Experimental field exclosure of birds and bats in agricultural systems ? Methodological insights, potential improvements, and cost-benefit trade-offs

Experimental exclosure of birds and bats constitutes a powerful tool to study the impacts of wildlife on pests and crop yields in agricultural systems. Though widely utilized, exclosure experiments are not standardized across studies. Indeed, key differences surrounding the design, materials, and protocols for implementing field-based exclosure experiments of flying vertebrates increase heterogeneity across studies, and limit our understanding of biodiversity-friendly land use management. We reviewed the available literature on studies in which bird and bat exclosures were applied to study pest control in agricultural settings, and isolated 30 studies from both tropical and temperate land use systems, involving 12 crop types across 14 countries. Focusing on exclosure effects on crop yield, we analyzed effect detectability for a subset of suitable data. We then analyzed the potential of exclosure methods and possible extensions to improve our understanding of complex food webs and ecosystem services affecting the productivity of agricultural systems. While preferences exist in materials (e.g., nylon nets and bamboo frames), experimental exclosure studies of birds and bats differed greatly in their respective design, related costs, and effort ? limiting the generalization and transferability of results at larger spatial scales. Most studies were based on experiments conducted in the United States and the Neotropics, mainly in coffee and cacao farms. A lack of preliminary or long-term data with repeated measurements makes it impossible to apply power analysis in most studies. Common constraints include, among other things, the choice of material and experimental duration, as well as the consideration of local versus landscape factors. We discuss such limitations, related common pitfalls, and options for optimization to inform improved planning, design, and execution of exclosure studies. By doing so, we aim to promote more comparable and transferable approaches in future field research on biodiversity-mediated ecosystem services

Data from: Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

AbstractThe idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies