Abstract
AbstractResearch on the functional importance of biodiversity, motivated by global species loss, has documented that plant species richness affects many plant‐related ecosystem functions. Less is known about the effects of plant species richness on functions related to higher trophic levels, such as the consumption of biomass by animals, that is, herbivory. Previous studies have shown positive, neutral, or negative effects of plant species richness on herbivory. In the framework of a grassland biodiversity experiment (the Jena Experiment), we investigated herbivory (the proportion of leaf area damaged and the amount of leaf biomass consumed by arthropod herbivores) along two experimental gradients of plant species richness ranging from 1 to 60 species (Main Experiment) and from 1 to 8 species (Trait‐Based Experiment) biannually for five and three years, respectively. Additionally, plant functional diversity, based on traits related to plant growth, was manipulated as the number of functional groups in a community (Main Experiment) or a gradient of functional trait dissimilarity (Trait‐Based Experiment). Herbivory at the level of plant communities ranged from 0% to 31% (0 and 33.8 g/m2) in the Main Experiment and 0% to 8% (0 and 13.7 g/m2) in the Trait‐Based Experiment, and it was on average higher in summer than in spring. For both experimental gradients and all years investigated, we found a consistent increase in damaged leaf area and consumed biomass with increasing plant species richness. As mechanistic explanations for effects of plant species richness, we propose changes in plant quality and herbivore communities. The presence of specific plant functional groups significantly affected herbivory, likely related to traits affecting plant defense and nutritional value, but we found little evidence for effects of plant functional diversity. The general positive relationship between plant species richness and herbivory might contribute to effects of plant species richness on other ecosystem functions such as productivity and nutrient mineralization and can cascade up the food web also affecting higher trophic levels.
Highlights
The global loss of species in recent centuries (Butchart et al 2010) has raised questions about the functional importance of biodiversity (Schl€apfer and Schmid 1999)
In the framework of a grassland biodiversity experiment, we investigated herbivory along two experimental gradients of plant species richness ranging from 1 to 60 species (Main Experiment) and from 1 to 8 species (Trait-Based Experiment) biannually for five and three years, respectively
Plant diversity can affect ecosystem functions mediated by these consumers (Scherber et al 2010, Ebeling et al 2014a) and multi-trophic interactions can be stabilized by high plant diversity (Haddad et al 2011, Ebeling et al 2012)
Summary
The global loss of species in recent centuries (Butchart et al 2010) has raised questions about the functional importance of biodiversity (Schl€apfer and Schmid 1999). Most studies investigating the effect of plant species loss on ecosystems focused on plant-related ecosystem variables like primary productivity, nutrient cycling, and invasion resistance (Hector et al 1999, van Ruijven and Berendse 2005, Roscher et al 2011b, Reich et al 2012). Plant diversity has been demonstrated to affect abundance and diversity of invertebrates (Scherber et al 2010, Haddad et al 2011, Borer et al 2012, Hertzog et al 2016). Plant diversity can affect ecosystem functions mediated by these consumers (Scherber et al 2010, Ebeling et al 2014a) and multi-trophic interactions can be stabilized by high plant diversity (Haddad et al 2011, Ebeling et al 2012). Herbivory can cause important feedback effects such as changes in plant community composition and diversity (Brown and Gange 1999) and increased speed of nutrient cycling (Belovsky and Slade 2000, Nitschke et al 2015)
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