For this week’s University Press Week Blog Tour, Lucia Jacobs offers us a glimpse of environmental stewardship as seen through the activities of the ubiquitous squirrel, a species native to the Americas, Africa, and Eurasia from the Eocene Epoch onward.
Lucia Jacobs is Professor of Psychology and Neuroscience at UC-Berkeley and was a 2019 Radcliffe Fellow. Her work synthesizes concepts from ecology, animal behavior, cognitive science, and neuroscience in order to understand the evolution of universal cognitive traits such as spatial memory and navigation. Her new book on animal behavior and economics is under contract with Harvard University Press.
As a young child, I spent so much time with one favorite sapling that my mother fashioned me a stick chair so that I could sit more comfortably next to my beloved Oaky (who turned out to be a sweet gum). Perhaps I should not have been surprised a couple of decades later when I committed myself to a life of trees and squirrels, tromping the paths among the mighty oaks and beeches of the Institute for Advanced Study at Princeton, as a Ph.D. student.
At Princeton, I was trying to answer a deceptively simple question: why do two kinds of squirrels, living almost on top of each other, have two different banking systems? The eastern gray squirrel, the classic denizen of Central Park, is a stockbroker. This squirrel acquires diverse types of stocks all through August, September, and October, spreading out the risk by hiding each nut in a different location so that if one is found the rest will be safe. Having made this initial investment, the squirrel then spends November through March working furiously on her or his portfolio, checking its value with internal calculations: Is the nut present or has it been stolen by a competitor? Or, has the nut germinated and its caloric value come crashing down in an annual rhythm of hyperinflation, with all the precious nut calories escaping and becoming useless (to a squirrel) green leaf calories?
But that is only one system. The red squirrel, a small neat package with white eyeliner and a big mouth, practices a whole other economy. This squirrel uses its big mouth to scream out warnings to all animals (humans included) who would encroach on its precious space. Quite unlike the flannel-suited grays, the little red squirrel has solved the problem of winter survival by another time-tested method: build a castle of pine cones and scream obscenities at anyone who passes by.
Why two such different economies in two squirrel species that can often be found in the same forest? The gray’s acorns and hickory nuts are big and juicy. But are also tiny time bombs of hyperinflation in case of germination. The red squirrel, unlike its gray neighbors, can subsist on pine cones. That is why reds are found in the piney ends of a forest. Pine cones are poor provender in comparison to nuts and acorns but they come with a hidden advantage. When covered with the debris of torn and de-seeded cones that accumulate over time, pine cones can last, without maintenance, for many years. In this case, the pine tree has lost. The cone has not stayed on the tree long enough for the scales to open and the tiny seeds to be wind-dispersed. The baby pine trees die as embryos. And like Chanticleer on his dung heap, the murderous red squirrel sits on top of the midden proclaiming his wealth and property to all in earshot. Because cones refrigerated in the midden can last, the squirrel only has to defend its small property, a few pine trees, to survive.
Why does the gray not follow the red’s strategy? Even if her bounty germinates, why does a gray not defend a single tree and put all her acorns in one basket? Well, because trees are not stupid either. The tree exacts its price for prior years of large-seeded "free gifts” by occasionally falling silent and remaining fruitless. Not just one tree but whole forests of oaks and hickories vary their production unpredictably. Branches groan with seed one year but produce only a smattering for two years after that. This is known as the masting strategy of trees, and it brutally reestablishes the balance between the squirrel population and tree reproduction. When the stocks crash, squirrels starve or emigrate. Trees depend on squirrels to propagate their offspring which, over time, become our forests. If there are too few squirrels, then the nuts will fall to the ground and be eaten by weevils, under the shade of parental branches. If there are too many squirrels, then all the offspring are eaten. But throw out a couple of masting years and regain the balance—just enough squirrels to help bury just enough nuts that could lead to the germination of thousands of baby trees. This is how large-seeded tree species, producing the seeds that are worth caching, achieve a delicate balance with the squirrels.
So, there you have it—the two economies of two squirrels, the red and the gray. Choose the life of the red: a territorial bantam cock, all bristling fur and trilling pronouncements, protecting precious small territory of cone-bearing trees, never being able to let down your guard. Or choose the life of a gray: a flannel-suited stockbroker, workaholic while the stocks are available in the fall, investing the bounteous crops into a diverse portfolio, which must be managed, never counting on any one stock for your long-term survival. Know that if you take the acorn eater’s path (and your path was taken many millions of years ago and is now firmly inscribed in your genetic code) you permanently forgo the larder and live instead the life of a wanderer, caching treasures, relying on your wits and memory to stay ahead of the competition. It is the gray squirrels and their two cousins, the fox and the little southern flying squirrel, that are the environmental stewards of our forests. They are an important key to how our forests are planted, how they grow, and how they persist.
