Population dynamics of a northern‐adapted mammal: disentangling the influence of predation and climate change

Abstract

Community structure and interspecific interactions are particularly vulnerable to rapidly changing climatic regimes. Recent changes in both climate and vertebrate community assemblages have created a unique opportunity to examine the impacts of two dynamic forces on population regulation. We examined the effects of warming winter conditions and the reestablishment of a previously extirpated predator, the fisher (Martes pennanti), on regulatory mechanisms in a northern-adapted mammal, the porcupine (Erethizon dorsatum), along their southern range boundary. Using a long-term (17-year) capture-recapture data set, we (1) quantified the impacts of climate change and increased fisher predation on the survival of adult porcupines at their regional southern terminus, (2) assessed recruitment (via both adult fecundity and juvenile survival) of porcupines, and (3) modeled the relative importance of predation and winter conditions on the demography and population growth rate (λ). Severe winters and abundant predators interacted synergistically to reduce adult survivorship by as much as 44%, while expanding predator populations led to near reproductive failure among porcupines. Increasing predatory pressure, disruptions in this community module, and more frequent extreme winter weather events led to predicted extirpation within 50 years, whereas in the absence of predators, the population was viable. Our results provide a mechanistic understanding behind distributional shifts resulting from climate change and may be broadly relevant for predicting future distributional shifts in other northern-adapted mammalian species.

Climate change surpasses land-use change in the contracting range boundary of a winter-adapted mammal

“…Fisher (Pekania penannti), which were rare during historical surveys, are now quite common in the region. Predator communities can drive shifts in prey species' ranges, particularly when in conjunction with environmental perturbations like climate change [47]. Although predation is likely central to this range shift, the relationship between extinction and snow cover duration would suggest that the conditions that mediate predation are more important than predator community composition.…”

Predation risks suppress lifetime fitness in a wild mammal

“…These indirect costs translate into lower recruitment (DeWitt et al ). Pokallus and Pauli () have previously modelled this particular porcupine population and estimate that fisher predation has the potential to extirpate the population within 50 years depending on climatic conditions. Our results suggest that projected declines result from the combined effects of predation risk on female growth and over winter mass loss, as well as the direct effect of predation on survival (Pokallus and Pauli , DeWitt et al ).…”

“…Pokallus and Pauli () have previously modelled this particular porcupine population and estimate that fisher predation has the potential to extirpate the population within 50 years depending on climatic conditions. Our results suggest that projected declines result from the combined effects of predation risk on female growth and over winter mass loss, as well as the direct effect of predation on survival (Pokallus and Pauli , DeWitt et al ). By considering both top–down and bottom–up processes through shared mass term, we are able to clearly show that climate, direct predation, and indirect predation all play a pivotal role in porcupine populations, as evidenced by declines in both individual growth and reproductive parameters (Pokallus and Pauli , DeWitt et al ).…”

“…We focus on female growth and reproductive success in a wild North American porcupine Erethizon dorsatum population located in central Wisconsin, USA. This population was monitored continuously as fisher Pekania pennanti recolonized the region, facilitating analyses of naturally occurring variation arising from both predation risk and environmental conditions (Pokallus and Pauli , , DeWitt et al ). Porcupines are a long‐lived species with low annual recruitment rates mirroring many large mammals (Roze ).…”

“…Porcupines are a long‐lived species with low annual recruitment rates mirroring many large mammals (Roze ). Although porcupines are generally well protected from predation, fishers account for over half of porcupine mortalities in eastern North America (Mabille et al , Pokallus and Pauli ) and there is evidence that poor female nutrition arising from non‐consumptive predation effects and low summer forage productivity suppress recruitment (DeWitt et al ). Here, we model how the non‐consumptive effects of predation risk influence female growth and lifetime reproductive success.…”