The Inadequate Environment

Annual home-range size indices for 36 male and 52 female adult brown bears Ursus arctos in two study areas in central and northern Scandinavia were estimated to evaluate factors believed to influence home-range size. Male home ranges were larger than home ranges of lone females after controlling for the sexual size dimorphism acting on metabolic needs. Further, home ranges of females with cubs were smaller than home ranges of lone females and females with yearlings. Thus, differences in metabolic need were not able to explain the variation in range size among females of different reproductive categories or between males and females, suggesting roaming behaviour of males in this promiscuous species. Home-range size in both males and females was inversely related to population density along a density gradient that was not linked to food availability. This contradicts the hypothesis that females use the minimum areas that sustain their energy requirements. However, on a large geographical scale a negative relationship between range size and food availability was evident. The annual home ranges in inland boreal environments in Scandinavia are the largest reported for brown bears in Eurasia, and similar to those in inland boreal and montane environments in North America.

Home ranges in adult Scandinavian brown bears (Ursus arctos): effect of mass, sex, reproductive category, population density and habitat type

Insular lizards, birds, and mammals in high-density populations often exhibit reduced situation-specific aggression toward conspecifics. This aggressive behavior can be expressed in the form of (1) reduced territory sizes, (2) increased territory overlap with neighbors, (3) acceptance of subordinates on the territory, (4) reduced aggressiveness to certain classes of conspecifics, or (5) abandonment of territorial defense. These behavioral traits can be explained by two nonexclusive hypotheses. The resource hypothesis suggests that territorial behavior is primarily adjusted to resource densities, and that resources are more abundant on islands than on the mainland (e.g., because of a lack of competing species). The defense hypothesis suggests that, in addition to any effects of resources, the costs of defense against both territorial intruders and contenders for vacant territories are higher on islands. Recent theoretical and empirical studies indicate that these behavioral changes can occur as a result of elevated defense costs, independent of resource densities. Reduced predation, more benign climates, and an absence of habitat sinks on islands would all tend to increase the density of potential intruders and contenders, and hence the costs of defense for owners of insular territories. The two hypotheses differ in their predictions about the rates of biomass production (growth or reproduction) for holders of insular territories. Reproductive and growth data from insular-mainland pairs indicate the importance of elevated defense costs, and also suggest that many insular vertebrates reallocate their breeding resources so as to produce young that are more competitive. The suite of ecological and behavioral traits exhibited by insular territorial vertebrates can best be explained by three factors operating in concert: higher available resource densities, higher defense costs, and (sometimes) a reallocation of resources to produce young that are more competitive.

The territorial defense hypothesis and the ecology of insular vertebrates.

While migrating southward each summer along the Sierra Nevada Mountain Range in California, nectar-feeding rufous hummingbirds (Selasphorus rufus) establish feeding territories within isolated meadows. We investigated the effect of variable food density upon territory area and time budgeting by controlled removals and additions of flowers of Castilleja linariaefolia within the territories of immature birds. The experiments were replicated three times with generally consistent results. Within one day following a 50% decrease in flower density: (1) territory area usually about doubled, resulting in (2) the number of defended flowers remaining similar to the premanipulation value; (3) foraging time increased significantly from about 21% to about 26% of the day as the result of (4) a significant increase in foraging bout duration, with (5) bout frequency remaining unchanged; (6) daily sitting time decreased significantly from about 76% to about 71% of the day; and (7) daily defense time did not change signifi...

Territory Area, Flower Density, and Time Budgeting in Hummingbirds: An Experimental and Theoretical Analysis

Life-history theory allows predictions of how changes in environmental selection pressures along a species' geographic distribution result in discrete shifts in life-history traits We tested for spatial patterns of 24 populations of brown bears Ursus arctos across North America that grouped according to the following environmental and population parameters: evapotranspiration as a correlate of primary productivity of vegetation, coefficient of variation of monthly evapotranspiration values as a measure of seasonality, population density, and adult female weight Cluster analysis grouped brown bear populations into two regions: Pacific-coastal populations characterized by high population density and large females that lived in areas of high primary productivity and low seasonality, and inland and barren-ground populations characterized by relatively low density and small bears that lived in areas of low productivity and high seasonality For each region, we tested whether life-history traits (age at maturity and interbirth interval) related to primary productivity or seasonality High altitude (interior; > 1000 m) and high latitude (barren-ground; > 65°N) populations respond to extremes in seasonality with risk-spreading adaptations For example, age at maturity and interbirth interval increased with greater seasonality In contrast, Pacific-coastal populations living on the western edge of brown bear geographic range respond to intraspecific competition at high densities by maximizing offspring competitive ability For example, age at maturity increased with greater primary productivity and high population density In each region, the female parent decided on the life-history trade-offs required to reduce the risks of offspring mortality depending on the environmental pattern

Effect of energy availability, seasonality, and geographic range on brown bear life history

We report on a series of experiments performed on a population of free-living eastern chipmunks, Tamias striatus, inhabiting a forest in northwestern Pennsylvania. The experiments were designed to examine, via perturbations of food supply and/or population density, the relationship between home range size, food availability, and population density. When food levels were increased within an area, a simultaneous effect was noted: mean home range size decreased and population density increased through recruitment from neighboring habitats. Whether the cause of the decreased patterns of movement was the increased food supply or the elevated population density was deter- mined in subsequent experiments. When population density was held constant and food supplies were experimentally increased, there was a significant reduction in mean home range sizes when compared to the normal (control) situation. When food supplies were undisturbed, but population density was greatly reduced, there was no change in the mean home range size over that determined at higher densities. Our results suggest that, in eastern chipmunks, food supply is a primary determinant of mean home range size, whereas population density, at least at the levels we examined experimentally, has no effect on movement patterns. These results are in accord with those theories relating movement patterns to resource abundance, but are not in accord with hypotheses suggesting that home range sizes and population density are inversely associated.

https://www.jstor.org/stable/pdfplus/1938940.pdf

An Experimental Analysis of Social Spacing in Tamias Striatus

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An Experimental Analysis of Social Spacing in Tamias Striatus