The meat of the matter: a rule of thumb for scavenging dogs?

Animals that scavenge in and around human settlements need to utilise a broad range of resources, and thus generalist scavengers are likely to be better adapted to human-dominated habitats. In India, free-ranging dogs (<i>Canis lupus familiaris</i>) live in close proximity with humans in diverse habitats, from forest fringes to metropolises, and are heavily dependent on humans for their food. It has been argued that the ability to digest carbohydrates was one of the driving forces for dog domestication. Though dogs are better adapted to digest carbohydrates than other canids, pet dogs show a clear preference for animal proteins. Our observations on streets of urban and semi-urban localities show that the free-ranging dogs are scavengers which primarily receive carbohydrate-rich food from humans. Their source for animal protein is typically garbage bins and leftovers, and such resources are rare. Using a series of field-based experiments, we test if the free-ranging dogs have adapted to a generalist scavenging lifestyle by losing preference for animal protein. Our experiments show that the free-ranging dogs, which are descendants of the decidedly carnivorous gray wolf (<i>Canis lupus lupus</i>), have retained a clear preference for meat, which is manifested by their choice of anything that smells of meat, irrespective of the actual nutrient content. The plasticity in their diet probably fosters efficient scavenging in a competitive environment, while a rule of thumb for preferentially acquiring specific nutrients enables them to sequester proteins from the carbohydrate-dominated environment.

在人类定居点及其周边活动的食腐动物需利用多样资源，因此广食性食腐动物更能适应人类主导的生境。在印度，流浪犬 (free-ranging dogs，<i>Canis lupus familiaris</i>) 栖息于从林缘到大都市的多样生境中，与人类活动区域高度毗邻，其食物来源极大程度依赖人类供给。已有研究指出，碳水化合物消化能力是犬类驯化的核心驱动力之一。尽管相较于其他犬科动物，犬类的碳水化合物消化适应性更强，但伴侣犬仍表现出对动物蛋白的明确偏好。我们在城市及半城区街道开展的观测显示，流浪犬作为食腐动物，主要从人类处获取富含碳水化合物的食物；而其动物蛋白来源多为垃圾桶内的残羹剩饭，这类资源实则较为匮乏。我们通过一系列野外实验，探究流浪犬是否通过丧失对动物蛋白的偏好，以适应广食性食腐的生活模式。实验结果表明，作为严格肉食性灰狼（<i>Canis lupus lupus</i>）的后裔，流浪犬仍保留了对肉类的明确偏好：它们会选择任何带有肉类气味的食物，而非考量其实际营养成分。其饮食的可塑性或许使其在竞争激烈的环境中能高效开展食腐活动；而优先获取特定营养的行为准则，则帮助它们在以碳水化合物为主的生境中获取足够蛋白质。