Spatio-temporal dynamics of willow beetle (Phratora vulgatissima) in short-rotation coppice willows grown as monocultures or a genetically diverse mixture

1 Phratora vulgatissima (Chrysomelidae) is the major pest of short-rotation coppice willows in the U.K., capable of causing severe defoliation in monoculture plantations. As this beetle shows feeding preferences between willow clones, knowledge of the spatio-temporal dynamics of P. vulgatissima is needed in order to assess the effects of mixed clonal plantings on the management of this pest. 2 Distribution patterns of adult P. vulgatissima were monitored over a season at a spatial scale of every tree or every other tree in single clone plantings (monocultures) of three willow clones and in a regular row mixture of these clones. 3 Distribution indices (deviation from Complete Spatial Randomness) demonstrated that P. vulgatissima adults were spatially aggregated on favourable clones in the monocultures and the mixture. The degree of aggregation (measured by the k-parameter of the negative binomial) differed between willow clones. Beetles were highly aggregated at the start of the season, but less so later. 4 Dispersal studies of P. vulgatissima adults over time showed a pattern of beetle infestation along rows of the preferred clones in a regularly structured mixture. In the monocultures, movement was less directional. 5 Plantation design offers some potential for more effective non-chemical pest management for P. vulgatissima. Monitoring of the pest must take account of our findings that adults occur in mobile aggregations.     

Contrasting alternative hypotheses about rodent cycles by translating them into parameterized models

Ecologists working on population cycles of arvicoline (microtine) rodents consider three ecological mechanisms as the most likely explanations of this long-standing puzzle in population ecology: maternal effects, interaction with specialist predators, and interaction with the food supply. Each of these hypotheses has now been translated into parameterized models, and has been shown to be capable of generating second-order oscillations (that is, population cycles driven by delayed density dependence). This development places us in a unique situation for population ecology. We can now practice "strong inference" by explicitly and quantitatively comparing the predictions of the three rival hypotheses with data. In this review, we contrast the ability of each hypothesis to explain various empirically observed features of rodent cycles, with a particular emphasis on the well-studied case of Microtus agrestis and other small rodents in Fennoscandia (Finland, Sweden and Norway). Our conclusion is that the current evidence best supports the predation hypothesis.     

Economics of Willow Pyrolysis After Phytoextraction

The Campine is a vast cross-border area in the northeast of Belgium and southeast of the Netherlands that has been contaminated with heavy metals. As traditional excavation techniques are too expensive, phytoremediation is preferred. Economically viable conversion techniques for the biomass are researched in order to lower reclamation costs and to guarantee the income of the local farmers, mainly cultivating roughage for dairy cattle rearing. Energy generation by means of pyrolysis of willow from short-rotation coppice seems to be very interesting. This article aims to search for the maximum possible biomass price so that the net present value of the profits stemming from energy conversion based on pyrolysis is at least positive.     

Host tolerance does not impose selection on natural enemies

Coevolution between hosts and their natural enemies is believed to operate through the evolution of resistance traits. Although the importance of tolerance to natural enemies as an alternative defensive strategy has been recognized, there is still no consensus about the possible role of host tolerance in the evolutionary outcome of the interaction. Here, using bioassay experiments, we tested the hypothesis that variation in host tolerance among selected plant genotypes could impose a selection pressure upon a specialist herbivore. Tolerance did not affect herbivore larvae survival, weight gain, efficiency of food consumption, total food consumption, developmental time and adult mass. These results therefore do not support the hypothesis that host tolerance could affect natural enemy performance. However, resistance did negatively affect herbivore larva survival. Genetic variation in herbivore larva survival was detected, thus suggesting the potential for a coevolutionary response. Our results indicate that host tolerance would reduce opportunities for a coevolutionary response by the natural enemies of the host. Contrary to predictions from previous models, our results suggest that host tolerance may constitute an evolutionarily unstable defensive strategy.     

不同邻居物种的基因型多样性对冷蒿生长的影响

植物物种多样性与基因型多样性对群落的结构和功能具有重要的生态作用,近年来植物基因型多样性对植物间相互作用的影响已成为研究者关心的重要科学问题。实验选择退化草原优势种冷蒿(Artemisia frigida)为目标植物,稳定群落建群种羊草(Leymus chinensis)和群落伴生种洽草(Koeleria cristata)为邻居植物,来研究基因型多样性不同的邻居植物对冷蒿生长表现(株高、地上生物量、地下生物量和总生物量)的影响,并通过测量植物相对竞争强度及邻居植物性状变异来进一步探究邻居植物基因型多样性对目标植物影响的内在机制。结果表明:(1)邻居物种为羊草时,基因型多样性对冷蒿的生长表现影响显著,当邻居为6基因型时,冷蒿的株高、地上生物量以及总生物量显著低于单基因型和3基因型时的表现(P0.05),且相对竞争强度高于其他两种处理;而邻居物种为洽草时,基因型多样性对冷蒿所有观测指标以及相对竞争强度的影响均不显著(P0.05)。(2)利用主成分分析法来分析基因型多样性对自身性状变异的影响发现,邻居物种为羊草时,基因型多样性对性状变异响应显著,主要表现为3基因型时,羊草种群的株高、总生物量、地上生物量显著高于单基因型时的表现(P0.05);而邻居物种为洽草时,基因型多样性对性状变异影响不显著(P0.05)。(3)邻居物种为羊草时,羊草总生物量和比叶面积与冷蒿的地上生物量和总生物量呈显著负相关(P0.05);邻居物种为洽草时,洽草各性状与冷蒿性状间无显著相关性(P0.05)。实验结果揭示,基因型多样性对目标植物生长的效应受邻居植物种类的影响,稳定群落建群种羊草高基因型组合能显著抑制冷蒿的生长,这可能与羊草高基因型多样性种群性状变异大且对冷蒿有较高的相对竞争强度有关。所得结果为建群种基因型多样性影响种间相互作用提供了实验证据,为草原的合理利用和保护提供了理论指导。     

内蒙古昆虫物种多样性分布格局及其机制

物种多样性的地理分布格局及其机制是宏生态学和生物地理学的核心问题之一。区域尺度与局域尺度的影响因素, 如温度、降水、海拔变化、生境过滤、捕食、竞争与互惠等, 共同影响昆虫物种多样性的分布格局。然而, 迄今为止少有研究同时讨论不同尺度驱动因子对昆虫多样性地理分布格局的影响。本文基于内蒙古自治区86个旗县的昆虫多样性数据, 结合各地年平均气温、年降水量、古气候变化、海拔变化及植物多样性, 探讨昆虫物种多样性分布格局及其主要驱动因子。结果发现内蒙古昆虫多样性主要受到植物多样性与海拔变化的影响, 而气候因子对昆虫物种多样性的影响并不大。这一结果表明种间关系(食物多样性)与生境异质性可能对内蒙古昆虫多样性的分布格局起着主导作用。