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941.
Eric Griffin 《Natural resources forum》1996,20(2):153-161
The following article is an attempt to reconcile the opinions of various activist-oriented non-governmental organizations (NGOs) on the use of gender analysis as a policy tool in the field of international development and macroeconomic policy. Of special concern to the author is the evolving relationship between international financial institutions (IFIs) and grassroots environmental NGOs seeking reform in macroeconomic policy initiation, implementation and evaluation. The ideas presented below are those of the author alone, and are solely intended to facilitate dialogue between the aforementioned parties as an alternative to the characteristic set of untenable demands and concomitant uncompromising resistance. Thus stated, the reader is challenged to remove his/her professional hat to accept or reject the validity of the propositions with an equal proportion of reason and intuition. 相似文献
942.
Eric Trachtenberg Clayton Ogg 《Journal of the American Water Resources Association》1994,30(6):1109-1118
ABSTRACT: According to the 1990 National Water Quality Inventory nutrient runoff from agriculture is one of the largest contributors to watershed contamination. Nutrient balance studies suggest that many farmers use more fertilizer than necessary because of insufficient crediting for nutrients coming from manure and legumes. Using data from the USDA's 1990 Farm Costs and Returns Survey, we found that farmers raising only conventional crops spend between $470 to $624 million more per year on fertilizer than necessary. This accounts for a range of 24 percent to 32 percent of total annual nitrogen (N) purchases. The excess N amounts to between 2.5 to 3.3 billion pounds N and has considerable water pollution potential. Farmers and the fertilizer industry have responded positively to highly focused research and education programs which support improved crediting of these nutrients. 相似文献
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Amy M. Breman Jennifer C. Chow Lance U'Ren Elizabeth A. Normand Sadeem Qdaisat Li Zhao David M. Henke Rui Chen Chad A. Shaw Laird Jackson Yaping Yang Liesbeth Vossaert Rachel H. V. Needham Elizabeth J. Chang Daniel Campton Jeffrey L. Werbin Ron C. Seubert Ignatia B. Van den Veyver Jackie L. Stilwell Eric P. Kaldjian Arthur L. Beaudet 《黑龙江环境通报》2016,36(11):1009-1019
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948.
Predator diversity and identity drive interaction strength and trophic cascades in a food web 总被引:3,自引:0,他引:3
Declining predator diversity may drastically affect the biomass and productivity of herbivores and plants. Understanding how changes in predator diversity can propagate through food webs to alter ecosystem function is one of the most challenging ecological research topics today. We studied the effects of predator removal in a simple natural food web in the Sierra Nevada mountains of California (USA). By excluding the predators of the third trophic level of a food web in a full-factorial design, we monitored cascading effects of varying predator diversity and composition on the herbivorous beetle Chrysomela aeneicollis and the willow Salix orestera, which compose the first and second trophic levels of the food web. Decreasing predator diversity increased herbivore biomass and survivorship, and consequently increased the amount of plant biomass consumed via a trophic cascade. Despite this simple linear mean effect of diversity on the strength of the trophic cascade, we found additivity, compensation, and interference in the effects of multiple predators on herbivores and plants. Herbivore survivorship and predator-prey interaction strengths varied with predator diversity, predator identity, and the identity of coexisting predators. Additive effects of predators on herbivores and plants may have been driven by temporal niche separation, whereas compensatory effects and interference occurred among predators with a similar phenology. Together, these results suggest that while the general trends of diversity effects may appear linear and additive, other information about species identity was required to predict the effects of removing individual predators. In a community that is not temporally well-mixed, predator traits such as phenology may help predict impacts of species loss on other species. Information about predator natural history and food web structure may help explain variation in predator diversity effects on trophic cascades and ecosystem function. 相似文献
949.
Indirect effects and traditional trophic cascades: a test involving wolves, coyotes, and pronghorn 总被引:2,自引:0,他引:2
The traditional trophic cascades model is based on consumer resource interactions at each link in a food chain. However, trophic-level interactions, such as mesocarnivore release resulting from intraguild predation, may also be important mediators of cascades. From September 2001 to August 2004, we used spatial and seasonal heterogeneity in wolf distribution and abundance in the southern Greater Yellowstone Ecosystem to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus), accounts for high rates of coyote predation on pronghorn (Antilocapra americana) fawns observed in some areas. Results of this ecological perturbation in wolf densities, coyote densities, and pronghorn neonatal survival at wolf-free and wolf-abundant sites support the existence of a species-level trophic cascade. That wolves precipitated a trophic cascade was evidenced by fawn survival rates that were four-fold higher at sites used by wolves. A negative correlation between coyote and wolf densities supports the hypothesis that interspecific interactions between the two species facilitated the difference in fawn survival. Whereas densities of resident coyotes were similar between wolf-free and wolf-abundant sites, the abundance of transient coyotes was significantly lower in areas used by wolves. Thus, differential effects of wolves on solitary coyotes may be an important mechanism by which wolves limit coyote densities. Our results support the hypothesis that mesopredator release of coyotes contributes to high rates of coyote predation on pronghorn fawns, and demonstrate the importance of alternative food web pathways in structuring the dynamics of terrestrial systems. 相似文献
950.
With the discovery of previously unreported populations of hemoglobin-possessing Ophiactis from the Texas coast in the Gulf of Mexico, an investigation into its population structure, including populations of O. simplex from the Pacific coast of California and O. rubropoda from the Atlantic coast of Florida, was undertaken using DNA sequence data from the mitochondrial COI gene. The reconstructed
haplotype network suggests that California populations contain the ancestral source of mtDNA variation, and there is no evidence
of recent introductions into Texas. Population genetic analyses reveal the California, Florida, and Texas Ophiactis populations to each be significantly differentiated from one another. Sequence divergence among the three areas is shallower
than would be predicted given biogeographic history. Texas and Florida populations are equally genetically diverged from California
populations as they are to one another, despite the greater potential for gene flow between these areas. The genetic distinctiveness
of the Texas populations and the concordance of this pattern with phylogeographic patterns in other brittle star systems indicate
an isolated and independent evolutionary history and we hypothesize that the three geographic regions included in this study
each serve as hypotheses of population-level lineages that remain to be tested with independent sources of data. 相似文献