By Dennis Prichard
I hear this all the time: “What good are ____?” Snakes, in this example. My reply is that you are asking the wrong question. It is not the “good” that an animal possesses but the role it fills. “We” are the ones that give it worth, and in our own terms. Nature, on the other hand, doesn’t value things in terms of “good” or “bad.” It is what it is, and if that isn’t existential enough, just read along for a more cerebral explanation of snakes and their prey.
Snakes are adapted to follow the mice down their holes, around bends, and through thickets to procure the meal. Rodents have adapted strategies to cope with the predator by reproducing quicker. More mice are produced than the snakes can catch and eat. If snakes ate all the rodents, the snakes would have to look elsewhere for another food, which means they would have to change digestive systems, methods of hunting them, and maybe even new habitats in which to find the prey. That’s asking a lot.
Nature keeps all this in check by producing enough food for the number of snakes around. In times of bounty, say ample rains cause grains to grow better with greater amounts produced, the rodents respond by producing more babies. These in turn help predators feed their own young, and thus produce more babies themselves.
The problem arises as the snakes in this case reproduce slower than the rodents. So, the rats are plentiful at the same time the snakes are just getting ramped up to support more offspring. By the time the snakes respond with their own population boom, the rodents have eaten all the grain stores and have cut back on their birthrate.
This can be easily illustrated by the mathematical bell curve graph. As the curve starts upward for the rodents, the snakes have yet to respond. By the time snakes realize there is a spike coming in the rodent population, the mice are already plentiful. The snake population then starts to rise to meet the supply of food, but the rodent population has devoured all the grain surplus and is in a decline. The snakes peak out later and fall back, following the rodent’s decline. Thus, a continuing cycle of ups and downs chases itself.
“Good” comes of this by keeping populations within this equilibrium range, not completely eliminating all of one species. If that happened, the extinctions would crescendo until all life ceased. That would definitely NOT be good. It has happened in the past to certain species for various reasons, but generally to a very limited degree – there was another plant or animal that took the role, or niche, left behind. As I said earlier, nature looks for an equilibrium, and it will find a way to bring chaos into order.
If rodents were all the snakes ate, this would be an easier scenario. Young snakes eat slower food like insects and small lizards before tackling bigger prey like mice. Older snakes may revert to eating these things also if the rodent population is in a downturn. The equilibrium gets offset somewhat by this coping mechanism, making the bell curve a little less drastic. Let’s dwell on that later. For now, to paraphrase a great quote, “Ask not for what good is an animal, ask what good the animal is doing.”
Dennis Prichard is a retired park ranger. He’s worked and studied wildlife at many National Parks and Wildlife Refuges including Carlsbad Caverns, Mammoth Caves, the Everglades, Sequoyah NWR in Oklahoma, Sevilleta NWR in New Mexico, and Isle Royale National Park, to name a few. He travels in a fifth wheel with his wife and dog, a Labrador named Cricket.
Read previous RoVing Naturalist articles here.
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Indeed a bullsnake did good for me. S/he lived in the loft of my garage/workshop and kept the area free of rodents – hooray!