Disinterested Affection: Dogs, Humans and Evolution: The advantages of being a scavenger, and the evolution of dogs

Monday, July 21, 2014

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.

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Tens of thousands of dogs are bitten each year by snakes. The USA has about 25 species of venomous snakes; they occur in all states except Alaska, Hawaii, and Maine. Learn what simple steps you can take to protect your dog from snake envenomation. Learn what to do if you or, your dog, is bitten by a venomous snake. If you hunt, fish, camp or hike with your dog in areas where poisonous snakes occur you will want the information in this book. If you live in an area with rattlesnakes, you will want the information in Dogs & Snakes, Avoiding the bite.

This Blog

This blog is about dogs, dog-human relationships, and my thoughts on the origins and the domestication of dogs. When I say my thoughts, it needs qualification because much of the writing is not the result of my original thinking, but of reading research and anecdotes about dogs and humans, studies of fossils and archeological remains, anatomy, DNA, and behavior. The posts will be documented in standard fashion with author and date, and the literature cited and references are listed on a reference page or at the bottom of the post. The title comes from William Youatts’ 1846 [1857 edition] book, The Dog. On page 14 he wrote, "The dog is the only animal that is capable of disinterested affection. He is the only one that regards the human being as his companion, and follows him as his friend; the only one that seems to possess a natural desire to be useful to him, or from a spontaneous impulse attaches himself to man." Youatt’s book is remarkably insightful for the mid-19th century; he opens Chapter 1 with a comment about dogs being the most intelligent animal other than humans; notes the emotional attachments dogs and humans form, including the sense of loss when dogs loose the humans they have bonded with; and supports the idea that dogs were descended from wolves. This is an idea that was rejected and re-accepted numerous times in the 19th and 20th centuries, and one that will be discussed here.

John C. Murphy

John C. Murphy is a retired science teacher and science administrator. His most recent book Secrets of the Snake Charmer examines what we have learned about snakes in the first decade of the 21st century. Previous books include Tales of Giant Snakes, Amphibians and Reptiles of Trinidad and Tobago, and Homalopsid Snakes, Evolution in the Mud. Current interests and projects include, numerous squamate systematic projects that focus on the Neotropics and aquatic snakes. His interests also have expanded to dogs and their evolution. He is an avid photographer and a research associate in Science & Education at the Field Museum in Chicago.