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Anthropogenic induced changes including fire suppression, increased atmospheric carbon, and unmanaged livestock grazing contribute to this environmental change ( Roques et al., 2001 D’Odorico et al., 2012). Globally, grassy and savanna biomes are changing as woody species increase understory density and close canopies ( Spector and Putz, 2006). One global environmental change that may be altering how species interact is woody plant encroachment hereinafter, woody encroachment ( Eldridge et al., 2011 Stanton et al., 2018). Understanding these patterns is critical to predicting how human activities will alter ecological communities. However, on the local level, fragmentation may favor species that are superior competitors, especially when resources are scarce ( Ditchkoff et al., 2006). On a landscape, increased habitat edge from fragmentation may favor species that are poor competitors but can cross the matrix separating patches ( Marvier et al., 2004). However, humans also change environments at more localized scales ( Wilbanks and Kates, 1999), such as by suppressing fire or altering the number of trees within a forest patch through forest management. Habitat loss and fragmentation, two major features of anthropogenic environmental change, are typically assessed at landscape spatial scales ( Fischer and Lindenmayer, 2007). Nevertheless, the mechanism by which common, human-driven environmental changes alter how species interact at multiple scales is poorly understood ( Tews et al., 2004). It is hypothesized that these multi-scale and dimensional competitive advantages allow similar species to co-occur ( Kneitel and Chase, 2004). For example, local competitive advantage may be coupled with reductions in a species’ ability to colonize new sites across a landscape ( Cadotte, 2007). The benefits of ecological specialization at one scale often come with fitness costs at other scales ( Fry, 2003 Bonsall et al., 2004). Changes in community composition are likely to be pronounced for ecologically similar species that often co-occur through specializations on multiple dimensions which result in multi-scale “trade-offs” ( Kneitel and Chase, 2004). These activities can alter species interactions and co-existence dynamics and change species distributions and community composition ( Lyons et al., 2016). Human activities are changing the environments that animal communities utilize ( Lewis and Maslin, 2015). Our results support the importance of considering species interactions at multiple scales when predicting and addressing changes in community composition in human modified and managed systems. These findings support the hypothesis that species interactions can be an important factor in structuring biotic communities however, the strength of the effect changes across spatial scales. The intensity of interaction was modified by fine-scale canopy cover and understory density. Fox squirrel occupancy probability declined in the presence of gray squirrels. Increased fine-scale canopy closure correlated with increased fox and gray squirrel occupancy, while increased fine-scale understory cover correlated with decreased gray and fox squirrel occupancy. The best model to explain fox and gray squirrel co-occurrence at fine scales was an additive fine-scale understory and tree canopy closure model. We found evidence that fox and gray squirrels compete at fine scales but not at local and landscape scales. We used single-season, two-species occupancy modeling to understand what factors influence competition between the squirrels at three spatial scales. Eastern fox ( Sciurus niger) and gray ( Sciurus carolinensis) squirrels occur sympatrically throughout the southeastern United States. To elucidate these effects, we investigated the co-occurrence of two interacting species in a rapidly changing ecosystem. These multi-scale processes are likely to change species interactions and distributions in unexpected ways. A global consequence of human activity is increased woody cover, which changes environmental conditions on landscape, local, and fine spatial scales. Human activities are changing the environments that animal communities utilize, altering competition and co-existence dynamics as well as changing species distributions. 3Department of Wildlife Ecology, University of Florida Institute of Food and Agricultural Sciences, Gainesville, FL, United States.2Weyerhaeuser Company, Columbus, MS, United States.1Department of Forestry and Natural Resources, University of Kentucky College of Agriculture, Food and Environment, Lexington, KY, United States.
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