Bighorn sheep habitat use and selection near an urban environment

To further understand the impact of urban development on wildlife populations, we examined habitat use and selection by female bighorn sheep Ovis canadensis in two endangered subpopulations near a metropolitan area in southern California. One subpopulation, which had previously been found to have low reproductive success, selected urban environments while the other did not use urban areas. In the subpopulation that used urban areas, females had smaller core activity areas and selected lower elevations and gentler slopes. These females used urban sources of water but a clear relationship between levels of urban use and periods of increased water need was not evident. Diet quality was higher among females that selected urban areas, and this increase was correlated with the level of urban use. Thus, optimal foraging behavior may have contributed to the selection of urban areas. Urban use was lowest during peak months of parturition, suggesting that reproductive strategies may also have influenced temporal patterns of urban use. Although urban areas provided bighorn sheep with forage and water resources, the use of these areas may have substantial costs. For example, females using urban areas had internal parasites that were not found elsewhere in the Peninsular Ranges.     

Identifying, understanding, and describing spatial processes in agricultural landscapes — four case studies

To evaluate the quality of the ecosystem and for making resources and land management decisions landscapes have to be assessed quantitatively. For a better understanding of landscape processes and their characterization, the analysis of the inherent variability is a major factor. Four case studies in which problems associated with landscape analysis are discussed. Spatial processes remain a main focus, as their analysis provides information on the relation between relevant state variables in agricultural landscapes. Variogram analysis showed that mineral soil nitrogen (N_min) sampled in a field at different scales, domains, and times is an instationary spatial process. Spatial association of grain yield, soil index and remotely sensed vegetation index may not be identifiable from kriged contour maps as local coincidence may be obscured behind classified areas. Crop yield in subsequent years and remotely sensed information are not related if a unique response is assumed. An alternative data stratification procedure is described here for the identification of different response functions in agricultural ecosystems. Processes of crop yield and underlying variables are described in autoregressive state-space models. This technique incorporates both deterministic and stochastic relations between different variables and is based on relative changes in space.     

The simultaneous analysis of mixed discrete and continuous outcomes using nonlinear threshold models

Mixed discrete and continuous outcomes are commonly measured on each experimental unit in dose-response studies in toxicology. The dose-response relationships for these outcomes often have dose thresholds and nonlinear patterns. In addition, the endpoints are typically correlated, and a statistical analysis that incorporates the association may result in improved precision. We propose an extension of the generalized estimating equation (GEE) methodology to simultaneously analyze binary, count, and continuous outcomes with nonlinear threshold models that incorporates the intra-subject correlation. The methodology uses a quasi-likelihood framework and a working correlation matrix, and is appropriate when the marginal expectation of each outcome is of primary interest and the correlation between endpoints is a nuisance parameter. Because the derivatives of threshold models are not continuous at each point of the parameter space, we describe the necessary modifications that result in asymptotically normal and consistent estimators. Using dose-response data from a neurotoxicity experiment, the methodology is illustrated by analyzing five outcomes of mixed type with nonlinear threshold models. In this example, the incorporation of the intra-subject correlation resulted in decreased standard errors for the threshold parameters.     

Longitudinal growth strain as a log and wood quality predictor for plantation-grown <Emphasis Type="Italic">Eucalyptus nitens</Emphasis> sawlogs

Peripheral longitudinal growth strain (LGS) was measured on a total of 81, 22-year-old pruned Eucalyptus nitens trees from five thinning treatments in a plantation thinning trial in Tasmania. Growth strain data were gathered at breast height on each tree using the CIRAD-Forêt method. The effects of thinning treatment and tree diameter on LGS and its relationships to solid-wood traits determined in a processing trial were examined. LGS was significantly higher in the direction of the prevailing wind and was not significantly affected by either thinning treatment or tree diameter. An index of log end splitting was positively related to tree diameter, sawlog position (upper/lower), and LGS, which explained up to an additional 20% of the variance after tree diameter and log position were accounted for in a linear regression model. High LGS and log end splitting were significant indicators of increased board end splitting.     

Effect of boreal forest logging on nectar production of four understory herbs

The rate of floral nectar production, an important trait for supporting populations of pollinators, is known to be affected by local environment. This study examines the effect, 9 years after an anthropogenic disturbance—variable retention logging,—on the rate of daily nectar production of four common herbs (Chamerion angustifolium, Delphinium glaucum, Mertensia paniculata and Vicia americana) in the boreal forest of Alberta, Canada. We measured daily nectar production rates 9 years after experimental logging in three treatments: clear cuts (all merchantable trees removed), 50% of trees retained, and unlogged controls. Per-flower nectar production rate was unaffected by logging for C. angusifolium, D. glaucum, and M. paniculata, and lower in unlogged controls than in the 50% logging treatment for V. americana. Overall, we found a surprising robustness of nectar production of these herbaceous plants to the physical and environmental changes following logging. While other research has shown boreal forest logging to affect the densities of understory herbs, the per-flower nectar production in boreal forest understory herbs appears to be relatively insensitive to this disturbance.     

Managing small remnants of native forest to increase biodiversity within plantation landscapes in the south west of Western Australia

Recent expansion of industrial-scale plantations into agricultural areas in Australia has the potential to assist biodiversity conservation by rehabilitating ecosystems at the landscape scale and reducing edge effects, isolation and disturbance within remnants of native vegetation. However, the efficient management of remnants for biodiversity within a plantation estate requires knowledge of both the causes and the consequences of remnant degradation. With this in mind, we examined key ecosystem features and processes relating to soil chemistry, decomposition, native tree health and regeneration and vertebrate abundance, within small forest remnants (1-4 ha) embedded within Eucalyptus globulus plantations in south west Western Australia. Soil nutrient enrichment was significantly associated with a scale of vegetation modification in order from: (1) intact forest, (2) remnants with native understorey (UDN), (3) remnants with exotic understorey (UDE), (4) plantation and (5) pasture. We propose that, in this region, UDE remnants will often remain in a degraded state even after plantation establishment and the cessation of stock grazing. This is due, in part, to more rapid rates of nutrient turnover sustaining higher nutrient availability in the soil following the replacement of ligneous understorey plants with annual ones. Cotton strips placed in surface soils were often disintegrated in UDE remnants and largely intact in UDN remnants, indicating that decomposition was accelerated in the former. Continued tree decline and regeneration failure within UDE remnants will also reinforce the UDE condition. There was less canopy seed set and little or no seedling establishment in UDE remnants compared to UDN remnants. Therefore, management interventions to assist native tree regeneration in UDE remnants are needed. Fauna trapping highlighted the desirability of retaining, and preferably restoring, small remnants in plantations. Small native mammals were found exclusively in remnants and fewer introduced Mus musculus were present in UDN remnants. Higher numbers of native lizards were found in UDN remnants, but this result was not significant (marginally).     

Adaptive phenotypic plasticity in response to climate change in a wild bird population

Rapid climate change has been implicated as a cause of evolution in poorly adapted populations. However, phenotypic plasticity provides the potential for organisms to respond rapidly and effectively to environmental change. Using a 47-year population study of the great tit (Parus major) in the United Kingdom, we show that individual adjustment of behavior in response to the environment has enabled the population to track a rapidly changing environment very closely. Individuals were markedly invariant in their response to environmental variation, suggesting that the current response may be fixed in this population. Phenotypic plasticity can thus play a central role in tracking environmental change; understanding the limits of plasticity is an important goal for future research.     

Comment on "Wandering minds: the default network and stimulus-independent thought"

Mason et al. (Reports, 19 January 2007, p. 393) attributed activity in certain regions of the "resting" brain to the occurrence of mind-wandering. However, previous research has demonstrated the difficulty of distinguishing this type of stimulus-independent thought from stimulus-oriented thought (e.g., watchfulness). Consideration of both possibilities is required to resolve this ambiguity.     

The role of technology in enhancing low resource agriculture in Africa

Traditional forms of farming, herding, and fishing are remarkably adapted to African conditions but these traditional approaches are being overtaken by modern pressures, particularly population growth. According to a report published by the Office of Technology Assessment (OTA), a nonpartisan analytical support agency of the U. S. Congress, one promising way to help African farmers and herders would be for development assistance organizations to focus more attention on the various forms of low-resource agriculture that predominate in Africa. In keeping with OTA's mission and primary audience, “Enhancing Agriculture in Africa: A Role for U. S. Development Assistance” (1988) is a policy-oriented synthesis of available technical information. The report provides Congress with a range of options that, if pursued, could help Africans enhance agriculture, increase their food security, and improve their lives. This paper is drawn from the larger OTA report, and it focuses on the role technology might play in enhancing low-resource agriculture. Readers should see the full assessment (OTA, 1988) for more information on policy considerations; the specific technologies mentioned; or a complete list of advisory panel members, workshops and participants, and commissioned papers. OTA's report comes at a critical time: for a variety of reasons—ranging from changing values to increased budget constraints—U. S. foreign assistance policy is undergoing a fundamental reevaluation. This review of the potential of low-resource agriculture, and options the United States might pursue to enhance this approach, was intended to aid in this reevaluation.