Carrying Capacity of Fox Squirrels on Friends University Campus
By Heather Chamberlain
Introduction: Fox squirrels can be found throughout much of Central and Eastern United States, as well as further north into southern Canada. These squirrels are identified by their brownish-reddish fur and orange underbellies. Surprisingly, fox squirrels are omnivores. Though they may prefer to eat nuts, they will eat just about anything they can get their hands on; from wild fruit, seeds, insects, mushrooms, even occasionally bird eggs, to tree bark, and anything trying to sprout up in your garden. In summer, they build nests of leaves and/or twigs high up in forked branches of a shady tree. They do not hibernate, so in winter a preferred nesting site would be a hollow tree in which plant material can be brought in to create a warm rest area.
In Kansas, fox squirrels are the most commonly encountered type of squirrel of the three species inhabiting the state. Friends University in Wichita is an optimal habitat for these squirrels to thrive. However, every supporting ecosystem has its limits. Carrying Capacity is the maximum number of a species that an environment can sustain before its resources are depleted. Even an ideal environment, such as Friends University, can only carry so many squirrels for so long. The resources fox squirrels benefit from at this university are an abundance of multiple species of shady trees, and about half of them nut- and fruit-producing. According to Darwin’s idea of biotic potential, a population of squirrels in an area of bountiful resources will continue to grow. As it does, the population will need to expand to new grounds or risk exhausting resources, or even possibly extinction. The objective of this report is to determine how many fox squirrels the Friends University campus may successfully sustain.
Methods: The Friends University Campus measures 54.5 acres. The experiment was conducted using a sample of trees from roughly 2 acres of campus landscape. The trees in this area were measured by circumference and determined as nesting and/or food sites. The number of trees examined in this sample equaled approximately 54. On the 54.5 acres of campus, there are 18 buildings. Using the dimensions of the largest building on campus, estimates were made as to how many of those acres contain biotic vs. abiotic features. One acre is the equivalent of 43,560 square feet. Davis Hall measures 77,474 square feet. Rounding this number up, the building equals roughly 2 acres. If we roughly estimate the other 17 buildings on campus as about half the size of Davis Hall, also incorporating additional features not directly measured like walkways and other small areas non-sustainable for squirrels, this roundabout estimate leaves us with 35 acres of land left. There are just about as many parking lots as there are buildings, and they measure an even greater number of feet; not to mention the length of the football field. We’ll take another 25 acres off our total for those features as well.
Results: What is left is a very rough estimate of 10 acres for wildlife habitat. If we take our calculations for the 2 acres of land examined, and apply it to another 8 acres, it should give us an approximate idea as to how many squirrels can sustainably live on Friends University. Of the sample of 54 trees examined, 49 were deemed suitable for nesting. Based on the circumference of each sufficient tree, numbers from previous experiments may determine how many nests each tree can support. By analyzing measurements gathered in this experiment: of 54 trees on 2 acres of land, in 49 ideal trees optimal for nesting, 85 nests could be supported. If each nest can support 2 squirrels, by these numbers, an estimated 170 squirrels can comfortably live on these two acres. If we multiply this number by our rough estimate of an available 10 acres of habitat, an approximate 850 squirrels can adequately be sustained on this campus. Experts say that eastern fox squirrels are not territorial, so it is possible that they could overcrowd on a land if they do not disperse.
Food producing trees in a squirrel’s habitat greatly affect carrying capacity as well. Again, of the 54 trees examined, a total of only 22 were found to produce a food supply. A squirrel’s primary food source is nuts, and then, if necessary, berries and seeds. Eighteen trees were discovered to produce nuts or berries. Four trees were conifers and, therefore, produce cones (which a squirrel may substitute in its diet). Results from a previous study determine that, due to a tree’s size, of our 18 nut and berry producers, a total of 47 squirrels can be supported. An additional 7 squirrels can be supported if cones of conifer trees are supplemented. These totals suggest only 54 squirrels can be supported with food resources from 2 acres on Friends University campus. Again, if we multiply that to include our additional 8 acres of available environment, we find that 270 squirrels can be supported by food resources.
Discussion: If a potential population of 850 squirrels can comfortably live in an area, but only 270 are supported by food, what do these number variances mean? One possibility may be that not all of the squirrels are eating their preferred food sources. They may be resorting to other sources listed above, such as insects, or green sprouts. Perhaps a study could be conducted to calculate in these other food sources. Our inhabiting squirrels may be foraging in more distant territories than Friends University campus. However, a squirrel usually stays pretty close to home (an estimated 10 hectares or less). Those squirrels living on the edges of campus may have home territories within 10 hectares but not on the property of the college campus. One research article stated that a single squirrel may build several nests. Our squirrel numbers might be lower than we estimated if we decide to take this possibility into consideration.
Our calculations in this study represent the maximum number of squirrels that can theoretically be supported by the resources available at Friends University. This may not represent realistic population numbers. An addition to this research may be to reevaluate the dimensions of this experiment to create a more realistic representation. Squirrel populations experience a fairly steady mortality rate, but reproduction rate is pretty stable as well. Also, how squirrels obtain water resources on this campus would be an interesting aspect to look into.