QUANTIFYING THE INVASION POTENTIAL OF LATE PLEISTOCENE MOLLUSKS IN SOUTHERN CALIFORNIA

Coastal ecosystems are warming rapidly due to climate change, causing species to migrate and adapt to environmental changes through ecological and evolutionary processes. These shifts in species’ distribution alter biodiversity patterns and can have negative ecological effects. The sedimentary record of Southern California marine terraces preserves evidence of the profound paleoclimatic shifts of the Quaternary Period. Fossil assemblages from these deposits are often considered to be thermally anomalous, containing species found outside their modern-day biogeographic range. These extralimital species,­ or local invasives, showed a dynamic distribution range during glacial-interglacial cycles and can thus be utilized as potential migrators during climate warming conditions. However, it is important to understand if these extralimitals were well established or temporarily lived in novel ranges. In this study, we quantified the invasiveness using a mathematical framework that evaluates the performance of extralimital species in their introduced and native ranges by using inter and intra-specific comparisons. While this method has been used in modern invasion ecology, our goal is to apply it to the fossil record. By doing so, we hope to gain a deeper understanding of a species’ potential invasiveness in the past, present as well as future range dynamics. Our results showed only 7.5% of the total invaders from the Late Pleistocene are considered “good invaders” (well established), and 60% are weak performers in the introduced ranges. This framework suggests that not all invaders become well-established due to their eco-evolutionary differences, which might suppress most species from becoming successful invaders. Our next step is to understand the limitations of this method in fossil records and facilitate a more comprehensive performance analysis by incorporating biomass, population density, and other demographic parameters for assessing invasion success.