Large manipulative experiments revealed variations of insect abundance and trophic levels in response to the cumulative effects of sheep grazing

Jingchuan Ma,Guangjun Wang,Guilin Du,Jun Hong,Yong Ding,Wenyuan Gao,Xinghu Qin,Zhuoran Zhang,Xinyi Li,Zehua Zhang,Xunbing Huang,Ning Wang

doi:10.1038/s41598-017-11891-w

Abstract

Livestock grazing can affect insects by altering habitat quality; however, the effects of grazing years and intensities on insect abundance and trophic level during manipulative sheep grazing are not well understood. Therefore, we investigated these effects in a large manipulative experiment from 2014 to 2016 in the eastern Eurasian steppe, China. Insect abundance decreased as sheep grazing intensities increased, with a significant cumulative effect occurring during grazing years. The largest families, Acrididae and Cicadellidae, were susceptible to sheep grazing, but Formicidae was tolerant. Trophic primary and secondary consumer insects were negatively impacted by increased grazing intensities, while secondary consumers were limited by the decreased primary consumers. Poor vegetation conditions caused by heavy sheep grazing were detrimental to the existence of Acrididae, Cicadellidae, primary and secondary consumer insects, but were beneficial to Formicidae. This study revealed variations in insect abundance and trophic level in response to continuous sheep grazing in steppe grasslands. Overall, our results indicate that continuous years of heavy- and over- sheep grazing should be eliminated. Moreover, our findings highlight the importance of more flexible sheep grazing management and will be useful for developing guidelines to optimize livestock production while maintaining species diversity and ecosystem health.

Highlights

Excessive grazing on grassland ecosystems by livestock poses a serious threat to the grasslands by lowering productivity, biodiversity and stability[1], leading to ecological deterioration[2], especially for insect diversity[3]
The results showed that the grasslands subjected to heavy grazing (HG) and over grazing (OG) were characterized by decreased plant coverage, biomass, density and height (Fig. 5, Table S2)
The cumulative effects of sheep grazing intensities and years on insect abundance and trophic level were analyzed by a large manipulative experiment over three years

Summary

Introduction

Excessive grazing on grassland ecosystems by livestock poses a serious threat to the grasslands by lowering productivity, biodiversity and stability[1], leading to ecological deterioration[2], especially for insect diversity[3]. Some studies have shown that grazing may increase insect diversity[7,8,9], while others showed decreased insect diversity[10, 11] or no change in insect diversity[12, 13] in response to grazing These inconsistent results may be due to factors such as variation in vegetation[6], intensity of grazing[14, 15], and herbivore size[6]. The effects of continuous manipulative grazing on other insect groups, such as Formicidae, Acrididae, Cicadellidae, and on various trophic levels, are not well understood Such knowledge will facilitate reasonable grazing management and maintenance of species diversity and ecosystem health. The specific goals of this study were to determine (i) how dominant insect groups respond to various intensities and years of sheep grazing; (ii) how insect trophic levels change with sheep grazing; and (iii) potential reasons for insect abundance variation for sheep grazing. Suggestions regarding how to manage sheep grazing to maintain insect diversity are discussed

Objectives

Methods

Results

Conclusion