Abstract
Given documented social dominance and intraspecific predation in bear populations, the ideal despotic distribution model and sex hypothesis of sexual segregation predict adult female grizzly bears (Ursus arctos) will avoid areas occupied by adult males to reduce risk of infanticide. Under ideal despotic distribution, juveniles should similarly avoid adult males to reduce predation risk. Den-site selection and use is an important component of grizzly bear ecology and may be influenced by multiple factors, including risk from conspecifics. To test the role of predation risk and the sex hypothesis of sexual segregation, we compared adult female (n = 142), adult male (n = 36), and juvenile (n = 35) den locations in Denali National Park and Preserve, Alaska, USA. We measured elevation, aspect, slope, and dominant land cover for each den site, and used maximum entropy modeling to determine which variables best predicted den sites. We identified the global model as the best-fitting model for adult female (area under curve (AUC) = 0.926) and elevation as the best predictive variable for adult male (AUC = 0.880) den sites. The model containing land cover and elevation best-predicted juvenile (AUC = 0.841) den sites. Adult females spatially segregated from adult males, with dens characterized by higher elevations ( = 1,412 m, SE = 52) and steeper slopes ( = 21.9°, SE = 1.1) than adult male (elevation: = 1,209 m, SE = 76; slope: = 15.6°, SE = 1.9) den sites. Juveniles used a broad range of landscape attributes but did not avoid adult male denning areas. Observed spatial segregation by adult females supports the sex hypothesis of sexual segregation and we suggest is a mechanism to reduce risk of infanticide. Den site selection of adult males is likely related to distribution of food resources during spring.
Highlights
Animal distribution theory has two pervasive models: the ideal free distribution and ideal despotic distribution models
Den-site elevation varied by gender/age class (F2,63 = 2.49, P = 0.091), with adult females denning at higher elevations than adult males (T58 = 2.22, P = 0.075)
As predation risk is similar for juveniles and adult females, we suggest that observed sexual segregation is a consequence of adult females avoiding adult males to reduce risk of infanticide
Summary
Animal distribution theory has two pervasive models: the ideal free distribution and ideal despotic distribution models. The ideal free distribution model applies to non-territorial animals and states individuals are distributed proportionately to resources available [1]. Under this model, individuals assess the quality of available habitats and move unhindered among habitat units to select those considered best [1]. The ideal despotic distribution model applies to territorial animals, with dominant individuals displacing subordinates from higher quality habitats [2]. Subordinates’ selection of habitat is constrained by the distribution and behavior of dominant individuals [2] This displacement in part forms an animal’s realized niche [3]. Evidence for ideal despotic distribution has been demonstrated across a broad range of taxa [4,5,6,7]
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