įurthermore, when species have similar body sizes, and overlap widely in their use of resources, the likelihood of interference encounter increases. Niche partitioning is, therefore, contingent on heterogeneity along the niche axes. ), (3) habitat or food-resource partitioning to allow exclusive use of resources - and thus the persistence of a given density of each competitor based on those resource dynamics. Examples of coexistence mechanisms include (1) differential tolerance to abiotic factors, which can lead to spatial interdependence between the population growth rate and a given resource density, (2) temporal or spatial segregation to avoid interference (e.g. Hence, although interspecific competition is a frequent community feature, it seldom leads to competitive exclusion, indicating coexistence mechanisms must be widespread. Niche theory forecasts niche optima separation as a condition for similar species to coexist. Exploitation and interference competition typically increase together, likely because the rate of encounter of consumers with both competitors and their prey are driven by movement patterns.

) its strength thus increases with competitor density and may not depend on resource availability (e.g. Interference competition is direct, as individuals prevent others from accessing resources along a behavioral continuum from passive blocking to interspecific killing (e.g. Exploitation competition is indirect, as competitors negatively affect each other by depleting a resource its strength thus depends on spatio-temporal patterns of resource abundance. Two forms of competition are classically described (e.g., ).

Wherever ecologically similar species are sympatric, competition can occur over limited shared resources with varied intensity levels, depending on the similarity of the competitors' ecological niches. Interspecific competition is a structuring force of carnivore communities. A spread of habitats and resources favorable to expanding species may promote higher densities of antagonistically dominant newcomers, which may lead to extirpation of native species. However, due to ongoing climate change, systems are usually not at equilibrium. Dominant expanding competitors may benefit from interference, but usually lack adaptations to abiotic conditions at their expansion front, favoring rear-edge subordinate species in exploitation competition. Furthermore, the scarcity of habitats favored by expanding species may emphasize intraspecific competition between newcomers over interspecific competition, thus creating the potential for self-limitation of expanding populations. Heterogeneous landscapes may relax interspecific competition between expanding and native species, allowing exclusive use of some resources. Red and Arctic foxes used habitat differentially, with near-exclusive use of forest patches by red foxes and marine habitats by Arctic foxes. If anything, intraspecific competition between red foxes may be stronger than interspecific competition. No obvious differential use of areas shared by heterospecific neighbors suggested low interference. Low home-range overlap between neighbors suggested territoriality and substantial exploitation competition for space. However, our results from 17 collared foxes suggested that expanding and native competitors may coexist when expanding species occur at low densities. Our morphometric comparison involving 236 foxes found that the potential for escalated interference between these species was high due to intermediate size difference. We used time-LoCoH to quantify space and habitat use, and Minta's index to quantify spatio-temporal interactions between neighbors. We then used satellite telemetry to evaluate competition in a heterogeneous landscape by examining space use early during the foxes' reproductive period, when resource scarcity, increased-food requirements and spatial constraints likely exacerbate the potential for interference. We first quantified size differences between an expanding habitat generalist, the red fox ( Vulpes vulpes), and a circumpolar habitat specialist, the Arctic foxes ( Vulpes lagopus), at the edge of the Arctic, where climate-related changes occur rapidly, to predict the likelihood of the larger competitor escalating interference to intraguild killing. Range expansion of species, a major consequence of climate changes, may alter communities substantially due to competition between expanding and native species.

Arctic fox vs bird predator prey