Resource availability influences group size but not territory size of North American Beaver ( <i>Castor canadensis</i> ), a territorial social species

Abstract Resource availability is a key component of habitat quality and an important driver of animal density. For a territorial social species, population density can be determined by group size, territory size, or both. In this study, we investigated the mechanisms by which food resource density affects North American Beaver (Castor canadensis) populations in temperate riparian forest habitats dominated by ash (Fraxinus spp.) in diversified stands. In 2021, we captured 25 beavers from different colonies in Plaisance National Park (Quebec, Canada) and equipped them with a Global Positioning System (GPS) unit to track their movements and delimit their respective territories. We determined group size by counting the beavers in each territory using aerial imagery obtained from a drone. We measured the density of various food resources such as ash trees, poplars (Populus spp.), or aquatic vegetation, and included these data in generalized linear models to assess their effect on group size or territory size. We observed that group size was positively related to ash tree density with a model-averaged regression coefficient of 0.04 (95% confidence interval: 0.01 to 0.06), but we did not find any relationship between territory size and resource density. These results suggest that the cost of territorial defense may be outweighed by the benefit of securing high-resource territories that support larger groups. This pattern may also indicate that beavers respond to the Resource Dispersion Hypothesis, where territory size is shaped by resource distribution. Alternatively, unmeasured factors such as colony establishment order could influence territory size and warrant further investigation.