Abstract
Global warming is predicted to change ecosystem functioning and structure in Arctic ecosystems by strengthening top‐down species interactions, i.e. predation pressure on small herbivores and interference between predators. Yet, previous research is biased towards the summer season. Due to greater abiotic constraints, Arctic ecosystem characteristics might be more pronounced in winter. Here we test the hypothesis that top‐down species interactions prevail over bottom‐up effects in Scandinavian mountain tundra (Northern Sweden) where effects of climate warming have been observed and top‐down interactions are expected to strengthen. But we test this ‘a priori’ hypothesis in winter and throughout the 3–4 yr rodent cycle, which imposes additional pulsed resource constraints. We used snowtracking data recorded in 12 winters (2004–2015) to analyse the spatial patterns of a tundra predator guild (arctic fox Vulpes lagopus, red fox Vulpes vulpes, wolverine Gulo gulo) and small prey (ptarmigan, Lagopus spp). The a priori top‐down hypothesis was then tested through structural equation modelling, for each phase of the rodent cycle. There was weak support for this hypothesis, with top‐down effects only discerned on arctic fox (weakly, by wolverine) and ptarmigan (by arctic fox) at intermediate and high rodent availability respectively. Overall, bottom‐up constraints appeared more influential on the winter community structure. Cold specialist predators (arctic fox and wolverine) showed variable landscape associations, while the boreal predator (red fox) appeared strongly dependent on productive habitats and ptarmigan abundance. Thus, we suggest that the unpredictability of food resources determines the winter ecology of the cold specialist predators, while the boreal predator relies on resource‐rich habitats. The constraints imposed by winters and temporary resource lows should therefore counteract productivity‐driven ecosystem change and have a stabilising effect on community structure. Hence, the interplay between summer and winter conditions should determine the rate of Arctic ecosystem change in the context of global warming.
Highlights
Global warming is one of the main anthropogenic drivers of biodiversity loss, and of changes in ecosystem structure and functioning (Montoya and Raffaelli 2010)
While global warming may induce a dominance of topdown processes on tundra ecosystem functioning, bottomup effects might still overrule competition and predation pressures, especially during periods of strong constraints
In the case of our study, the results did not support the a priori hypothesis that top-down interactions prevail over bottom-up effects in winter. It shows that seasonality and pulsed resources can influence this dominance ratio and be key to the maintenance of ecosystem functioning and structure in sub-Arctic tundra
Summary
Global warming is one of the main anthropogenic drivers of biodiversity loss, and of changes in ecosystem structure and functioning (Montoya and Raffaelli 2010) These effects are most pronounced in Arctic and sub-Arctic regions, where climate and resources should impose relatively strong constraints on the structure and functioning of tundra ecosystems (CAFF 2013). Hypotheses on biodiversity patterns in northern latitudes suggest that the relative contribution of top-down and bottom-up control changes at high latitudes and altitudes; that herbivore biomass is controlled bottom-up in unproductive tundra, but top-down in productive tundra and boreal forest (Oksanen and Oksanen 2000, Aunapuu et al 2008) In line with this theory, herbivory intensity decreases at lower latitudes while predation pressure increases, suggesting that top-down effects would increase with warmer temperatures in tundra ecosystems (Legagneux et al 2014). Interactions between trophic levels would be affected, and interference within the predator guild, as illustrated by the mesopredator release phenomenon, where top predators can control medium-sized predators through competition or intraguild killing and in turn benefit small herbivores (Soulé et al 1988, Elmhagen and Rushton 2007, Elmhagen et al 2010, Pasanen-Mortensen et al 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
