The advantages of being a scavenger, and the evolution of dogs

Dogs are scavnegers. JCM

 One night in the tropics I had to stop to change a tire. My companion was looking along the roadside for snakes while I set up the jack, removed the tire from the trunk and jacked-up the car. It was just about this time when I heard him vomiting. He returned to the car muttering – “oh that was horrible.” At first I thought he was talking about dinner.  After inquiring about his health he said, he was ok, but had seen something vile –telling me not to look. Needless to say I did look and found the remains of a goat, which had been tied along the road and hit by a vehicle. Actually when I say remains - the only remains of the goat was a seething mass of maggots in the perfect outline of the goat. Decomposition repels humans- the odor, the bloat, the liquefaction – horrible stuff but it eventually happens to all of us when the ecosystem recycles our molecules.

Animals die from a variety of causes other than predation. Accidents and disease take their toll and when they die the carcass is a valuable source of calories, proteins, and nutrients for any animal that can scavenge the remains. In the tropics scavengers are in a race with the decomposers (bacteria and fungi) to obtain those nutrients, but at high latitudes where cooler temperatures prevail decomposition is much slower. Large animal carcasses may stay around for months or even years if it is in an area of permafrost, because temperatures do not favor bacterial or fungal growth.

Virtually any vertebrate predator can be a scavenger, even predators that are dedicated predator may eat carrion on occasion.

DeVault et al. (2002) note, “The costs and benefits associated with carrion use influences the evolution of scavenging behavior in vertebrates, resulting in a continuum of facultative scavengers that use carrion to varying degrees. The realized usage of carrion by a vertebrate species is influenced by the speed and efficiency with which it forages, its visual and olfactory abilities, and its capacity for detoxifying products of decomposition. A deeper understanding of carrion use by facultative scavengers will improve our knowledge of community and ecosystem processes, especially the flow of energy through food webs.”

Making a living scavenging carrion has its advantages: the animal is dead so there is no chance the prey will injure the predator as it is killed and there is little effort involved in actually getting to the meal, but, there may be completion from other scavengers.

To be sure wolves do act as scavengers, but when they kill prey they also provide food for other scavengers in the community.

So, under what conditions might a population of wolves be selected to be scavengers instead of predators? The possible answers to this question will provide clues as to how a population of wolves evolved into dogs sometime between 135,000 and 40,000 YBP (years before present).

Citation

DeVault TL, Rhodes OE Jr, and Shivik JA 2003. Scavenging by vertebrates: behavioral, ecological, and evolutionary perspectives on an important energy transfer pathway in terrestrial ecosystems. USDA National Wildlife Research Center – Staff Publications Paper 269.

Dogs are scavengers first

Much of what has been written about dogs is undoubtedly nonsense. And, we will leave the critique of popular TV dog shows for the future. While dogs and wolves undoubtedly shared a common ancestor, it seems improbable that dogs were originally modified from wolves by artificial selection by humans. After all, abandoned dogs do not revert to being wolves, they become just feral dogs. Have humans selected dogs for various traits (color, body size, temperament, etc.) in recent times – undoubtedly they have. But, humans probably had little to do with getting a population of wolves to evolve into the dog. The animal that is generally considered the oldest domesticated species.

A free-ranging dog scavenging leatherback sea turtle nests

on Grande Riviere Beach on the north coast of Trinidad. Note

the large number of black vultures also present. JCM

In chapter 10 of the recently published book, Domestic Dog Cognition and Behavior, titled “A Dog’s-Eye View of Canine Cognition” by Udell, Lord, Feuerbacher and Wynne the authors suggest the following.

Most dogs are scavengers and live on the periphery of human society. These dogs are more likely to avoid human contact than seek it. While pet dogs have been a major focus of recent research is unlikely that the human-dog bond is a special adaptation that is the result of co-evolution, but rather the bond is the expression of basic processes such as conditioning, socialization and biological traits that are shared by domestic and wild canids. Individual dogs that have been socialized to humans and become dependent on them have high levels of sensitivity to human actions. Udell and colleagues argue that the fundamental differences between dog and wolf behavior lie at more basic levels: in the processes of socialization, foraging, and reproduction. Small but crucial intertwined changes in the ancestral dog population led dogs to (1) become more promiscuous than any other canid, (2) be able to reproduce more rapidly than wolves, (3) be a much less effective hunter but (4) dogs are more efficient scavenger than other canids. The authors view the indirect consequences of these changes as producing dogs, and suggest that while “…it may be a little less flattering to the human species, we believe this perspective on dogs is at least as fascinating and closer to the historical truth than the story that humans created dogs.”

Citation

Udell, M. A., Lord, K., Feuerbacher, E. N., & Wynne, C. D. (2014). A Dog’s-Eye View of Canine Cognition. In Domestic Dog Cognition and Behavior (pp. 221-240). Springer Berlin Heidelberg. A pdf of this chapter can be found on-line.