Past rapid spread of introduced livestock coincided with vegetation clearance on Madagascar

Debates persist around the past and present effects of introduced livestock on the native biodiversity of Madagascar. Indeed, the variable habitat and past rate of spread of livestock across the island's distinct ecoregions are poorly known. Sets of 14C and stable isotope data from bovid bone collagen give a direct approach to estimating past introduction events and animal diet. We sampled more than 100 bovid bones collected at 23 sites across the island and present a compiled dataset of stable carbon and nitrogen isotope data from 126 specimens (94 of which are directly 14C-dated) belonging to Bos (cattle), Ovis (sheep) and Capra (goat). The earliest documented presence of bovids in the island's interior approximately 1200 years ago probably reflects a rapid spread of livestock across the island before the start of the past millennium. Isotopic data suggest that, since cattle introduction, these livestock have come to rely more on plants in increasingly wet habitat and approximately 10% more on carbon from some combination of C4 grasses or succulents that use crassulacean acid metabolism (CAM). We argue that a potential variety of causal mechanisms connect past changes in livestock diet with changes in climate, vegetation and endemic large herbivore abundance, and we highlight productive areas for future research.