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- 1. The movement of organisms and dispersal of propagules is fundamental to the maintenance of populations over time. However, the existence of barriers, created through the spatial configuration of habitats, may significantly affect dispersal patterns and thus influence community dynamics and resource sustainability.
- 2. Within marine environments unstructured or open habitats may form partial or complete ecological barriers due to elevated risk of predation or physical stresses associated with them. The existence and effects of such barriers may be of particular importance when considering the establishment of marine protected areas with a fisheries enhancement focus.
- 3. In this paper, the spillover of post‐settlement queen conch (Strombus gigas) from a protected area in the Turks and Caicos Islands is investigated. It is hypothesized that the reserve boundaries overlap with a series of shallow, sand habitats that effectively enclose the protected population, reducing the spillover of conch into the adjacent fished areas.
- 4. To test this, density gradient maps for juvenile and adult conch populations were constructed using underwater visual survey data at 68 sites within and surrounding the protected area. These maps illustrate very low densities coinciding with poor, shallow sand habitats along the two marine boundaries of the reserve where spillover is expected to take place.
- 5. These sand habitats are thought to create ecological barriers to a slow, sedentary gastropod largely due to their shallowness (physical stresses of solar exposure or anoxia) and lack of food reducing the tendency of individuals to move across these areas, despite the 10‐times higher density of adult queen conch observed in the protected area compared with outside.
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Pathogen spread or ‘spillover’ can occur when heavily infected, domestic hosts interact with closely-related wildlife populations. Commercially-produced bumble bees used in greenhouse pollination often have higher levels of various pathogens than wild bumble bees. These pathogens may spread to wild bees when commercial bees escape from greenhouses and interact with their wild counterparts at nearby flowers. We examined the prevalence of four pathogens in wild bumble bee populations at locations near and distant to commercial greenhouses in southern Ontario, Canada. Bumble bees collected near commercial greenhouses were more frequently infected by those pathogens capable of being transmitted at flowers (Crithidia bombi and Nosema bombi) than bees collected at sites away from greenhouses. We argue that the spillover of pathogens from commercial to wild bees is the most likely cause of this pattern and we discuss the implications of such spillover for bumble bee conservation. 相似文献
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选取产业技术效率作为外溢获利的衡量指标,以技术效率作为因变量构建随机前沿模型,以农业生产性服务业发展水平、区域距离、政策配套环境及农业价值整合力等要素作为引入因子交叉项,检验农业生产性服务业在上述各类因素方面对农业技术外溢获取能力影响与实现渠道。结果表明,农业生产性服务业与农业技术外溢获利能力提升呈正相关,但后者能力提升与地理差距因素呈负相关,并受制于政策环境因素,二者存在显著利润差,需进一步从人力资本要素投入及政策配套和准入条件上予以优化。 相似文献
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引用政府补偿政策干预对企业与农户合作模式进行重复博弈分析。针对政府干预下的企业与农户行为特征,借用知识溢出模型得出相应的效用函数,并通过均衡分析,得出政府促进企业与农户合作的策略:第一,达成合作的策略需要保障贴现因子在特定的区间内波动;第二,对于政府补偿政策而言,需要增强农户与企业沼气能源使用率,减小博弈双方知识储备差异的,通过政府资金支持和技术支持增强沼气能源技术的追赶能力,同时合理的规划养殖企业和农户之间地理位置的距离等方式保证合作进行。 相似文献
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瘤胃微生物将一些ATP用来维持代谢,剩余的ATP用来进行储备碳水化合物合成和能量溢出(进行无效循环并产热),因此,瘤胃微生物蛋白质合成效率较低。瘤胃原虫贮存的碳水化合物占绝大部分。在一些细菌纯培养实验中发现有能量溢出,最近研究发现在混合瘤胃菌群中也能发生能量溢出。通过精确测定碳水化合物贮存和能量溢出的量,以及二者对微生物生长效率的影响,可以预测微生物蛋白质产量,制定提高瘤胃微生物蛋白质生产效率的措施。综述了瘤胃微生物能量溢出和糖原储备规律方面的研究进展,以期为估测微生物蛋白质合成量,提高饲料蛋白质利用效率提供参考。 相似文献
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根据投资者情绪是股票价格形成重要影响因素这一研究观点,围绕投资者情绪是否构成系统性风险及其对不同类型股票的差异化影响,运用我国股市交易数据进行的实证研究结果表明,投资者情绪不构成股市的系统性风险,但对不同市值的股票有着差异化的影响,随着股票的“投机性”增加,投资者情绪对其影响也增大。此外,投资者情绪会削弱股票收益与其波动的正相关性,且对于“投机性”越高的股票,这一影响也越大。 相似文献
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金融资产收益率波动是资产定价和金融风险管理的核心部分,而跳跃是收益率波动中的重要组成部分。基于修正z一检验,本文检测识别我国股市波动中跳跃行为,并且研究了跳跃的时序特征,统计结果表明,在市场大波动时期,和连续成份相比,跳跃对于波动率具有极其重要的贡献。建立包含跳跃的已实现波动率非齐次自回归模型,在波动模型中纳入滞后绝对日收益率和杠杆效应预测股指收益率波动。实证分析结果显示,对于短期的波动预测,包含跳跃和两种影响因素的波动模型表现最好,然而对于提前1月的长期预测,跳跃和连续波动成份分离模型预测明显优于其它模型,这些事实说明跳跃对股指波动率预测具有重要的影响,好坏消息对波动率非对称性具有短期显著影响,而对长期水平的波动率预测影响不显著。 相似文献
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运用随机Kernel密度函数,将空间因素引入研究框架,对1998~2005年广西县域收入分布演进进行分析。结果表明,广西县域收入差距具有持续稳固的特点;区域收入分布演进总体呈单峰俱乐部收敛,表现出多俱乐部收敛的趋势,贫穷俱乐部的规模远大于其他较高收入俱乐部;县域收入分布演进明显具有空间依赖性,近邻效应显著,邻域富裕的县域向较高收入水平演进的机会较大,并且导致县域经济增长表现为局部空间俱乐部收敛特征。 相似文献