Understanding Caribou Population Cycles

• Main Author: St. John, Jack R
• Format: Text
• Language: unknown
• Published: ScholarWorks at University of Montana 2022
• Subjects: caribou; reindeer; population cycles; Rangifer tarandus; ecology; climate; Behavior and Ethology; Biodiversity; Other Animal Sciences; Population Biology; Terrestrial and Aquatic Ecology; Zoology; Tundra
• Online Access: https://scholarworks.umt.edu/utpp/355; https://scholarworks.umt.edu/context/utpp/article/1377/viewcontent/Understanding_Caribou_Population_Cycles___St._John.pdf

The complex population dynamics of caribou (Rangifer tarandus) were studied to determine the patterns of their population cycles and the processes driving them. It is well established, via previous archaeological research and Indigenous knowledge, that large migrating caribou herds found in and around the tundra at northern latitudes experience population boom and busts roughly every several decades. However, the processes driving the dynamics of these cycles are relatively unknown, which makes managing caribou herds for recreational and subsistence harvests difficult. It has been hypothesized that a combination of intrinsic and extrinsic factors shape these cycles, with density-dependence, predation, harvest, climate, and others likely all playing a role. I aimed to determine whether caribou herds experience population cycling and, if so, estimate the period and amplitude of their cycles and determine which factors drive them. I collected population data on 43 caribou herds throughout the world, and in doing so, assembled the largest caribou population database to date. I used statistical interpolation to fill in the gaps between available data due to low sampling frequency. I quantified whether herds were cycling by fitting populations to sine waves and using periodograms to distinguish cycling tendencies from white-noise stochasticity. I collected additional information on other factors hypothesized to affect caribou cycles, including predator presence data, climate oscillation data, subspecies and ecotype data, and the latitudes of each herd. I used the interpolated data for each herd to determine the variables influencing the periods and amplitudes of caribou population cycles. The median period length was 40.5 years and the amplitude, standardized about the mean population size, was .871; period length and amplitude were also positively correlated. In addition, cycle amplitude was best predicted by period length, subspecies, biome, and average winter minimum temperature. Period length was best predicted by ...