In the Arctic tundra, recurrent periods of food scarcity force predators to rely on a wide variety of resources. In particular most predators use ungulate carcasses as an alternative food supply, especially in winters when live preys are scarce. As important and localized resource patches, carrion promotes co-occurrence of different individuals, and its use by predators is likely to be affected by interspecific competition. Here, we studied how interspecific competition and resource availability impact winter use of carrion by Arctic and red foxes in low Arctic Fennoscandia. We predicted that presence of red foxes limits Arctic foxes' use of carrion, and that the outcome of competition for carrion depends on the availability of alternative food resources, such as rodents. We monitored Arctic and red fox presence at experimentally supplied carrion using camera traps, between 2006 and 2021 in late winter. Using a multi-species dynamic occupancy model at a week-to-week scale, we evaluated use of carrion by foxes, while accounting for the presence of competitors, rodent availability and supplemental feeding provided to Arctic foxes. Competition primarily affected carrion use by increasing both species' probability to leave occupied carcasses to a similar extent, suggesting a symmetrical avoidance. Rodent abundance was associated with an increase in the probability of colonizing carrion for both species. For Arctic foxes, however, this increase was only observed in carcasses unoccupied by red foxes, showing greater avoidance when alternative preys are available. Contrary to expectations, we did not find strong signs of asymmetric competition for carrion in winter. Our results suggest that interactions for resources at a short time scale are not necessarily aligned with interactions at the scale of the population. In addition, we found that competition for carcasses depends on the availability of other resources, suggesting that interactions between predators depend on the ecological context.

Long-term studies of cyclic rodent populations have contributed fundamentally to the development of population ecology. Previous research has shown macroecological patterns of population dynamics in relation to latitude, but without disentangling the role of underlying ecological and climate drivers. We collected 26 rodent time-series from the tundra biome and assessed how population dynamics characteristics of the most prevalent species varied with latitude and environmental variables. While we could not find a relationship between latitude and population cycle peak interval, other characteristics of population dynamics had latitudinal patterns. The environmental predictor variables provided insight into causes of these patterns, as i) increased proportion of optimal habitat in the landscape led to higher population cycle amplitudes in all species and ii) mid-winter climate variability had negative impacts on cycle amplitude in Norwegian lemmings and grey-sided voles. These results indicate that biome-scale climate and landscape change can be expected to have profound impacts on rodent population cycles and that the macro-ecology of such functionally important tundra ecosystem characteristics is likely to be subjected to transient dynamics.

Ecologists are still puzzled by the diverse population dynamics of herbivorous small mammals that range from high-amplitude, multi-annual cycles to stable dynamics. Theory predicts that this diversity results from combinations of climatic seasonality, weather stochasticity and density-dependent food web interactions. The almost ubiquitous 3-5-yr cycles in boreal and arctic climates may theoretically result from bottom-up (plant-herbivore) and top-down (predator-prey) interactions. Assessing empirically the roles of such interactions, and how they are influenced by environmental stochasticity, has been hampered by food web complexity. Here, we take advantage of a uniquely simple High-Arctic food web, which allowed us to analyze dynamics of a graminivorous vole population not subjected to top-down regulation. This population exhibited high-amplitude, non-cyclic fluctuations - partly driven by weather stochasticity. However, the predominant driver of the dynamics was direct density dependence, which alternated between being weak in summer and strong (overcompensatory) in winter that the population frequently crashed. Model simulations showed that this season-specific density dependence would yield regular 2-year cycles in absence of stochasticity. While such short cycles have not yet been observed in mammals, they are theoretically plausible if graminivorous vole populations are deterministically bottom-up regulated. When incorporating weather stochasticity in the model simulations, cyclicity became disrupted and the amplitude was increased - akin to the observed dynamics. Our findings contrast with the 3-5-yr population cycles involving delayed density dependence that are typical of graminivorous small mammals in more complex food webs, suggesting that top-down regulation is an important component of such dynamics.

Scavenging can have important consequences for food web dynamics, for example, it may support additional consumer species and affect predation on live prey. Still, few food web models include scavenging. We develop a dynamic model that includes predators, scavengers, live prey, and a carrion pool to show ramifications of scavenging for predation in simple food webs. We explicitly model carrion biomass and scavenging behavior and investigate the effect of scavenging for predation under different assumptions. Our modeling suggests that the presence of scavengers can both increase and decrease predator kill rates and overall predation in model food webs and the impact varies (in magnitude and direction) with context. In particular, we explore the impact of the amount of dynamics allowed in the predator, scavenger, and prey populations as well as the direction and magnitude of interference competition between predators and scavengers. We provide a road map to the different outcomes and link these theoretical outcomes to evidence from different empirical studies.

Scavenging can have important consequences for food web dynamics, for example, it may support additional consumer species and affect predation on live prey. Still, few food web models include scavenging. We develop a dynamic model that includes predators, scavengers, live prey, and a carrion pool to show ramifications of scavenging for predation in simple food webs. We explicitly model carrion biomass and scavenging behavior and investigate the effect of scavenging for predation under different assumptions. Our modeling suggests that the presence of scavengers can both increase and decrease predator kill rates and overall predation in model food webs and the impact varies (in magnitude and direction) with context. In particular, we explore the impact of the amount of dynamics allowed in the predator, scavenger, and prey populations as well as the direction and magnitude of interference competition between predators and scavengers. We provide a road map to the different outcomes and link these theoretical outcomes to evidence from different empirical studies.