Integrating ecology and evolution in deep time: using Ecological Niche Modeling to study species' evolutionary responses to climate change from the Pliocene to the present-day biodiversity crisis

Abstract

The aim of my dissertation was to elucidate how environmental changes have influenced evolutionary and distributional patterns in the near-shore molluscan fauna of the Atlantic Coastal Plain (southeastern U.S.) over the past three million years. Disentangling the long-term evolutionary responses of species to environmental change is important for understanding the mechanisms controlling evolutionary processes and for assessing how current and future climate changes will impact Earth's biodiversity. My dissertation was comprised of three chapters that integrated both paleontological and neontological data to study the molluscan record of the Atlantic Coastal Plain. The first study in my dissertation focused on 14 extant marine mollusk species and their potential responses to future climate changes over the next ~100 years. Two hypotheses were tested: that suitable areas will shift northwards for these species, and that they will show varied responses to future climate change based on species-specific niche attributes. I found that species were not predicted to shift pole-ward, but rather showed varied responses to future warming. Many of the studied species will be hard hit by future climate changes, such that over 20% of their suitable area will disappear by the end of this century. The second study statistically analyzed whether the niches of mollusk species remained stable across three million years of profound environmental changes. Prior to this research, the long-term evolutionary dynamics of species' niches to differing climatic regimes remained uncertain, even though the question is vital to understanding the fate of biodiversity in a rapidly changing world. I found that species' tolerances were statistically similar from the Pliocene to the present-day, which suggest that species will respond to current and future warming by altering distributions to track suitable habitat, or, if the pace of change is too rapid, by going extinct. The last study tested whether niche breadth and/or geographic range size was a better predictor of extinction selectivity for mollusk species from the Pliocene. I hypothesized that species that went extinct post Pliocene would have smaller geographic ranges and smaller niche breadths compared with those species that are still extant. I found that only realized niche breadth (i.e., the breadth of the environment actually occupied by a species) and geographic range size, rather than fundamental niche breadth, are inversely related to extinction probability. This finding has implications for assessing which species are more at risk as a consequence of current and future climate changes, and helps to sharpen our understanding of which macroevolutionary processes shape patterns of diversity over evolutionary time scales. Together, these studies indicated that abiotic, environmental factors play a fundamental role in governing species' distributions in deep time. More specifically, species did not seem to rapidly evolve in response to new environmental conditions, but tracked preferred habitat or faced extirpation if conditions exceeded their tolerance limits. These findings can be used to ensure that paleobiology does not become the biology of the future.