Current interactions
Overall, predators, herbivores and the pooled arthropod assemblages including all feeding guilds (predators, herbivores, detritivores, parasitoids, omnivores) were strongly influenced by the presence of leaf rolls on plants (Fig. 2). Arthropod abundance, species richness, biomass and mean body size were significantly higher in rolled compared to control leaves (i.e., positive Hedges’ d values, with 95% confidence intervals not spanning 0).
The effects of leaf rolls on pooled arthropod assemblages were not significantly influenced by any moderator (Table 1). The effects of leaf rolls on predators were mediated solely by climate, but the effects of precipitation and temperature varied depending on predator metrics (abundance, richness, biomass). The magnitude of the effect of leaf rolls on predator abundance and species richness increased with drought (PC1precipitation, Table 1, Fig. 3). Predator abundance on plants was strongly positively correlated with predator species richness (r = 0.86, t=12.2, P<0.001), and thus the effects of leaf shelters on both community metrics were similarly influenced by precipitation gradients (Table 1, Fig. 3). In contrast, the positive effects of leaf rolls on predator biomass increased with greater temperature variability, but decreased in warmer regions (Table 1, Fig. 3). Latitude did not directly influence refuge usage by arthropods, but had a positive indirect effect via temperature gradient on the increase in predator biomass in leaf shelters (PC1temperature, β = 0.28, Fig. S5c). Predator biomass within leaf shelters and on control leaves was positively correlated with predator body size (shelter: r = 0.82, t=9.6, P<0.001; control: r = 0.94, t =16.6, P<0.001), but not with predator abundance (shelter: r = 0.23, t = 1.6, P = 0.11; control: r = 0.14, t=0.98, P=0.33). Thus, shelter usage, mostly by larger predators, increased toward higher latitudes, where temperature variability is higher.
In contrast to the effect of leaf rolls on predators, positive effects of leaf shelters on the magnitude of the effect on herbivore abundance and biomass were stronger in wet sites, but also on plants with a higher abundance of predators (Table 1, Fig. 3). Herbivore biomass within leaf shelters and on control leaves was strongly positively correlated with the mean body size of the individuals (shelter: r = 0.88, t=12.4, P<0.001; control: r = 0.74, t=6.7, P<0.001), but not with their abundance (shelter: r = 0.05, t=0.37, P=0.71; control: r = 0.13, t=0.88, P=0.38). Average herbivore body size was 41% smaller than average predator body size (Fig. S6).
Likewise, data visualization performed using linear mixed effects modelling with raw data revealed contrasting patterns of leaf shelter usage by herbivores and predators (Fig. S7). Predator abundance, species richness and biomass increased within refuges in a drier climate and with increasingly variable temperatures. In contrast, herbivores were more likely to use shelter under wetter climates (Fig. S7). Other moderators such as elevation, ecosystem productivity, topography and local average temperature did not directly influence the effects of shelters on arthropods (Table 1).