Invasive species and biodiversity decline: Investigating the connection between biogeographic and evolutionary patterns during the Late Devonian biodiversity crisis

This study examines the interaction between biogeography and evolution during the Late Devonian (Frasnian-Famennian) biodiversity crisis using GIS mapping, phylogenetics, cladistic biogeography, and niche modeling methods. The combination of multiple methodological approaches provides a comprehensive understanding of biogeographic and evolutionary changes during the Late Devonian biodiversity crisis. GIS based spatial analysis techniques provide insight into temporal and areal changes within species ranges, while cladistic techniques provide a rigorous evolutionary framework against which to test patterns of biogeographic change.; Spatial and temporal mapping of species ranges using GIS permits statistical comparison of species' geographic range with sea level fluctuations, environmental variables, and species survival through the biodiversity crisis interval. Species ranges are related to sea level in two ways: the size of a species range within a single basin is positively correlated with sea level; and transgressive events promote interbasinal species invasions. Species' ranges also increase with increasing water depth. Species with larger geographic ranges and species whose history includes episodes of interbasinal invasions are more successful in surviving the biodiversity crisis interval than species with smaller ranges that are restricted to a single tectonic basin throughout their evolutionary history. Niche modeling using GARP (Genetic Algorithm using Rule-set Prediction) further supports the importance of range size for species survival; however, a survival advantage is only conferred when species obtain large or expanding ranges during the linguiformis conodont zone (terminal Frasnian).; Species-level phylogenetic analyses of brachiopod and bivalve clades provide insight into patterns of biogeographic change. Cladistic biogeography revealed a relative decline in speciation by vicariance compared to dispersal in these Devonian taxa when compared with the modern biota, which may reflect a fundamental shift in speciation mode during the Late Devonian. The observed shift away from vicariant speciation may partly explain the reduction in Late Devonian speciation rates. This reduction in vicariant speciation may be related to the prevalent range expansion observed during the Late Devonian within the spatial analyses. Species invasions, therefore, appear to create a barrier to vicariant speciation and consequently result in reduced speciation rates, resulting in biodiversity decline.