Data from: The fluctuating world of a tundra predator guild: bottom-up constraints overrule top-down species interactions in winter

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 year 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 stabilizing 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.