Temporal changes of local and regional processes in the assembly of herbivorous insect communities

Abstract

Herbivorous insect communities are structured by multiple processes operating locally (e.g. bottom–up effects of plants) and regionally (e.g. dispersal limitation). Although the relative strength of these processes has been well documented, how it varies in time is less understood, especially in relation with the temporal dynamics of plant communities. If temporal turnover of local plant species composition is too rapid for insect community assembly to keep up with, bottom–up effects are expected to be weak. Here, in plant and herbivorous insect communities in Japanese grasslands, we studied how the relative importance of local (bottom–up effects of plants, structures of plant communities and top–down effects of predators) and regional (dispersal limitation) processes varies over the growing season. In addition, we tested the hypothesis that larger temporal turnover of plant species composition is related to the weaker bottom–up effects, that is, the lower explanation power of plant communities for insect communities. We found that, throughout the growing season, the insect species composition was mainly explained by local variables (plant species composition, vegetation height and predator abundance), and their explanation power was higher during later phases of the season (late summer). Furthermore, the variation not explained by plant species composition was correlated with the degree of temporal turnover of plants, suggesting that insect communities failed to track the temporal turnover of plant species. These results were pronounced when we focused on leaf sucker insects, whose host plant range is presumably more limited. We conclude that herbivorous insect communities are mainly regulated by local processes, especially bottom–up effects from plants, while stochasticity may have played a role in early phases of the season. Furthermore, we underscore the importance of considering relative time scale of community assembly and environmental shifts, especially in systems characterized by dynamic changes.

Spatiotemporal dimensions of community assembly

“…By explicitly modeling the effects of spatial and temporal variation of environments on species composition, they showed cases where communities are unable to track current environmental status when the environment temporally varies (see box 1 in Jabot et al, 2020). Shinohara and Yoshida (2021) extended this idea to a multi‐trophic level context in grassland communities. As plant communities can serve as an “environment” for their consumer herbivorous insects, they predicted that a larger temporal turnover of plant species composition (i.e., abrupt shifts of the environment) weakens the bottom‐up effect of plants on insect communities.…”

“…Their data supported the prediction, providing empirical evidence that insect communities lagged behind compositional shifts of plant communities. Considering that a community at a given trophic level can serve as an environment for a higher trophic level community, the authors argued that the lag of community assembly could amplify when moving up through trophic levels, which they coined a term “trophic cascade of lag” (Shinohara & Yoshida, 2021).…”

Variation in ground-dwelling arthropod communities across differently managed infiltration basins

“…Arthropod communities have been found to experience significant turnover throughout the year (Thomsen et al 2015; Seifert et al 2021): it therefore makes sense that the more temporally distant collection dates yielded less overlap than the temporally closer ones did. This annual turnover can partially be attributed to bottom-up processes driven by temporal (Ekholm et al 2019; Shinohara and Yoshida 2021) and spatial (Sobek et al 2009) turnover of plant species. In one study, Auchenorrhyncha species abundance changed significantly across the year and related directly to the number of grass structures present at the site, which peaked in late summer (Stinson and Brown 1983).…”

Plant volatiles and priority effects interactively determined initial community assembly of arthropods on multiple willow species

“…At the same time, induced responses such as induced resistance and compensatory regrowth are herbivore‐species‐specific and deterministic (Kessler & Halitschke, 2007 ; Van Zandt & Agrawal, 2004a ), which in turn affect the subsequent community assembly (Stam et al, 2018 ; Van Zandt & Agrawal, 2004b ), forming feedback between plant traits and arthropods (i.e., plant–arthropod feedback, Utsumi et al, 2010 ; Yoneya et al, 2023 ). When such feedback is initiated by the earliest colonizers on a plant whose identity can vary stochastically (Bacca et al, 2021 ; Shinohara & Yoshida, 2021 ), it results in a priority effect (Chase, 2003 ; Fukami, 2015 ) because of the combination of stochastic and deterministic processes (Chase, 2010 ), which contribute to the divergence of community composition even within a plant population.…”