Getting cosy in freshwater: Assumed to be brackish pike are not so brackish after all

Pike (Esox lucius) occupy coastal streams and rivers of the Baltic Sea, where they attain large sizes (>5 kg). These large sizes are perhaps due to the fact that they can tolerate relatively high salinities and can thus forage in the nearby more productive brackish environments. In an attempt to quantify the extent to which pike utilise brackish environments, and to provide some insight into the underlying causes for brackish water migrations, we tagged 30 pike from a western Baltic river with acoustic transmitters and were able to track 21 individuals for 1 year. Based on experienced from local anglers, this population was assumed to be brackish in nature, where individuals underwent freshwater migrations to spawn. Our findings however suggest that the smallest and most active individuals make short exits into brackish waters and do so on rare occasions. Our results further indicate that neither sex nor size is related to activity level. We suggest that these patterns reflect two distinct behaviours—active and passive—and that large pike can be supported by the food availability in the river, without the need to venture into coastal zones, thus defying the conventional view that Baltic pike are all brackish in nature.     

Shifts in microbial diversity through land use intensity as drivers of carbon mineralization in soil

Land use practices alter the biomass and structure of soil microbial communities. However, the impact of land management intensity on soil microbial diversity (i.e. richness and evenness) and consequences for functioning is still poorly understood. Here, we addressed this question by coupling molecular characterization of microbial diversity with measurements of carbon (C) mineralization in soils obtained from three locations across Europe, each representing a gradient of land management intensity under different soil and environmental conditions. Bacterial and fungal diversity were characterized by high throughput sequencing of ribosomal genes. Carbon cycling activities (i.e., mineralization of autochthonous soil organic matter, mineralization of allochthonous plant residues) were measured by quantifying ¹²C- and ¹³C-CO₂ release after soils had been amended, or not, with ¹³C-labelled wheat residues. Variation partitioning analysis was used to rank biological and physicochemical soil parameters according to their relative contribution to these activities. Across all three locations, microbial diversity was greatest at intermediate levels of land use intensity, indicating that optimal management of soil microbial diversity might not be achieved under the least intensive agriculture. Microbial richness was the best predictor of the C-cycling activities, with bacterial and fungal richness explaining 32.2 and 17% of the intensity of autochthonous soil organic matter mineralization; and fungal richness explaining 77% of the intensity of wheat residues mineralization. Altogether, our results provide evidence that there is scope for improvement in soil management to enhance microbial biodiversity and optimize C transformations mediated by microbial communities in soil.     

物种多样性-生态系统功能关系的影响因素

物种多样性和生态系统功能的关系是生态学研究的重要科学问题.综述影响物种多样性和生态系统功能关系的因素,可为今后的相关研究提供借鉴和参考.物种多样性-生态系统功能之间的关系受多种因素影响,实验类型的不同引起物种多样性-生态系统功能关系的改变;小规模时空尺度下的人工调控实验结论对于区域范围的普遍意义具有较大的局限性;天然草...     

Herbivory, pathogens, and epiphylls in Araucaria Forest and ecologically-managed tree monocultures

Over the last centuries, natural forests have been replaced by extensive and homogeneous tree monocultures that cause strong impacts on ecological interactions and ecosystem processes. We expect, however, that ecologically-sustainable management practices can help to mitigate these effects. This study investigates how the replacement of Araucaria Forest by ecologically-managed tree monocultures affects leaf damage patterns produced by external chewers, internal chewers, leaf miners, galling insects, and pathogens, as well as the incidence of epiphylls. The study was performed in the São Francisco de Paula National Forest (southern Brazil) on 12 1-ha plots of Araucaria Forest and ecologically managed plantations of Araucaria, Pinus and Eucalyptus. Overall, 9955 leaves of the understory community (up to 1 m tall) were sampled and analyzed. The mean and the frequency distribution pattern of leaf damage were very similar between Araucaria Forest and all three tree monocultures. Also, there was no difference between habitats in the percentage of leaves attacked by different feeding guilds of insect herbivores and by pathogens. Araucaria Forest had a higher percentage of leaves with epiphylls than Eucalyptus plantation, probably due to its shadier and moister microclimate. Ecologically managed tree monocultures sustain a wide variety of herbivorous insects, pathogens and epiphylls which helps the maintenance of key ecological interactions and the functioning of the ecosystem.     

Terrestrial ecosystem processes of Victoria Land, Antarctica

Terrestrial environments of Victoria Land, Antarctica are ideal systems to test hypotheses about the sensitivity of ecosystem processes to climate variability, and the relationships between soil biodiversity and ecosystem functioning because of their high sensitivity to climate change and their limited diversity. This region is also considered among the most pristine of ecosystems, and therefore may serve as an indicator for detecting the response of other ecosystems to global environmental change. Rates and controls over key ecosystem processes remain poorly documented over much of Victoria Land, but it is generally held that the distribution and functioning of soil communities are most limited by the availability of liquid water and organic carbon. Here we review examples of ecosystem processes from several sites in North and South Victoria Land and develop a regional synthesis accounting for variation in the availability of soil resources (i.e. liquid water, organic matter, inorganic nutrients). Variation in soil microclimate, organic matter, moisture and salinity encountered over gradients of coastal to interior sites, latitude, and soil chronosequences are the primary controls over the structure of soil communities and their functioning. Imbalanced stoichiometric nutrient ratios frequently encountered in Victoria Land ecosystems also contribute to limited distribution of soil biota, and where they occur these elemental imbalances indicate lower biological activity and little biotic control over bulk element ratios in soils. Priorities and future directions of Victoria Land soil and ecosystem research are also discussed.     

Spatiotemporal density patterns of the pest predator Rhynchium haemorrhoidale (F.) along a land-use gradient in cacao agroforestry systems

Tropical insect species show year-round breeding activity due to favourable climatic conditions. However, most species also display seasonal reproductive peaks, but little is known about underlying causes of temporal density changes. We investigated population dynamics of the pest predator Rhynchium haemorrhoidale (F.) (Hymenoptera: Eumenidae) and its natural enemies in relation to season, climate and varying shade tree composition in cacao agroforestry systems in Central Sulawesi (Indonesia). Nesting of R. haemorrhoidale showed clear seasonality with highest densities in the wet season and lowest in the dry season, which was not related to changes in temperature. Wasp densities increased with land-use intensity, presumably because less-shaded areas offer more favourable climatic conditions and higher densities of the major prey, the cacao pest Agathodes caliginosalis (Lepidoptera: Pyralidae). Pupal body size was higher in June than in November indicating increasing intraspecific competition due to high wasp densities and food shortage at the beginning of the wet season. Body size between habitat types was similar, thus season appeared to be more important than habitat in terms of food supply. High wasp densities in the wet season were associated with high diversity of the altogether seven parasitoid species. In conclusion, we found a pronounced seasonality of the wasp R. haemorrhoidale and a preference for little shaded agroforestry, which may be due to enhanced temperature and density of its prey. Our data indicate a high potential for biological control of a major cacao pest by management of nesting sites of R. haemorrhoidale.     

Canopy vs. understory: Does tree diversity affect bee and wasp communities and their natural enemies across forest strata?

Bees and wasps provide important ecosystem services such as pollination and biocontrol in crop-dominated landscapes, but surprisingly little information is available on hymenopteran communities in temperate forest ecosystems. Species richness and abundance of bees and wasps can be hypothesised to increase with plant diversity, structural complexity, and availability of food and nesting resources. By experimentally exposing standardised nesting sites, we examined abundance and species richness of cavity-nesting bees (pollinators), wasps (predators) and their associated parasitoids across a tree diversity gradient in a temperate deciduous forest habitat. In addition, spatial distribution of individuals and species across forest strata (canopy vs. understory) was tested. Abundance and species richness was high for predatory wasps, but generally low for pollinators. Species-rich forest stands supported increased abundance, but not species richness, of pollinators and predatory wasps, and also increased abundance and species richness of natural enemies. In addition, the forests showed a distinct spatial stratification in that abundance of bees, wasps and parasitoids as well as parasitism rates were higher in the canopy than understory. We conclude that particularly the canopy in temperate forest stands can serve as an important habitat for predatory wasp species and natural enemies, but not bee pollinators. Enhanced tree diversity was related to increased hymenopteran abundance, which is likely to be linked to an increase in nesting and food resources in mixed forest stands.     

精细农业推进现代农业发展:机理分析和现实依据

精细农业是一种现代化农业理念,也是现代农业的重要板块和有效推手。新时期需要发挥精细农业的功能和作用,推动现代农业精细化发展,实现农业提质增效。精细农业是通过提高农业中生产投入的精细化程度、生产过程的精细化程度和农业产出的精细化程度来推进现代农业发展的。但是,中国农业发展过程中,依旧存在着农业生产要素扭曲错配、现代信息技术应用不足、农村新型经营主体发育不完善、资源环境发展不平衡、农业"三本齐升"现象突出和农产品供给失衡等问题,这些问题倒逼中国加快精细农业的发展。精细农业推进现代农业发展,需要建立精细化农产品基地,建立精细农业的生产体系、产业体系和经营体系,提高农业劳动力素质和培育"三农"工作队伍,加快科技兴农、质量兴农和绿色兴农步伐。     

基于Ecopath模型的巢湖生态系统结构与功能初步分析

为分析和掌握巢湖生态系统结构与功能的特征参数,结合2007—2010年巢湖渔业资源调查数据,应用Ecopath with Ecosim 6.1软件构建了巢湖生态系统的食物网模型。模型由16个功能组组成,包括初级生产者、主要鱼类、无脊椎动物和有机碎屑等。结果显示,巢湖生态系统食物网主要由4个整合营养级构成,系统规模总流量、总生产量和总消耗量都较大,分别为41 003.08、17 937.42和4 486.67 t/(km2·a);能量流动主要发生在Ⅱ、Ⅲ营养级间;参照Odum的生态系统成熟程度判定指标发现,巢湖生态系统高的生产量和呼吸比值(TPP/TR)和净初级生产量(NPP),以及较低的系统连接指数(CI)、系统杂食指数(SOI)、Finn's循环指数(FCI)和Finn's平均路径长度(FMPL)都表明:巢湖生态系统结构与功能的特征参数远没有达到成熟生态系统的标准,且劣于富营养化的太湖生态系统。从生态系统结构分析发现,导致巢湖生态系统退化的关键原因是浮游植物生物量、生产量过高,被生态系统利用的效率极低,从而导致生物多样性下降、食物网趋于简单、能量流动不畅。     

Herb-layer diversity in deciduous forests: Raised by tree richness or beaten by beech?

Where natural production capacity permits, modern silvicultural management in Central Europe frequently aims at the development of mixed broadleaved stands, instead of pure European beech (Fagus sylvatica) stands. It is crucial to study the effects of these tree-layer diversity variations on herb-layer vegetation, since herb-layer vegetation contributes significantly to ecosystem functioning in forests. In Hainich National Park (Thuringia, Germany), we conducted observational research in deciduous stands to investigate whether herb-layer diversity was related to canopy-layer diversity, and to ascertain possible causal mechanisms. We found that herb-layer vegetation of deciduous forest stands rich in canopy species appeared to be more diverse than herb-layer vegetation of beech-dominated stands. We surmise that herbaceous understorey diversity was indirectly influenced by canopy tree species through the medium of the altered environmental factors soil pH and litter layer thickness. Apparently, lower beech proportion had a more profound effect than the number of secondary tree species. There were no correlations between herb-layer diversity and light transmissibility of the canopy layer, indicating that the light factor was not crucial for herb-layer diversity. At least for the Hainich research sites, our results indicated that small-scale light and soil heterogeneity is insignificant for herb-layer diversity. We found several herb-layer species whose occurrence was particularly correlated with tree-layer diversity and environmental factors. Remarkably, all species positively correlated with soil pH were important for the phytosociological classification of the research sites. Beech-dominated research sites showed high tree-layer volumes, whereas research sites with high tree-layer diversity tended to feature lower tree-layer volumes. These findings could be the result of differing former silvicultural systems and varying soil clay contents affecting tree species composition. In contrast, herb-layer biomass was positively correlated with tree-layer diversity. Herb-layer productivity might be promoted in more diverse research sites by increased nutrient supply and base saturation. It is also possible that greater beech proportion interfered with herb-layer productivity. However, herb-layer biomass was also positively correlated with herb-layer diversity. Hence, our study hints that positive diversity-functioning relationships might occur in the herb-layer of the deciduous forest under investigation.