Support for the size-mediated sensitivity hypothesis within a diverse carnivore community

Carnivore community dynamics are governed by a complex set of often interacting biotic, abiotic and anthropogenic factors that are increasingly volatile as a result of global change. Understanding how these changing conditions influence carnivore communities is urgent because of the important role carnivores play within ecosystems at multiple trophic levels, and the conservation threats that many carnivores face globally. While a great deal of research attention has historically been focused on large carnivores within ecosystems, the size-mediated sensitivity hypothesis has recently been proposed where the smallest carnivore in a system is likely to be the most responsive to the diverse suite of ongoing environmental and anthropogenic changes within ecological communities. We deployed camera traps at 197 sites over 4 years to monitor a diverse suite of mammalian carnivores within the Blue Ridge Mountains of western North Carolina and then used a two-step occupancy modelling-structural equation modelling framework to investigate the relative support for four primary hypothesized drivers (interspecific competition/predation, habitat complexity, food availability and anthropogenic disturbance) on carnivore occurrence. We found that each of the 10 carnivores in our system responded differently to conditions associated with each of these four hypothesized drivers, but that small and medium-sized carnivores had a greater number of significant (p < 0.05) pathways by which these conditions were influencing occupancy relative to large carnivores. In particular, the smallest carnivore observed in our study was the only species for which we found support for each of the four hypothesized drivers influencing occupancy. Collectively, our study supports the size-mediated sensitivity hypothesis and suggests that small carnivores are ideal sentinel species for global change. We echo recent calls for adopting a middle-out approach to investigations into carnivore community dynamics by refocusing sustained monitoring and research efforts on smaller carnivores within systems.

Reproductive state influences the degree of risk tolerance for a seasonally breeding mesopredator

The risk of predation can alter the way animals perceive costs and benefits in their environment, on which foraging decisions are made. To maximize fitness, animals with offspring show the most pronounced alteration in behavior because mothers experience increased nutritional requirements and increased vulnerability to predation. Therefore, the tolerance of risk is shaped, in part, by reproductive state. Like prey species, mesopredators balance a trade-off between food and predation to maximize fitness. However, few studies have acknowledged its importance. We investigated how mesopredators may alter their space use between periods when young are and are not vulnerable. Investigating the fine-scale space use of 19 packs of African wild dogs Lycaon pictus in the Kruger National Park, we found lower risk tolerance of denning packs; they re-visited area less frequently as lion and impala density increased and thus reduced the likelihood of risky encounters by avoiding areas where both risk and reward were high. By contrast, non-denning packs re-visited area less frequently as lion density increased and impala density decreased and thus avoided areas where reward was low, especially if risk was high. These results suggest that wild dogs shift their patterns of space use when the pack is most vulnerable. Ultimately, we found evidence of decreased risk tolerance by denning packs, likely because of increased vulnerability of lactating mothers and immobile pups. More broadly, our findings suggest that risk tolerance is dependent on reproductive state for mesopredators and should be considered as a possible mechanism for other mesopredators as well.

Predicted climate-induced reductions in scavenging in eastern North America

Scavenging is an important function within ecosystems where scavengers remove organic matter, reduce disease, stabilize food webs, and generally make ecosystems more resilient to environmental changes. Global change (i.e., changing climate and increasing human impact) is currently influencing scavenger communities. Thus, understanding what promotes species richness in scavenger communities can help prioritize management actions. Using a long-term dataset from camera traps deployed with animal carcasses as bait along a 1881 km latitudinal gradient in the Appalachian Mountains of eastern USA, we investigated the relative impact of climate and humans on the species richness and diversity of vertebrate scavengers. Our most supported models for both mammalian and avian scavengers included climatic, but not human, variables. The richness of mammalian and avian scavengers detected was highest during relatively warm (5-10°C) and dry (100-150 mm precipitation) winters, when food was likely limited and both reliance on and detection of carrion was high. The diversity of mammalian and avian scavengers detected was highest under drier conditions. We then used these results to project the future species richness of scavengers that would be detected within our sampling area and under the climate scenario of 2070 (emissions level RCP8.5). Our predictions suggest up to 80% and 67% reductions, respectively, in the richness of avian and mammalian scavengers that would be detected at baited sites. Climate-induced shifts in behavior (i.e., reduction in scavenging, even if present) at this scale could have cascading implications for ecosystem function, resilience, and human health. Further, our study highlights the importance of conducting studies of scavenger community dynamics within ecosystems across wide spatial gradients within temperate environments. More broadly, these findings build upon our understanding of the impacts of climate-induced adjustments in behavior that can likely have negative impacts on systems at a large scale.

Attracting Diverse Students to Field Experiences Requires Adequate Pay, Flexibility, and Inclusion

Access to field experiences can increase participation of diverse groups in the environmental and natural resources (ENR) workforce. Despite a growing interest among the ENR community to attract and retain diverse students, minimal data exist on what factors undergraduate students prioritize when applying for field experiences. Using a nationwide survey of US undergraduate ENR students, we show that attracting most students to field experiences—especially racial or ethnic minority students—will require pay above minimum wage. However, the concurrent landscape of pay in ENR fell short of meeting many students’ pay needs. Aside from pay, ENR students valued training in technical field skills and analytical or research skills, working with their desired study species or taxa, and working near school or family. Additional barriers beyond limited pay included incompatible schedules and noninclusive work environments. Our findings provide important insights for attracting a diverse workforce to this critical stage in career advancement for students in ENR.