Want to know if you live in a healthy environment? Find a snake.
All snakes are carnivores, which means they eat other animals. If their prey is present, it means healthy plants are also around. Snakes serve as touchstones of unpolluted, undisturbed habitats.
Despite some less-than-charitable attitudes toward these sinuous reptiles, the absence of snakes in places where they should be may indicate problems in the natural world. Snakes are present in most natural habitats in tropical and warm temperate zones.
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The presence of a wide assortment of snake species in most regions south of Canada indicates a sufficiently diverse food web.
Food webs and food chains reveal relationships between top predators and their food sources.
A food web refers to the complexity of feeding patterns among organisms, the pathways that energy takes as it passes through the ecosystem — sun to plant to herbivore (prey) to carnivore (predator). Animals eat plants and each other in a bewildering array of configurations.
A food chain is the path of energy flow through a specific part of an ecosystem. An oak tree captures the sun’s energy and stores calories. The calories are passed on when a white-footed mouse eats the oak’s acorns. The food chain lengthens when a ratsnake eats the mouse and lengthens even further if the ratsnake falls victim to a kingsnake or a hawk.
The predators would be unable to persist without prey, which would not be around without plants. The very fact that a predator is present means lower links in a food chain are operating properly.
Certain animals, including some snakes, are dietary specialists, eating primarily one prey species or perhaps a few select ones.
For example, eastern hognose snakes in the wild survive on a near-exclusive diet of toads. Adult mud snakes eat primarily large salamanders, and tiny crowned snakes eat centipedes. The prey of snakes may even be predators themselves, making for a longer food chain. Thus toads require insects; giant salamanders eat crawfish; centipedes use their pincers to capture soil invertebrates for food.
In some regions, where suitable habitats are available, all the snakes mentioned above might be found within a few feet of each other. Their collective presence in the ecosystem indicates that a healthy lower-level food base exists in the form of plants and prey.
If all snakes characteristic of a region are around and doing fine, we can have confidence that a properly functioning habitat is available to support them. Whatever other problems might beset a habitat, having a robust food web in operation is essential for any environment.
Another point we should consider is that if the snakes are missing, what else might be absent? Are hognose snakes missing because no toads are to be found? Are the toads absent because of an insufficient supply of insects? Has something happened at the lower levels of the food chain, resulting in a problem that is expressed at the top?
When something goes wrong at the bottom of a food chain, an environmental domino effect can result that may not be apparent by simply looking at the landscape.
The revelation that a rich biodiversity of native snakes exists in a region should be viewed as a positive sign. You may not be fond of snakes, but when they are not found where they are supposed to be you may dislike the deeper-lying environmental problems even more.
With the arrival of spring, snakes will be out and about for months. Although a few are venomous, snakes are overhyped as a threat to humans. Learn what you should about your odds of encountering a snake and what to do if you have the misfortune to be bitten.
Next week: How do you avoid snakebites and what do you do if you don’t.
Whit Gibbons is professor of zoology and senior biologist at the University of Georgia’s Savannah River Ecology Laboratory. If you have an environmental question or comment, email ecoviews@gmail.com.
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