The effects of large herbivore grazing on meadow steppe plant and insect diversity

Abstract

Summary 1.The interactions between adjacent trophic levels are essential for ecosystem functioning and stability. Grazing by domestic herbivores is an essential interaction in grasslands, but little information is available on the nature of relationship between plant and insect diversity under grazing by large herbivores. 2. We examined the effects of large herbivores on the relationship between plant and insect diversity with five grazing treatments (control, cattle, goat, sheep and a mixture of the three grazing types) across three plant diversity levels (low: 4-5 species, intermediate: 8-9 species and high: 15-17 species) in a meadow steppe. 3. We found that the grazing treatments did not significantly affect plant species richness, but reduced plant biomass, plant height and cover. Grazers affected variation in plant height differently at different plant diversity levels, and this variation increased at the low plant diversity level and decreased at the high plant diversity level after grazing. A similar pattern was observed for insect species richness: grazing had a positive impact at the low plant diversity level, but had a negative impact at the high plant diversity level. 4. In the absence of grazing, insect species richness was positively associated with plant species richness, but it decreased with increasing plant diversity in the grazing treatments. This was attributed to strong responses of insect species richness to plant height heterogeneity under grazing by large herbivores, implying that plant structural heterogeneity is more important than plant diversity in influencing insect diversity in grazed grasslands. 5. Synthesis and applications. Grazing by large herbivores may reverse the positive relationship between plant diversity and insect diversity by modifying plant structural heterogeneity. Therefore, the spatial heterogeneity of vegetation structure should be given more attention in future work on plant-insect interactions. This study further highlights the importance of using large herbivore grazing in management actions, not only to maintain diversity but also to mediate trophic interactions in grasslands.

Interactive effects of large herbivores and plant diversity on insect abundance in a meadow steppe in China

“…Plants samples were air forced oven-dried for 48 h at 80 C, and weighed. Some vegetation attributes, such as plant species richness, plant cover, plant height, plant structural heterogeneity, and plant biomass in this study were calculated in our previous paper (Zhu et al, 2012), and here we did not show these results. Plant diversity (Shannon-Wiener index) was calculated as H = ÀS s 1 ðP i  lnP i Þ, where P i is the proportion of individuals represented by species i, and s is the number of plant species.…”

“…Each block for each plant diversity level was one plant community, and the plant community composition (species, and individual number of each plant species) that was similar with other blocks in same plant diversity level, and was different from the blocks in other plant diversity levels. Detailed descriptions of experimental plant diversity treatments of pre-grazing can be found in Zhu et al (2012). Grazing treatments were nested within the block of each plant diversity treatment, and no grazing and three single grazing treatments with one grazer in each grazed plot were used.…”

“…Surprisingly, while most efforts have been devoted to the effects of grazing intensity on insect community, little attention has been given the effects of grazer species (Jáuregui et al, 2008). Different large herbivore species may alter vegetation features due to diet selection and body size, potentially influencing insect community, because grazing affect insect community through modifying plant communities (Kruess and Tscharntke, 2002b;Jonas and Joern, 2007;Zhu et al, 2012;van Klink et al, 2015). Therefore, the resulting 'species-specific' of grazing management difficultly renders the development and application of general management principles for biological conservation.…”

“…Zhu et al (2012) showed that large herbivores strongly affected insect species richness by modifying plant structural heterogeneity, which reversed the positive relationship between plant and insect diversity. Zhong et al (2014) found that the positive interactions between large herbivores and grasshoppers were driven by differential herbivore foraging preferences for plant resources that break down the associational plant defense between grasses and forbs.…”

Variação nas concentrações de compostos fenólicos e nas taxas de herbivoria em Aspidosperma pyrifolium Mart. em áreas antropizadas de Caatinga

“…Áreas utilizadas frequentemente como pastagens para animais de criação podem ficar tão comprometidas que, além de influenciarem as características das espécies vegetais menos resilientes, como alterações na biomassa, na altura e na amplitude de cobertura do solo pela projeção da copa, podem inverter a relação positiva entre a diversidade de plantas e a diversidade de insetos, modificando a heterogeneidade estrutural vegetal original da localidade (Zhu et al, 2012).…”