Dogs occupying grassy habitat near protected areas in eastern Madagascar rely on foods from forests

Abstract

Societal Impact Statement: Identifying where introduced animals fit in a food web relative to each other and to endemic species is key for biodiversity conservation planning. Using a multiproxy study of dog feces from eastern Madagascar, we infer that even dogs that spend time in derived grasslands typically eat forest-derived foods. Regardless of the time that dogs spend in cleared forest, their impacts are likely concentrated on forest-dwelling prey. If dogs in forests mostly consume threatened endemic animals (and not other introduced animals such as rats), then the exclusion of dogs from protected forests should be a priority. Summary: Introduced predators on islands can help control invasive species yet can also contribute to the extirpation and extinction of endemic taxa. The spread of dogs on Madagascar by ~1000 years ago coincided with the introduction of livestock and spread of grazer-adapted grasslands, and we help evaluate the extent to which modern dogs are part of novel grassland food webs. To infer dog diet, we identified food remains, where possible, and conducted stable isotope ratio analysis for n = 100 modern dog feces collected in derived grassland at varying distances from protected forest edges around Analamazoatra and Andasibe-Mantadia National Park in eastern Madagascar. Animal remains in feces and the observed range of fecal δ15N values are consistent with dog meals at multiple trophic levels. However, the observed distribution of fecal δ13C values suggest that few dogs in the study area consumed food derived from open C4 grasslands. Existing data suggest that dogs rely primarily on C3 consumers inhabiting forest biomes (forest-dwelling animals) for their prey, which may include endemics such as tenrecs, Malagasy rodents, and lemurs and introduced rodents such as rats. These findings indicate that dogs are not confined to the anthropogenic niche defined by grazer-adapted grasslands, but rather use and impact animal food resources associated with protected forests. Higher resolution study of dog diet and mobility can further clarify the potential for dogs to exploit endemic prey, compete with endemic predators, and spread disease across ecotones.