Colonisation lags predict sympatric diversity in birds

Ecological communities are assembled over time, suggesting a crucial role for evolutionary history in determining the diversity of species assemblages. Indeed, differences in the build-up of sympatric diversity across space, time and clades may reflect variation in the historical patterns of speciation and thus time available for colonisation. However, quantifying the role of evolutionary history is challenging and thus its potential effects have received far less attention than the effects of ecological limits to diversity. Here we use a dynamic model of assembly by allopatric speciation, colonisation, and local extinction to test how evolutionary history predicts variation in sympatric diversity across clades of passerine birds. We show that the clade-specific history of speciation strongly impacts the build-up of sympatry over time, and that phylogenetic tree shape statistics are key predictors of differences in sympatric diversity between clades. Within clades the proportion of species that are sympatric is highest in old, species-poor, and phylogenetically balanced clades. These historical factors all promote the average age of extant species, providing more time for species to expand their geographic distributions and colonise communities. We further show that phylogenetic patterns in community structure frequently interpreted as evidence that community assembly is limited by the saturation of ecological niche space can be explained simply by the lag-time to colonisation following speciation. Our results show that the macroevolutionary history of speciation and assembly time is essential in explaining variation in the structure and diversity of ecological communities.