Relative role of deterministic and stochastic determinants of soil animal community: a spatially explicit analysis of oribatid mites

1. Ecologists are debating the relative role of deterministic and stochastic determinants of community structure. Although the high diversity and strong spatial structure of soil animal assemblages could provide ecologists with an ideal ecological scenario, surprisingly little information is available on these assemblages.
2. We studied species-rich soil oribatid mite assemblages from a Mediterranean beech forest and a grassland. We applied multivariate regression approaches and analysed spatial autocorrelation at multiple spatial scales using Moran's eigenvectors. Results were used to partition community variance in terms of the amount of variation uniquely accounted for by environmental correlates (e.g. organic matter) and geographical position. Estimated neutral diversity and immigration parameters were also applied to a soil animal group for the first time to simulate patterns of community dissimilarity expected under neutrality, thereby testing neutral predictions.
3. After accounting for spatial autocorrelation, the correlation between community structure and key environmental parameters disappeared: about 40% of community variation consisted of spatial patterns independent of measured environmental variables such as organic matter. Environmentally independent spatial patterns encompassed the entire range of scales accounted for by the sampling design (from tens of cm to 100 m). This spatial variation could be due to either unmeasured but spatially structured variables or stochastic drift mediated by dispersal. Observed levels of community dissimilarity were significantly different from those predicted by neutral models.
4. Oribatid mite assemblages are dominated by processes involving both deterministic and stochastic components and operating at multiple scales. Spatial patterns independent of the measured environmental variables are a prominent feature of the targeted assemblages, but patterns of community dissimilarity do not match neutral predictions. This suggests that either niche-mediated competition or environmental filtering or both are contributing to the core structure of the community. This study indicates new lines of investigation for understanding the mechanisms that determine the signature of the deterministic component of animal community assembly.

Fortune favours the bold: a higher predator reduces the impact of a native but not an invasive intermediate predator

Emergent multiple predator effects (MPEs) might radically alter predictions of predatory impact that are based solely on the impact of individuals. In the context of biological invasions, determining if and how the individual-level impacts of invasive predators relates to their impacts in multiple-individual situations will inform understanding of how such impacts might propagate through recipient communities. Here, we use functional responses (the relationship between prey consumption rate and prey density) to compare the impacts of the invasive freshwater mysid crustacean Hemimysis anomala with a native counterpart Mysis salemaai when feeding on basal cladoceran prey (i) as individuals, (ii) in conspecific groups and (iii) in conspecific groups in the presence of a higher fish predator, Gasterosteus aculeatus. In the absence of the higher predator, the invader consumed significantly more basal prey than the native, and consumption was additive for both mysid species - that is, group consumption was predictable from individual-level consumption. Invaders and natives were themselves equally susceptible to predation when feeding with the higher fish predator, but an MPE occurred only between the natives and higher predator, where consumption of basal prey was significantly reduced. In contrast, consumption by the invaders and higher predator remained additive. The presence of a higher predator serves to exacerbate the existing difference in individual-level consumption between invasive and native mysids. We attribute the mechanism responsible for the MPE associated with the native to a trait-mediated indirect interaction, and further suggest that the relative indifference to predator threat on the part of the invader contributes to its success and impacts within invaded communities.

The predictive science of community ecology

Body mass measures provide a tantalizing tool for explaining both variation in emergent community-level patterns and as a mechanistic basis for fundamental processes such as metabolism, consumption and competition. The unification of body mass, abundance and food web (ecological network) structure in community ecology is an effective way to explore future scenarios of environmental change. However, constraints over the availability of data against which to validate model predictions limit the application of size-based approaches. Here, I explore issues over the use of body size for predicting interaction strengths and hence the dynamics of natural ecosystems. The advantages, disadvantages, opportunities and limitations of such approaches are explored. © 2011 The Author. Journal of Animal Ecology © 2011 British Ecological Society.

Dynamics of macronutrient self-medication and illness-induced anorexia in virally infected insects

Some animals change their feeding behaviour when infected with parasites, seeking out substances that enhance their ability to overcome infection. This 'self-medication' is typically considered to involve the consumption of toxins, minerals or secondary compounds. However, recent studies have shown that macronutrients can influence the immune response and that pathogen-challenged individuals can self-medicate by choosing a diet rich in protein and low in carbohydrates. Infected individuals might also reduce food intake when infected (i.e. illness-induced anorexia). Here, we examine macronutrient self-medication and illness-induced anorexia in caterpillars of the African armyworm (Spodoptera exempta) by asking how individuals change their feeding decisions over the time course of infection with a baculovirus. We measured self-medication behaviour across several full-sib families to evaluate the plasticity of diet choice and underlying genetic variation. Larvae restricted to diets high in protein (P) and low in carbohydrate (C) were more likely to survive a virus challenge than those restricted to diets with a low P : C ratio. When allowed free choice, virus-challenged individuals chose a higher protein diet than controls. Individuals challenged with either a lethal or sublethal dose of virus increased the P : C ratio of their chosen diets. This was mostly due to a sharp decline in carbohydrate intake, rather than an increased intake of protein, reducing overall food intake, consistent with an illness-induced anorexic response. Over time the P : C ratio of the diet decreased until it matched that of controls. Our study provides the clearest evidence yet for dietary self-medication using macronutrients and shows that the temporal dynamics of feeding behaviour depends on the severity and stage of the infection. The strikingly similar behaviour shown by different families suggests that self-medication is phenotypically plastic and not a consequence of genetically based differences in diet choice between families. © 2013 British Ecological Society.

3D coupled thermomechanical finite element analysis of ultrasonic consolidation

A 3-D coupled temperature-displacement finite element analysis is performed to study an ultrasonic consolidation process. Results show that ultrasonic wave is effective in causing deformation in aluminum foils. Ultrasonic vibration leads to an oscillating stress field. The oscillation of stress in substrate lags behind the ultrasonic vibration by about 0.1 cycle of ultrasonic wave. The upper foil, which is in contact with the substrate, has the most severe deformation. The substrate undergoes little deformation. Apparent material softening by ultrasonic wave, which is of great concern for decades, is successfully simulated. The higher the friction coefficient, the more obvious the apparent material softening effect.

Predicting invasive species impacts: a community module functional response approach reveals context dependencies

Summary
-Predatory functional responses play integral roles in predator–prey dynamics, and their assessment promises greater understanding and prediction of the predatory impacts of invasive species.
-Other interspecific interactions, however, such as parasitism and higher-order predation, have the potential to modify predator–prey interactions and thus the predictive capability of the comparative functional response approach.
-We used a four-species community module (higher-order predator; focal native or invasive predators; parasites of focal predators; native prey) to compare the predatory functional responses of native Gammarus duebeni celticus and invasive Gammarus pulex amphipods towards three invertebrate prey species (Asellus aquaticus, Simulium spp., Baetis rhodani), thus, quantifying the context dependencies of parasitism and a higher-order fish predator on these functional responses.
-Our functional response experiments demonstrated that the invasive amphipod had a higher predatory impact (lower handling time) on two of three prey species, which reflects patterns of impact observed in the field. The community module also revealed that parasitism had context-dependent influences, for one prey species, with the potential to further reduce the predatory impact of the invasive amphipod or increase the predatory impact of the native amphipod in the presence of a higher-order fish predator.
-Partial consumption of prey was similar for both predators and occurred increasingly in the order A. aquaticus, Simulium spp. and B. rhodani. This was associated with increasing prey densities, but showed no context dependencies with parasitism or higher-order fish predator.
-This study supports the applicability of comparative functional responses as a tool to predict and assess invasive species impacts incorporating multiple context dependencies.

A sting in the spit: widespread cross-infection of multiple RNA viruses across wild and managed bees

Declining populations of bee pollinators are a cause of concern, with major repercussions for biodiversity loss and food security. RNA viruses associated with honeybees represent a potential threat to other insect pollinators, but the extent of this threat is poorly understood. This study aims to attain a detailed understanding of the current and ongoing risk of emerging infectious disease (EID) transmission between managed and wild pollinator species across a wide range of RNA viruses. Within a structured large-scale national survey across 26 independent sites, we quantify the prevalence and pathogen loads of multiple RNA viruses in co-occurring managed honeybee (Apis mellifera) and wild bumblebee (Bombus spp.) populations. We then construct models that compare virus prevalence between wild and managed pollinators. Multiple RNA viruses associated with honeybees are widespread in sympatric wild bumblebee populations. Virus prevalence in honeybees is a significant predictor of virus prevalence in bumblebees, but we remain cautious in speculating over the principle direction of pathogen transmission. We demonstrate species-specific differences in prevalence, indicating significant variation in disease susceptibility or tolerance. Pathogen loads within individual bumblebees may be high and in the case of at least one RNA virus, prevalence is higher in wild bumblebees than in managed honeybee populations. Our findings indicate widespread transmission of RNA viruses between managed and wild bee pollinators, pointing to an interconnected network of potential disease pressures within and among pollinator species. In the context of the biodiversity crisis, our study emphasizes the importance of targeting a wide range of pathogens and defining host associations when considering potential drivers of population decline.