In many taxa, individual social traits appear to be consistent across time and context, thus meeting the criteria for animal personality. How these differences are maintained in response to changes in population density is unknown, particularly in large mammals, such as ungulates. Using a behavioral reaction norm (BRN) framework, we examined how among- and within-individual variation in social connectedness, measured using social network analyses, change as a function of population density. We studied a captive herd of elk (Cervus canadensis) separated into a group of male elk and a group of female elk. Males and females were exposed to three different density treatments and we recorded social associations between individuals with proximity-detecting radio-collars fitted to elk. We constructed social networks using dyadic association data and calculated three social network metrics reflective of social connectedness: eigenvector centrality, graph strength, and degree. Elk exhibited consistent individual differences in social connectedness across densities; however, they showed little individual variation in their response to changes in density, i.e., individuals oftentimes responded plastically, but in the same manner to changes in density. Female elk had highest connectedness at an intermediate density. In contrast, male elk increased connectedness with increasing density. Whereas this may suggest that the benefits of social connectedness outweigh the costs of increased competition at higher density for males, females appear to exhibit a threshold in social benefits (e.g. predator detection and forage information). Our study illustrates the importance of viewing social connectedness as a density-dependent trait, particularly in the context of plasticity. Moreover, we highlight the need to revisit our understanding of density dependence as a population-level phenomenon by accounting for consistent individual differences not only in social connectedness, but likely in other ecological processes (e.g., predator-prey dynamics, mate choice, disease transfer).

Competition is a driving factor in shaping ecological communities and may act directly or indirectly through apparent competition. We examined a classic example of parasite-mediated competition between northern ( Glaucomys sabrinus ) and southern flying squirrels ( G. volans ) via the intestinal nematode, Strongyloides robustus, and tested whether it could act as a species barrier in a flying squirrel hybrid zone. We live-trapped flying squirrels ( G. sabrinus and G. volans ), grey squirrels ( Sciurus carolinensis ), red squirrels ( Tamiasciurus hudsonicus ), and chipmunks ( Tamias striatus ) from June–September 2019 at 30 woodlots in Ontario, Canada. Fecal samples from squirrels were collected and analyzed for the presence of endoparasite eggs. For each individual, we calculated Scaled Mass Index (SMI) as a measure of body condition to assess the effect of S. robustus on squirrels. We found eggs of S. robustus in all species except chipmunks. Infection with S. robustus did not appear to affect body condition of southern flying squirrels and grey squirrels, but we did find a weak negative effect on northern flying squirrels and red squirrels. Despite a weak asymmetric effect of S. robustus on flying squirrels, we did not find any evidence that parasite-mediated competition could lead to competitive exclusion from woodlots. Furthermore, S. robustus eggs were common in feces of the red squirrel, a species largely sympatric with northern flying squirrel.

Invasive species are a major contributor to biodiversity loss worldwide. Wild pigs (Sus scrofa Linnaeus, 1758) are highly invasive in their introduced ranges; they modify habitat and threaten native species. As recent invaders in Canada, it is unknown what habitats wild pigs occupy at the northern edge of their range and how they affect mammalian diversity. We examined habitat factors that we predicted would affect co-occurrence of wild pigs with native mammals. We randomly placed 17 camera traps in four stratified habitat types (deciduous forest, grassland, cropland, and wetland) for 2 years to examine species co-occurrence in these habitats. We analyzed camera-trap data using nonmetric multidimensional scaling. Wild pig detection during winter was greatest in wetland and cropland and positively associated with occurrence of moose (Alces alces (Linnaeus, 1758)) and coyote (Canis latrans Say, 1823) and negatively associated with the presence of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)), mule deer (Odocoileus hemionus (Rafinesque, 1817)), and humans. In summer, we detected wild pigs only in grassland; these detections were positively associated with moose and mule deer and negatively associated with domesticated cattle (Bos taurus Linnaeus, 1758), elk (Cervus canadensis Erxleben, 1777), and humans. We conclude that invasive wild pig occurrence at the northern edge of their Canadian range varies seasonally, by habitat, and is negatively affected by the presence of humans. Moreover, apparent co-occurrence with native fauna and avoidance of domestic species provides early evidence for potential competitive interactions.

Shifting range boundaries can lead to secondary contact of closely related species, which might in turn lead to hybridization when the evolution of reproductive isolation is incomplete. We examined winter nest use of northern (Glaucomys sabrinus Shaw, 1801) and southern flying squirrels (G. volans Linnaeus, 1758) in an area of recent secondary contact and known hybridization in Ontario, Canada to test for evidence of reinforcement due to different and diverging nesting behaviours. We radio-collared 26 flying squirrels (12 G. sabrinus and 14 G. volans) between two survey periods (winters of 2008-9 and 2019-20) and identified all nest trees used by individuals throughout each winter. For each nest tree we identified the nest type and collected tree classification information to compare differences in nest use between species. We also present a novel application of habitat suitability modelling to test for evidence of divergence in nest use through time, which would suggest reinforcement. We found southern flying squirrels used a higher proportion of cavities in large, hardwood trees, whereas northern flying squirrels used more external nests and softwood trees. Conditional probabilities provided some evidence for increased differentiation in nest use by flying squirrels through time. Overall, we found relatively little overlap in winter nest use between flying squirrel species, despite evidence for hybridization at this site, and some weak evidence for increased divergence between species in nest use over 11 years

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