Shared patterns of spatial accumulation of lineages across terrestrial vertebrates

Aim: Whether species co-occur with closely related taxa has long been thought to influence both the rate of species formation and maximum clade diversity. However, it is unclear whether these processes act concordantly across entire clades, and between taxa with disparate dispersal and life history strategies. Quantifying these patterns will yield a better understanding of the factors regulating biodiversity. I investigate whether allopatry promotes lineage diversification leading to greater clade richness. I also test whether slowdowns in diversification and family richness are correlated with increased sympatry.

Location: Global

Taxon: Birds, mammals, and amphibians

Methods: Posterior distributions of speciation rate estimates were compared between different definitions of lineage allopatry. Temporal changes in speciation rate were compared against family diversity as well as the mean and maximum number of overlapping familial ranges.

Results: More diverse families accumulate more overlapping ranges, but this process is non-random with predominantly non-sister taxa overlapping. Sister species in allopatry have higher speciation rates, with rates generally suppressed when allopatry is defined using all confamilial taxa, suggesting that the effect changes over the course of a radiation. Slowdowns in diversification are uncorrelated with the maximum and mean number of regionally sympatric species, therefore appearing to be either an idiosyncratic feature of certain clades, or at least not related to spatial packing of confamilial species.

Main conclusions: Allopatry of sister species is correlated with rapid diversification at 1 – 3Ma timescales. At the family level, maximal clade diversity is achieved through increased sympatry of member species, i.e. packing of related species within a single geographic area.