Testing the time‐for‐speciation effect in the assembly of regional biotas

Abstract

Summary1. Rates of evolutionary diversification play a fundamental role in the assembly of regional communities, but the relative balance of diversity‐dependent and diversity‐independent rate control remains controversial. Recent studies have reported a significant relationship between the amount of time a geographic region has been occupied and species richness, implying that feedbacks between species interactions and diversification rates may be less important than diversity‐independent mechanisms in generating regional species pools.2. Previous analyses of the regional age‐diversity relationship have used a range of metrics to quantify the amount of ‘evolutionary time’ that a region has been occupied, but the relative performance of these metrics has not been quantified.3. Here, I evaluate the performance of the most commonly used methods and data transformations for assessing the regional age‐diversity relationship.4. I find that process‐based models of diversification are more appropriate than process‐independent models for evaluating the influence of time on species richness. I also demonstrate that time should not be log‐transformed when testing the regional time‐for‐speciation hypothesis, as in some recent studies.5. Application of this framework to patterns of elevational richness in several recent studies provides support for a logistic model of diversity accumulation within elevational bands and implies that evolutionary age alone cannot fully account for current species richness.6. These results indicate that process‐based models, in concert with appropriate data transformation, provide a robust foundation for inference on the causes of regional diversity gradients.