Natural disturbance and treefalls in a pine-oak forest on the Peninsula of Baja California,Mexico

The magnitude of natural disturbances by treefalls and their spatial occurrence were studied in a pine-oak forest of Sierra de La Laguna, located at the southern part of the Peninsula of Baja California in Mexico.Twenty transects covering 4 ha, perpendicular to north- and south-facing slopes were sampled. The percentages of rocky outcrops, slope, orientation, and gap size created by treefalls were recorded. The mode of tree death, treefall direction, trunk length, and basal diameter were also measured. Data were analyzed using principal component analysis, one-way ANOVA, multiple comparison tests by contrasts, and chi-square independence tests.Results suggest that exogenous disturbances have an important effect in this community. A mean number of 80 gaps per ha was recorded comprising 18.1% of the observed area. Gap sizes were fitted to a lognormal distribution as 2.3±1.4 and patches were found to be created by single treefalls. Analysis of dead material shows that there are significant differences between numbers of fallen trees on N vs S facing slopes, and that forms of dead trees are significantly associated with species. Snapped trees represent 39.5% of treefalls, dead standing trees 26.4%, uprooted trees 20.5% and cut-down trees 0.9%. The frequency of occurrence of various forms of the dead trees suggests that the cause of mortality is primarily due to the high incidence of tropical hurricanes, and secondly to the combined effect of wind and natural fire which occurs during the rainy summer season.     

Occurrence of Acremonium endophytes in wild populations of Lolium spp. in European countries and a relationship between level of infection and climate in France

Infection with endophytic fungi (Acremonium spp.) was detected in wild populations of Lolium spp. from 15 of 20 European countries. Of 523 populations examined, 38% contained no infection, 48% contained 1–50% infection and 14% contained 51–100% infection. Level of infection was slightly but significantly associated with abundance of Lolium in the sward. For data from France, significant correlations were obtained between level of infection and five climate variables; the highest correlations were with evapotranspiration (0.66, P < 0.001) and water supply deficit (-0.66, P < 0.001). A model established using multiple regression analysis and incorporating five climatic variables, accounted for 56% of total variation; water supply deficit alone accounted for 43%. These climatic variables were shown by geostatistical analysis to account for a spatial structure in infection level. Groups of Lolium populations with a high level of infection were located mostly in Mediterranean regions, where stress from summer drought is common.     

西南喀斯特石漠化生态系统土壤有机碳分布特征及其影响因素

喀斯特石漠化已成为制约我国西南地区社会经济可持续发展最严重的生态地质环境问题,其恢复重建已成为我国社会经济建设中一项重要内容。土壤有机碳作为土壤质量评价的重要指标,可以综合反映土地生产力、环境健康功能,另一方面土壤有机碳也间接影响了陆地生物碳库,是陆地生态系统碳平衡的主要因子,它的转化和积累变化直接影响全球碳循环动态,已成为生态科学领域研究的热点之一。系统的总结了西南喀斯特石漠化地区不同土地覆被/土地利用、不同等级石漠化环境土壤有机碳的空间和季节分布特征。结合前人研究成果,进一步分析了影响喀斯特石漠化地区土壤有机碳分布的自然(气候、地形与土壤性质、植被等)和人为(土地覆被/土地利用变化、农业管理措施等)各因素,并提出增加喀斯特石漠化地区土壤有机碳含量的对策。研究结果为喀斯特石漠化退化生态系统恢复重建、石漠化地区土壤综合利用、增加碳截存应对全球碳循环减源增汇等提供了重要的科学参考。     

Forbidden versus permitted interactions: Disentangling processes from patterns in ecological network analysis

Several studies have identified the tendency for species to share interacting partners as a key property to the functioning and stability of ecological networks. However, assessing this pattern has proved challenging in several regards, such as finding proper metrics to assess node overlap (sharing), and using robust null modeling to disentangle significance from randomness. Here, we bring attention to an additional, largely neglected challenge in assessing species’ tendency to share interacting partners. In particular, we discuss and illustrate with two different case studies how identifying the set of “permitted” interactions for a given species (i.e. interactions that are not impeded, e.g. by lack of functional trait compatibility) is paramount to understand the ecological and co‐evolutionary processes at the basis of node overlap and segregation patterns.     

Notes on compositional diversity

This paper tries to show some ways and means of simple (binary) modelling, whereby diversity can be interconnected with other attributes of a community. A new type of scaling (called characteristic scaling) is introduced for further use.     

密度制约作用对箭叶淫羊藿有性繁殖时期形态特征的影响

运用回归分析和非参数检验方法，研究了箭叶淫羊藿(Epimedium sagittatum)在有性繁殖的三个时期克隆片段密度对其各个形态特征的影响，以揭示其资源和繁殖投资情况。结果表明：箭叶淫羊藿在三个有性繁殖期间克隆片段密度对其各个形态特征的影响显著。从回归分析的R2指数来看，其克隆片段密度增大对三个生长时期的制约作用是由弱到强，同时在有性繁殖期间随克隆片段密度的增加其资源投资趋向于有性繁殖；从非参数检验结果来看，有性繁殖期间箭叶淫羊藿明显增加其叶数、叶宽等来获取更多的资源用于提高其繁殖能力，以取得生存。     

棘冠海星暴发及其对珊瑚礁的生态影响研究进展

棘冠海星的反复暴发是导致印度-太平洋区域珊瑚礁生态系统退化的最主要原因之一。然而，我国对棘冠海星的研究非常有限。本文综述了国内外关于棘冠海星及其暴发的生态影响和应对策略的研究进展，得出以下主要结论：1）雌性棘冠海星个体每年产卵数量高达50万-2亿个，环境因素变化只要导致幼虫和幼体存活率的轻微提高，成体就将得到大量补充；2）棘冠海星暴发的阈值为1000-1500个/km²，暴发周期为10-27 a，每次暴发持续1-10 a，最终可能以"种群集体感染疾病而崩溃"结束；3）棘冠海星暴发对印度洋及太平洋东部和北部珊瑚礁的破坏性非常小，却直接导致太平洋的西部和南部珊瑚礁90%以上的珊瑚死亡，并通过改变珊瑚群落组成、减少珊瑚和鱼类多样性而对珊瑚礁产生间接影响；4）关于棘冠海星暴发原因的假说中"陆地营养物质输入假说"和"捕食者过度捕捞假说"得到了最普遍的认可，但都不能解释所有的暴发事件；5）应对棘冠海星暴发的主要策略有改善水质、设立保护区、投放天敌和人工清理等，其中人工清理是最直接有效的策略，但迄今并没有发现可长期抑制棘冠海星暴发的方法。因此，急需加强对棘冠海星的深入研究，探查其暴发的根本原因和对策。