Quaternary extinction-colonization dynamics in insular lizards reveal patterns of selectivity and increasing community heterogeneity
To maintain biodiversity in our rapidly changing biosphere, perspective from the past is essential. The field of conservation paleontology provides a long-term perspective on how communities change at various temporal and spatial scales. We use a paleontological dataset of insular lizards to evaluate extinction trends in this widespread and charismatic group, focusing on islands in the Caribbean with fossil records as well as those that were connected as island banks during lower Pleistocene sea levels. We then evaluate how community structure is impacted by extinction-colonization events through the late Quaternary.
We found that extinction is size-biased and lineage-specific in lizards, a result that is concordant with other taxonomic groups. At one site, the disappearance of the large-bodied Leiocephalus in the early Holocene coincides with smaller-bodied Anolis becoming the most dominant lizard, and resulted in high turnover, decreased evenness, and decreased species richness—a trend that continues to the present.
We show that island communities with fossil records and from previously continous island banks became less similar over time. The Lesser Antilles collectively, however, has undergone biotic homogenization, consistent with global patterns of biodiversity loss. The discrepancy across scales is due to (1) the lack of fossil data for the majority of islands in the Lesser Antilles, which results in a distorted baseline of starting community similarity, and (2) increased similarity of faunas as spatial scale increases. Our fossil data reveal that the Lesser Antillian fauna began more similar and has subsequently been eroded by human-mediated extinction and species introductions. Our results illustrate the importance of fossil data in assessing community change over time and in identifying species to prioritize for conservation in the Anthropocene, which is especially important for Caribbean lizards because little demographic data exists for most species.