Owen T. Lewis

Higher predation risk for insect prey at low latitudes and elevations

Risky in the tropics It is well known that diversity increases toward the tropics. Whether this increase translates into differences in interaction rates among species, however, remains unclear. To simplify the problem, Roslin et al. tested for predation rates by using a single approach involving model caterpillars across six continents. Predator attack rates were higher toward the equator, but only for arthropod predators. Science, this issue p. 742 Like diversity, predation rates among insects increase toward the equator and at lower altitudes. Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution.

Quantifying immediate and delayed effects of anthelmintic exposure on ecosystem functioning supported by a common dung beetle species

Dung beetles (Coleoptera: Scarabaeoidea) support numerous ecosystem functions in livestock-grazed pastures. Exposure to veterinary anthelmintic residues in livestock dung can have lethal and sublethal effects on dung beetles, and can reduce rates of dung removal, but the immediate and longer-term consequences for other dung beetle mediated functions have rarely been studied. We investigated the consequences of anthelmintic exposure on survival of the dung beetle Aphodius fossor and its delivery of four ecosystems functions that underpin pasture production: dung removal, soil fauna feeding activity, primary productivity, and reduction of soil compaction. We tested whether anthelmintic exposure had immediate or delayed effects on these functions individually and simultaneously (i.e., ecosystem multifunctionality). We found no evidence that ivermectin residues had a lethal effect on adult beetles. For dung removal, we found a significant interaction between the timing of exposure and functioning: while dung removal was impaired by concurrent exposure to high levels of ivermectin, functioning was unaffected when beetles that had been exposed previously to the same concentration of anthelmintic later interacted with untreated dung. Other ecosystem functions were not affected significantly by anthelmintic exposure, and there was no evidence to suggest any persistent impact of anthelmintic exposure on ecosystem multifunctionality. While anthelmintic residues remain a significant threat to dung beetle populations, for adult beetles, we found no evidence that residues have detrimental consequences for ecosystem functioning beyond the immediate point of exposure.

The importance of species identity and interactions for multifunctionality depends on how ecosystem functions are valued

Studies investigating how biodiversity affects ecosystem functioning increasingly focus on multiple functions measured simultaneously (multifunctionality). However, few such studies assess the role of species interactions, particularly under alternative environmental scenarios, despite interactions being key to ecosystem functioning. Here we address five questions of central importance to ecosystem multifunctionality using a terrestrial animal system. (1) Does the contribution of individual species differ for different ecosystem functions? (2) Do inter-species interactions affect the delivery of single functions and multiple functions? (3) Does the community composition that maximizes individual functions also maximize multifunctionality? (4) Is the functional role of individual species, and the effect of interspecific interactions, modified by changing environmental conditions? (5) How do these roles and interactions change under varying scenarios where ecosystem services are weighted to reflect different societal preferences? We manipulated species relative abundance in dung beetle communities and measured 16 functions contributing to dung decomposition, plant productivity, nutrient recycling, reduction of greenhouse gases, and microbial activity. Using the multivariate diversity-interactions framework, we assessed how changes in species identity, composition, and interspecific interactions affected these functions in combination with an environmental driver (increased precipitation). This allowed us to identify key species and interactions across multiple functions. We then developed a desirability function approach to examine how individual species and species mixtures contribute to a desired state of overall ecosystem functioning. Species contributed unequally to individual functions, and to multifunctionality, and individual functions were maximized by different community compositions. Moreover, the species and interactions important for maintaining overall multifunctionality depended on the weight given to individual functions. Optimal multifunctionality was context-dependent, and sensitive to the valuation of services. This combination of methodological approaches allowed us to resolve the interactions and indirect effects among species that drive ecosystem functioning, revealing how multiple aspects of biodiversity can simultaneously drive ecosystem functioning. Our results highlight the importance of a multifunctionality perspective for a complete assessment of species functional contributions.

Effect of dung beetle species richness and chemical perturbation on multiple ecosystem functions

1. The relationship between biodiversity and ecosystem functioning is typically positive but saturating, suggesting widespread functional redundancy within ecological communities. However, theory predicts that apparent redundancy can be reduced or removed when systems are perturbed, or when multifunctionality (the simultaneous delivery of multiple functions) is considered.

Predicting the effect of habitat modification on networks of interacting species

A pressing challenge for ecologists is predicting how human-driven environmental changes will affect the complex pattern of interactions among species in a community. Weighted networks are an important tool for studying changes in interspecific interactions because they record interaction frequencies in addition to presence or absence at a field site. Here we show that changes in weighted network structure following habitat modification are, in principle, predictable. Our approach combines field data with mathematical models: the models separate changes in relative species abundance from changes in interaction preferences (which describe how interaction frequencies deviate from random encounters). The models with the best predictive ability compared to data requirement are those that capture systematic changes in interaction preferences between different habitat types. Our results suggest a viable approach for predicting the consequences of rapid environmental change for the structure of complex ecological networks, even in the absence of detailed, system-specific empirical data.In a changing world, the ability to predict the impact of environmental change on ecological communities is essential. Here, the authors show that by separating species abundances from interaction preferences, they can predict the effects of habitat modification on the structure of weighted species interaction networks, even with limited data.

Flower preferences and pollen transport networks for cavity-nesting solitary bees: Implications for the design of agri-environment schemes

Abstract Floral foraging resources are valuable for pollinator conservation on farmland, and their provision is encouraged by agri‐environment schemes in many countries. Across Europe, wildflower seed mixtures are widely sown on farmland to encourage pollinators, but the extent to which key pollinator groups such as solitary bees exploit and benefit from these resources is unclear. We used high‐throughput sequencing of 164 pollen samples extracted from the brood cells of six common cavity‐nesting solitary bee species (Osmia bicornis, Osmia caerulescens, Megachile versicolor, Megachile ligniseca, Megachile centuncularis and Hylaeus confusus) which are widely distributed across the UK and Europe. We documented their pollen use across 19 farms in southern England, UK, revealing their forage plants and examining the structure of their pollen transport networks. Of the 32 plant species included currently in sown wildflower mixes, 15 were recorded as present within close foraging range of the bees on the study farms, but only Ranunculus acris L. was identified within the pollen samples. Rosa canina L. was the most commonly found of the 23 plant species identified in the pollen samples, suggesting that, in addition to providing a nesting resource for Megachile leafcutter bees, it may be an important forage plant for these species. Higher levels of connectance and nestedness were characteristic of pollen transport networks on farms with abundant floral resources, which may increase resilience to species loss. Our data suggest that plant species promoted currently by agri‐environment schemes are not optimal for solitary bee foraging. If a diverse community of pollinators is to be supported on UK and European farmland, additional species such as R. canina should be encouraged to meet the foraging requirements of solitary bees.

First detection of bee viruses in hoverfly (syrphid) pollinators

Global declines of insect pollinators jeopardize the delivery of pollination services in both agricultural and natural ecosystems. The importance of infectious diseases has been documented in honeybees, but there is little information on the extent to which these diseases are shared with other pollinator orders. Here, we establish for the first time the presence of three important bee viruses in hoverfly pollinators (Diptera: Syrphidae): black queen cell virus (BQCV), sacbrood virus (SBV) and deformed wing virus strain B (DWV-B). These viruses were detected in two Eristalis species, which are behavioural and morphological bee mimics and share a foraging niche with honeybees. Nucleotide sequences of viruses isolated from the Eristalis species and Apis mellifera were up to 99 and 100% identical for the two viruses, suggesting that these pathogens are being shared freely between bees and hoverflies. Interestingly, while replicative intermediates (negative strand virus) were not detected in the hoverflies, viral titres of SBV were similar to those found in A. mellifera. These results suggest that syrphid pollinators may play an important but previously unexplored role in pollinator disease dynamics.