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Data from: Phase-dependent climate-predator interactions explain three decades of variation in neonatal caribou survival
Bastille-Rousseau, Guillaume; Schaefer, James A.; Lewis, Keith P.; Mumma, Matthew; Ellington, E. Hance; Rayl, Nathaniel D.; Mahoney, Shane P.; Pouliot, Darren; Murray, Dennis L.; Mumma, Matthew A. — 2016-10-27 1. Climate can have direct and indirect effects on population dynamics via changes in resource competition or predation risk, but this influence can be modulated by density- or phase-dependent processes. We hypothesized that for ungulates, climatic conditions close to parturition have a greater influence on the predation risk of neonates during population declines, when females are already under nutritional stress triggered by food limitation. 2. We examined the presence of phase-dependent climate-predator interactions on neonatal ungulate survival by comparing spatial and temporal fluctuations in climatic conditions, cause specific mortality, and per capita resource limitation. We determined cause-specific fates of 1384 caribou (Rangifer tarandus) from 10 herds in Newfoundland, spanning more than 30 years during periods of numerical increase and decline, while exposed to predation from black bears (Ursus americanus) and coyotes (Canis latrans). 3. We conducted Cox proportional hazards analysis for competing risks, fit as a function of weather metrics, to assess pre- and post-partum climatic influences on survival on herds in population increase and decline phases. We used cumulative incidence functions to compare temporal changes in risk from predators. 4. Our results support our main hypothesis; when caribou populations increased, weather conditions preceding calving were the main determinants of cause-specific mortality, but when populations declined, weather conditions during calving also influenced predator-driven mortality. Cause-specific analysis showed that weather conditions can differentially affect predation risk between black bears and coyotes with specific variables increasing the risk from one species and decreasing the risk from the other. 5. For caribou, nutritional stress appears to increase predation risk on neonates, an interaction which is exacerbated by susceptibility to climatic events. These findings support the phase-dependent climate-predator (PDCP) interactions framework, where maternal body condition influences susceptibility to climate-related events and, subsequently, risk from predation.
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Data from: Intrinsic traits of woodland caribou Rangifer tarandus caribou calves depredated by black bears Ursus americanus and coyotes Canis latrans
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Mumma, Matthew A.; Bastille-Rousseau, Guillaume; Gullage, Steve E.; Soulliere, Colleen E.; Mahoney, Shane P.; Waits, Lisette P. — 2019-05-20 Individuals in substandard physical condition are predicted to be more vulnerable to predation. Support for this prediction is inconsistent partly as a result of differences across systems in the life histories of predator and prey species. Our objective was to examine the physical condition of woodland caribou (Rangifer tarandus caribou) calves depredated by two predators with different life histories in Newfoundland, Canada. Black bears (Ursus americanus) are capable of chasing calves at high speeds over short distances and primarily prey on calves <1 month of age. Coyotes (Canis latrans) are cursorial predators that pursue prey over longer distances, which is expected to result in the selection of substandard individuals. We hypothesized that (i) black bears will kill calves in substandard physical condition, while (ii) coyotes will kill calves from across the distribution of individual conditions. We used mitochondrial DNA species identification tests to assign predator species to calf mortalities. We then used molecular identifications and field observations to build a predictive model using generalized boosted trees to predict the predator species where a molecular identification was unavailable. We tested our hypotheses using Cox proportional hazards models under a competing risks framework. Bears killed younger calves and lighter calves, while coyotes killed heavier calves. Coyotes also killed more late-born calves, which might suggest prey switching as calves become more abundant later in the season. Our findings suggest that the physical constraints of predators play a greater role than predator hunting strategies in this system, but other processes are likely influential. The tendency for coyotes to kill heavier calves might result from sustained coyote predation over time, following the removal by black bears of lighter calves during their first month of age. This research illuminates the complexity of predator-prey interactions in Newfoundland and highlights an important source of variability for predator-prey systems.

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(auteur : Mumma, Matthew A.)

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