Sea or summit? Wild reindeer spatial responses to changing high‐arctic winters

Abstract

Because of climate change, wildlife is facing altered environments, including profound shifts in temperature and precipitation regimes. In snow-dominated ecosystems, winter warming and resulting changes in snowpack properties impact forage accessibility for ungulates-often for the worse. The potential of individuals and populations to buffer negative fitness effects of harsh winters with "basal ice" (i.e., ice on the ground) and/or a harder or deeper snowpack depends on their ability to adjust behaviorally through changes in diet, dispersal, or small-scale habitat use. Here, we use ten years of late winter snowpack monitoring and population census data from three neighboring, semi-isolated coastal populations of high-arctic wild Svalbard reindeer to explore small-scale space use responses to annual variation in late winter-foraging conditions. Based on location data from the population censuses, we roughly classified individuals' spatial foraging strategy (i.e., habitat use) during late winter into "tundra" (foraging on tundra plains), "mountain" (foraging at high elevations, with low plant biomass but less snow and ice), or "shore" (foraging along the seashore, subsidizing terrestrial food with kelp and seaweed). Using multinomial logistic regression, we modeled the probability of reindeer adopting either of these strategies as a function of density-dependent winter severity. Our results suggest that effects of winter severity on habitat use are density-dependent and that snowpack depth and hardness (excluding basal ice, measured as "integrated ram hardness," IRH) have stronger influence on reindeer foraging behavior than basal ice, at least at such spatial scales. Particularly, high IRH increased the probability of reindeer seeking high-elevation and steep terrain instead of tundra lowlands, but not at low population density, that is, when competition for food is negligible. This strategy was most pronounced among adult males, possibly reflecting their risk-prone behavior and/or reduced competitiveness related to lack of antlers during winter. This study demonstrates important patterns of temporal, spatial, and demographic variation in reindeer's winter-foraging strategies, adding novel, nuanced insights into how climate change affects spatial processes in isolated ungulate populations. The results add to the impression of considerable behavioral flexibility, which may aid buffering the negative fitness effects of complex changes in foraging conditions due to environmental changes.

Five decades of terrestrial and freshwater research at Ny-Ålesund, Svalbard

“…Studies of the vertebrates of Brøggerhalvøya span a wide range of resident and migratory species and research topics, including physiological and behavioral adaptations to the High-Arctic environment (Gabrielsen et al 1985;Steen & Gabrielsen 1988;Gabrielsen et al 1991;Frafjord 1992;Fuglei 2000;Sandström et al 2014), growth and body size Bishop et al 1995;Tombre et al 1996;Loonen et al 1997), population ecology and dynamics Prestrud 1992;Hansen et al 2011;Pedersen et al 2014;Unander et al 2016;Layton-Matthews et al 2019), diseases and parasites (Prestrud 1992;Dolnik & Loonen 2007;Prestrud et al 2007;Sandström et al 2013), spatial ecology (Stahl & Loonen 1998;Fuglei & Tarroux 2019;Pedersen et al 2021), trophic interactions (e.g., van der Wal & Loonen 1998;Fuglei et al 2003;Dabert et al 2015;de Jong et al 2019;Layton-Matthews et al 2020) and climate change impacts (Hansen et al 2011;Layton-Matthews et al 2020;Layton-Matthews et al 2021). Some of the most extensive time series available for vertebrate populations in Svalbard originate from Ny-Ålesund and Brøggerhalvøya (Supplementary Table S1).…”

“…The effects of forage suppression, amplified by an over-abundance of reindeer, also triggered a substantial dispersal event, most likely across sea ice, and the subsequent establishment of new populations on coastal plains south of Brøggerhalvøya (Aanes et al 2000). ROS events have also led to increased reliance on marine food resources (e.g., marine kelp and seaweed [Hansen & Aanes 2012;) and the use of steep mountainous grazing grounds (Hansen et al 2009;Pedersen et al 2021). Svalbard reindeer movements have recently been severely restricted by a lack of fjord ice during winter, which can limit gene flow and contribute to further genetic differentiation among coastal subpopulations (Peeters et al 2020).…”