神农架地区河岸带中领春木种群数量特征与空间分布格局

 东亚特有珍稀濒危植物领春木(Euptelea pleiospermum)在神农架地区集中分布于河岸带中。为初步探讨领春木在河岸带集中分布的成因和维持机制, 在神农架地区4条河流——沿渡河、香溪河、南河和堵河的河岸带, 共设置了30个样方(20 m × 30 m), 从种群的大小级结构、静态生命表、存活曲线、空间分布格局及其动态5个方面分析了神农架地区河岸带中领春木种群的数量特征与空间分布格局。结果表明: 1) 幼龄期个体缺乏, 中龄期个体相对丰富, 老龄期个体数量稀少。纺锤型的大小级结构表明种群属于衰退型, 但是以萌蘖为主要更新方式使其种群在较长一段时间内得以维持; 2)现存的Ⅰ、Ⅱ级个体数少, 导致静态生命表中Ⅰ、Ⅱ级个体死亡率出现负值, 自疏现象造成第Ⅳ级个体出现死亡率高峰, 由于接近实际寿命, 在第Ⅶ级死亡率达到最高; 3) 虽然其幼苗存活率较低, 但由于其幼树的存活率较高, 其存活曲线接近DeeveyⅠ型, 表明该地区河岸带的环境条件较适宜领春木种群的生长; 4) 空间分布格局总体为聚集分布, 这与大多数珍稀植物种群一致。人为干扰和自然环境影响其分布格局, 使种群由聚集分布向随机分布发展。因此使领春木种群在河岸带中沿海拔呈现“一带多岛”现象; 5) 从幼龄期到中龄期再到老龄期, 不同发育阶段的领春木种群的分布格局由聚集分布逐渐变为随机分布。但由于分布格局受种群本身生物学特性、自然环境因素(如坡向和海拔)和人为干扰的影响, 领春木在不同河岸带中的分布格局有所差异。     

Contribution of terrestrial invertebrates to the annual resource budget for salmonids in forest and grassland reaches of a headwater stream

1. The annual input, contribution to the diet of salmonids, and quantitative input of terrestrial invertebrates to four reaches with contrasting forest (n=2) and grassland riparian vegetation (n=2) were compared in a Japanese headwater stream.
2. The annual input of terrestrial invertebrates falling into the forest reaches (mean±1 SE=8.7×10³±0.3×10³ mg m^?2 year^?1) was 1.7 times greater than that in the grassland reaches (5.1×10³±0.8×10³ mg m^?2 year^?1), with clear seasonality in the daily input of invertebrates in both vegetation types. The daily input, however, differed between the vegetation types only in summer, when it rose to a maximum in both vegetation types.
3. Fish biomass also differed among the seasons in both vegetation types, being less in the grassland reaches. The contribution of terrestrial invertebrates to the salmonid diet in the forest and grassland reaches was 11 and 7% in spring, 68 and 77% in summer, 48 and 33% in autumn, and 1 and 1% in winter, respectively. The prey consumption rate of fish, which was similar between the vegetation types, increased with stream temperature and was highest in summer. Terrestrial invertebrates supported 49% (mean±1 SE=5.3×10³±0.4×10³ mg m^?2 year^?1) of the annual, total prey consumption (10.9×10³±1.7×10³ mg m^?2 year^?1) by salmonids in the forest and 53% (2.0×10³±0.3×10³ mg m^?2 year^?1) (3.8×10³±0.6×10³ mg m^?2 year^?1) in the grassland reaches.
4. Salmonids were estimated to consume 51 and 35% of the annual total (falling plus drift) input of terrestrial invertebrates in the forest and grassland reaches, respectively. The input of terrestrial invertebrates by drift, however, was almost equal to the output in both vegetation types, suggesting that the reach‐based, in‐stream retention of terrestrial invertebrates almost balanced these falling in.
5. Difference in the riparian vegetation, which caused spatial heterogeneity in the input of terrestrial invertebrates, could play an important role in determining the local distribution of salmonids.     

A Coupled Ecosystem-Climate Model for Predicting the Methane Concentration in the Archean Atmosphere

A simple coupled ecosystem-climate model is described that canpredict levels of atmospheric CH₄, CO₂, and H₂during the Late Archean, given observed constraints on Earth'ssurface temperature. We find that methanogenic bacteria shouldhave converted most of the available atmospheric H₂ intoCH₄, and that CH₄ may have been equal in importance to CO₂ as a greenhouse gas. Photolysis of this CH₄ may have produced a hydrocarbon smog layer that would have shielded the surface from solar UV radiation. Methanotrophic bacteria would have consumed some of the atmospheric CH₄,but they would have been incapable of reducing CH₄ to modern levels. The rise of O₂ around 2.3 Ga would have drastically reduced the atmospheric CH₄ concentrationand may thereby have triggered the Huronian glaciation.     

Prey use by web-building spiders: stable isotope analyses of trophic flow at a forest-stream ecotone

A forest-stream trophic link was examined by stable carbon isotope analyses which evaluated the relationship of aquatic insects emerging from a stream to the diets of web-building spiders. Spiders, aquatic and terrestrial prey, and basal resources of forest and stream food webs were collected in a deciduous forest along a Japanese headwater stream during May and July 2001. The ¹³C analyses suggested that riparian tetragnathid spiders relied on aquatic insects and that the monthly variation of such dependence is partly associated with the seasonal dynamics of aquatic insect abundance in the riparian forest. Similarly, linyphiid spiders in the riparian forest exhibited ¹³C values similar to aquatic prey in May. However, their ¹³C values were close to terrestrial prey in both riparian and upland (150m away from the stream) forests during June to July, suggesting the seasonal incorporation of stream-derived carbon into their tissue. In contrast, araneid spiders relied on terrestrial prey in both riparian and upland forests throughout the study period. These isotopic results were consistent with a previous study that reported seasonal variation in the aquatic prey contribution to total web contents for each spider group in this forest, implying that spiders assimilate trapped prey and that aquatic insect flux indeed contributes to the energetics of riparian tetragnathid and linyphiid spiders.     

Parasites: Small Players with Crucial Roles in the Ecological Theater

Effective management of our natural resources requires an understanding of ecosystem structure and function; effectively, an ecosystem-based approach to management. Parasites occur, albeit cryptically, in almost all ecosystems, yet they are usually neglected in studies on populations and communties of organisms. Parasites can have pronounced or subtle effects on hosts affecting host behavior, growth, fecundity, and mortality. Furthermore, parasites may regulate host population dynamics and influence community structure. Many parasites have complex life cycles and depend for transmission on the presence of a variety of invertebrate and vertebrate intermediate hosts. Often transmission involves predator–prey interactions. Thus, parasites reflect the hosts position in the food web and are indicative of changes in ecosystem structure and function. Parasites can provide information on population structure, evolutionary hypotheses, environmental stressors, trophic interactions, biodiversity, and climatic conditions. I use examples from diverse freshwater and marine systems to demonstrate that parasites should be incorporated into research and monitoring programs to maximize information gathered in ecosystem-based studies and resource management.Supplementary Tables 3, 4, 5, 6 and additional references for this article are available for viewing by subscribers only at     

Question of Mutual Security: Exploring Interactions between the Health of Coral Reef Ecosystems and Coastal Communities

Coral reefs are the worlds most celebrated indicators of ocean health. While the global trajectory of coral reef degradation is now well documented, and the accompanying loss of economic benefits increasingly demonstrated, the consequences in terms of human health have been largely ignored. Reefs provide a wide array of benefits to humans, contributing most directly to the health of subsistence fishing communities located on adjacent coasts and islands. Interactions between human and marine ecosystem health are complex, bidirectional and nonlinear. We draw on a broad range of data and experience to identify key links in the ecological chain from the coral polyp to the human society. Our conclusions are that humans are components of coral reef ecosystems, few studies of reef health incorporate human health, few data are available to quantify the health services reefs provide to people, and human health security is essential to the preservation of coral reef ecosystems.     

Diversity–productivity–stability relationship in freshwater ecosystems: Whole-systemic view of all trophic levels

The idea of the diversity–productivity relationship in ecology was originated by Charles Darwin more than 100years ago and was highlighted by McNaughton in 1993. There have been extensive studies on this relationship, mostly conducted in grasslands. Many studies assert that a high level of biodiversity leads to high primary productivity, in accord with Darwin. However, these studies have mostly been done in grasslands (primary producer) and do not take into account effects from other trophic levels. The possibility remains that the positive diversity–production relationship does not hold in other types of ecological systems and that multitrophic effects influence and modify the relationship. In the present study, the diversity–productivity relationship is examined for freshwater foodwebs, including whole trophic compartments, by using indices of diversity and productivity more suitable for a whole systemic study on ecological systems. It seems that there are two trends in the relationship: productivity increases with the increase of diversity in ecosystems when diversity is small, and decreases with diversity in ecosystems when diversity is large. The first trend may be due to nutrient-limiting characteristics and the second trend may be due to photosynthetically active radiation–limiting characteristics. Also, both higher trophic and whole-systemic productivities are found to increase relative to primary productivity with the increase of diversity. Stability indices introduced previously, combined with the present results, reveal a positive correlation between relative productivity and stability in freshwater foodwebs, including all trophic compartments.     

Equivocal evidence for a change in balance between selfing and pollinator-mediated reproduction in annual Brassicaceae growing along a rainfall gradient

Because many plants ensure their reproductive success using some level of self-fertilization, it is predicted that the balance between pollinator-mediated pollen transfer and autonomous selfing will be correlated with habitat harshness and pollinator activity. To study these correlations, we used three annual species that differ in their self-incompatibility and compared their reproductive success in the form of fruit production and seed viability, with and without pollinators, along a rainfall gradient and in relation to pollinator activity. We found that pollinator activity decreased with increasing aridity. Although the reproductive success in the absence of pollinators fitted the species’ level of self-incompatibility, no clear trend was detected between pollinator visits or site harshness and relative reproductive success. Only one of the species, Sinapis alba, showed a consistent increase in autonomous selfing with both increased aridity and decreased pollinator visits, a finding that was supported by an increase in the viability of seeds produced in the absence of pollinators. Nevertheless, unlike our prediction, the absolute number of seeds produced per S. alba flower increased with aridity. Our overall findings suggest that despite decreasing pollinator abundance and diversity with increasing aridity, the reproductive success of annual species, even of those with high self-incompatibility, remains relatively high. Although there may be several mechanisms governing these results, the overall constant seed production despite environmental uncertainties may be part of the mechanism by which plants in arid ecosystems buffer environmental variations.     

Climate change,woodpeckers, and forests: Current trends and future modeling needs

The structure and composition of forest ecosystems are expected to shift with climate‐induced changes in precipitation, temperature, fire, carbon mitigation strategies, and biological disturbance. These factors are likely to have biodiversity implications. However, climate‐driven forest ecosystem models used to predict changes to forest structure and composition are not coupled to models used to predict changes to biodiversity. We proposed integrating woodpecker response (biodiversity indicator) with forest ecosystem models. Woodpeckers are a good indicator species of forest ecosystem dynamics, because they are ecologically constrained by landscape‐scale forest components, such as composition, structure, disturbance regimes, and management activities. In addition, they are correlated with forest avifauna community diversity. In this study, we explore integrating woodpecker and forest ecosystem climate models. We review climate–woodpecker models and compare the predicted responses to observed climate‐induced changes. We identify inconsistencies between observed and predicted responses, explore the modeling causes, and identify the models pertinent to integration that address the inconsistencies. We found that predictions in the short term are not in agreement with observed trends for 7 of 15 evaluated species. Because niche constraints associated with woodpeckers are a result of complex interactions between climate, vegetation, and disturbance, we hypothesize that the lack of adequate representation of these processes in the current broad‐scale climate–woodpecker models results in model–data mismatch. As a first step toward improvement, we suggest a conceptual model of climate–woodpecker–forest modeling for integration. The integration model provides climate‐driven forest ecosystem modeling with a measure of biodiversity while retaining the feedback between climate and vegetation in woodpecker climate change modeling.     

The role of fish life histories in allometrically scaled food‐web dynamics

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