractSlowdowns in lineage accumulation are often observed in phylogenies of extant species. One explanation for this is the presence of ecological limits to diversity and hence to diversification. Previous research has examined whether and how species richness (SR) impacts diversification rates, but rarely considered the evolutionary relatedness (ER) between species, even though phylogenetic distance can play a role in the degree of competition between species, which likely sets these ecological limits. To understand the influence of ecological limits represented by ER on species diversification, and to investigate the interplay between SR and ER effects on diversification, we present a new phylogenetic birth-death model in which the speciation rate depends on the ER between species. We use different metrics of ER that operate at different scales, from lineage-specific to clade-wide. We find that the different scales of ER effect yield distinct patterns in speciation rates and various tree statistics. When ER operates across the whole tree, we observe smaller and more balanced phylogenetic trees, with internal nodes concentrated more closely to the root and speciation rates distributed more evenly across the tips than in scenarios with lineage-specific ER effects. Importantly, we find that the presence of negative SR dependence can reduce the influence of ER on some of the tree statistics. This suggests that these tree statistics should not be used to detect an effect of evolutionary relatedness on clade diversification.