No abstract

Top predators largely affect ecosystems through trophic interactions, but they also can have indirect effects by altering nutrient dynamics and acting as ecosystem engineers. Arctic foxes (Vulpes lagopus) are ecosystem engineers that concentrate nutrients around their dens, creating biogeochemical hotspots with lush vegetation on the nutrient-limited tundra. Red foxes (V. vulpes) similarly engineer subarctic environments through their denning behavior, and have recently expanded onto the tundra where they now often occupy historically Arctic fox dens. We evaluated the impact of Arctic and red fox denning behavior on other tundra wildlife by comparing predator and herbivore visits to dens and adjacent control areas using camera traps in northeastern Manitoba, where both fox species are sympatric. Both the capture rates and species richness of wildlife were significantly greater at fox dens relative to control sites. Predators were detected almost exclusively on dens occupied by foxes, suggesting carcass or fox presence attracts predators to den sites. This is supported by observations of predators investigating and scavenging prey remains (carrion, feathers) from the dens. Caribou (Rangifer tarandus) visited dens more often than control areas, and we hypothesize they are attracted to the enhanced vegetation typically found on dens. Our results suggest Arctic fox ecosystem engineering has a prolonged, indirect effect on caribou by enriching vegetation at dens, whereas both Arctic and red foxes directly facilitate predators by provisioning resources. Understanding how predators affect other organisms via non-trophic interactions provides an enriched view of their functional roles within ecosystems.

Stable isotope analysis (SIA) of sequential dentine growth layer groups can be used to estimate the lifetime diet of individuals and infer major ontogenetic shifts such as the completion of nursing. We used SIA of dentine from narwhal Monodon monoceros embedded canine teeth to investigate ontogenetic dietary patterns, with a focus on nursing duration. We also determined whether nursing duration differed between sexes and between 2 periods during which narwhals may have undergone dietary shifts due to warming. Embedded teeth from both sexes were collected near Pond Inlet, Nunavut, Canada, in 1982 and 1983 (n = 17) and 2015 and 2017 (n = 14). Nursing duration ranged from ~2 to ~6 yr, with 60% of narwhals being nursed beyond the previously published estimate of <2 yr. The proportion of individuals nursed <2 yr versus >2 yr did not differ between sexes or periods. This study not only revealed that narwhals vary extensively in their nursing duration, but also indicated that extended nursing (>2 yr) with gradual introduction of solid food over this period was common. These findings provide insights into narwhal life-history strategies, as extended nursing may be another feature of a long-lived, slow-reproducing mammal adapted to unique polar conditions that are threatened by global warming.

While the impact of ecological changes on Arctic marine mammals remains largely unknown, quantifying variability in resource use among conspecifics can serve as an indication of adaptive plasticity and help assess species vulnerability to climate-induced changes. We measured withintooth δ 15 N and δ 13 C profiles of narwhals (Monodon monoceros) sampled 35 years apart from Baffin Bay, Nunavut, Canada, to evaluate intrapopulation variation in narwhal resource use. Narwhal dentine δ 15 N and δ 13 C were lower post-1983 (n = 7) by 0.83‰ and 0.52‰, respectively, compared to pre-1983 (n = 13), but isotopic niche breadth increased from 0.95‰ 2 to 1.12‰ 2 . Between sexes, the isotopic niche of males expanded from pre-1983 to post-1983 while that of females decreased, which may indicate increased flexibility in resource use for males and the opposite for females. Additional isotopic variation among narwhals (n = 23) suggests individual differences in diet composition and/or foraging location during both periods.Individual isotopic niches ranged between 0.08‰ 2 and 2.27‰ 2 , where a larger isotopic niche likely indicates more variable foraging strategies over time. Narwhal as a species is considered vulnerable to ecosystem change; however, the variability in resource use between sexes and among