排序方式: 共有32条查询结果,搜索用时 15 毫秒
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Effects of Landscape Disturbance on Animal Communities in Lake Tanganyika, East Africa 总被引:1,自引:0,他引:1
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Annalies Borrel Anna Taylor Marie McGrath rew Seal Elizabeth Hormann Laura Phelps & Frances Mason 《Disasters》2001,25(2):149-163
The preparation and dissemination of policy statements are necessary but insufficient to prevent the inappropriate use of infant-feeding products in emergencies. The widespread failure of humanitarian agencies operating in the Balkan crisis to act in accordance with international policies and recommendations provides a recent example of the failure to translate infant-feeding policies into practice. This article explores the underlying reasons behind the failures which include: (1) the weak institutionalisation of policies; (2) the massive quantities of unsolicited donations of infant-feeding products: (3) the absence of monitoring systems; (4) inadequate co-ordination mechanisms; (5) the high costs of correcting mistakes; and (6) the cumulative effects of poor practice. Efforts to uphold best practice during the crisis are also documented. Finally, the article identifies actions that could be undertaken in advance of and during future emergencies to enhance the application of infant feeding policies in emergencies. 相似文献
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Spatial Patterns in the Abundance of the Coastal Horned Lizard 总被引:7,自引:0,他引:7
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Joseph P. Dudley § Joshua R. Ginsberg † rew J. Plumptre † John A. Hart † Liliana C. Campos‡ 《Conservation biology》2002,16(2):319-329
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Andrew Balmford James C. Deutsch Rory J. C. Nefdt Tim Clutton-Brock 《Behavioral ecology and sociobiology》1993,33(1):57-65
Summary Hotspot models propose that leks have evolved because certain sites are associated with extremely high female encounter rates. In this paper we test five predictions of hotspot models, using data from studies of three species of lekking ungulates. As predicted, we found that lekking species generally had large female home ranges. However, in contrast to other predictions of hotspot models, ungulate leks did not occur at sites of maximum adult female density, lekking was not associated with low overall female density, and the adult sex ratio and the proportion of females that were in oestrus both differed substantially between leks and off-lek areas. Our empirical results therefore confirm recent theoretical assessments of the hotspot process, suggesting that while hotspots may help explain broad patterns of male dispersion, further mechanisms are needed to generate the extent of territory clustering seen at leks.
Correspondence to: A. Balmford 相似文献
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Role of Propagule Size in the Success of Incipient Colonies of the Invasive Argentine Ant 总被引:4,自引:0,他引:4
Abstract: Factors that contribute to the successful establishment of invasive species are often poorly understood. Propagule size is considered a key determinant of establishment success, but experimental tests of its importance are rare. We used experimental colonies of the invasive Argentine ant ( Linepithema humile ) that differed both in worker and queen number to test how these attributes influence the survivorship and growth of incipient colonies. All propagules without workers experienced queen mortality, in contrast to only 6% of propagules with workers. In small propagules (10–1,000 workers), brood production increased with worker number but not queen number. In contrast, per capita measures of colony growth decreased with worker number over these colony sizes. In larger propagules ( 1,000–11,000 workers), brood production also increased with increasing worker number, but per capita brood production appeared independent of colony size. Our results suggest that queens need workers to establish successfully but that propagules with as few as 10 workers can grow quickly. Given the requirements for propagule success in Argentine ants, it is not surprising how easily they spread via human commerce. 相似文献
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Assessing strategies to reconcile agriculture and bird conservation in the temperate grasslands of South America 下载免费PDF全文
Globally, agriculture is the greatest source of threat to biodiversity, through both ongoing conversion of natural habitat and intensification of existing farmland. Land sparing and land sharing have been suggested as alternative approaches to reconcile this threat with the need for land to produce food. To examine which approach holds most promise for grassland species, we examined how bird population densities changed with farm yield (production per unit area) in the Campos of Brazil and Uruguay. We obtained information on biodiversity and crop yields from 24 sites that differed in agricultural yield. Density–yield functions were fitted for 121 bird species to describe the response of population densities to increasing farm yield, measured in terms of both food energy and profit. We categorized individual species according to how their population changed across the yield gradient as being positively or negatively affected by farming and according to whether the species’ total population size was greater under land‐sparing, land‐sharing, or an intermediate strategy. Irrespective of the yield, most species were negatively affected by farming. Increasing yields reduced densities of approximately 80% of bird species. We estimated land sparing would result in larger populations than other sorts of strategies for 67% to 70% of negatively affected species, given current production levels, including three threatened species. This suggests that increasing yields in some areas while reducing grazing to low levels elsewhere may be the best option for bird conservation in these grasslands. Implementing such an approach would require conservation and production policies to be explicitly linked to support yield increases in farmed areas and concurrently guarantee that larger areas of lightly grazed natural grasslands are set aside for conservation. 相似文献
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