Interference competition between wolves and coyotes during variable prey abundance

Interference competition occurs when two species have similar resource requirements and one species is dominant and can suppress or exclude the subordinate species. Wolves (Canis lupus) and coyotes (C. latrans) are sympatric across much of their range in North America where white-tailed deer (Odocoileus virginianus) can be an important prey species. We assessed the extent of niche overlap between wolves and coyotes using activity, diet, and space use as evidence for interference competition during three periods related to the availability of white-tailed deer fawns in the Upper Great Lakes region of the USA. We assessed activity overlap (Δ) with data from accelerometers onboard global positioning system (GPS) collars worn by wolves (n = 11) and coyotes (n = 13). We analyzed wolf and coyote scat to estimate dietary breadth (B) and food niche overlap (α). We used resource utilization functions (RUFs) with canid GPS location data, white-tailed deer RUFs, ruffed grouse (Bonasa umbellus) and snowshoe hare (Lepus americanus) densities, and landscape covariates to compare population-level space use. Wolves and coyotes exhibited considerable overlap in activity (Δ = 0.86-0.92), diet (B = 3.1-4.9; α = 0.76-1.0), and space use of active and inactive RUFs across time periods. Coyotes relied less on deer as prey compared to wolves and consumed greater amounts of smaller prey items. Coyotes exhibited greater population-level variation in space use compared to wolves. Additionally, while active and inactive, coyotes exhibited greater selection of some land covers as compared to wolves. Our findings lend support for interference competition between wolves and coyotes with significant overlap across resource attributes examined. The mechanisms through which wolves and coyotes coexist appear to be driven largely by how coyotes, a generalist species, exploit narrow differences in resource availability and display greater population-level plasticity in resource use.

Climate Tolerances and Habitat Requirements Jointly Shape the Elevational Distribution of the American Pika (Ochotona princeps), with Implications for Climate Change Effects

Some of the most compelling examples of ecological responses to climate change are elevational range shifts of individual species, which have been observed throughout the world. A growing body of evidence, however, suggests substantial mediation of simple range shifts due to climate change by other limiting factors. Understanding limiting factors for a species within different contexts, therefore, is critical for predicting responses to climate change. The American pika (Ochotona princeps) is an ideal species for investigating distributions in relation to climate because of their unusual and well-understood natural history as well as observed shifts to higher elevation in parts of their range. We tested three hypotheses for the climatic or habitat characteristics that may limit pika presence and abundance: summer heat, winter snowpack, and forage availability. We performed these tests using an index of pika abundance gathered in a region where environmental influences on pika distribution have not been well-characterized. We estimated relative pika abundance via scat surveys and quantified climatic and habitat characteristics across two North-Central Rocky Mountain Ranges, the Wind River and Bighorn ranges in Wyoming, USA. Pika scat density was highest at mid-elevations and increased linearly with forage availability in both ranges. Scat density also increased with temperatures conducive to forage plant growth, and showed a unimodal relationship with the number of days below -5°C, which is modulated by insulating snowpack. Our results provide support for both the forage availability and winter snowpack hypotheses. Especially in montane systems, considering the context-dependent nature of climate effects across regions and elevations as well as interactions between climatic and other critical habitat characteristics, will be essential for predicting future species distributions.

Vegetation structure and composition determine snowshoe hare (Lepus americanus) activity at arctic tree line

Snowshoe hares (Lepus americanus Erxleben, 1777) are keystone herbivores supporting many boreal-forest predators. Understanding habitat use of hares can help predict how hares and their predators will be affected by disturbances such as climate change, which will have a particularly strong effect at tree line. We examined hare activity at arctic tree line near Churchill, Manitoba, using fecal pellet transects established in August 2012. We counted all hare fecal pellets at two plots per transect and measured plant abundance and vegetation structure surrounding the plots, then used model selection to determine the combinations of habitat features or plant species that best explained hare activity or presence. Hare pellets occurred at a higher density where tall shrub cover was high. Pellet density also increased with increasing canopy cover, tree size, tree density, visibility, and small shrub cover, but was negatively correlated with medium-sized shrub and herb cover. Hares preferred areas with willow (genus Salix L.) and avoided areas with unpalatable black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.). With climate warming, tree line is expected to advance northward and the increased tall shrub and willow cover predicted with increasing temperatures should benefit hares by providing greater predator protection and food.

The landscape of fear: habitat use by a predator (Canis latrans) and its main prey (Lepus californicus and Sylvilagus audubonii)

We evaluated the degree of mutual exclusivity of distributions of coyotes ( Canis latrans Say, 1823) and their main prey (two lagomorph species: the black-tailed jackrabbit, Lepus californicus Gray, 1837, and the desert cottontail rabbit, Sylvilagus audubonii (Baird, 1858)) within the landscape by testing two models. The first assumes that prey seek high resource patches and, subsequently, predators seek prey within these patches, and predicts a high degree of overlap in patch use by both. The second model assumes that predator and prey balance not only food resources but reciprocal levels of predation risk and predation success in making decisions on whether or not to use a patch. This model predicts discordance in patch use between predator and prey. We used a combination of GPS-telemetry and camera-trapping data to assess habitat use patterns of predator and prey. Results from this study support the second model regarding spatial use of the landscape by a predator and its prey. Where the use of the landscape by predators and prey seem to be mediated by environmental constraints, both will adjust their predatory or antipredatory strategies based on these constraints. This results in a partial spatial separation of predator and prey across the landscape, providing patches of relative safety for prey but sufficient areas of overlap for predators to be successful.

Mapping potential core areas for lynx (Lynx canadensis) using pellet counts from snowshoe hares (Lepus americanus) and satellite imagery

We used location data from radio-collared Canada lynx ( Lynx canadensis Kerr, 1792), pellet-count data from snowshoe hares ( Lepus americanus Erxleben, 1777), and cover-type data from satellite imagery to evaluate the relationship between the scale of habitat measurement and the potential for persistence of lynx in northeastern Minnesota, USA, at the southern extent of their range. We counted hare pellets at transects throughout northeastern Minnesota to index hare abundance in cover types. Pellet counts were highest in coniferous forest, regenerating–young forest, and shrubby grassland, and these cover types were greater inside lynx use areas than outside of them. Proportions of regenerating–young forest were greater at scales ≥5 km2. We used these results and satellite imagery to map potential lynx core areas. We predicted that 7%–20% of the study area was suitable for lynx. Areas that we predicted to be suitable for lynx corresponded with known core areas, including those withheld from analyses. To maintain habitat for lynx persistence, forest management should retain current levels of 10- to 30-year-old coniferous forest and include ≥5 km2 areas containing 40% of 10- to 30-year-old coniferous forest. Mapping of potential core areas would be improved if cover-type data from satellite imagery identified conifer regeneration.

An appraisal of the fitness consequences of forest disturbance for wildlife using habitat selection theory

Isodar theory can help to unveil the fitness consequences of habitat disturbance for wildlife through an evaluation of adaptive habitat selection using patterns of animal abundance in adjacent habitats. By incorporating measures of disturbance intensity or variations in resource availability into fitness-density functions, we can evaluate the functional form of isodars expected under different disturbance-fitness relationships. Using this framework, we investigated how a gradient of forest harvesting disturbance and differences in resource availability influenced habitat quality for snowshoe hares (Lepus americanus) and red-backed voles (Myodes gapperi) using pairs of logged and uncut boreal forest. Isodars for both species had positive intercepts, indicating reductions to maximum potential fitness in logged stands. Habitat selection by hares depended on both conspecific density and differences in canopy cover between harvested and uncut stands. Fitness-density curves for hares in logged stands were predicted to shift from diverging to converging with those in uncut forest across a gradient of high to low disturbance intensity. Selection for uncut forests thus became less pronounced with increasing population size at low levels of logging disturbance. Voles responded to differences in moss cover between habitats which reflected moisture availability. Lower moss cover in harvested stands either reduced maximum potential fitness or increased the relative rate of decline in fitness with density. Differences in vole densities between harvested and uncut stands were predicted, however, to diminish as populations increased. Our findings underscore the importance of accounting for density-dependent behaviors when evaluating how changing habitat conditions influence animal distribution.

Transformation of abandoned farm fields into coniferous plantations: Is there enough vegetation structure left to maintain winter habitat of snowshoe hares?

Natural forests will likely be unable to sustainably fulfill society needs for wood fibers and intensively managed plantations could be an alternative source of timber in the future. Abandoned farm fields are often targeted for conversion, as they are already disturbed sites; however, they also represent high-quality habitat for species such as snowshoe hares ( Lepus americanus Erxleben 1777), a keystone mammal in the boreal forest. We evaluated the effect of converting abandoned farm fields (n = 22) to conifer plantations (n = 19) on habitat use by snowshoe hares, using pellet counts and snow-tracking surveys. Both survey techniques yielded similar results: winter habitat use by hares is mostly affected by vegetation cover rather than habitat type. In the short term, plantations do not offer less protective cover than the one found in abandoned farm fields. However, upon reaching a certain height (≥7 m), plantations are mechanically pruned and lose their protective quality. Promoting silvicultural techniques that maintain lateral cover beyond a critical threshold (70%) could preserve the quality of hare habitat for an extended proportion of rotation time of the plantation.

Habitat preference of Canada lynx through a cycle in snowshoe hare abundance

We assessed habitat preference of a lynx (Lynx canadensis) population through 8 years of a snowshoe hare (Lepus americanus) cycle. Seventy-four percent of our southern Yukon study area was approximately 30-year-old regenerating forest resulting from a large wildfire. The study area was not trapped and lynx density was very high compared with other populations in North America. Contrary to our prediction, there was no discernable shift in habitat preference through the hare cycle; however, our habitat types were coarsely mapped and our radiolocations relatively inaccurate. Lynx may have altered their habitat preferences at finer scales (for patches <2 ha). Lynx showed strong preference for regenerating habitats over mature white spruce (Picea glauca) and alpine–subalpine. Lodgepole pine (Pinus contorta) dominated regenerating stands were preferred over spruce–willow (Salix spp.) stands of equal age. Riparian willow stands were also preferred over mature spruce forest and alpine. Lynx used riparian willow stands more in winter, but we detected no other shifts in habitat preference between snow-free and winter periods. We did not detect any difference in habitat preference between sexes. Independent juveniles made greater use of mature forest and perhaps riparian willow than adults, but no other difference in preference between the two age groups was noted. Lynx preference for regenerating habitat over mature forest suggests that burns will benefit lynx, especially if the regenerating community is pine dominated. Logging will only likely provide similar benefits if a dense pine understory results, which is unlikely in intensively managed stands. The suppression of forest fires in recent decades may have contributed to the decline of lynx numbers in the south of their range.