Working Through the St. Matthew Island Reindeer Case Study
The St. Matthew Island reindeer experiment is one of those standard ecology cases you see assigned constantly. Twenty-nine reindeer were introduced to the island in 1944 by the U.S. Coast Guard. By 1963, the population had exploded to over six thousand. Then it collapsed to fewer than fifty animals by 1966. The worksheet answer keys floating around education sites usually follow a predictable pattern, and honestly, a lot of them are either wrong or simplified to the point of being misleading. Most of the questions on these worksheets track population growth rates, carrying capacity, and overshoot dynamics. The standard calculation involves using the exponential growth formula, N(t) = Ne^rt, to model the initial phase before resources became limiting. If your worksheet asks for the intrinsic rate of increase, r, you're typically solving for that variable using two known population points. The math is straightforward algebra, but students routinely make mistakes with the natural logarithm step, forgetting to divide by the time interval. I spent a week trying to debug why my students' calculated r values kept coming out wrong. Turned out the worksheet source material used the 1957 population estimate rather than the 1963 peak when defining the "initial" population, which shifted the entire curve. The answer key I eventually produced used N = 29 at t = 0 (1944) and N = 6000 at t = 19 (1963), giving r approximately 0.268 per year. That number matches the published data from Carpenter and Smith in their 1988 analysis, which is probably the most reliable source available on this case.
The carrying capacity question comes up frequently. The tricky part here is that St. Matthew Island's actual carrying capacity for reindeer was never formally measured. The common worksheet answer states a K value around 1,300 to 1,500 animals based on winter forage availability, but that is a back-calculation, not an observation. The real lesson is that the reindeer overshot whatever the island could sustainably support, consumed their lichen reserves completely, and then starved. Lichen growth on this island is extremely slow — maybe a few grams per square meter per year — so recovery would take decades even if the herd had stayed within bounds. Another point worksheets often gloss over is the role of weather in the population crash. The winter of 1963–1964 was unusually harsh with ice crust formation that prevented the reindeer from accessing lichen underneath. Some instructors treat the crash as purely density-dependent, but it had a strong density-independent component too. When grading or checking answers, it's worth noting that both factors operated simultaneously, not sequentially. If you're looking for a download or trying to verify an existing key, the most defensible answers rely on the original Coast Guard records and the later analysis by David B. McDonald and colleagues. Any key claiming a precise carrying capacity number without acknowledging that uncertainty is probably pulling from an outdated textbook edition. The population crash timing is also debated — some sources say the collapse happened between 1963 and 1966, while others narrow it to late 1963 through spring 1964 based on aerial survey data. Your worksheet should probably allow for both ranges depending on which source the author used.
