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. A bstract. A heterogeneity index, D, derived from the point-quarter technique was significantly correlated with bird species diversity (BSD) for several shrub and forest areas. It predicted BSD for a series of similar brushlands where other indices had failed. Species richness increased faster than species overlap in a series of increasingly complex habitats up to the forest stage. Species overlap was negatively correlated with patchiness. Additional species may be accommodated in preforest habitats primarily by horizontal spatial segregation facilitated by the presence of additional patches. New patches result from the addition of layers of vegetation. In late shrub or forest stages other kinds of segregation such as vertical segregation become important to species packing.Patchiness, as measured here, has a proximate effect on avian diversity. The extent or existence of latitudinal gradients in habitat patchiness and the effect on bird species diversity is unknown. The need remains for a universal, simple, yet meaningful, heterogeneity index which incorporates both horizontal and vertical variability of vegetation.
In the mid‐Atlantic region, urban sprawl and development have resulted in habitat alterations and fragmentation; however, the effects on eastern box turtle (Terrapene carolina carolina) populations are unclear. To investigate the status of eastern box turtle populations in a fragmented landscape, we used mark—recapture and radiotelemetry to estimate population density, sex ratio, age structure, and survival on 4 study areas with differing degrees of isolation and human disturbance in northern New Castle County, Delaware, USA. We estimated adult population densities ranging from 0.81 turtles/ha to 3.62 turtles/ha among our 4 study areas. Sex ratios were male‐biased at 2 study areas and balanced at 2 study areas. Proportion of juveniles ranged from 0% to 31%. Estimated annual survival rate ranged from 0.813 to 0.977. Mortality of radiotagged and marked turtles was primarily due to natural causes, but mowing was the primary cause of human‐induced mortality. We found evidence of population decline at one study area due to low survival and recruitment. Human disturbances, isolation, and habitat composition appear to have the greatest influence on the box turtle populations we studied. To minimize mortality from human disturbance, we suggest planting crops adjacent to forest habitat that require no mowing or mowing at a height ≥15 cm. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):745–753; 2008)
Data from a 22‐yr study of individually marked Wood Thrushes (Hylocichla mustelina) in a Delaware forest fragment were analyzed to determine temporal and demographic patterns of nesting success, recruitment of local young into the population (fitness), and adult return rates (survival). Clutch size, number of eggs incubated, and number of eggs hatched were greater in early nests than in late nests. Although no difference existed in the average number of fledglings produced from early and late nests, fledglings from early nests were more likely to be recruited as breeders in the local population. Pairs of yearling (SY) birds produced equal numbers of recruits per nest from early and late nests, whereas pairs of older (≥2‐yr‐old, ASY) birds produced more recruits from early nests. The probability of fledging at least one young tended to be greater for late nests, and the percentage of eggs that eventually fledged was also greater for late nests. All nests were most likely to fail in the laying stage than during any other nest stage. Early nests failed in the laying stage at a greater rate than late nests. The number of Wood Thrushes that hatched was the most important demographic, reproductive, or date variable measured that positively influenced seasonal fledging success. Year of breeding also positively influenced success. ASY birds returned to breed at higher rates than did SY birds. SY males returned at a higher rate than did SY females. There was no difference in return rates between ASY males and ASY females. Producing at least one Wood Thrush fledgling positively influenced the likelihood of return for SY females. Neither annual success nor any other demographic, reproductive, or date variable that we measured influenced the return probabilities of other age or sex classes of adult birds. Based on these temporal patterns of fitness and survival, we propose that life history strategies among Wood Thrushes vary as a function of late‐season reproductive effort and winter‐related factors that affect survival.
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