Furry Cricket Catcher and the “Balance of Nature”

By David Spector Gazette Contributing Writer

One September day I looked out the window and saw a gray fox walking through my yard, pouncing on the grasshoppers and crickets that it startled. Among the benefits of my infrequent lawn-mowing is that the taller grass and more abundant wildflowers provide food for many interesting insects, including an abundant supply of crickets and grasshoppers. These, in turn, are food for a variety of other animals, including my visitor. As often happens, this observation led me to reflect on something larger: the so-called “balance of nature” and why I don’t find the concept useful.

The gray fox is just as interesting and beautiful as its dapper distant cousin, the red fox. This species has shorter legs than those of the red fox, allowing it to climb trees. The plain name “gray fox” does not do justice to such a lovely animal. The gray of much of the fur is actually gray, white and black hairs mixed in a complex pattern that blends into a rich reddish on the head and along the flanks. The black tip of the tail identifies the animal as a gray, not a red, fox.

Gray foxes subsist largely on small mammals for much of the year. In the late summer and fall, however, insects (as I observed) and fruit often make up a large part of their diet.

The relationship between two species or groups of species, such as foxes and the grasshoppers and crickets is complex. The availability of grassland insects depends on many things, including fire (both natural and human-caused) and the changing density—numbers of individuals in a given area—of large grass-eating mammals, which might be native (e.g., bison), domestic (e.g., cattle), or human (e.g., using lawn mowers). The density of foxes also depends on many factors, including the density of small mammals, the prevalence of diseases, and the density of such larger predators as coyotes.

A fox is naturally more likely to catch a weak or injured grasshopper. Is this culling of the insects beneficial? The individual who is eaten does not benefit! That individual’s species benefits only in the sense that future generations might be more resistant to being caught by foxes. A grasshopper encountering a potential predator has several options: freeze, hop, walk or fly. Those with a genetically based propensity for the wrong response to a fox are more likely to be caught by a fox, leaving more of those with better escape choices to serve as parents to subsequent generations. Grasshoppers, though, face many predators; the best response to a fox might not be the best escape from a bird or a frog. Thus, the culling of fox- vulnerable individuals might or might not result in a net gain in predator resistance for a species of grasshopper.

A plant’s perspective?

What might be the perspective of a plant? Is the gray fox beneficial? Grasshoppers and crickets eat grass and other vegetation, so the fox might benefit those plants. Recall, though, that gray foxes prey largely on small mammals during most of the year. Many small mammals, in turn, often eat insects. Suppose that an individual fox over the course of a year eats 100 grasshoppers and 100 small mammals each of which, on average, would have killed 10 grasshoppers. In this case the fox might not have a net benefit for the plants. The interaction between fox and plants depends on the actual numbers and on many other things (e.g., the extent to which some of the small mammals also eat those plants).

Is this interaction an instance of a balance of nature? Some may find comfort in the belief that the interactions among species are automatically stabilized by what they perceive as a system of checks and balances, preventing big fluctuations in species abundance. Instead, I find fascination in the changing complexities of natural interactions and patterns that don’t necessarily follow such convenient human constructs.

From the simple observation of a fox pouncing on an insect I can think about relationships that include many other organisms and time scales that span seasons and generations. As a scientist I look for pattern, and I do so with the knowledge that the patterns of nature may be complex and changing, not always easy to untangle or to sum up in a simple catchphrase.

David Spector is a former board president of the Hitchcock Center for the Environment and teaches biology at Central Connecticut State University.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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