Habitat management for optimum population densities and maximum utilization of snowshoe hares

To develop habitat management procedures for optimum population densities and maximum utilization of snowshoe hare

The snowshoe hare filter to spruce establishment in boreal Alaska

Thesis (Ph.D.) University of Alaska Fairbanks, 2018Interior Alaska is a heterogeneous landscape within the circumpolar boreal forest and is largely composed of black and white spruce (Picea mariana and P. glauca). Improving our understanding of the factors affecting patterns in spruce regeneration is particularly important because these factors ultimately contribute to shaping the boreal forest vegetation mosaic. Herbivory by snowshoe hares (Lepus americanus) is one factor that likely drives patterns in spruce establishment. The interaction between spruce and snowshoe hares provides an opportunity to study how plant-herbivore interactions can affect succession, vegetation community composition, and consequently, how herbivory influences landscape heterogeneity. I explored how herbivory by snowshoe hares alters the survival and growth of spruce seedlings across Interior Alaska's boreal forest. I hypothesized that the survival and growth rate of regenerating spruce is significantly reduced by snowshoe hare herbivory and that snowshoe hare herbivory influences the pattern of spruce establishment across time and space. To address this hypothesis, I conducted research in three distinct vegetation communities across the region: productive lowland floodplains (Chapters 1 and 2), treeline (Chapters 3 and 4), and recently burned stands of black spruce (Chapter 5). Together these five chapters reveal that snowshoe hares affect spruce establishment across much of boreal Alaska. Where and when hares are abundant, spruce can be heavily browsed, resulting in suppressed seedling growth and increased seedling mortality. The results of these studies also reveal a consistent and predictable pattern in which this plant-herbivore interaction takes place. The snowshoe hare filter acts as a 'spatially aggregating force' to spruce establishment, where the potential for optimal regeneration is highest during periods of low hare abundance and where hares are absent from the landscape.Introduction -- Chapter 1. Stage-dependent effects of browsing by snowshoe hares on successional dynamics in a boreal forest ecosystem -- Chapter 2. Asynchronous recruitment dynamics of snowshoe hares and white spruce in a boreal forest -- Chapter 3. Can snowshoe hares control treeline expansions? -- Chapter 4. Functional responses of white spruce to snowshoe hare herbivory at treeline -- Chapter 5. Herbivory by snowshoe hares on regenerating black spruce foreshadows future capacity to influence postfire succession -- Conclusion

Genetic sampling for estimating density of common species.

Understanding population dynamics requires reliable estimates of population density, yet this basic information is often surprisingly difficult to obtain. With rare or difficult-to-capture species, genetic surveys from noninvasive collection of hair or scat has proved cost-efficient for estimating densities. Here, we explored whether noninvasive genetic sampling (NGS) also offers promise for sampling a relatively common species, the snowshoe hare (Lepus americanus Erxleben, 1777), in comparison with traditional live trapping. We optimized a protocol for single-session NGS sampling of hares. We compared spatial capture-recapture population estimates from live trapping to estimates derived from NGS, and assessed NGS costs. NGS provided population estimates similar to those derived from live trapping, but a higher density of sampling plots was required for NGS. The optimal NGS protocol for our study entailed deploying 160 sampling plots for 4 days and genotyping one pellet per plot. NGS laboratory costs ranged from approximately $670 to$3000 USD per field site. While live trapping does not incur laboratory costs, its field costs can be considerably higher than for NGS, especially when study sites are difficult to access. We conclude that NGS can work for common species, but that it will require field and laboratory pilot testing to develop cost-effective sampling protocols

Moving forward in circles: challenges and opportunities in modelling population cycles

Population cycling is a widespread phenomenon, observed across a multitude of taxa in both laboratory and natural conditions. Historically, the theory associated with population cycles was tightly linked to pairwise consumer–resource interactions and studied via deterministic models, but current empirical and theoretical research reveals a much richer basis for ecological cycles. Stochasticity and seasonality can modulate or create cyclic behaviour in non-intuitive ways, the high-dimensionality in ecological systems can profoundly influence cycling, and so can demographic structure and eco-evolutionary dynamics. An inclusive theory for population cycles, ranging from ecosystem-level to demographic modelling, grounded in observational or experimental data, is therefore necessary to better understand observed cyclical patterns. In turn, by gaining better insight into the drivers of population cycles, we can begin to understand the causes of cycle gain and loss, how biodiversity interacts with population cycling, and how to effectively manage wildly fluctuating populations, all of which are growing domains of ecological research

Healthy Ecosystems

Objectives: Students will be able to show and explain the predator/prey population relationship between the Canada lynx and the snowshoe hare using the TI-84 graphing calculator. Students will understand the importance of species balancing each other out in order to establish a healthy ecosystem

Interacting effects of climate and biotic factors on mesocarnivore distribution and snowshoe hare demography along the boreal-temperate ecotone

The motivation of my dissertation research was to understand the influence of climate and biotic factors on range limits with a focus on winter-adapted species, including the Canada lynx (Lynx canadensis), American marten (Martes americana), and snowshoe hare (Lepus americanus). I investigated range dynamics along the boreal-temperate ecotone of the northeastern US. Through an integrative literature review, I developed a theoretical framework building from existing thinking on range limits and ecological theory. I used this theory for my second chapter to evaluate direct and indirect causes of carnivore range limits in the northeastern US, using data collected from 6 years (2014–2019) of fieldwork. My third chapter again used this theory and classical understanding of density-dependence to evaluate factors influencing snowshoe hare populations along their trailing edge in the northeastern US. Finally, for my fourth chapter, I used the model outputs from the second chapter to compare current and future distributions based on causal and correlational frameworks given projected changes in snowpack and forest biomass

A cautionary note on using the scale prior for the parameter N of a binomial distribution

Statistical analysis of ecological data may require the estimation of the size of a population, or of the number of species with a certain population. This task frequently reduces to estimating the discrete parameter N representing the number of trials in a binomial distribution. In Bayesian methods, there has been a substantial amount of discussion on how to select the prior for N. We propose a prior for N based on an objective measure of the worth that each value of N has in being included in the model space. This prior is compared (through the analysis of the popular snowshoe hare dataset) with the scale prior which, in our opinion, cannot be understood from solid objective considerations