Eco-evolutionary simulation of biodiversity gradients

Abstract

Earth’s biodiversity is vast. However, the drivers that have led to this vast biodiversity are not well understood. Biodiversity varies predictably with factors such as latitude, depth, altitude, and time but, despite decades of observational research, it is not clear through what mechanisms these predictors drive the diversification of species. This lack of understanding stems, in large part, from the fact that many putative drivers are correlated in space. At the same time, the spatial and temporal scale of the processes involved make it difficult to study their operation through experiments. Eco-evolutionary simulation tools present an opportunity to circumvent these problems: by independently varying input parameters, simulations can decouple putative drivers of biodiversity that are rarely decoupled in nature. Furthermore, fast computation allows these tools to simulate ecosystems over longer timescales than observational and real-world experimental studies can investigate. In this thesis, the putative drivers of species diversification are discussed, and an eco-evolutionary simulation tool, the Rapid Evolutionary Simulator (REvoSim), is employed to decouple them. A series of case studies are presented, each investigating independently the effects on simulated ecosystems of a different putative driver of species diversification. In addition, existing descriptive models of eco-evolutionary patterns are re-evaluated using simulations and real-world data. This work suggests that many of the putative drivers of species diversification in the real world have the capacity to drive such diversification even in very simple, abstracted systems. Consequently, it is likely that many of these drivers do contribute to observed species diversity gradients in the real world, and that, generally, no single driver is responsible for such gradients. Collectively, this work demonstrates both the potential of simulation systems to recreate and analyse real-world eco-evolutionary patterns, and the difficulties of working on the timescale of the speciation process: a timescale that is poorly understood, where intuitive concepts, such as ‘species’, sometimes fail.