Many of the types of changes that contemporary taxa are experiencing have occurred in the geologic past, and the fossil record preserves a rich history of community and ecosystem responses to species invasions, climatic instability, and other environmental changes. As such, the patterns and processes that occurred in the geologic past can be studied as analogs for understanding implications of similar changes within modern ecosystems. In particular, biotic invasion events, the dispersal of taxa from their ancestral biogeographic area to another, have impacted biodiversity throughout geologic time. Invasion events associated with biodiversity increases have been linked to ecologic and evolutionary processes such as niche partitioning, species packing, and higher speciation rates. Yet substantial biodiversity decline has also been documented following invasion events due to elevated extinction and/or reduced speciation rates. In this contribution, I will explore the relationships among invasion events, community and ecosystem structure, and biodiversity during a regional invasion event that occurred within the shallow seas covering eastern North America during the Late Ordovician Period (~450 Ma). The impact of the invasion event on the community and ecosystem will be examined by combining ecological niche modelling and phylogenetic biogeography of common taxa, emphasizing brachiopod and trilobite clades.
Results/Conclusions (200 words)
The focal taxa exhibited high fidelity in habitat tracking, ecological niches stable, and community structure was conserved during the pre-invasion Interval characterized by gradual abiotic change. The onset of the invasion, however, is marked by fundamental community restructuring, statistically lower niche stability and increased niche evolution. The only native taxa to persist through the invasion interval were ecological generalists. The post-invasion niche occupation of these species represented a subset of their original fundamental niche dimensions rather than a shift to new ecospace. Niche contraction is interpreted as a response to increased competition from invasive species via niche partitioning within the ecosystem. The invasion interval is further marked by a speciation gap. Based on phylogenetic biogeographic analyses, this gap develops primarily from reduced speciation by vicariance, likely due to extinction of small populations or limited opportunity to maintain genetic isolation. Results of the Ordovician case study indicates that modern species invasion could produce novel ecosystems dominated by generalist taxa via a two-pronged effect of homogenizing taxa across large regions while suppressing generation of new species to replace specialists currently experiencing high extinction pressure.