Max Planck Institute for Geoanthropology Jena, Thuringen, Germany
Abstract: Climate drying and biological invasion threaten endemic taxa on biodiverse islands such as Madagascar, and it is unclear what combination of these stressors drove past extinction. The fossil record prior to extinction captures how the realized niches of species varied in response to resource constraints and biotic interactions over millennia. We used stable nitrogen isotope (δ15N) content of protein preserved in the ancient bone of Madagascan pygmy hippos (Hippopotamus spp., n=28) and giant tortoises (Aldabrachelys spp., n=23) to infer the responses of these animals to past changes in water availability around a cluster of palaeontological sites in arid SW Madagascar. The relatively low δ15N values of pygmy hippo protein reflected the expected preference of these animals for relatively mesic habitat. However, during arid intervals within the past 5,000 years, elevated protein δ15N values suggest that pygmy hippos successfully exploited arid habitat. To explore past co-occurrence among introduced and currently extinct large herbivores in the study area, we directly radiocarbon dated protein preserved in the bone of 67 individuals belonging to five taxa. Consistent with regional data, the extirpation of endemic large herbivores (pygmy hippos, giant tortoises, and elephant birds) closely coincided with the arrival of introduced livestock (cattle and goats) ~1,000 years ago. Though the Madagascan fossil record documents divergent responses of endemic large herbivores to past drought, the disappearance of this suite of animals is most parsimoniously explained by competition with introduced livestock accompanying human population expansion.
