Search

Complex interactions such as interference competition and predation, including intraguild predation, are now recognized as important components in animal community structure. At the lower end of a guild, weasels may be highly affected by other guild members due to small body size in relation to other predators. In 2000 and 2001, we radio-collared 24 ermines Mustela erminea and 25 long-tailed weasels M. frenata in 2 areas that differed in abundance of guild members. We tested the hypothesis that when faced with an increased density of other guild members, weasels would modify space and habitat use to reduce the risk of predation associated with encounters involving guild members. We predicted that weasels would increase use of specific habitats (such as refuges) to reduce encounter rates in the presence of a greater number of guild members. Because M. erminea is smaller than M. frenata and thus better able to take advantage of small rodent burrows as refuges from predators and as feeding grounds, we also predicted that M. frenata would show a stronger response to a higher abundance of guild members than M. erminea. Results were consistent with our predictions. Faced with an increased abundance of guild members, M. frenata showed increased habitat selectivity and reduced activity levels, which resulted in increased daily travel distances and increased home ranges. Mustela erminea responded to an increased abundance of guild members through reduced use of preferred habitat which M. frenata already occupied. The contrasting pattern of habitat selection observed between the 2 mustelid species suggested cascading effects, whereby large-predator pressure on M. frenata relaxed pressure of M. frenata on M. erminea. Our results draw attention to the likelihood that competitive intraguild interactions play a facilitating role in M. erminea– M. frenata coexistence. [ABSTRACT FROM AUTHOR]

We studied the population dynamics of snowshoe hare in 2 areas of the southern boreal forest of eastern North America that differed with respect to furbearer harvest. We predicted that hare density and survival would be higher in the area with trapping (TRAP) than in the protected area (PROT) as a response to differential predator abundance. Indices of predator density suggested that predation risk was slightly higher in PROT than TRAP, particularly during the first year of our 3-year study. Predators killed 86% of the radiomarked hares (body mass >900 g) that died during the study (n = 71). Hare density was higher in TRAP (56 ± 4 hares/100 ha) than PROT (30 ± 5 hares/ 100 ha). Furthermore, hare densities were relatively stable in both areas between 1998 and 2000. Additional data from the previous 2 years in TRAP indicated that hare density had remained relatively unchanged for 5 years. These findings were in agreement with regional trends in hunter harvests which were low and stable throughout the 1990s. Annual survival of radiomarked hares (>900 g) was high in both areas but decreased during the study. Survival exhibited a sex*area interaction, and was lower for females in TRAP than PROT (46% vs. 76%) but higher for males in TRAP than PROT (64% vs. 37%); hare survival did not differ when sexes were combined. Differential survival of older hares could therefore not explain the difference in hare densities in the 2 areas. Gestation rates were similar in both areas, but the numbers of young hares (300-900 g) entering the population and young: female ratios were higher in TRAP than PROT. Survival of young hares during their first summer was variable between time periods, and tended to be higher in PROT than TRAP Thus, it is likely that improved survival of juveniles (<300 g) soon after birth explains the increased hare density in TRAP. Study results show that managers cannot assume the existence of cyclicity in all hare populations, and must be aware that complex trophic interactions can generate unexpected responses to perturbations. [ABSTRACT FROM AUTHOR]

Omnivores feed on animals with dynamic distributions and on plants with static distributions. The search tactics they adopt will not only define the risk for the targeted prey, but also for other prey that may be consumed when encountered. The potential impact of omnivores on the dynamics of multi-prey systems thus depends on resource selection and on the tactics used to find their prey. We present an approach that can clarify the foraging decisions of omnivores by combining analyses of habitat selection, local residency time, and interpatch movements. We use this framework to evaluate whether predation by omnivorous black bears on ungulate neonates resulted from an active search or from incidental encounters. We monitored 12 bears, 22 forest-dwelling caribou, and 36 moose during calving seasons. We estimated the spatial patterns in relative occurrence probability of ungulate neonates using Resource Selection Functions (RSFs). We also mapped plant abundance from vegetation surveys. RSF were then built to assess the link between bear distribution and the distribution of these three food types (vegetation, moose calves, caribou fawns). We further evaluated the search tactic used by bears that led to this spatial dependency by exploring patterns of residency times and interpatch movements. Bears did not select areas with a high probability of encounter with neonates, but selected areas with abundant vegetation. Surprisingly, bears displayed shorter residency times in vegetation-rich areas. The selection for vegetation-rich areas was therefore achieved by moving preferentially, but frequently, between areas offering abundant vegetation. Such frequent interpatch movements could result in high rates of fortuitous encounters with neonates, even if bears are not actively searching for them. To mitigate the impacts of forest harvesting on threatened caribou populations, vegetation-rich areas selected by bears (e.g. roadsides) should be segregated from large patches of mature conifer forest suitable for caribou. [ABSTRACT FROM AUTHOR]