Mesopredator release facilitates range expansion in fisher

Abstract

Some central and eastern populations of fisher Pekania [Martes] pennanti are expanding their ranges following historic range contractions, while many western populations have yet to do so. We investigated whether expanding fisher populations are benefiting from a mesopredator release following reductions in their carnivore predator communities. This hypothesis posits that local extinctions of the largest predators 'release' mesopredator populations from direct predation and competition, leading to an increase in their abundance, expansion of their range and potentially to shifts in their morphology and ecological niche. Our comparison of the conservation status and predator communities of fishers across four geographic regions of their range supports the mesopredator release hypothesis, especially in their eastern range. Our meta-analysis of fisher diet also suggests that released fisher populations may benefit by complementing their diverse diets with more large-bodied prey species, whereas those with more specialized diets (e.g. northwestern populations) or diverse diets with small amounts of largebodied prey (e.g. populations within California) have experienced little range expansion. Further, measurements of museum specimens suggest that individuals within released populations have evolved a larger body size since the time of their most contracted range, which may help them hunt larger prey species that are expected to be more available in the absence of larger carnivores. Collectively, these data support the hypothesis that a reduced predator community is contributing to the geographic variation in modern fishers' range expansion. In addition to harvest restrictions, habitat protection and translocations, future conservation plans should consider the potential effects of the predator community, emphasizing the need to quantify fisher mortality sources and fisher-predator interactions.

Niche overlap of competing carnivores across climatic gradients and the conservation implications of climate change at geographic range margins

“…Community interactions may be particularly influential in determining marten and fisher distributions, not only because of the interaction between their relative competitive abilities and their mobility in snow but also because of interactions with larger predators. For example, fishers have responded to the absence of larger predators in some parts of their range by increasing their distribution and body size (LaPoint et al 2015).Ecological modeling reveals variation in whether the presence of one species can predict the occurrence of the other. Several studies conducted in the snow-free season discovered that model fit was not improved by using one species to predict the other (Gompper et al 2016,…”

“…Community interactions may be particularly influential in determining marten and fisher distributions, not only because of the interaction between their relative competitive abilities and their mobility in snow but also because of interactions with larger predators. For example, fishers have responded to the absence of larger predators in some parts of their range by increasing their distribution and body size (LaPoint et al 2015).…”

Can we predict which species win when new habitat becomes available?

“…Land cover change can destroy habitats of some species, however, it can let other species to shift their habitat into new habitats by releasing them from competitions. Species expansion through release from competition has been found in animals where a reduced predator community contributed to modern fishers’ range expansion [56]. The competitive release is a more realistic mechanism for the change in species prevalence in open habitat than the evolution of Acaena species’ climatic niche, because evolutionary processes of adaptions to new environments generally take a long time.…”

Habitat selection and spatiotemporal interactions of a reintroduced mesocarnivore

“…Trapping and logging in the early twentieth century led to a major range contraction of fishers (Powell 1993, Lewis et al 2012. Regulations and trapping bans resulted in recovery of fishers across much of their eastern and central range in the northern United States and southern Canada, but fishers remain a species of conservation concern in California, Oregon, and Washington, USA (Powell 1993, Lewis et al 2012, Lapoint et al 2015, Stewart et al 2017).…”

“…Fishers in western North America coexist with a more diverse carnivore community than fishers in the east (Lapoint et al 2015), and intraguild predation is a major mortality source in California, particularly from bobcats and cougars (Puma concolor; Wengert et al 2014, Gabriel et al 2015. Bobcats and coyotes act as competitors and predators for fishers (Wengert et al 2014), leading to a possible food-safety tradeoff for fishers (Bischof et al 2014), where areas with abundant prey for fishers may also have a high abundance of bobcats and coyotes.…”