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.

Multiscale habitat relationships of snowshoe hares (Lepus americanus) in the mixed conifer landscape of the Northern Rockies, USA: Cross-scale effects of horizontal cover with implications for forest management

Snowshoe hares (Lepus americanus) are an ecologically important herbivore because they modify vegetation through browsing and serve as a prey resource for multiple predators. We implemented a multiscale approach to characterize habitat relationships for snowshoe hares across the mixed conifer landscape of the northern Rocky Mountains, USA. Our objectives were to (1) assess the relationship between horizontal cover and snowshoe hares, (2) estimate how forest metrics vary across the gradient of snowshoe hare use and horizontal cover, and (3) model and map snowshoe hare occupancy and intensity of use. Results indicated that both occupancy and intensity of use by snowshoe hares increased with horizontal cover and that the effect became stronger as intensity of use increased. This underscores the importance of dense horizontal cover to achieve high use, and likely density, of snowshoe hares. Forest structure in areas with high snowshoe hare use and horizontal cover was characterized as multistoried with dense canopy cover and medium-sized trees (e.g., 12.7-24.4 cm). The abundance of lodgepole pine (Pinus contorta) was associated with snowshoe hare use within a mixed conifer context, and the only species to increase in abundance with horizontal cover was Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa). Our landscape-level modeling produced similar patterns in that we observed a positive effect of lodgepole pine and horizontal cover on both occupancy and use by snowshoe hares, but we also observed a positive yet parabolic effect of snow depth on snowshoe hare occupancy. This work is among the first to characterize the multiscale habitat relationships of snowshoe hares across a mixed conifer landscape as well as to map their occupancy and intensity of use. Moreover, our results provide stand- and landscape-level insights that directly relate to management agencies, which aids in conservation efforts of snowshoe hares and their associated predators.

Demographic differences in diet breadth of Canada lynx during a fluctuation in prey availability

Population dynamics of specialist carnivores are closely linked to prey availability, but the extent of variability in diet breadth of individual carnivores relative to natural variability in the abundance of their primary prey is not well understood. Canada lynx (Lynx canadensis) specialize on snowshoe hares (Lepus americanus) and exhibit cyclic fluctuations in abundance that lag 1–2 years behind those of snowshoe hares. Declining hare densities spur demographic changes in lynx, but it is unclear whether a corresponding increase in diet breadth occurs: (1) broadly across a lynx population; (2) only among individuals who are able to effectively switch to alternative prey; or (3) only among individuals who cannot capture sufficient primary prey. We measured stable isotope ratios of lynx muscle tissue spanning a cyclic increase and decline in hare density (1998–2001) in Fort Providence, NT, Canada. We found that lynx cohorts responded differently to hare population change, with yearling animals having broader diets at low hare densities, while adults and dependent juveniles maintained a constant diet through the initial decline in hare density. This result was consistent irrespective of lynx sex and indicates that yearling lynx likely are forced to adopt a broader diet when primary prey densities decline. Our results imply that select cohorts of specialist carnivores can exhibit high dietary plasticity in response to changes in primary prey abundance, prompting the need to determine whether increased diet breadth in young lynx is a successful strategy for surviving through periods of snowshoe hare scarcity. In this way, cohort‐specific niche expansion could strongly affect the dynamics of organisms exhibiting population cycles.

Habitat-specific and season-specific faecal pellet decay rates for five mammalian herbivores in south-eastern Australia

The accuracy of population abundance estimates of mammalian herbivores from faecal pellet counts is potentially affected by pellet decay. We collected fresh pellet groups from hog deer (Axis porcinus), European rabbit (Oryctolagus cuniculus), eastern grey kangaroo (Macropus giganteus), swamp wallaby (Wallabia bicolor) and common wombat (Vombatus ursinus) (n = 300 per species) at Wilsons Promontory National Park, Victoria, Australia. We deposited five pellet groups per species per month within each of five vegetation types in the park, then monitored pellet group decay over 24 months. We demonstrate that age estimation of pellet groups was inaccurate and is unlikely to improve the efficiency of pellet counts. We present habitat- and species-specific estimates of pellet and pellet group decay using two measures: decay rate (the proportion of pellets surviving per unit of time); and mean time to decay. We explain how our data can be used to optimise faecal pellet count design, and to improve the accuracy of both indices and estimates of abundance from pellet counts. The variability observed in the decay of pellet groups among vegetation types, and for species among seasons, suggests that caution should be used if applying pellet decay rates over long time-frames or to locations with differing environmental conditions.

Synchrony in the snowshoe hare (Lepus americanus) cycle in northwestern North America, 1970–2012

Snowshoe hares (Lepus americanus Erxleben, 1777) fluctuate in 9–10 year cycles throughout much of their North American range. Regional synchrony has been assumed to be the rule for these cycles, so that hare populations in virtually all of northwestern North America have been assumed to be in phase. We gathered qualitative and quantitative data on hare numbers and fur returns of Canada lynx (Lynx canadensis Kerr, 1792) in the boreal forest regions of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe synchrony in the time window of 1970–2012. Broad-scale synchrony in lynx fur returns was strong from 1970 to about 1995 but then seemed to break down in different parts of this region. Hare populations at 20 sites in Alaska, the Yukon, and Northwest Territories showed peak populations that lagged by 1–4 years during the 1990s and 2000s cycles. The simplest hypothesis to explain these patterns of asynchrony in hare cycles is the movement of predators from British Columbia north into the Yukon and then east into the Northwest Territories and west into Alaska. A traveling wave of these cycles is clearly seen in the lynx fur returns from western Canada and Alaska from 1970 to 2009. One consequence of a failure of synchrony is that hare predators like Canada lynx and Great-horned Owls (Bubo virginianus (Gmelin, 1788)) can move from one adjacent area to the next within this region and survive long enough to prolong low densities in hare populations that have declined earlier.

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.