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Matthias Schmid Torsten Hothorn Kelly O. Maloney Donald E. Weller Sergej Potapov 《Environmental and Ecological Statistics》2011,18(4):709-733
Indices of biotic integrity have become an established tool to quantify the condition of small non-tidal streams and their
watersheds. To investigate the effects of watershed characteristics on stream biological condition, we present a new technique
for regressing IBIs on watershed-specific explanatory variables. Since IBIs are typically evaluated on an ordinal scale, our
method is based on the proportional odds model for ordinal outcomes. To avoid overfitting, we do not use classical maximum
likelihood estimation but a component-wise functional gradient boosting approach. Because component-wise gradient boosting
has an intrinsic mechanism for variable selection and model choice, determinants of biotic integrity can be identified. In
addition, the method offers a relatively simple way to account for spatial correlation in ecological data. An analysis of
the Maryland Biological Streams Survey shows that nonlinear effects of predictor variables on stream condition can be quantified
while, in addition, accurate predictions of biological condition at unsurveyed locations are obtained. 相似文献
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Barbara Neumann Michael Lütz Beatrice Schüpbach Erich Szerencsits 《Regional Environmental Change》2009,9(3):197-207
Spatial modelling of environmental indicators has been well established in landscape ecology and in nature conservation on
regional and national scales over the recent past. Yet, using spatial information as a basis for the coordination of environmental
measures on a trans-national European level reveals several shortcomings and hindrances, ranging from data quality issues
and methodological aspects to discussions on how to define ecological indicators across Europe. This paper analyzes the potential
of spatial modelling for the development and implementation of agri-environmental measures as part of rural development policies,
discussing critical aspects of spatial environmental modelling as well as chances, trends and demands. 相似文献
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The aim of this study was to investigate reproductive strategies and their consequences in gray mouse lemurs (Microcebus murinus), small solitary nocturnal primates endemic to Madagascar. Previous reports of sexual dimorphism in favor of males and females,
respectively, a high potential for sperm competition and pheromonal suppression of mating activity among captive males, led
us to investigate mechanisms of intrasexual competition in a wild population. Based on 3 years of mark-recapture data, we
demonstrate that sexual dimorphism in this species fluctuated annually as a result of independent changes in male and female
body mass. Male body mass increased significantly prior to the short annual mating season. Because their testes increased
by 100% in the same period and because their canines are not larger than those of females, we suggest that large male size
may be advantageous in searching for estrous females and in enabling them to sustain periods of short-term torpor. In contrast
to reports from captive colonies, we found no evidence for two morphologically distinct classes of males. Finally, we also
show that most adult males are active throughout the cool dry season that precedes the mating season, whereas most adult females
hibernate for several months. This is in contrast to other solitary hibernating mammals, where males typically emerge 1–2
weeks before females. Thus, this first extended field study of M.␣murinus clarified previous conflicting reports on sexual dimorphism and male reproductive strategies in this primitive primate by
showing that their apparent deviation from predictions of sexual selection theory is brought about by specific environmental
conditions which result in sex-specific life history tactics not previously described for mammals. A general conclusion is
that sexual selection can operate more strongly on males without resulting in sexual dimorphism because of independent selection
on the same traits in females.
Received: 6 July 1997 / Accepted after revision: 28 March 1998 相似文献
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