JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. We compiled studies that report data on the relationship between animal population density and patch or island area for 287 individual species and 21 faunas. We tested the assumption of the equilibrium theory of island biogeography that population densities are independent of area by performing a meta-analysis using the linear correlation coefficient, r, as a measure of the effect of area on population density. We fit meta-analyses that used a random-effects model to these data to test for the effects of taxa, habitat, latitude, spatial scale, and overall population density. We also fit meta-analyses that used a fixedeffect model to the same data to estimate the repeatability of measurements of the correlation between population density and area within species.Contrary to the equilibrium theory of island biogeography, our results indicate that, on average, animal population densities are positively correlated with area, which suggests that density compensation may be uncommon. This result was found for individual species, but not for faunas. We found taxonomic differences in the correlation between population density and area, with insects and birds having on average large or moderately large positive correlations, respectively, and mammals having correlations near zero. Observations within individual species showed considerable repeatability. The observed overall positive correlation between the population density of individual animal species and area is best explained in the context of the resource concentration hypothesis.Our results imply that the regional abundance and persistence of animal populations may depend strongly on the presence and,continued persistence of a few large patches of suitable habitat, rather than on a regional network of small and large habitat patches.

Ecologists often assume that dispersing individuals experience increased predation risk owing to increased exposure to predators while moving. To test the hypothesis that predation risk is a function of movement distance or rate of movement, we used radio-telemetry data collected from 193 ruffed grouse (Bonasa umbellus) during 1996-1999 in southeastern Ohio. Cox's proportional hazards model was used to examine whether the risk of predation was affected by the rate of movement and site familiarity. We found evidence indicating that increased movement rates may increase the risk of predation for adult birds but not juveniles. We also found juvenile and adult birds inhabiting unfamiliar space were consistently at a much higher risk of predation (three to 7.5 times greater) than those in familiar space. Our results indicate that although movement itself may have some effect on the risk of being preyed upon, moving through unfamiliar space has a much greater effect on risk for ruffed grouse. This supports the hypothesis that increased predation risk may be an important cost of dispersal for birds.

We compiled studies that report data on the relationship between animal population density and patch or island area for 287 individual species and 21 faunas. We tested the assumption of the equilibrium theory of island biogeography that population densities are independent of area by performing a meta‐analysis using the linear correlation coefficient, r, as a measure of the effect of area on population density. We fit meta‐analyses that used a random‐effects model to these data to test for the effects of taxa, habitat, latitude, spatial scale, and overall population density. We also fit meta‐analyses that used a fixed‐effect model to the same data to estimate the repeatability of measurements of the correlation between population density and area within species. Contrary to the equilibrium theory of island biogeography, our results indicate that, on average, animal population densities are positively correlated with area, which suggests that density compensation may be uncommon. This result was found for individual species, but not for faunas. We found taxonomic differences in the correlation between population density and area, with insects and birds having on average large or moderately large positive correlations, respectively, and mammals having correlations near zero. Observations within individual species showed considerable repeatability. The observed overall positive correlation between the population density of individual animal species and area is best explained in the context of the resource concentration hypothesis. Our results imply that the regional abundance and persistence of animal populations may depend strongly on the presence and continued persistence of a few large patches of suitable habitat, rather than on a regional network of small and large habitat patches.

1999. Density-related predation by the Carolina chickadee, Poecile carolinensis, on the leaf-mining moth Cameraria hamadryadella at three spatial scales. -Oikos 87: 105-112.The impact of predation by the Carolina chickadee, Poecile carolinensis, on populations of the leaf-mining moth Cameraria hamadryadella, was inversely spatially density-dependent at each of three spatial scales: among woodlands, among trees, and among leaves. P. carolinensis exhibited an aggregative response to the density of C. hamadryadella at the scale of woodlands, but did not preferentially forage in trees or on leaves with high densities of leaf mines. P. carolinensis exhibits no numerical response to the abundance of C. hamadryadella. The functional response of P. carolinensis suggests that per capita foraging efficiency is actually lower in high-density populations of C. hamadryadella. This may arise because of predator confusion and because of mechanical limitations to foraging behavior. Human subjects, used as surrogates for chickadees, took more time to discover and discovered fewer leaf-miner larvae on leaves with higher proportions of the leaf-area mined. Chickadees hang "upside down" to attack leaf-miner larvae and this posture may limit the duration of foraging bouts. Either predator confusion or mechanical limitation, alone or in combination, could account for the observed inversely density-dependent impact of predation at the leaf scale. In outbreak populations of C. hamadryadella where P. carolinensis is a common predator, the inversely density-dependent attack by P. carolinensis on C. hamadryadella complements the strongly density-dependent mortality caused by intra-specific competition. Therefore, the pattern of predation by P. carolinensis contributes more to suppression of C. hamadryadella than would occur if P. carolinensis foraged in a density-dependent manner. Birds in the family Paridae appear to be the dominant avian predators of leaf-mining insects. We suggest that their altered leg musculature permits them to use a hanging

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