Environmental Science and Policy

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    Intraspecific aggregation decreases local species diversity of arthropods
    (Ecological Society of America, 2003) Veech, Joseph A.; Crist, Thomas O.; Summerville, Keith S.
    Abstract. The aggregation model of species coexistence predicts that insect species diversity within a community is maintained by intraspecific aggregation among resource patches. An untested corollary of this prediction is that diversity within resource patches should decrease with increasing intraspecific aggregation. The recently derived species–aggregation relationship provides a general formulation of this prediction: as intraspecific aggregation increases within a geographic area, the species richness within samples of the area decreases. We tested this prediction by compiling and analyzing 76 data sets of arthropod species distribution and abundance. For each data set, we determined the mean amount of intra- and interspecific aggregation and three types of within-sample or local species diversity: species richness, evenness, and dominance. Using regression, we found a negative relationship between intraspecific aggregation and all three types of local diversity. Intraspecific aggregation explained a significant percentage of the variation in species diversity, typically between 20% and 60%. By comparison, interspecific aggregation usually explained <1% of the variation in species diversity. Our study provides empirical support for the species–aggregation relationship as a general macroecological pattern that emerges from intraspecific aggregation.
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    "Effects of timber harvest on forest lepidoptera: community, guild, and species responses"
    (Ecological Society of America, 2002) Summerville, Keith S.; Crist, Thomas O.
    Abstract. Two pressing questions for forestry and conservation biology are whether periodic logging in forest ecosystems significantly changes biodiversity and whether the changes can be mitigated through appropriate harvest methods. Such questions of timber resource management, however, are rarely applied to nonpest insect species, particularly in temperate forest systems. We studied the effects of timber harvest on species richness, abundance, and community composition of forest Lepidoptera (moths). Moths were sampled in 16 forest stands occurring in two watersheds (managed and wilderness) in southeastern Ohio during summer 2000. Stands were chosen from one of four management categories: clear-cut, selectively logged, unlogged, and wilderness. Specifically, we tested the following predictions: (1) shifts in moth community composition would be affected by postharvest changes in stand structure and floristic composition, (2) variation in species richness would be determined by the magnitude of the logging disturbance, and (3) unlogged stands within managed landscapes would contain different species assemblages compared to wilderness stands. Canonical correspondence analysis (CCA) revealed significant compositional differences among moth communities sampled from forest stands differing in harvest regime. Variation among moth communities was mainly attributable to postharvest changes in stand floristic composition rather than stand structure. Postdisturbance shifts in moth community composition were related to the magnitude of displacement of a given forest stand to earlier successional stages. We also found that both species richness of the overall moth community and several feeding guilds were significantly lower in clear-cut stands, but species richness did not differ between selectively logged and unlogged stands. Thus, selective logging appears to be a better strategy for timber harvest when concern is for maintaining species richness of Lepidoptera within stands. Finally, although no differences were detected in overall species richness or abundance of moths sampled from stands in managed or wilderness watersheds, the CCA suggested that the surrounding landscape influenced the variation in community composition within and among forest stands. Therefore, we suggest that the long-term maintenance of lepidopteran species diversity and community composition within temperate deciduous forests managed for timber may ultimately depend on successful regeneration of harvested stands to precut floristic composition as well as the preservation of larger areas of unlogged forests.
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    "Species traits as predictors of lepidopteran composition in restored and remnant tallgrass prairies"
    (Ecological Society of America, 2006) Summerville, Keith S.; Conoan, Christopher J.; Steichen, Renae M.
    Restoration ecologists are increasingly turning to the development of trait-filter models, which predict how evolved traits limit species membership within assemblages depending on existing abiotic or biotic constraints, as a tool to explain how species move from a regional species pool into a restored community. Two often untested assumptions of these models, however, are that species traits can reliably predict species' broadscale distribution and that the effects of traits on community membership do not vary between restored and remnant habitats. The goals of this study were to determine whether combinations of ecological traits predispose moth species toward recolonization of restored prairies and to assess the degree to which restored prairies contain moth assemblages comparable with prairie remnants. In 2004, we collected 259 moth species from 13 tallgrass prairie remnants and restorations in central Iowa. Principal components analysis (PCA) was used to identify significant combinations of ecological traits that were shared by groups of moth species. Logistic regression was then employed to test for significant effects of the trait combinations on the frequency of prairie sites occupied by moth species. PCA partitioned moth traits into four axes that explained a total of 81.6% of the variance. Logistic regression detected significant effects for all four PCA axes on the fraction of sites occupied by moths. Species frequently filtered from the regional species pool into prairies were those that had long flight periods and were multivoltine, displayed a feeding preference for legumes but not other forb families, and were regionally abundant but relatively small in body size. Ordination revealed significant differences in moth communities among prairies, suggesting that species traits and habitat characteristics likely interact to create observed patterns of species recolonization of restorations. Thus, the optimal approach to restoring the lepidopteran fauna of tallgrass prairies may involve locating prairie plantings adjacent to habitat remnants.© 2006 by the Ecological Society of America.
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    "The effect of income choice on bias in policy decisions made using cost-benefit analyses"
    (Elsevier Science Incorporated, 2004-12-01) Courard-Hauri, David
    Cost-Benefit Analysis (CBA) is often used in policy decisions to determine the economic value of various choices. Although the effects of income disparity are well accepted, one of the reasons for the success of this type of analysis is that many policy-makers and analysts consider the results of a well-crafted analysis to be largely free of partisan or political bias. Here I propose that tradeoff between the benefits of various possible jobs or careers introduce a significant bias into values imputed based upon willingness to pay measures. In particular, I demonstrate why we might expect the values of various segments of society to be differentially appreciated by CBA. Empirical evidence is presented indicating that there is a significant negative correlation between the importance an individual places on income and the willingness of that individual to forgo consumption in favor of environmental improvement, as well as a correlation between the importance of income and actual income. These results suggest that CBA as a tool of welfare economics is likely to be biased against environmental protection because concerned individuals are likely to choose careers which do not maximize consumption, thus decreasing their ability to pay for both real and hypothetical environmental improvements. Moreover, the size of this bias appears to be large.