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.     

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.     

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.     

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.     

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.

     

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).     

群落食物网间的相似性测度

群落是指一定地段或生境里各种生物种群构成的结构单元。群落内各物种不是孤立存在的,它们之间存在着极为复杂的营养联系。一种植物常有多种害虫取食,一种害虫可取食多种植物,同时又被多种天敌捕食或寄     

Effects of deforestation on fish community structure in Ecuadorian Amazon streams

SUMMARY 1. There is little information on the impacts of deforestation on the fish fauna in neotropical streams, and on parameters influencing species diversity and community structure of fish. We analysed these aspects in 12 stream sites in the Ecuadorian Amazon. The stream sites represented a large gradient in canopy cover and were located in an area of fragmented forest. While some streams had been deforested, they had not suffered gross degradation of the habitat.
2. The species richness of stream fish was not related to deforestation. Local fish diversity (Fisher's Alpha) was positively related to the surface area of stream pools (m²). Beta diversity was higher among forested than deforested sites, indicating greater heterogeneity in species composition among forested than deforested sites. The percentage of rare species was positively correlated with canopy cover.
3. Total fish density increased with deforestation, and the fish community changed from dominance by omnivorous and insectivorous Characiformes at forested sites to dominance of periphyton-feeding loricariids at deforested sites.
4. Multidimensional statistical analysis of fish community structure showed that six environmental variables (the area of stream bottom covered by leaves, relative pool area, particulate organic matter, mean depth, conductivity and suspended solids) were related to the ordination axes. The presence of leaves, which was strongly correlated to canopy cover, was the variable most closely related to fish community structure, while relative pool area was the second strongest variable. Thus, fish community structure was strongly affected by deforestation.     

The spatial population structure of a harpacticoid copepod community in spring

The spatial population patterns of an assemblage of meiobenthic harpacticoid copepod species were analysed for two sets of samples resulting from a systematic survey of an intertidal, estuarine, sandy beach in spring. The fauna was characterised by mesopsammic species, the 6 most abundant of which showed a great degree of interassociation, such that they could not be considered to distribute themselves independently. Populations of each of the 6 species were overdispersed, such that a negative binomial distribution adequately fitted all population samples. Spatial segregation of closely related species was indicated during the late spring sample, so leading to a patchy population distribution. It is proposed that during early spring, during periods of extreme disturbance in the seasonal r-selecting environment, the species populations do not interact, but that during periods of less extreme perturbation an interactive community evolves.     

Effects of planktivorous fish mass mortality on the plankton community of Lake Mendota,Wisconsin: implications for biomanipulation

Massive mortality of planktivorous fish had a dramatic impact on plankton community dynamics of Lake Mendota, Wisconsin, USA. After fish mortality, the largerDaphnia pulicaria replaced the smallerDaphnia galeata mendotae, resulting in greater grazing pressure on phytoplankton. This was accompanied by a much longer spring clear-water period and lower summer phytoplankton biomass compared to years before the fish mortality. Analysis of historical data (from the mid-1970's) showed that previous fluctuations in planktivorous abundance had similar effects onDaphnia abundance and species composition, and on spring phytoplankton biomass. However, the mid-1970's fish fluctuations had no detectable effect on summer phytoplankton. Concentrations of phosphorus were much higher in the 1970's (spring P 80–135 μg 1⁻¹) than in the 1980's (spring P 19–36 μg 1⁻¹) and it is possible that high P concentrations may reduce trophic cascade effects on summer phytoplankton communities. This suggests that the success of biomanipulation programs may be dependent on lake nutrient status.     

Trophic network structure emerges through antagonistic coevolution in temporally varying environments

Understanding the mechanisms underlying ecological specialization is central to our understanding of community ecology and evolution. Although theoretical work has investigated how variable environments may affect specialization in single species, little is known about how such variation impacts bipartite network structure in antagonistically coevolving systems. Here, we develop and analyse a general model of victim-enemy coevolution that explicitly includes resource and population dynamics. We investigate how temporal environmental heterogeneity affects the evolution of specialization and associated community structure. Environmental productivity influences victim investment in resistance, which will shape patterns of specialization through its regulating effect on enemy investment in infectivity. We also investigate the epidemiological consequences of environmental variability and show that enemy population density is maximized for intermediate lengths of productive seasons, which corresponds to situations where enemies can evolve higher infectivity than victims can evolve defence. We discuss our results in the light of empirical studies, and further highlight ways in which our model applies to a range of natural systems.     

Effects of group size and personality on social foraging: the distribution of sheep across patches

Group cohesion in social animals foraging in patchy environmentsdepends on 2 opposite forces, intraspecific competition, andattraction. The decision to leave or stay in a group may varyaccording to the individual personality. We investigated therole of personality when feeding competition increases as aresult of increasing group size. Individuals referred as "bold"and "shy" were identified from an indoor exploration test accordingto their propensity to leave the group to explore a novel environment,using 12 novel objects placed at increasing distances from thegroup. Groups of 2, 4, 6, or 8 shy or bold sheep were testedin 45 x 5–m grass arenas, with one 5 x 5–m patchof preferred vegetation at each end. Sheep grazed on or closeto these patches, but the number grazing the patches seldomreached more than 4–5 individuals, suggesting that crowdingmight affect foraging at the highest densities. The smallestgroups grazed together on the same patch, but there was an increasinglikelihood of splitting into subgroups as group size increased,with equal-sized subgroups most commonly grazing the 2 patchessimultaneously. This effect was greatest in bold sheep, whichtended to split into subgroups at smaller group sizes than shysheep. This study provides new insight into the mechanisms bywhich group-living herbivores distribute themselves across patchyresources in a way that minimizes interference competition anddemonstrates the importance of individual variability for spatialorganization at the level of the group.     

Global-scale predictions of community and ecosystem properties from simple ecological theory

We show how theoretical developments in macroecology, life-history theory and food-web ecology can be combined to formulate a simple model for predicting the potential biomass, production, size and trophic structure of consumer communities. The strength of our approach is that it uses remote sensing data to predict properties of consumer communities in environments that are challenging and expensive to sample directly. An application of the model to the marine environment on a global scale, using primary production and temperature estimates from satellite remote sensing as inputs, suggests that the global biomass of marine animals more than 10(-5) g wet weight is 2.62 x 10(9)t (=8.16 gm(-2) ocean) and production is 1.00 x 10(10) tyr-1 (31.15 gm(-2)yr(-1)). Based on the life-history theory, we propose and apply an approximation for distinguishing the relative contributions of different animal groups. Fish biomass and production, for example, are estimated as 8.99 x 10(8)t (2.80 gm(-2)) and 7.91 x 108 t yr(-1) (2.46 gm(2)yr(-1)respectively, and 50% of fish biomass is shown to occur in 17% of the total ocean area (8.22 gm(-2)). The analyses show that emerging ecological theory can be synthesized to set baselines for assessing human and climate impacts on global scales.     

海拔对辽东栎林地土壤微生物群落的影响

以北京东灵山辽东栎林地土壤为对象,运用氯仿熏蒸-浸提法及磷脂脂肪酸分析(PLFA)法,研究林木生长季节土壤微生物群落随海拔梯度的变化特征.结果表明:随着海拔升高,辽东栎林土壤微生物生物量碳、氮,以及微生物各类群含量均有差异但不显著;土壤细菌/真菌升高,而革兰氏阳性菌(G+)/革兰氏阴性菌(G-)降低.土壤微生物生物量碳、氮以及细菌、真菌、G+细菌、G-细菌的含量与土壤含水量、有机碳、全氮呈显著正相关,土壤真菌含量与土壤碳氮比值呈正相关.土壤微生物群落组成结构(细菌/真菌和G+细菌/G-细菌)的变化主要受土壤温度和土壤含水量的显著影响,说明土壤微生物群落结构对环境条件的变化敏感.随着全球变暖的加剧,暖温带辽东栎林地土壤真菌和G+细菌的比例有升高的趋势.