Response of epiphytic algae to nutrient loading and fish density in a shallow lake: a mesocosm experiment

Studies on the effect of eutrophication on the ecology of shallow lakes, usually pay scant attention to changes within the epiphytic algal community, though the contribution of this to the ecosystem dynamics is transcendental. In order to test the influence of nutrient loadings and fish densities in the structure of algal epiphyton in a shallow lake, an experiment was performed using in situ mesocosms. Nutrient additions were related to significant decreases in the total epiphyton biovolume and that of bacillariophyceans and zygnematophyceans, but with increases in the abundance of cyanobacteria. The different response of algal groups at the higher nutrient concentrations (increases or decreases in their abundance and/or biovolume) can be related to their ecophysiological constraints such as different resistance to toxicant ammonium accumulation. Plant-associated macroinvertebrates numbers were positively correlated with total numbers of epiphyton. The presence of planktivorous fish enhanced the abundance and biovolume of all algal groups, except cyanobacteria. Fishes enhanced the abundance of plant-associated animals and of total epiphyton. Fish indirect effects (e.g., nutrients release) and their dietary particularities were among the factors that together with nutrients influenced epiphyton growth. The role of indirect effects of fishes and the importance of their dietary particularities are stressed as key factors to understand the processes controlling epiphyton ecology and the food web structure of shallow lakes. Handling editor: D. Ryder.     

腾格里沙漠沙坡头地区人工植被蒸散耗水与水量平衡的研究

运用大型称重式电子蒸散系统研究沙坡头地区人工植被蒸散耗水量与水分平衡,结果表明∶固沙造林初期,年平均降水量１８６．６ ｍ ｍ 能够满足植物正常生长需要,是保证植物固沙成功的基本条件． 正常降水年份,植物（密度为７５ 株／１００ ｍ ２）蒸散耗水量大于降水量． 油蒿（Ａｒｔｅｍ ｉｓｉａ ｏｒｄｏｓｉｃａ Ｋｒａｓｃｈｅｎ．）和柠条（Ｃａｒａｇａｎａ ｋｏｒｓｈｉｎｓｋｉｉＫｏｍ ．）的蒸散量分别占同期降水量的１３６．６％ 和１３１．１％ ,两种植物的蒸腾量分别占其蒸散量的４５．６％ 和４３．４％ ． 在１００～２００ ｍ ｍ 降水范围内,沙地物理蒸发量与降水量的比值随降水量的减少而增大;降水量１００ｍ ｍ 时,是人工固沙植被所需降水的最低下限． 降水的时空分布和地表结皮的形成对人工植被水分平衡与水分利用产生较大的影响     

人工鱼礁建设对浙江嵊泗海域营养盐与水质的影响

根据2003-2007年对嵊泗人工鱼礁海域11个航次调查所获得的实验数据,运用鱼礁区和对照区相比较的方法,分析了该海域不同季节氮、磷营养盐和水质在投放人工鱼礁后的变化,并对海域水质状况进行评价。结果表明,无机氮大多数处于阈值范围或低于最小阈值,活性磷酸盐含量则严重超标,N/P值范围为0.6280-14.8273,嵊泗海域处于氮限制,溶解氧不成为该海域浮游生物的生长限制因子。投放人工鱼礁后,生态效应不能在短期里得以体现,鱼礁区的水质情况要好于对照区,海域对P的富集强度大于N,人工鱼礁建设对再生生产力影响较大,对新生产力的贡献很小。     

The M-NIP: a macrophyte-based Nutrient Index for Ponds

In Swiss ponds, eutrophication represents one of the major threats to biodiversity. A biological method to assess the trophic state would, therefore, be particularly useful for monitoring purposes. Macrophytes have already been successfully used to evaluate the trophic state of rivers and lakes. Considering their colonizing abilities and their roles in pond ecosystem structure and function, macrophytes should be included in any assessment methods as required by the European Water Framework Directive. Vegetation survey and water quality data for 114 permanent ponds throughout Switzerland were analysed to define indicator values for 113 species including 47 with well-defined ecological response to total water phosphorus (TP). Using indicator values and species cover, a Macrophyte Nutrient Index for Ponds (M-NIP) was calculated for each site and assessed with both the original pond data set and a limited validation data set. The resulting index performed better when considering only species with narrow responses to TP gradient and was more applicable, but less accurate when including all species. Despite these limitations, the M-NIP is a valuable and easy tool to assess and monitor the nutrient status of Swiss ponds and was shown to be robust and relatively sensitive to slight changes in phosphorus loading with a validation subset. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Exploring spatio-temporal patterns of plankton diversity and community structure as correlates of water quality in a tropical stream

Ecology of plankton in the downstream reaches of Kaduna River, Zungeru, Niger state, Nigeria was investigated between April and August 2015. Plankton and surface water samples were collected monthly from three stations for analysis of plankton diversity and physico-chemical parameters respectively. Station 1 is relatively unperturbed station located at the outskirts of Zungeru town, station 2 with moderate human activity located in Zungeru town while station 3 with minimal level of anthropogenic activities was located in Wushishi town about 7 km from station 2. The result revealed that the minimum and maximum values for pH water temperature, air temperature, conductivity, dissolved oxygen (DO) biochemical oxygen demand (BOD), phosphate, Nitrate, and secchi disc transparency were 5.38–6.79, 25–31 °C, 26–31 °C, 32–72 μs/cm, 3.50–8.20 mg/l, 1.00–5.00 mg/l, 0.06–1.13 mg/l 0.44–1.31 mg/l, 39.140 cm respectively. A total of 26 species of zooplankton and 24 species of phytoplankton were encountered in the study. The highest number of plankton (20 taxa) was recorded at station 2 while station 1 with 18 taxa and station 3 with 13 representative taxa. For zooplankton, the highest number of taxa was recorded at station 1 (20 taxa), followed by station 3 (14 taxa) and 10 taxa in station 2 were identified. Copepoda of the order cyclopidae dominated all the three stations while Bacillariophyta dominated the three stations for phytoplankton diversity. Canonical correspondence analysis (CCA) ordination was used to determine phytoplankton and zooplankton abundance in relation to the physico-chemical parameters. Nitrate, phosphate and dissolved oxygen had over riding influence on the distribution of the plankton in the water body which indicate that the river is still very productive in terms of providing starter food organisms for higher aquatic life. However, care should be taken to protect the river from further deterioration due to various degrees of human activities.     

不同植被恢复方式下红壤线虫数量特征

退化红壤不同植被恢复方式下土壤线虫数量的顺序为：保护荒地＞干扰荒地＞马尾松＞小叶栋＞木荷＞混交林（木荷—马尾松）。土壤线虫数量的季节波动明显：春季和冬季较多,秋季居中,而夏季极显著少于其它季节（尸＜ｏ．０１）。就线虫数量季节变异系数所体现的群落稳定性而言,马尾松林地的变异系数最高（Ｐ＜０．０５）,指示其群落最不稳定。线虫数量在土壤剖面中呈明显的垂直梯度分布。在表层土壤,线虫数量与代表碳氮和生物活性水平的土壤质量指标,如有机碳、全氮、速效氮磷、微生物量、潜在可矿化碳氮、基础呼吸、酶活性等,一般呈极显著正相关（Ｐ＜０．０１）;而与代表土壤物理性质及交换性能的指标,如含水量、容重、颗粒组成、速效钾等一般没有相关性。鉴别分析（ＣＤＡ）将不同植被下的祥地分为３组,自荒１和自荒２为１组,小叶栋、木荷和混交林为１组,而马尾松单独为１组。总之,不同植被恢复下线虫数量的分异韧步体现了线虫指示红壤质量的潜力。     

Trophic exploitation in grassland food chains: simple models and a field experiment

This study provides insight into the importance of top carnivores (top-down control) and nutrient inputs (bottom-up control) in structuring food chains in a terrestrial grassland system. Qualitative predictions about food chain structure are generated using 4 simple models, each differing in assumptions about some key component in the population dynamics of the herbivore trophic level. The four model systems can be classified broadly into two groups (1) those that assume plant resource intake by herbivores is limited by search rate and handling time as described by classic Lotka-Volterra models; and (2) those that assume plant resource intake by herbivores is limited externally by the supply rate of resources as described by alternatives to Lotka-Volterra formulations. The first class of models tends to ascribe greater importance to top-down control of food chain structure whereas the second class places greater weight on bottom-up control. I evaluated the model predictions using experimentally assembled grassland food chains in which I manipulated nutrient inputs and carnivore (wolf spider) abundance to determine the degree of top-down and bottom-up control of grassland plants and herbivores (grasshoppers). The experimental results were most consistent with predictions of the second class of models implying a predominance of bottom-up control of food chain structure.     

Differential effects of food availability on population growth and fitness of three species of estuarine, bacterial-feeding nematodes

The significance of bottom-up controls on biological communities has been a long-standing topic of interest in ecology. However, before environmental effects on communities can be properly assessed, a thorough knowledge of the individual species' responses is required. We studied effects of food availability on population development and on different life-history traits in three species of bacterial-feeding nematodes, Diplolaimelloides oschei, Diplolaimelloides meyli (both Monhysteridae) and Pellioditis marina (Rhabditidae), which co-occur on macrophyte detritus in the Westerschelde Estuary (SW Netherlands). The bacteria Escherichia coli was offered in five food-availability treatments corresponding to initial cell densities from 3 × 10¹⁰ cells ml^− 1 to 3 × 10⁷ cells ml^− 1. The three bacterial-feeding nematode species studied here showed differential responses to food availability, which agreed with the general idea that Rhabditidae have extreme colonization abilities under very high food availability, while Monhysteridae tend to have a somewhat slower population development and comparatively lower food requirements. Several life-history traits, including juvenile mortality and development time, did not exhibit a clear food-availability dependence, but bioenergetics-related parameters did. Results on the F1 generation may, however, be affected by strong maternal effects on life-history traits of their progeny. Patterns of food-availability dependence of population increase and size at maturity were similar in P. marina. Both Diplolaimelloides species, however, exhibited a large body size at maturity but a very low population increase at the highest food availability, suggesting a trade-off between biomass and reproduction. Comparison with published data on other nematode species reveals that nematode responses to food availability as well as to other environmental factors are highly species-specific.     

Importance of dietary nitrogen and carbohydrates to survival, growth, and reproduction in adults of the grasshopper Ageneotettix deorum (Orthoptera: Acrididae)

Key demographic traits in insect herbivores (survival, growth, and egg production) are often responsive to variation in diet quality, especially to dietary nitrogen (N) levels. Soluble carbohydrates may also be limiting. Using defined diets under controlled laboratory conditions, we examined survival, growth, and egg production in response to a range of diet qualities in adult females of a grass-feeding grasshopper Ageneotettix deorum (Scudder). Diets varied factorially within naturally occurring ranges of total N (1–7%) and carbohydrate (4–27%) levels. N concentrations significantly impacted weight gain, egg production rate, the elapsed time until the first egg pod, and the time between the first and second egg pod. These responses were typically quadratic in nature with a maximum response near 4–5% total N. The rate of pod production rather than number of eggs per pod best explained changes in reproductive rate. Dietary carbohydrate levels seldom exerted a significant impact on demographic parameters except when interacting with N on survival, egg weight, and the period between egg pods. Clearly, factors that alter the availability of quality diet, especially total N levels, can contribute to demographic responses in A. deorum. Received: 5 August 1996 / Accepted: 26 April 1997     

The relative importance of herbivory and carnivory on the distribution of energy in a stochastic tri-trophic food web

A three-state, discrete-time Markov chain is used to model the dynamics of energy flow in a tri-trophic food web. The distribution of energy in the three trophic levels is related to the rates of flow between the trophic levels and calculated for the entire range of possible flow values. These distributions are then analysed for stability and used to test the idea that plants are resource-limited and herbivores are predation-limited. Low rates of death and decomposition, when coupled with low rates of herbivory and carnivory, tend to destabilize this food web. Food webs with higher rates of death and decomposition are relatively more stable regardless of rates of herbivory and carnivory. Plants are more prone to resource-limitation and herbivores are, in general, limited by their predators, which supports Hairston et al. (Am. Nat. 94 (1960) 421). The rate of decomposition often mediates the roles of top-down and bottom-up control of energy flow in the food web.     

Meeting water requirements of an expanding world population

Water availability in the root zone (green water) is a critical component of plant production, but is often deficient in many Third World regions. When deficient, runoff water (blue water) can be added. Focusing on ten physiographic regions in Africa and Asia, characterized by mainly or partly dry climates and rapid population growth, this study analyses whether in a 30-years'' perspective enough blue water could be provided to allow food self-sufficiency. It is assumed that for food self-sufficiency some 900 cubic metres of water per person per year has to be provided. In judging the realism it is assumed that a maximum 25 per cent increase in water mobilization rate would be manageable in a 30-year period. The study suggests that by 2025, water scarcity will make regions populated by some 55 per cent of the world''s population dependent on food imports. For water-wasting regions in Central Asia, water saving might, however, free the water needed. The paper closes by proposing some urgent measures. <br>     

Differences in swimming and diving abilities between two sympatric species of water shrews: <Emphasis Type="Italic">Neomys anomalus</Emphasis> and <Emphasis Type="Italic">Neomys</Emphasis><Emphasis Type="Italic">fodiens</Emphasis> (Soricidae)

Swimming and diving abilities of two syntopic species of water shrews, Neomys anomalus and Neomys fodiens, were tested in aquaria using video recordings taken from three views (lateral distant, lateral close and dorsal). The frequency and total duration of diving, as well as the mean duration of diving and floating bouts, were significantly higher in N. fodiens than in N. anomalus. Frequency of paddling during surface swimming was lower in N. fodiens than in N. anomalus. N. fodiens dived mainly for long distances at the bottom of the aquarium and performed a wider range of dive profiles than N. anomalus, which preferred rather short and shallow dives. The two species differed also significantly in their fineness ratios (describing how streamlined their bodies are) when diving. When swimming, N. fodiens had a relatively wider body and performed narrower movements with its tail than N. anomalus. These results show quantitatively and qualitatively for the first time that N. fodiens is more proficient at swimming and diving than N. anomalus. The results also help to explain the inter-specific differences in efficiency of underwater foraging, and support the idea of segregation of ecological niches of these species based on their different foraging modes (diving vs. wading).     

Reconciling the new demands for food protection with environmental needs in the management of livestock wastes

Government policy in many countries has been to promote manure management methods to reduce the negative impacts related to water and air pollution. The central strategy of encouraging manure as a fertiliser rather than treating it as a waste, is under threat from new concerns on public health and especially food quality. Restrictions on manure applications to certain food crops and the stipulation of treatment to 70 °C for 1 h (in the case of manure products) represent barriers to the use of such material as a useful organic product in the farming and horticultural industries. However, the sensible development of spreading plans in which high and low risk land is identified can enable appropriate and effective treatment for each situation and minimise overall cost. In the high risk situations, processes based on heat treatment remain the most reliable but there still remains the need to ensure a minimum temperature to ensure a satisfactory treatment. Direct application of heat available from biogas coupled with heat recovery may make thermal treatment of effluents a viable option where no effective environmental friendly alternatives exist.     

Rainfall, food abundance and timing of parturition in African bats

We used published results from studies in Africa to test the hypothesis that the timing of parturition in the Chiroptera is constrained by rainfall. Comparison of year-round rainfall and insect data at various latitudes showed that insect abundance peaks approximately a month after peak rainfall. A similar comparison of parturition time to rainfall showed that with the possible exception of the molossids, the Microchiroptera commonly give birth a month before peak rainfall. With an average 6-week lactation period in the Microchiroptera, the timing of parturition is such that young bats are weaned just before the period of maximum insect abundance. We suggest that the needs of the young in this post-weaning period may be more important than the energetic demands of lactation on the mother in determining the timing of parturition on an evolutionary scale. A similar conclusion is implied for the African Megachiroptera, but there is insufficient information on their reproduction to adequately test the main hypothesis for these bats. Received: 4 October 1996 / Accepted: 14 March 1997     

昆虫蛀蚀对鼠类介导下的锐齿槲栎种子扩散的影响

森林鼠类的种子贮藏行为对植物的扩散和自然更新有着非常重要的影响。然而,鼠类是否具有鉴别虫蛀种子的能力还存在一定的争议。此外,鼠类的鉴别能力是否受到食物丰富度变化的影响也未见相关报道。采用标签标记法,2011年秋季(9—11月,食物丰富季节)和2012年春季(4—6月,食物匮乏季节)分别在秦岭南坡的佛坪国家级自然保护区内,调查了森林鼠类对完好和虫蛀锐齿槲栎(Quercus aliena)种子的选择差异。结果显示:1)在秋季,尽管2种类型种子的存留动态没有显著差异,但是在后期虫蛀种子的存留时间相对更长;而在春季2种类型种子的存留动态则极为显著,几乎所有的完好种子(99%)在释放后的第3天就被鼠类全部扩散,虫蛀种子的存留时间则相对较长。2)在秋季,鼠类更喜好扩散后取食完好种子;而在春季,鼠类则喜好在原地取食绝大部分的种子,并且优先取食完好种子。3)在秋季,鼠类贮藏了更多的完好种子;而在春季,尽管完好种子在释放后第1天便达到贮藏高峰,然而由于后期的大量被捕食,2种类型种子在贮藏动态上没有显示出显著差异。研究结果表明秦岭地区森林鼠类可以准确区分完好与虫蛀种子,但是食物丰富度会影响鼠类对种子的选择策略。在食物丰富的秋季,鼠类更多地选择贮藏完好种子;而在食物相对匮乏的春季,鼠类更倾向于同时取食2种类型种子。森林鼠类通过对2种类型种子的鉴别和选择,影响不同种子的命运,从而可能对种子的扩散和自然更新产生重要影响。