Climate variability and aridity modulate the role of leaf shelters for arthropods: A global experiment

04.03.2022

Current climate change is disrupting biotic interactions and eroding biodiversity worldwide. However, species sensitive to aridity, high temperatures, and climate variability might find shelter in microclimatic refuges, such as leaf rolls built by arthropods. To explore how the importance of leaf shelters for terrestrial arthropods changes with latitude, elevation, and climate, we conducted a distributed experiment comparing arthropods in leaf rolls versus control leaves across 52 sites along an 11,790 km latitudinal gradient. We then probed the impact of short- versus long-term climatic impacts on roll use, by comparing the relative impact of conditions during the experiment versus average, baseline conditions at the site. Leaf shelters supported larger organisms and higher arthropod biomass and species diversity than non-rolled control leaves. However, the magnitude of the leaf rolls' effect differed between long- and short-term climate conditions, metrics (species richness, biomass, and body size), and trophic groups (predators vs. herbivores). The effect of leaf rolls on predator richness was influenced only by baseline climate, increasing in magnitude in regions experiencing increased long-term aridity, regardless of latitude, elevation, and weather during the experiment. This suggests that shelter use by predators may be innate, and thus, driven by natural selection. In contrast, the effect of leaf rolls on predator biomass and predator body size decreased with increasing temperature, and increased with increasing precipitation, respectively, during the experiment. The magnitude of shelter usage by herbivores increased with the abundance of predators and decreased with increasing temperature during the experiment. Taken together, these results highlight that leaf roll use may have both proximal and ultimate causes. Projected increases in climate variability and aridity are, therefore, likely to increase the importance of biotic refugia in mitigating the effects of climate change on species persistence.

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Romero, G. Q., Gonçalves‐Souza, T., Roslin, T., Marquis, R. J., Marino, N. A., Novotny, V., ... & Koricheva, J. (2022). Climate variability and aridity modulate the role of leaf shelters for arthropods: A global experiment. Global Change Biology, 28(11), 3694-3710.

Gradients of baseline precipitation (a) and temperature variability (b) projected across the globe. The color gradients represent the first axis (PC1) of the principal component analysis of climatic variables. Negative values represented by light colors (greenish to yellow) denote unstable climatic conditions and arid regions, and positive values (dark, blue to purple colors) denote stable temperature and precipitation conditions. The main bioclimatic variables contributing to positive and negative values of the PC1 scores are presented below the color gradient legends, along with their Pearson moment correlation coefficients, r, with PC1. Open circles indicate the study sites. See Table S3 for definitions of the bioclimatic variables.
Schematic representation of the experimental design, effect size calculations (a), moderators, and analytical steps to achieve the results, including model selection (b). Construction of predictive maps, as well as cross-validation to validate the maps (c).
Effect sizes (Hedges' d) of ecosystem engineering on richness, biomass (standing stock) and body size of predators, herbivores and all surveyed organisms pooled together (predators, herbivores, detritivores, omnivores, and parasitoids). Error bars represent 95% confidence intervals. Effects are considered significantly different from 0 if 95% confidence intervals do not cross.

Effects of experiment temperature on effect size (Hedges' d) of community biomass (a) and average body size (b) of all surveyed organisms pooled together (predators, herbivores, detritivores, omnivores, and parasitoids). Each dot represents a site.

Effects of baseline historic precipitation stability (PC1precipitation) on effect size (Hedges' d) of predator richness (a). Effects of experiment temperature (°C) and precipitation (mm) on Hedges' d of predator community biomass (standing stock) (b), average predator body size (c), and herbivore richness (d). Effects of predator abundance upon leaves (# per leaf) on Hedges' d of herbivore biomass (e). Each dot represents a site.

Difference in Hedges' d values between the future climate (2070) and baseline climatic effect size for predator richness. A value of zero (0) denotes no shift, whereas positive values imply an increased effect size, and negative values imply a decreased effect size. Predicted values for richness were based on precipitation of the driest month (bio14) and temperature annual range (bio7), respectively, assuming the RCP8.5 (MIROC5) global climate model (see Methods).

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