IAB Research Project Description

Long-Term Ecological Research: Population ecology of snowshoe hare in Alaska taiga forests

Principal Investigator Knut Kielland gently encourages a snowshoe hare into a pillowcase so he can take its vital statistics. Kielland's research group is studying broad ecological questions regarding trophic interactions of plants, herbivores (hares), and predators (lynx, raptors) in the context of the snowshoe hare cycle in Interior Alaska.

Suzanne Worker, graduate student of Knut Kielland, carefully releases a snowshoe hare, newly equipped with ear tags and a transmitter, after recording its vital statistics in September 2011. Principal Investigator Kielland's research group is studying broad ecological questions regarding trophic interactions of plants, herbivores (hares), and predators (lynx, raptors) in the context of the snowshoe hare cycle in Interior Alaska.

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The 10-year snowshoe hare cycle is one of the most striking phenomena of herbivore populations anywhere on Earth, and a unique feature of the boreal forest. As a critical species through its interaction with vegetation processes and population dynamics of several mammalian and avian predators, snowshoe hares represent an important link in the trophic structure of these low-productivity, low diversity ecosystems. The cyclic abundance of snowshoe hares and lynx, a facultative specialist predator on snowshoe hares, has attracted the curiosity of both historians and biologists since Charles Elton and Mary Nicholson’s 1942 compilation of a near-200 year record of lynx fur returns to the Hudson’s Bay Company. While ecologists largely agree that the cyclic abundance of lynx is directly tied to that of snowshoe the causative agents of the snowshoe hare cycle are considered to be the result of complex trophic dynamics that include predation, food quality, stress, and perhaps climatic variability.

Since 1999 we have monitored populations of snowshoe hares in the Bonanza Creek Long Term Ecological Research (BNZ LTER) site in Fairbanks, Alaska. We have documented a twentyfold range in snowshoe hare densities during the course of a near-complete hare population cycle.

Building on eight years of mark-recapture population data on snowshoe hares we will address the interactive effects of snowshoe hare abundance on soil processes and vegetation dynamics, hare demography, and the ecology of their principal predator, the lynx, through a complete 10-year population cycle of snowshoe hares. This project will be the first time such a coordinated study of soil processes, primary producers, herbivores, and predators has been conducted for any terrestrial ecosystem where large populations of native herbivores remain a dominant component of ecosystem structure and function. We will combine observational studies of temporal changes in animal abundance and distribution (using mark-recapture and telemetry) with vegetation composition and chemistry, as well as experimental manipulations of herbivore distributions.

We have two nine-hectare live-trapping grids (one in a black spruce forest and one in a riparian shrub community) at the BNZ-LTER site. The grids consist of 50 traps arranged in a 5 x 10 grid with a 50 meter intertrap distance. Hares are trapped four times per year (spring, summer, autumn, and winter) with each trapping session lasting four nights. Captured snowshoe hares are sexed, weighed (±5g), and the right hind foot is measured (mm). Newly captured hares are tagged in each ear. Snowshoe hare abundance are estimated using maximum likelihood estimators assuming population closure.

Abundance estimates (N) are used to inform a recent model of population density (d) that neither relies on the size of the trapping grid nor estimation of the effective trapping area. The method relies on the estimated population size (N) and capture probability, as well as the mean distance between successive captures, which provide an estimate of the scale of individual movements. These closed population capture-recapture data are used as inputs to the simulation model of the trapping process based on: 1) spatially-defined trap locations, 2) the magnitude of individual hare movements, 3) the overall capture probability, and 4) the spatial scale of the detection function describing capture probabilities. Our frequent trapping schedule allows us to estimate population growth rates, sex and age composition, and apparent recruitment.

As part of the snowshoe hare survival studies we also conduct investigations regarding lynx ecology. Whereas all the major predators on snowshoe hares (lynx, coyotes, goshawks, and Great Horned owls) are common in our study area, lynx appear to be the major mammalian predator on hares.

Project Funding

IAB Project #235

Media Contact

Marie Thoms
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Institute of Arctic Biology
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University of Alaska Fairbanks
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