A FRAMEWORK FOR DEVELOPING MULTI-CAUSAL EXPLANATIONS FOR LONG-TERM CHANGES IN BIODIVERSITY

While we are beginning to gain a sophisticated understanding of the trajectory of biodiversity change through the Phanerozoic (whether via Sepkoski's synoptic compendia of marine fossil families and genera, or through locality-based databases such as the Paleobiology Database [http://paleodb.org]), we still understand very little about the causes of Phanerozoic changes in diversity. Most of our attention has been focused on specific time intervals characterized by major origination events (such as the Cambrian explosion), or major extinction events (particularly the end-Permian and end-Cretaceous). We probably understand extinction events better than origination intervals (although Dave Jacob's analysis of the origins of the living California biota is a notable exception). But even for extinction events where we understand something of the primary cause(s) of the extinction (e.g., the bolide impact at the end of the Cretaceous) we still have a poor understanding how the primary cause (e.g., the bolide impact) translated into the observed extinctions. Here, rather than focusing on a specific event or time interval, I will develop a general framework for understanding the causes of changes in biodiversity by considering the factors that control total diversity, regardless of whether we know how to evaluate the numerical role each factor plays in the standing diversity at any given time. The key factors include: total habitable surface area (A); the total amount of usable energy entering the system (E); extrinsic barriers to gene flow between populations, such as mountain ranges, rivers, etc., (B_ex); intrinsic barriers to gene flow between populations (B_in); and, the complex relationship between the genetic potential for morphological and behavioral innovation (the morphogenetic rules, M), the tasks (T) the organisms needs to perform to leave viable offspring, and the biotic (E_b) and abiotic environments (E_ab). Armed with this framework, I believe it will be possible to develop a general understanding of how changes in biodiversity are related to the evolving Earth System.