title: Phase-dependent climate-predator interactions explain three decades of variation in neonatal caribou survival.
abstract: Climate can have direct and indirect effects on population dynamics via changes in resource competition or predation risk, but this influence may 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. We examined the presence of phase-dependent climate-predator (PDCP) 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). 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. 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. 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 PDCP interactions framework, where maternal body condition influences susceptibility to climate-related events and, subsequently, risk from predation.
authors.affiliation: Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, K9J 7B8, Canada.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bastille-Rousseau
authors.affiliation: Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, K9J 7B8, Canada.
authors.forename: James A
authors.initials: JA
authors.lastname: Schaefer
authors.affiliation: Newfoundland and Labrador Department of Environment and Conservation, P.O. Box 8700, St. John's, Newfoundland and Labrador, A1B 4J6, Canada.
authors.forename: Keith P
authors.initials: KP
authors.lastname: Lewis
authors.affiliation: Department of Fish and Wildlife Sciences, College of Natural Resources, University of Idaho, Moscow, ID, 83844, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Mumma
authors.affiliation: Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, K9J 7B8, Canada.
authors.forename: E Hance
authors.initials: EH
authors.lastname: Ellington
authors.affiliation: Department of Environmental Conservation, University of Massachusetts, Amherst, Massachusetts, 01003, USA.
authors.forename: Nathaniel D
authors.initials: ND
authors.lastname: Rayl
authors.affiliation: Newfoundland and Labrador Department of Environment and Conservation, P.O. Box 8700, St. John's, Newfoundland and Labrador, A1B 4J6, Canada.
authors.forename: Shane P
authors.initials: SP
authors.lastname: Mahoney
authors.affiliation: Natural Resources Canada, Canada Centre for Remote Sensing, Ottawa, Ontario, K1A 0E4, Canada.
authors.forename: Darren
authors.initials: D
authors.lastname: Pouliot
authors.affiliation: Environmental and Life Sciences Graduate Program, Trent University, Peterborough, Ontario, K9J 7B8, Canada.
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Murray
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002980:Climate; D046029:Coyotes / Q000502:physiology; D005260:Female; D020387:Food Chain; D008136:Longevity; D008297:Male; D008954:Models, Biological; D009523:Newfoundland and Labrador; D011235:Predatory Behavior; D016016:Proportional Hazards Models; D012053:Reindeer / Q000502:physiology*; D001503:Ursidae / Q000502:physiology; D014887:Weather
keywords: black bear (Ursus americanus); caribou (Rangifer tarandus); cause-specific survival analysis; climate-predator interactions; conservation biology; coyote (Canis latrans); population dynamics