Effects of predator-specific defence on biodiversity and community complexity in two-trophic-level communities

Summary Antipredator strategies employed by prey may be specific (effective against only one type of predator) or non-specific (effective against all predators). To examine the effects of the specificity of antipredator behaviour on biodiversity and community complexity, we analyse mathematical models including both evolutionary and population dynamics of a system including multiple prey species and multiple predator species. The models assume that all predator species change in their prey choice and all prey species have evolutionary change in their antipredator effort in evolution. The traits of each species change in an adaptive manner, whose rate is proportional to the slope of their fitness function. We calculate community complexity, resource-overlap between predators, an index of biodiversity and other properties of the coevolutionarily stable community for two cases: (1) all prey species have non-specific antipredator behaviour and (2) all prey species have predator-specific defence. Predator-specificity in defence increases community complexity, resource-overlap between predators, the total abundance of predators and the ratio of predator to prey abundance. Specific defence also decreases the number of isolated subwebs within the entire foodweb.     

Aphid-parasitoid community structure on genetically modified wheat

Since the introduction of genetically modified (GM) plants, one of the main concerns has been their potential effect on non-target insects. Many studies have looked at GM plant effects on single non-target herbivore species or on simple herbivore-natural enemy food chains. Agro-ecosystems, however, are characterized by numerous insect species which are involved in complex interactions, forming food webs. In this study, we looked at transgenic disease-resistant wheat (Triticum aestivum) and its effect on aphid-parasitoid food webs. We hypothesized that the GM of the wheat lines directly or indirectly affect aphids and that these effects cascade up to change the structure of the associated food webs. Over 2 years, we studied different experimental wheat lines under semi-field conditions. We constructed quantitative food webs to compare their properties on GM lines with the properties on corresponding non-transgenic controls. We found significant effects of the different wheat lines on insect community structure up to the fourth trophic level. However, the observed effects were inconsistent between study years and the variation between wheat varieties was as big as between GM plants and their controls. This suggests that the impact of our powdery mildew-resistant GM wheat plants on food web structure may be negligible and potential ecological effects on non-target insects limited.     

Effects of predatory ants on lower trophic levels across a gradient of coffee management complexity

1. Ants are important predators in agricultural systems, and have complex and often strong effects on lower trophic levels. Agricultural intensification reduces habitat complexity, food web diversity and structure, and affects predator communities. Theory predicts that strong top-down cascades are less likely to occur as habitat and food web complexity decrease. 2. To examine relationships between habitat complexity and predator effects, we excluded ants from coffee plants in coffee agroecosystems varying in vegetation complexity. Specifically, we studied the effects of eliminating ants on arthropod assemblages, herbivory, damage by the coffee berry borer and coffee yields in four sites differing in management intensification. We also sampled ant assemblages in each management type to see whether changes in ant assemblages relate to any observed changes in top-down effects. 3. Removing ants did not change total arthropod densities, herbivory, coffee berry borer damage or coffee yields. Ants did affect densities of some arthropod orders, but did not affect densities of different feeding groups. The effects of ants on lower trophic levels did not change with coffee management intensity. 4. Diversity and activity of ants on experimental plants did not change with coffee intensification, but the ant species composition differed. 5. Although variation in habitat complexity may affect trophic cascades, manipulating predatory ants across a range of coffee agroecosystems varying in management intensity did not result in differing effects on arthropod assemblages, herbivory, coffee berry borer attack or coffee yields. Thus, there is no clear pattern that top-down effects of ants in coffee agroecosystems intensify or dampen with decreased habitat complexity.     

Resource availability affects the structure of a natural bacteria-bacteriophage community

Antagonistic networks are known to be structured in the wild, but knowledge on how this structure may change as a response to environmental perturbations is scarce. We describe a natural bipartite network between bacteria and lytic bacteriophages, and investigate how it is affected by environmental productivity in the form of different resource levels for the bacteria. We report that low amounts of resource decrease phage generality and lead to less robust and less stable communities. We discuss how resource levels in nature may alter the structure of complex communities.     

Effects of temperature variability on community structure in a natural microbial food web

Climate change research has demonstrated that changing temperatures will have an effect on community‐level dynamics by altering species survival rates, shifting species distributions, and ultimately, creating mismatches in community interactions. However, most of this work has focused on increasing temperature, and still little is known about how the variation in temperature extremes will affect community dynamics. We used the model aquatic community held within the leaves of the carnivorous plant, Sarracenia purpurea, to test how food web dynamics will be affected by high temperature variation. We tested the community response of the first (bacterial density), second (protist diversity and composition), and third trophic level (predator mortality), and measured community respiration. We collected early and late successional stage inquiline communities from S. purpurea from two North American and two European sites with similar average July temperature. We then created a common garden experiment in which replicates of these communities underwent either high or normal daily temperature variation, with the average temperature equal among treatments. We found an impact of temperature variation on the first two, but not on the third trophic level. For bacteria in the high‐variation treatment, density experienced an initial boost in growth but then decreased quickly through time. For protists in the high‐variation treatment, alpha‐diversity decreased faster than in the normal‐variation treatment, beta‐diversity increased only in the European sites, and protist community composition tended to diverge more in the late successional stage. The mortality of the predatory mosquito larvae was unaffected by temperature variation. Community respiration was lower in the high‐variation treatment, indicating a lower ecosystem functioning. Our results highlight clear impacts of temperature variation. A more mechanistic understanding of the effects that temperature, and especially temperature variation, will have on community dynamics is still greatly needed.     

Effects of trophic similarity on community composition

Understanding how ecological processes determine patterns among species coexisting within ecosystems is central to ecology. Here, we explore relationships between species’ local coexistence and their trophic niches in terms of their feeding relationships both as consumers and as resources. We build on recent concepts and methods from community phylogenetics to develop a framework for analysing mechanisms responsible for community composition using trophic similarity among species and null models of community assembly. We apply this framework to 50 food webs found in 50 Adirondack lakes and find that species composition in these communities appears to be driven by both bottom‐up effects by which the presence of prey species selects for predators of those prey, and top‐down effects by which prey more tolerant of predation out‐compete less tolerant prey of the same predators. This approach to community food webs is broadly applicable and shows how species interaction networks can inform an increasingly large array of theory central to community ecology.     

How to predict community responses to perturbations in the face of imperfect knowledge and network complexity

Recent attempts to predict the response of large food webs to perturbations have revealed that in larger systems increasingly precise information on the elements of the system is required. Thus, the effort needed for good predictions grows quickly with the system''s complexity. Here, we show that not all elements need to be measured equally well, suggesting that a more efficient allocation of effort is possible. We develop an iterative technique for determining an efficient measurement strategy. In model food webs, we find that it is most important to precisely measure the mortality and predation rates of long-lived, generalist, top predators. Prioritizing the study of such species will make it easier to understand the response of complex food webs to perturbations.     

Soil food web components affect plant community structure during early succession

There is a growing awareness among ecologists of the strong links that exist between above- and belowground food webs. So far, the majority of studies have considered these links from the microbial point of view, usually with single plants or very simple plant communities. Here, we report the interactions between two components of the soil food web, root-feeding insects and arbuscular mycorrhizal (AM) fungi, and their effects on the structure and development of early successional plant communities. We use long-term field experiments that employ manipulations of these organisms, both singly and in combination. Both groups have strong effects on plant community structure, with root-feeding insects increasing and AM fungi decreasing plant species richness. Root-feeding insects appear to accelerate the process of early succession, while AM fungi retard it. There are strong interactions between the insects and fungi. The effect of insects is greatest when AM fungi are present. It is suggested that this is a consequence of plant physiology, rather than any direct interaction between the groups involved. Meanwhile, AM fungi have their greatest effect on plant communities when insects are absent, suggesting that there is some disruption of the symbiosis by the invertebrates. In developing plant communities, the rate and direction of the succession is therefore determined by the relative abundance of these two members of the soil food web. The next challenge will be to understand the roles of other members of the subterranean web in terms of their interactions with insects and AM fungi and effects on plant community development.     

Beneficial Effects of Pharmacotherapy on Weight Loss,Depressive Symptoms,and Eating Patterns in Obese Binge Eaters and Non-Binge Eaters

ALGER, SHARON A., MARGARET MALONE, JENNIFER CERULLI, STEVEN FEIN, LYN HOWARD. Beneficial effects of pharmacotherapy on weight loss, depressive symptoms, and eating patterns in obese binge eaters and non-binge eaters. Obes Res. Objective: The purpose of this study was to compare the impact of drug therapy on weight loss, Beck Depression Inventory (BDI) scores, and binge eating patterns (BES) between obese binge eaters and non-binge eaters. Research Methods and Procedures: 22 severe binge eaters, 17 moderate binge eaters, and 16 non-binge eaters received phentermine resin 15mg/day and dl-fenfluramine 20mg three times daily over a 6 month period for weight loss. All data are reported as mean±S. Results: The percent weight loss compared to baseline within the 3 groups ranged from 8. 9% to 11. 3% at 3 months and 10. 6% to 14. 9% at 6 months. After 6 months, 73% of the severe binge eaters, 59% of moderate binge eaters and 69% of non-binge eaters had experienced more than 10% weight loss. BDI scores were significantly higher in the severe group at baseline when compared to non-binge eaters (p<0. 006). After 3 and 6 months BDI scores improved in all groups but remained significantly different between the severe and non-binge eaters until the 6-month assessment. BES scores declined in all groups over the 6-month period. Echocardiograms were performed in 35 of 55 subjects following reports of a possible association between fenfluramine and valvular changes. Fifteen (43%) of subjects had no abnormal findings and 20 (57%) had evidence of valvular insufficiency occurring in one or more valves. Seven patients (20%) had significant valve damage according to the DHHS and FDA criteria. Conclusion: After 24 weeks of treatment severe binge eaters improved their eating pattern, depression scores, and achieved weight loss similar to non-binge eaters. These data suggest that pharmacologic intervention for weight loss and subsequent weight maintenance can be as successful in binge eaters as non-binge eaters. A relationship was seen between duration of drug treatment and valvular insufficiency in subjects treated for an average of 52 weeks. These findings validate the FDA requirement for studies of at least 1 year duration to evaluate both the safety and efficacy of pharmacologic treatment for obesity.     

象山港电厂温排水增温对浮游细菌群落空间分布的影响

沿海电厂产生的温排水已造成了较严重的环境问题,如生物病害和赤潮暴发频率增加。现有研究多关注温排水增温对浮游动、植物多样性的影响,而缺乏在物质能量循环过程起核心纽带作用的微生物对增温的响应和反馈。考虑到生态系统对增温的反馈取决于浮游植物的初级生产力和微生物异养呼吸之间的平衡,利用Illumina测序技术结合水体理化性质研究了象山港电厂温排水增温梯度下浮游细菌的空间分布特征。温排水预期的海水增温显著地增加了水体中硝氮(P=0.041,单因素方差分析)、化学需氧量(P0.001)、油污(P=0.004)和余氯(P=0.003)的浓度;但降低了溶解氧(P=0.034)和叶绿素a(P=0.045)的含量。此外,相似性分析发现温排水增温显著地(r=0.338;P=0.042)改变了浮游细菌群落结构,空间分布遵循空间距离-群落相似性衰减(r=-0.582;P=0.026)模型,周转速率为0.0013。细菌多样性主要受水体溶解氧、化学需要量和叶绿素a的影响,分别控制了34.6%、20.1%和10.0%的多样性变异。冗余分析(RDA)群落变异主要受环境因子(包括温度、油污、溶解氧和叶绿素a)的影响,一共解释了55.6%的群落变异;增温仅解释了4.8%的群落变异。因此,浮游细菌群落结构主要受环境因子的影响,这种各因子对群落变异相对贡献比例的特征与增温主要通过改变水质和浮游植物特征,以间接作用影响细菌群落组成的观念一致。此外,细菌多样性和群落组成受不同环境因子的驱动。相比而言,空间距离只控制了较小比例的群落变异(7.1%)。此外,筛选到11个细菌科,这些科的相对丰度与增温幅度显著相关,变化特征与各科已知的生态功能相吻合,如海洋螺菌科(Oceanospirillaceae)中有些菌株能够降解石油污染物,其相对丰度在高油污浓度站点增加(油污浓度与增温幅度正相关,r=0.558;P=0.030);嗜温的弧菌科相对丰度与增温幅度正相关。综上,研究结果初步明确了浮游细菌群落对电厂温排水增温的响应特征,并筛选到敏感的细菌科来指示和预测增温对生态功能的潜在影响。     

Effects of drought on fish across axes of space, time and ecological complexity

• 1 We evaluate the position of 50 previously published studies of fish and drought with respect to spatial scale of study (individual stream pools to subcontinents), length of the dry period (weeks to centuries), and level of system complexity (individual fish to ecosystems). Most papers address short (months to a year) droughts or dry periods, in local reaches of streams, and impacts on populations or local assemblages. In these 50 papers, the most frequently demonstrated effects of drought were population declines, loss of habitat, changes in the community, negative effects from changes in water quality, movement within catchments, and crowding of fish in reduced microhabitats. Thirteen other less frequent effects also were identified.
• 2 Gaps in knowledge exist on effects of long‐term droughts (decades to centuries), influence of drought on fish effects in ecosystems, and at the spatial scale of river basins to subcontinents. However, some of these gaps have recently been addressed, particularly additive effects of repeated drying episodes and whole‐lake or basin‐wide effects of drought, and in using molecular techniques to seek signals of drought at wide geographic scales because of events in the deep past. Gaps in knowledge remain for effects of very short dry periods, on drought effects on higher levels of complexity, and on the manner in which droughts at the scale of decades affect fish.
• 3 Data from streams in Oklahoma and elsewhere in the south‐western U.S.A. suggest that most droughts may leave little persistent signal in the existing fish fauna, i.e. that recovery from drought by fish populations or assemblages in the region can be rapid. However, species that are vulnerable to drought or water loss in streams may have disappeared from some basins in the region before the mid‐1900s, and recent evidence also suggests that extreme droughts do sometimes alter fish assemblages.
• 4 Little is known about mechanisms by which droughts have direct or indirect effects on fish, the roles of droughts in the evolution of fish species, and the ways droughts alter effects of fish in ecosystems. Global climate changes may have serious consequences for future local or regional fish faunas, but ongoing studies of fish experiencing drought may aid in future conservation of what will become species at risk under climate‐change scenarios.

     

大豆田节肢动物群落优势种群时间生态位及营养关系分析

【目的】阐明大豆田节肢动物群落时间生态位及营养关系,为大豆害虫生态调控手段的实施提供坚实的理论依据。【方法】以大豆田节肢动物群落为研究对象,通过两年的田间系统调查分析。【结果】统计得到种类220余种,物种可分为天敌、害虫和中性昆虫3个类群,以天敌物种丰富度最高;害虫中以烟蓟马Thrips tabaci(0.36902)和大豆蚜Aphis glycines(0.13122)优势度最高,且有着较高的生态位重叠指数(0.8163),蚜小蜂Aphytis sp.和大草蛉Chrysopa septempunctata对害虫的时间生态位重叠指数很高,其他天敌如异色瓢虫Harmonia axyridis、龟纹瓢虫Propylaea japonica、黑带食蚜蝇Zyistrophe balteata和黑食蚜盲蝽Deraeocoris punctulatus等对害虫的重叠指数居中;大豆田中各类群构成错综复杂的食物网结构。【结论】综合考虑天敌的种群数量,确定捕食性天敌是控制害虫种群数量的有效天敌。研究可知不能单纯从时间生态位的重叠指数的高低来判断天敌的控制能力。     

城市化对土壤动物群落结构和多样性的影响

城市化进程加快带来的环境挑战正威胁着地球上的生物多样性。土壤动物是生物多样性的重要组成部分, 对维持土壤健康及城市生态系统稳定性具有重要意义。近年来, 城市土壤动物群落结构和多样性的研究已经取得了一定进展, 但是仍缺乏系统的总结和综述。基于此, 本文梳理归纳了国内外已有的相关文献, 总结了城市化影响土壤动物的主要途径, 并阐述了城市中不同体型大小的优势土壤动物类群对城市化的响应。本文建议未来应利用分子生物学手段深入解析城市土壤动物多样性, 明晰城市土壤食物网的结构与功能, 关注土壤动物群落的保护与恢复, 揭示城市土壤动物肠道微生物组特征, 并挖掘城市土壤动物抑制人类致病菌的潜力, 以期为城市生物多样性保护、生态系统稳定和人类健康维持提供相关科学依据。     

Consequences of adaptive foraging in diverse communities

1.  Selective pressures acting on foraging activities constrain the strength of interaction, hence the stability and energetic availability in food webs.
2.  Because such selective pressures are usually measured at the individual level and because most experimental and theoretical works focus on simple settings, linking adaptive foraging with community scale patterns is still a far stretch.
3.  Some recent models incorporate foraging adaptation in diverse communities. The models vary in the way they incorporate adaptation, via evolutionary or behavioural changes, and define individual fitness in various ways.
4.  In spite of these differences, some general results linking adaptation to community structure and functioning emerge. In the present article, I introduce these different models and highlight their common results.
5.  Adaptive foraging provides stability to large food web models and predicts successfully interaction patterns within food webs as well as other topological features such as food chain length.
6.  The relationships between adaptive foraging and other structuring factors particularly depend on how well connected the local community is with surrounding communities (metacommunity aspect).     

红火蚁入侵对玉米植株上节肢动物群落的影响

在农业生态系统中,入侵性红火蚁Solenopsis invicta Buren是一种贪婪的节肢动物捕食者,会不加区分地攻击害虫和有益昆虫。本文以玉米地作为研究生境,系统调查并探讨红火蚁入侵对玉米植株上节肢动物群落的影响。结果表明,红火蚁入侵使得玉米地内节肢动物的种类下降了64.7%,而减少的种类主要隶属于半翅目、鳞翅目和双翅目,并且这种负面影响主要体现在玉米生长后期。随着玉米植株上红火蚁数量的增加,相应的节肢动物群落物种丰富度、多样性和均匀度指数减少,生态优势度指数增加。进一步通过系统聚类分析表明,红火蚁发生区玉米植株上节肢动物类群结构在时间序列上波动较大,其入侵已显著影响了生境内节肢动物群落。     

Habitat choice in shoals of roach as a function of water temperature and feeding rate

Temperature and food availability are two important factors which affect fish growth and therefore are expected to influence habitat choice in fish. In this study, shoals of 16 juvenile roach, Rutilus rutilus , were given a choice between two chambers that differed in temperature by 1·5°C or 3°C whereas food availability was the same in both chambers (ratio 1 : 1) or higher in the colder one (ratio 4 : 1). The number of fish in each chamber was recorded for 10 min each during a pre-feeding, feeding and post-feeding period. Roach generally preferred the warmer over the colder chamber during the pre-feeding periods. Temperature had a significant effect on the distribution of fish during all three time periods whereas food availability was a significant factor only during the feeding period. The important role of temperature was emphasized further by the fact that a relatively small difference in the temperature gradient of 1·5°C had a stronger effect on fish distribution than a four times higher feeding rate during the feeding period. The implications for growth rates of such short-term decision-making of roach are discussed.     

氯嘧磺隆对土壤微生物群落结构的影响

采用磷脂脂肪酸(PLFA)法研究了黑龙江省苇河地区不同氯嘧磺隆施药历史下土壤微生物群落结构的差异, 并测定了土壤中氯嘧磺隆的残留量.结果表明：不同施药历史下氯嘧磺隆在土壤中的残留量均很低;随着施用氯嘧磺隆年限的增加,土壤微生物的PLFA总量减少, 革兰氏阴性菌/革兰氏阳性菌（GN/GP）和真菌/细菌比降低,土壤微生物的压力指数增加.主成分分析表明,氯嘧磺隆显著改变了大豆田土壤微生物群落结构.     

Food web complexity and higher-level ecosystem services

Studies mostly focused on communities of primary producers have shown that species richness provides and promotes fundamental ecosystem services. However, we know very little about the factors influencing ecosystem services provided by higher trophic levels in natural food webs. Here we present evidence that differences in food web structure and the richness of herbivores in 19 plant‐herbivore‐parasitoid food webs influence the service supplied by natural enemies, namely, the parasitism rates on hosts. Specifically, we find that parasitoids function better in simple food webs than in complex ones, a result relevant to biological control practice. More generally, we show that species richness per se only contributes partially to the understanding of higher‐level ecosystem services in multitrophic communities, and that changes in food web complexity should also be taken into account when predicting the effects of human‐driven disturbances in natural communities.     

Effects of habitat complexity,dominance and personality on habitat selection: Ideal despotic cichlids

Habitat structure can impede visibility and movement, resulting in lower resource monopolization and aggression. Consequently, dominant individuals may prefer open habitats to maximize resource gain, or complex habitats to minimize predation risk. We explored the role of dominance on foraging, aggression and habitat choice using convict cichlids (Amatitlania nigrofasciata) in a two‐patch ideal free distribution experiment. Groups of six fish of four distinct sizes first competed for shrimp in one‐patch trials in both an open and complex habitat; half the groups experienced each habitat type first. Following these one‐patch trials, each group then chose between habitat types in a two‐patch trial while competing for food. Finally, each fish underwent an individual behavioural assessment using a battery of “personality” tests to determine if behaviour when alone accurately reflected behaviour within a social context. In the one‐patch trials, dominant fish showed similar food consumption between habitats, but chased more in the complex habitat. In the two‐patch choice trials, dominants preferred and defended the complex habitat, forming an ideal despotic distribution with more than half the fish and competitive weight in the open habitat. Within the groups, individual fish differed in foraging and chasing, with repeatabilities of 0.45 and 0.23 across all treatments. Although a higher foraging rate during the individual assessment predicted foraging rate and use of the complex habitat during the group trials, aggression and boldness tests were not reflective of group behaviour. Across groups, heavier dominants and those with higher foraging rate in the open habitat used the open habitat more, suggesting that both risk and energetic state affect habitat preference in dominant convict cichlids.