首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   145篇
  免费   85篇
基础理论   230篇
  2023年   6篇
  2022年   12篇
  2021年   15篇
  2020年   18篇
  2019年   13篇
  2018年   24篇
  2017年   18篇
  2016年   19篇
  2015年   24篇
  2014年   18篇
  2013年   10篇
  2012年   13篇
  2011年   15篇
  2010年   14篇
  2009年   6篇
  2008年   5篇
排序方式: 共有230条查询结果,搜索用时 46 毫秒
211.
Humpback whales (Megaptera novaeangliae) are managed by the International Whaling Commission as 7 primary populations that breed in the tropics and migrate to 6 feeding areas around the Antarctic. There is little information on individual movements within breeding areas or migratory connections to feeding grounds. We sought to better understand humpback whale habitat use and movements at breeding areas off West Africa, and during the annual migration to Antarctic feeding areas. We also assessed potential overlap between whale habitat and anthropogenic activities. We used Argos satellite‐monitored radio tags to collect data on 13 animals off Gabon, a primary humpback whale breeding area. We quantified habitat use for 3 cohorts of whales and used a state‐space model to determine transitions in the movement behavior of individuals. We developed a spatial metric of overlap between whale habitat and models of cumulative human activities, including oil platforms, toxicants, and shipping. We detected strong heterogeneity in movement behavior over time that is consistent with previous genetic evidence of multiple populations in the region. Breeding areas for humpback whales in the eastern Atlantic were extensive and extended north of Gabon late in the breeding season. We also observed, for the first time, direct migration between West Africa and sub‐Antarctic feeding areas. Potential overlap of whale habitat with human activities was the highest in exclusive economic zones close to shore, particularly in areas used by both individual whales and the hydrocarbon industry. Whales potentially overlapped with different activities during each stage of their migration, which makes it difficult to implement mitigation measures over their entire range. Our results and existing population‐level data may inform delimitation of populations and actions to mitigate potential threats to whales as part of local, regional, and international management of highly migratory marine species. Cuantificación de los Movimientos de Gran Amplitud y el Traslape Potencial con Actividad Antropogénica y las Ballenas Jorobadas en el Océano Atlántico Sur  相似文献   
212.
We systematically reviewed the literature on the tragedy of the commons and common‐property resources. We segregated studies by legal management regimes (de jure regimes) and management that develops in practice (de facto regimes) to understand how the structure of regime formation affects the outcome of community management on sustainability of resource use. De facto regimes, developed within the community, are more likely to have positive impacts on the resource. However, de facto regimes are fragile and not resilient in the face of increased population pressure and unregulated markets, and de facto management regimes are less successful where physical exclusion of external agents from resources is more difficult. Yet, formalization or imposition of de jure management regimes can have complicated impacts on sustainability. The imposition of de jure regimes usually has a negative outcome when existing de facto regimes operate at larger scales than the imposed de jure regime. In contrast, de jure regimes have largely positive impacts when the de facto regimes operate at scales smaller than the overlying de jure regimes. Formalization may also be counterproductive because of elite capture and the resulting de facto privatization (that allows elites to effectively exclude others) or de facto open access (where the disenfranchised may resort to theft and elites cannot effectively exclude them). This underscores that although the global movement to formalize community‐management regimes may address some forms of inequity and may produce better outcomes, it does not ensure resource sustainability and may lead to greater marginalization of users. Comparison of governance systems that differentiate between initiatives that legitimize existing de facto regimes and systems that create new de facto regimes, investigations of new top‐down de jure regimes, and studies that further examine different approaches to changing de jure regimes to de facto regimes are avenues for further inquiry.  相似文献   
213.
Livestock grazing is the most widespread land use on Earth and can have negative effects on biodiversity. Yet, many of the mechanisms by which grazing leads to changes in biodiversity remain unresolved. One reason is that conventional grazing studies often target broad treatments rather than specific parameters of grazing (e.g., intensity, duration, and frequency) or fail to account for historical grazing effects. We conducted a landscape‐scale replicated grazing experiment (15,000 km2, 97 sites) to examine the impact of past grazing management and current grazing regimes (intensity, duration, and frequency) on a community of ground‐dwelling herpetofauna (39 species). We analyzed community variables (species richness and composition) for all species and built multiseason patch‐occupancy models to predict local colonization and extinction for the 7 most abundant species. Past grazing practices did not influence community richness but did affect community composition and patch colonization and extinction for 4 of 7 species. Present grazing parameters did not influence community richness or composition, but 6 of the 7 target species were affected by at least one grazing parameter. Grazing frequency had the most consistent influence, positively affecting 3 of 7 species (increased colonization or decreased extinction). Past grazing practice affected community composition and population dynamics in some species in different ways, which suggests that conservation planners should examine the different grazing histories of an area. Species responded differently to specific current grazing practices; thus, incentive programs that apply a diversity of approaches rather than focusing on a change such as reduced grazing intensity should be considered. Based on our findings, we suggest that determining fine‐scale grazing attributes is essential for advancing grazing as a conservation strategy.  相似文献   
214.
Abstract: The umbrella‐species concept, which suggests that conservation strategies designed for one species may benefit co‐occurring species, has been promoted as a framework for conservation planning. Nevertheless, there has been considerable variation in the outcome of empirical tests of this concept that has led researchers to question its value, so we used data from 15 published studies in a meta‐analysis to evaluate whether conservation of putative umbrella species also conserves co‐occurring species. We tested the effectiveness of putative umbrella species categorized by taxonomic group, taxonomic similarity to co‐occurring species, body size, generality of resource use, and trophic level to evaluate criteria proposed to guide the selection of umbrella species. We compared species richness and number of individuals (by species and higher taxonomic group) between sites with and without putative umbrella species to test whether more co‐occurring species were present in greater abundances when the area or resource needs of umbrella species were met. Species richness and abundance of co‐occurring species were consistently higher in sites where umbrella species were present than where they were not and for conservation schemes with avian than with mammalian umbrella species. There were no differences in species richness or species abundance with resource generalist or specialist umbrella species or based on taxonomic similarity of umbrella and co‐occurring species. Taxonomic group abundance was higher in across‐taxonomic umbrella species schemes than when umbrella species were of the same taxon as co‐occurring species. Co‐occurring species had similar, or higher, species richness with small‐bodied umbrella species relative to larger‐bodied umbrella species. The only significant difference among umbrella species categorized by trophic level was that species richness was higher with omnivorous than it was with carnivorous avian umbrella species. Our results suggest there is merit to the umbrella‐species concept for conservation, but they do not support the use of the criteria we used to identify umbrella species.  相似文献   
215.
Abstract: Declining rural security and pressures to reduce public‐sector expenditures in the late 1990s spurred efforts to develop alternative funding models for Uganda's Kibale National Park (KNP). The Wild Coffee Project, established in 1999 with support from the U.S. Agency for International Development, the World Bank, and the Ford Foundation, sought to develop a market for wild coffee that had been harvested traditionally from areas within today's KNP. The Kibale Forest Foundation, a U.S.‐based nonprofit organization, was created to legalize harvests, obtain third‐party wild and organic certification, and coordinate management between KNP, the coffee industry, and local communities. Although the project was successful in legalizing, harvesting, and processing the world's first certified wild and organic coffee, efforts to gain entry into the international marketplace failed. Chief among the lessons learned from this project is that for many wild‐grown products, the value of “the story”—in both human and conservation terms—is likely to far exceed actual product values. This value differential should be captured through high‐value niche markets to avoid low commodity pricing and subsequent pressures to improve financial returns through over harvesting. In addition, local producers should hold significant assets in whatever brands are developed, creating a shared‐equity approach that serves social responsibility goals, fosters project sustainability, and ensures a steady stream of positive stories for use in marketing to build brand value. Shared equity—in this case ownership interest in the intellectual property embodied in the brand—provides a second incentive beyond transactional profits that can only be realized if resource conservation is maintained.  相似文献   
216.
Abstract: Active adaptive management looks at the benefit of using strategies that may be suboptimal in the near term but may provide additional information that will facilitate better management in the future. In many adaptive‐management problems that have been studied, the optimal active and passive policies (accounting for learning when designing policies and designing policy on the basis of current best information, respectively) are very similar. This seems paradoxical; when faced with uncertainty about the best course of action, managers should spend very little effort on actively designing programs to learn about the system they are managing. We considered two possible reasons why active and passive adaptive solutions are often similar. First, the benefits of learning are often confined to the particular case study in the modeled scenario, whereas in reality information gained from local studies is often applied more broadly. Second, management objectives that incorporate the variance of an estimate may place greater emphasis on learning than more commonly used objectives that aim to maximize an expected value. We explored these issues in a case study of Merri Creek, Melbourne, Australia, in which the aim was to choose between two options for revegetation. We explicitly incorporated monitoring costs in the model. The value of the terminal rewards and the choice of objective both influenced the difference between active and passive adaptive solutions. Explicitly considering the cost of monitoring provided a different perspective on how the terminal reward and management objective affected learning. The states for which it was optimal to monitor did not always coincide with the states in which active and passive adaptive management differed. Our results emphasize that spending resources on monitoring is only optimal when the expected benefits of the options being considered are similar and when the pay‐off for learning about their benefits is large.  相似文献   
217.
Abstract: Ecosystem management (EM) offers a means to address multiple threats to marine resources. Despite recognition of the importance of stakeholder involvement, most efforts to implement EM in marine systems are the product of top‐down regulatory control. We describe a rare, stakeholder‐driven attempt to implement EM from the bottom up in San Juan County, Washington (U.S.A.). A citizens advisory group led a 2‐year, highly participatory effort to develop an ecosystem‐based management plan, guided by a preexisting conservation‐planning framework. A key innovation was to incorporate social dimensions by designating both sociocultural and biodiversity targets in the planning process. Multiple obstacles hindered implementation of EM in this setting. Despite using a surrogate scheme, the information‐related transaction costs of planning were substantial: information deficits prevented assessment of some biodiversity targets and insufficient resources combined with information deficits prevented scientific assessment of the sociocultural targets. Substantial uncertainty, practical constraints to stakeholder involvement, and the existence of multiple, potentially conflicting, objectives increased negotiation‐related costs. Although information deficits and uncertainty, coupled with underinvestment in the transaction costs of planning, could reduce the long‐term effectiveness of the plan itself, the social capital and momentum developed through the planning process could yield unforeseeable future gains in protection of marine resources. The obstacles we identified here will require early and sustained attention in efforts to implement ecosystem management in other grassroots settings.  相似文献   
218.
Short‐term surveys are useful in conservation of species if they can be used to reliably predict the long‐term fate of populations. However, statistical evaluations of reliability are rare. We studied how well short‐term demographic data (1999–2002) of tartar catchfly (Silene tatarica), a perennial riparian plant, projected the fate and growth of 23 populations of this species up to the year 2010. Surveyed populations occurred along a river with natural flood dynamics and along a regulated river. Riparian plant populations are affected by flooding, which maintains unvegetated shores, while forest succession proceeds in areas with little flooding. Flooding is less severe along the regulated river, and vegetation overgrowth reduces abundance of tartar catchfly on unvegetated shores. We built matrix models to calculate population growth rates and estimated times to population extinction in natural and in regulated rivers, 13 and 10 populations, respectively. Models predicted population survival well (model predictions matched observed survival in 91% of populations) and accurately predicted abundance increases and decreases in 65% of populations. The observed and projected population growth rates differed significantly in all but 3 populations. In most cases, the model overestimated population growth. Model predictions did not improve when data from more years were used (1999–2006). In the regulated river, the poorest model predictions occurred in areas where cover of other plant species changed the fastest. Although vegetation cover increased in most populations, it decreased in 4 populations along the natural river. Our results highlight the need to combine disturbance and succession dynamics in demographic models and the importance of habitat management for species survival along regulated rivers. Precisión de Datos Demográficos de Corto Plazo en la Proyección del Destino de Poblaciones a Largo Plazo  相似文献   
219.
Abstract: Worldwide efforts have concentrated on developing monitoring methods that would enhance the assessment of progress toward achieving the 2010 conservation objectives of the Convention on Biological Diversity. Threat reduction assessment is one such method. It provides an indirect measure of the effects of a conservation project by evaluating changes in human‐induced direct threats to protected areas. We applied modified threat reduction assessments and the 2008 International Union for Conservation of Nature standardized lexicon for classification of threats to Horsh Ehden and Al‐Shouf Cedar nature reserves in Lebanon. Our goal was in part to test the suitability of this tool for improving monitoring and management effectiveness of protected forests in Lebanon. In Horsh Ehden, composite threats decreased by 24% from 1997 to 2002, and then increased from 2002 to 2009 by 78% in the core area of the reserve and by 118% in the reserve's buffer zone (surrounds core area, conservation and recreational activities allowed). In Al‐Shouf Cedar reserve threats decreased by 51% from 2006 to 2009. Management teams from both reserves have integrated the use of this method to prioritize actions for new management plans. We believe that in Lebanon and other countries with limited resources and weak monitoring programs or that are experiencing political instability threat reduction assessments could be used to improve the effectiveness of protected areas management.  相似文献   
220.
Abstract: Networks of sites of high importance for conservation of biological diversity are a cornerstone of current conservation strategies but are fixed in space and time. As climate change progresses, substantial shifts in species’ ranges may transform the ecological community that can be supported at a given site. Thus, some species in an existing network may not be protected in the future or may be protected only if they can move to sites that in future provide suitable conditions. We developed an approach to determine appropriate climate‐change adaptation strategies for individual sites within a network that was based on projections of future changes in the relative proportions of emigrants (species for which a site becomes climatically unsuitable), colonists (species for which a site becomes climatically suitable), and persistent species (species able to remain within a site despite the climatic change). Our approach also identifies key regions where additions to a network could enhance its future effectiveness. Using the sub‐Saharan African Important Bird Area (IBA) network as a case study, we found that appropriate conservation strategies for individual sites varied widely across sub‐Saharan Africa, and key regions where new sites could help increase network robustness varied in space and time. Although these results highlight the potential difficulties within any planning framework that seeks to address climate‐change adaptation needs, they demonstrate that such planning frameworks are necessary, if current conservation strategies are to be adapted effectively, and feasible, if applied judiciously.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号