Abstract
In mountains, current land-use changes are altering plant communities of semi-natural grasslands with potential cascading effects on associated herbivores. Besides vegetation changes, temperature is also a key driver of insect diversity, and in the European Alps is predicted to increase by 0.25 °C per decade. Understanding herbivore responses to temperature and plant composition changes in mountain environments is of increasing importance. Our study aims at investigating the response to temperature and plant diversity and composition of two key herbivore groups (orthopterans and leafhoppers) belonging to contrasting feeding guilds (chewers vs. sap-feeders). We hypothesized that orthopteran diversity would be driven by temperature while leafhoppers by plant community composition. We selected 15 dry calcareous grasslands ranging from 100 to 1330 m a.s.l. along two independent gradients of plant diversity and temperature. We sampled orthopteran and leafhopper species richness and abundance by sweep-netting. Consistent with their low feeding specialisation, orthopteran species richness and community composition were only driven by temperature. By contrast, leafhopper species richness was not affected by temperature nor by plant diversity but leafhopper community composition was strongly influenced by plant species composition. This response can be explained by the higher host feeding specialisation of many leafhopper species. Species rarity and mobility did not change the response of the diversity of both groups, but orthopteran abundance increased with temperature only for highly mobile species. Altogether, our results suggest that future responses of grassland herbivores to vegetation changes and temperature warming are highly variable and depend on the feeding strategy and specialisation of the focal herbivore group.Implications for insect conservationLeafhoppers emerged to be particularly sensitive to potential management or climate-induced change in vegetation composition, while orthopterans are expected to respond directly to temperature warming due to their relaxed association with plant community diversity and composition.
Highlights
In the last decades, the loss and deterioration of speciesrich, semi-natural grasslands has been a major conservation problem throughout Europe (Hodgson et al 2005; Poschlod and WallisDeVries 2002; van Dijk 1991)
Our study aims to investigate the response to temperature and plant diversity and composition of two key herbivore groups (Auchenorrhyncha, hereafter referred to as leafhoppers; and Orthoptera specialised in grassland environments, hereafter referred to as orthopterans) in dry calcareous grasslands
By selecting 15 dry calcareous grasslands under the same extensive management, similar rainfall conditions and surrounding landuse, but along two independent gradients of plant diversity and temperature we addressed the following questions: (1) Does herbivore diversity increase with temperature? (2) Do shifts in plant composition and diversity explain variation in herbivore communities? (3) Do the two taxa belonging to contrasting feeding guilds exhibit a common response to these drivers? (4) Do herbivore responses to the considered drivers change depending on their regional rarity and mobility?
Summary
The loss and deterioration of speciesrich, semi-natural grasslands has been a major conservation problem throughout Europe (Hodgson et al 2005; Poschlod and WallisDeVries 2002; van Dijk 1991). Journal of Insect Conservation (2021) 25:287–296 by moving to higher elevations reshuffling local plant communities (Lenoir et al 2008). Both climate and local management changes often result in shifts in plant community composition and in the loss of plant diversity (Marini et al 2009a) with potential cascading effects on associated insect diversity (Van der Putten et al 2010). A large body of research reports a strong bottom-up effect of plant composition and diversity on herbivore communities (Deraison et al 2015; Moreira et al 2016). Low-mobile and specialised herbivores are more likely to be strongly affected by changes in plant composition, whereas the diversity of generalists should exhibit weaker responses because they are less limited to feed on specific host plants (Jactel and Brockerhoff 2007; Koricheva et al 2000)
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