Simulating the Latitudinal Biodiversity Gradient over Deep Time

The Latitudinal Biodiversity Gradient (LBG), the phenomenon where biodiversity increases along a pole-to-equator transect, is one of the most widely recognized patterns in macroecology, and understanding what generates it and how it relates to climate is fundamental to any attempt to understand how biodiversity will react to ongoing global warming. Many mechanisms for LBG generation have been proposed, but the relative merits of these explanations remain poorly resolved - we do not fully understand why the LBG exists. In part, this is because of the simplicity of the pattern observed in the Recent, which lacks sufficient information to enable us to decide between mechanisms. Palaeontological data, however, suggest that, for some groups at least, the LBG observed in the Recent does not have a long geological history; it differed in the past, in complex ways that are still being investigated. The investigation of past latitudinal biodiversity variation hence provides a more information-rich dataset with which to compare predictions from models for LBG generation.

This project will approach the LBG problem from a novel angle. An evolutionary simulation system (RevoSim) developed by the IC supervisor (MDS) will be used to investigate the development of LBG-like patterns in synthetic environments, under a variety of conditions that simulate suggested mechanisms for LBG-generation. This will enable experimental (rather than theoretical) investigation which mechanisms are plausible, and which elements of real biological systems are required for the pattern to appear (e.g. ecological interactions? seasonality?). The student will compare simulations with the LBG from (a) the Recent, and (b) from palaeontological time-slices for which environmental data are also available. Determining what combination of causal models and simulation parameters best fits the real world data over geological time will drive a more nuanced understanding of the underlying cause(s) of the LBG phenomenon.
RevoSim uses an efficient bottom-up evolutionary model, capable of simulating large populations over geological timescales using modest hardware. It simulates at the level of individual organisms, and models the core aspects of biological evolution. RevoSim uses an environmental 'grid' of colour pixels, which can be spatially/temporally homogenous/heterogeneous, as desired. Organisms possess an evolvable binary genome, procreate through recombination (i.e. sexually), and are subject to selection based on fitness to their environment. Species arise naturally; the software identifies and tracks these, enabling generation and quantification of biodiversity. RevoSim is highly customizable, allowing the assessment of the impact of many variables, and additions to the model for specific purposes.

The student who undertakes this project will: undertake simulation runs and coding of RevoSim to test a range of LBG scenarios; further develop palaeontological understanding of the LBG, building on existing work by one supervisors (PM) but broadening data sampling (using the Paleobiology Database [www.paleobiodb.org]), both taxonomically and stratigraphically; synthesise results from simulation work and time-slice analysis into a new and fuller understanding of the drivers of the LBG; finally, analyze the potential significance of these results for the effects of climate change on the LBG.