Movement away from an area or social group in response to increasing density (density‐dependent dispersal) is known for most species; why it evolves is fundamental to our understanding of ecology and evolution. However, we have yet to fully appreciate how individuals of varying conditions (e.g., age and sex) might differently consider effects of density (quorum) when deciding to disperse or not, and scale dependence in their sense of quorum. We tracked movements of all individuals of a naturalized population of feral horses (Equus ferus caballus; Sable Island National Park Reserve, Nova Scotia, Canada) during a period of rapid population growth (N increased from 375 to 484 horses from 2008 to 2010). Permanent dispersal from breeding groups (bands) was positively density dependent for all age and sex categories with respect to local density (horses/km², bounded by the 99th percentile of individual movements [8000 m]), but was negatively and positively density dependent for males and females, respectively, in relation to group (band) size. Dispersal was generally female biased, with the exception of foals which moved with their mothers (no sex effect), and for yearlings and subadults when band sizes were smaller than average, in which case males dispersed at higher rates than females. Dispersal distance was positively related to local density. We conclude that dispersal rate can be both positively and negatively density dependent for feral horses, contingent on the state of individuals and the scale at which quorum with respect to choosing to disperse or not is assessed. Scale effects and interactions of density‐dependent and sex‐ and age‐biased dispersal may have both ecological and evolutionary consequences through effects on resource and mate competition.

Between May 1995 and June 1999, we equipped 81 barren-ground grizzly bears (Ursus arctos) with satellite radio collars within a study area of 235 000 km², centred 400 km northeast of Yellowknife, Northwest Territories, Canada. We used data from radiotelemetry to estimate survival rates, reproductive parameters, and the finite rate of increase of the population (λ). The annual survival rate of adult females was estimated at 0.979 (95% confidence intervals (CI) = 0.955–0.998), while the survival rate of adult males was 0.986 (95% CI = 0.942–1.0). The cub survival rate was 0.737 (95% CI = 0.600–0.844) and the yearling survival rate was 0.683 (95% CI = 0.514–0.821). Cub litter size averaged 2.23 (SE = 0.13, n = 35), while yearling litter size decreased to a mean of 1.86 (SE = 0.12, n = 35). The mean litter size of females with 2-year-olds was 1.85 (SE = 0.15, n = 20). The mean birth interval was 2.8 years (SE = 0.3 years, n = 17). The mean reproductive interval, which is calculated by excluding the loss of whole litters from the sample, was 3.9 years (SE = 0.4 years, n = 9). Mean litter size divided by mean birth interval yielded an annual natality rate of 0.81 cubs per adult female per year. The mean age at first parturition was 8.1 years (SE = 0.5 years, n = 10). We believe the population to be currently stable or slightly increasing (λ = 1.033, 95% CI = 1.008–1.064).

Sea‐to‐land nutrient transfers can connect marine food webs to those on land, creating a dependence on marine webs by opportunistic species. We show how nitrogen, imported by gray seals,Halichoerus grypus, and traced through stable isotope (δ¹⁵N) measurements in marram grass, Ammophila breviligulata, significantly alters foraging behavior of a free‐roaming megaherbivore (feral horses,Equus ferus caballus) on Sable Island, Canada. Values of δ¹⁵N correlated with protein content of marram and strongly related to pupping‐seal densities, and positively influenced selective foraging by horses. The latter was density dependent, consistent with optimal foraging theory. We present the first demonstration of how sea‐to‐land nutrient transfers can affect the behavioral process of resource selection (resource use relative to availability) of terrestrial consumers. We hypothesize that persistence of horses on Sable Island is being facilitated by N subsidies. Our results have relevance to advancing theory on trophic dynamics in island biogeography and metaecosystem ecology.