Why species richness of plants and herbivorous insects do or do not correlate

Abstract

Unraveling the determinants of herbivorous insect diversity has been a significant challenge in ecology. Despite the strong association between insect and plant species, previous studies conducted in natural systems have shown great variation in the strength of the correlation between their species richness. Such variation could be attributed to the proportion of generalist insect species (generality). However, both higher and lower generality may weaken the correlation because (a) generalist insect species are less dependent on the number of plant species, and (b) specialist insect species utilize only a proportion of the total plant species. To explore these contradictory effects, we studied plant and herbivorous insect communities in seminatural grasslands in Japan. Plant–insect interactions were evaluated in a unique way with a particular focus on the staying and herbivory behaviors of insects, which reflect their habitat use as well as host use. We found that lower generality of insect communities strengthened the correlation between species richness of plants and insects, but this was not the case when plant species that had no interaction with insect species were also considered. This was because lower generality increased the number of plant species that did not interact with insects. The results indicate that insect generality has contradictory effects on the plant–insect diversity relationship, which emphasizes the importance of distinguishing the effects to understand the variation in the relationship between plant and insect diversity in natural systems.

Effects of the Climatic Region on Richness Correlations between Vascular Plants and Vertebrates in Nature Reserves of China

“…However, they were significantly different (Figure 2a). Our results echo those of previous studies that had no consistent conclusions about the effectiveness of vascular plants as an effective indicator taxon when the predictions varied with taxa [5,9,14,15,49,53]. However, vascular plants were considered indicator taxa because they were easy to survey, widely distributed, and stable in taxonomy [15,54].…”

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

“…Therefore, plant individuals at early season may have been less defensive, which made plant–herbivore interactions more generalized (Gadelha et al 2017). Such higher generality of plant–herbivorous insect relationship can weaken the explanation power of plant communities for herbivorous insect communities (Shinohara and Yoshida 2021), leading to the less predictable assembly because any insect species can be found at anywhere. This explanation concurs with our result that the increases in R 2 Local|Regional and R 2 Both values over time were more pronounced for the leaf sucker communities (Fig.…”

“…This landscape is called ‘Satoyama', a traditional Japanese agricultural landscape comprising a complex ensemble of agriculture, secondary forests and residential areas within a limited hilly area (Kadoya and Washitani 2011). Among the landscape, semi‐natural grasslands that are maintained by frequent mowing serve as important habitats for grassland plants and herbivorous insects (Okubo et al 2005, Uchida and Ushimaru 2014, Shinohara and Yoshida 2021). The grasslands are distributed patchily within the landscape and isolated each other by other land‐use types (mainly by rice fields) that are not very suited for grassland species.…”

“…Conversely, the time lag that herbivorous insects arrive before predators may make top–down effects weaker and thus bottom–up effects stronger at earlier phases. Alternatively, if the ratio of specialist/generalist insects in the regional species pool changed seasonally, the strength of bottom–up effects would vary accordingly, because generalist insects are less dependent on the identity or the number of plant species (de Araújo 2013, Shinohara and Yoshida 2021). The other local processes, top–down effects and influence of physical structures of vegetation, can vary as well because the abundance of predatory arthropods and the vegetation complexity changes seasonally (Boyer et al 2003, Gratton and Denno 2003, Ford et al 2017).…”

Climate, Land use and Plant Richness Differently Shape Herbivory on Major Plant Functional Groups

“…Further research should elaborate on linking functional invertebrate community compositions, e.g. degree of herbivore generality (Shinohara and Yoshida 2021), to herbivory on plant functional groups (differentiating several groups of forbs) in different habitat types for a deeper understanding of herbivory.…”