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1. Data and code from Artificial light at night increases top-down pressure on caterpillars: experimental evidence from a light-naive forest - 2021-2022

   https://doi.org/10.6073/pasta/71525c9c724db0a21249584afca9ddbd  

   Deitsch, John F; Kaiser, Sara A (January 2023, Environmental Data Initiative)

   This dataset has been prepared in support of a paper to be published in Proceedings of the Royal Society B: Biological Sciences. It includes both data files and R scripts used for the analysis in this publication: Deitch, J.F. and S.A. Kaiser. 2023. Artificial light at night increases top-down pressure on caterpillars: experimental evidence from a light-naive forest. Proceedings of the Royal Society B: Biological Sciences. (https://doi.org/10.1098/rspb.2023.0153) Artificial light at night (ALAN) is a globally widespread and expanding form of anthropogenic change that impacts arthropod biodiversity. ALAN alters interspecific interactions between arthropods, including predation and parasitism. Despite their ecological importance as prey and hosts, the impact of ALAN on larval arthropod stages, such as caterpillars, is poorly understood. We examined the hypothesis that ALAN increases top-down pressure on caterpillars from arthropod predators and parasitoids. We experimentally illuminated study plots with moderate levels (10-15 lux) of LED lighting at light-naive Hubbard Brook Experimental Forest, New Hampshire. We measured and compared between experimental and control plots: 1) predation on clay caterpillars and 2) abundance of arthropod predators and parasitoids. We found that predation rates on clay caterpillars and abundance of arthropod predators and parasitoids were significantly higher on ALAN treatment plots relative to control plots. These results suggest that moderate levels of ALAN increases top-down pressure on caterpillars. We did not test mechanisms, but sampling data indicates that increased abundance of predators near lights may play a role. This study highlights the importance of examining the effects of ALAN on both adult and larval life stages and suggests potential consequences of ALAN on arthropod populations and communities. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

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2. Decomposing an elevational gradient in predation by insectivorous birds

   https://doi.org/10.1002/ecs2.4790  

   Dean, Lydia_S; Vázquez‐González, Carla; Hellwitz, Sierra; Abdala‐Roberts, Luis; Mooney, Kailen_A (February 2024, Ecosphere)

   Abstract Insectivorous birds have ecologically important effects on prey abundance, behavior, and evolution, and through top‐down control, birds indirectly reduce herbivory and promote plant growth. While several studies sought to characterize biogeographic patterns in top‐down control by birds, variation in bird predation along elevational gradients is not well characterized in terms of both its commonness and the mechanisms underlying such variation. Here, we characterized variation in bird predation along a 700‐m montane elevation gradient using artificial clay caterpillars, assessing the roles of variation in aridity, other elevational effects not associated with aridity (e.g., most notably growing season length), and bird abundance and diversity. Multivariate models revealed increasing attack rates with aridity (when controlling for the effects of elevation) and elevation (when controlling for aridity). Because aridity declines with elevation, elevational patterns were not detectable in a univariate analysis. Bird abundance (but not diversity) decreased with elevation (but not aridity) and did not provide an explanation for our results, suggesting that the underlying mechanisms were behaviorally based. We speculate that the declining abundance of insect prey with elevation and aridity leads to increased bird foraging efforts and thus the likelihood of attacking clay caterpillars. If widespread, these dynamics have important consequences for both the interpretation of predation bioassays generally and our understanding of the multivariate drivers of variation in top‐down control by predators and predation risks experienced by prey. 

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3. Tree diversity enhances predation by birds but not by arthropods across climate gradients

   https://doi.org/10.1111/ele.14427  

   Vázquez‐González, Carla; Castagneyrol, Bastien; Muiruri, Evalyne_W; Barbaro, Luc; Abdala‐Roberts, Luis; Barsoum, Nadia; Fründ, Jochen; Glynn, Carolyn; Jactel, Hervé; McShea, William_J; et al (May 2024, Ecology Letters)

   Abstract Tree diversity can promote both predator abundance and diversity. However, whether this translates into increased predation and top‐down control of herbivores across predator taxonomic groups and contrasting environmental conditions remains unresolved. We used a global network of tree diversity experiments (TreeDivNet) spread across three continents and three biomes to test the effects of tree species richness on predation across varying climatic conditions of temperature and precipitation. We recorded bird and arthropod predation attempts on plasticine caterpillars in monocultures and tree species mixtures. Both tree species richness and temperature increased predation by birds but not by arthropods. Furthermore, the effects of tree species richness on predation were consistent across the studied climatic gradient. Our findings provide evidence that tree diversity strengthens top‐down control of insect herbivores by birds, underscoring the need to implement conservation strategies that safeguard tree diversity to sustain ecosystem services provided by natural enemies in forests. 

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4. Climate, predation, and the controls of island lizard abundance and community structure

   https://doi.org/10.1002/ecs2.70053  

   Folfas, Edita; Mahler, D Luke; Frishkoff, Luke O (November 2024, Ecosphere)

   Abstract Alternative ecological theories make divergent predictions about the relationship between predators and their prey. If predators exert top‐down ecosystem control, increases in predation should diminish prey abundance and could either diminish or enhance community diversity of prey species. However, if bottom‐up ecosystem controls predominate, predator populations should track underlying variation in prey diversity and abundance, which ultimately should reflect available energy. Past research, both across islands and comparing islands with the mainland, has frequently invoked the importance of predation in regulating lizard abundance and diversity, suggesting an important role of top‐down control when predators are present. However, others have posited a stronger role of food limitation, via competition or bottom‐up forces. If top‐down control predominates, then negative correlations between prey abundance and predator occurrence should emerge within and among islands. Using data from eBird, we inferred landscape‐level presence data for bird species on the islands of Jamaica and Hispaniola. By summing occurrence probabilities of all known anole‐predator birds, we estimated total avian predation pressure and combined these estimates with anole community data from a mark‐recapture study that spanned spatial and climatic gradients on both islands. Avian predators and anole lizards were both affected by climate, with total predator occurrence, anole abundance and anole species richness increasing with mean annual temperature. Anole abundance and predator occurrence showed a curvilinear relationship, where abundance and predator occurrence increased together until predator occurrence became sufficiently high that anole abundance was negatively impacted. This indicates that bottom‐up ecosystem controls drive richness of both anoles and their predators, mitigating the negative effects predators might have on their prey, at least until predator occurrence reaches a threshold. We did not detect consistent evidence of predator occurrence reducing anole community richness. These findings support past research showing that islands with more predators tend to have lower prey abundances, but it does not seem that these top‐down forces are strongly limiting species coexistence. Instead, bottom‐up forces linked with climate may be more important drivers of diversity in both lizards and their avian predators on these islands. 

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5. Lizard and frog removal increases spider abundance but does not cascade to increase herbivory

   https://doi.org/10.1111/btp.12909  

   Beard, Karen H.; Durham, Susan L.; Willig, Michael R.; Zimmerman, Jess K. (December 2020, Biotropica)

   Abstract Insectivorous vertebrates, especially on islands, can exert top‐down control on herbivorous prey, which can transfer through a food chain to reduce herbivory. However, in many systems insectivorous vertebrates feed on more than one trophic level, especially consuming arthropod predators, and this intraguild predation can diminish trophic cascades. Our goal was to determine, using an exclosure experiment, the relative importance of anole lizards and coqui frogs in controlling spider and arthropod abundances as well as herbivory rates in the understory of the Luquillo Experimental Forest, Puerto Rico. We found that exclosures removing both anoles and coquis doubled spider abundance compared to exclosures with anoles and coquis at natural densities. The effect of coquis on spiders was greater and occurred more quickly than that of anoles, potentially because of the higher natural densities of coquis and removal of both vertebrates produced no interactive effects. We found support for the idea that anoles, but not coquis, reduce foliar arthropod abundances on one of the two studied plant species. However, there was also evidence that anole removal decreased herbivory, the opposite of what we would expect if there was a trophic cascade. Potential explanations include that anoles reduced predatory arthropods on foliage more than they reduced herbivorous arthropods. Results highlight that the food web in tabonuco forest is not simple and that there are complex and dynamic relationships among vertebrate insectivores, predatory arthropods, and herbivorous arthropods that do not consistently result in a trophic cascade. Abstract in Spanish is available with online material 

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