Seasonality drives the survival landscape of a recovering forest carnivore in a changing world

Abstract

Ecological heterogeneity promotes species persistence and diversity. Environmental change has, however, eroded patterns of heterogeneity globally, stifling species recovery. To test the effects of seasonal heterogeneity on a reintroduced carnivore, American martens ( Martes americana ), we compared metrics of local and season-specific heterogeneity to traditional forest metrics on the survival of 242 individuals across 8 years and predicted a survival landscape for 13 reintroduction sites. We found that heterogeneity—created by forest structure in the growing season and snow in the winter—improved survival and outperformed traditional forest metrics. Spatial variation in heterogeneity created a distinct survival landscape, but seasonal change in heterogeneity generated temporal discordance. All translocation sites possessed high forest heterogeneity but there were greater differences in winter heterogeneity; recovery sites with the poorest snow conditions had the lowest viability. Our work links heterogeneity across seasons to fitness and suggests that management strategies that increase seasonal aspects of heterogeneity may help to recover other sensitive species to continuing environmental change.

Structural complexity characterizes fine‐scale forest conditions used by Pacific martens

“…in snow-free periods (Smith et al 2022b) and marten morphology is highly adapted to snow (Krohn et al 2005).…”

“…Vertical forest structural complexity should be collectively created by many of our predicted plot‐level features and may function primarily to alleviate marten mortality risk from larger‐bodied terrestrial and avian carnivores (Godbout and Ouellet 2010, Cheveau et al 2013, Smith et al 2022 b ). For instance, presence alone of larger trees or snags provides martens with options for escape from primary terrestrial predators (e.g., bobcat [ Lynx rufus ], coyote [ Canis latrans ]; Martin et al 2022) that are poorly suited to climbing (Hodgman et al 1997).…”

“…Extensive shrub cover is atypical of marten‐inhabited forests elsewhere in North America, which are generally located at higher latitudes or higher elevations that have deep and persistent winter snowpacks, such as at our Lassen study site. Snow provides heterogeneous conditions for martens that can only be created by forest structure in snow‐free periods (Smith et al 2022 b ) and marten morphology is highly adapted to snow (Krohn et al 2005). Snow simultaneously limits the presence of larger carnivores that lack similar morphological adaptations (Martin et al 2021, Smith et al 2022 b ) while also facilitating improved hunting efficiency of martens during an energetically demanding time of year (Buskirk and Harlow 1989, Gilbert et al 2009, Martin et al 2020).…”

“…Snow provides heterogeneous conditions for martens that can only be created by forest structure in snow‐free periods (Smith et al 2022 b ) and marten morphology is highly adapted to snow (Krohn et al 2005). Snow simultaneously limits the presence of larger carnivores that lack similar morphological adaptations (Martin et al 2021, Smith et al 2022 b ) while also facilitating improved hunting efficiency of martens during an energetically demanding time of year (Buskirk and Harlow 1989, Gilbert et al 2009, Martin et al 2020). Given the prevalence of shrubs and absence of snow in regions where Humboldt martens occur, we posit that shrub cover serves proxy functions for snow in areas where snow cover is inconsistent or not present.…”

Reciprocated competition between two forest carnivores drives dietary specialization

“…We used published isotopic values for F + m (Carlson et al, 2014; Kirby et al, 2018; Manlick, Woodford, Zuckerberg, et al, 2017) and supplemented our samples of fishers in M + f with published isotopic values (Manlick & Pauli, 2020; Table S1). To summarize landscape characteristics, we identified capture or sampling location(s) and buffered by the average activity area for marten (4.71 km 2 ) and fisher (19.7 km 2 ) for the region (Smith et al, 2022).…”