DISSERTATION RESEARCH: Investigating species interactions across 15,000 years of extinctions and invasions: an isotopic approach

Stanford University, Stanford CA

Investigators

Abstract

The highways and shipping routes that crisscross our planet are eroding the boundaries that once separated biological communities by introducing non-native species. These invasive species have come at an economic and ecological cost for the US, harming agriculture, fisheries, and our iconic landscapes. On islands, these invaders are even more detrimental, often competing with or eating native species to the brink of extinction and thus irreversibly damaging biodiversity hotspots. In this project, researchers will take an innovative approach to understand the consequences of invasive species by combining data from 15,000-year-old fossils and modern specimens alike. Using fossils excavated in the Dominican Republic, researchers will reconstruct the ecological interactions of native mammal species (such as sloths, monkeys, and rodents) before and after the arrival of prehistoric humans (6,000 years ago), as well as after the arrival of Europeans (500 years ago) and the invasive species that accompanied them. A baseline of how native species respond to extinction will provide context for understanding where invasive species fit within the modern ecosystem. For example, do invasive herbivores such as goats consume vegetation similar to what was consumed by extinct native sloths? This research integrates paleontology with conservation science to directly inform ecosystem restoration efforts. The lessons learned from this research will be broadly applicable to species invasions on islands and continents alike. The researchers excavated a cave deposit extending from the modern day back across the Late Pleistocene-Holocene transition, a period known globally for climatic changes and megafaunal extinctions. This fossil record provides ecological snapshots of species interactions through evolutionary time. Using stratigraphic layers and radiocarbon dating, the researchers will establish a temporal framework for the fossil remains, describing which mammalian species were present at what time periods in the past. This chronology permits researchers to test ecological hypotheses of how species respond to environmental and anthropogenic perturbations through time. Food webs, species interactions, and changes in resource use can be reconstructed using stable isotopes of carbon and nitrogen. Through applying these isotopes, researchers will assess the trophic position and niche breadth of each native species in response to extinction and invasion events, thereby testing broad ecological concepts such as competitive release and niche contraction. They will also evaluate the longstanding assumption that invasive species have wider niche breadths relative to native species in the ecosystems they invade.