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 δ ¹⁵N values are consistent with dog meals at multiple trophic levels. However, the observed distribution of fecal δ ¹³C values suggest that few dogs in the study area consumed food derived from open C ₄ grasslands.

• Existing data suggest that dogs rely primarily on C ₃ 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.

Summary

L'identification de la place des animaux introduits dans la chaine alimentaire les uns par rapport aux autres et aux espèces endémiques est essentielle pour la planification de la conservation de la biodiversité. En utilisant une étude multiproxy sur les excréments de chiens de l'est de Madagascar, nous en déduisons que même les chiens qui passent du temps dans les prairies dérivées mangent généralement des aliments dérivés de la forêt. Quel que soit le temps que les chiens passent dans la forêt défrichée, leurs impacts sont probablement concentrés sur les proies vivant dans la forêt. Si la majeure partie de l'alimentation des chiens dans les forêts provient d'animaux endémiques menacés (et non d'autres animaux introduits tels que les rats), l'exclusion des chiens des forêts protégées devrait être une priorité.

Summary

Ny fahalalana manokana mahakasika ny anjara toerana sy fifampiakinany ireo biby samy tsy zanatany sy ireo zanatany eo amin'ny famatsiana sakafo dia tena zava‐dehibe tokoa eo amin'ny fahafahana miaro sy mametraka drafitra ho fiarovana azy ireo sy ny tontolo manodidina azy. Ny fampiasana ny atotam‐pahalalana sy hevitra mahakasika tain'alika any amin'ny ilany atsinanan'i nosy Madagasika, dia ahafahana milaza fa na dia ny alika izay monina eny aminy toerana tsy misy ala aza dia mihinana sakafo vokatra mivatana na akolana avy aminy ala. Na dia eo azy ny fotoana lanin'ny alika (mikarenjy) eny amin'ny toerana tsy misy ala. Ny trindry dia vinavinaina fa mianjerana amin'ny ireo biby fihaza miankina sy miaina ao anaty ala Raha mifototra aminy biby zanatany izay efa ho lany tamingana monina ao anaty ala mantsy ny ankamaroan'ny sakafon'alika, fa tsy amin'ireo biby tsy zanatany natsofoka teo aminy nosy toy ny voalavo, noho izany dia tena laharam‐pahamehana ary tsy azo iodivirana ny fanalana tanteraka ny alika aminy ireny ala voaharo ireny.