Human activities have led to a continuous decline in the number of animal populations on a global scale. The impact of herbivores on plants has thus received increasing scholarly attention. 

Bottom-up regulation has long been considered to have dominant effects on the structure and biodiversity of plant communities as resource availability (e.g., soil nutrients and water) can greatly affect plant growth and reproduction. 

But there has been much controversy over whether or not the plant community is controlled by herbivores (top-down regulation).  

On the one hand, the impacts of herbivores on plant communities are very complicated. For example, herbivores feed on plants, negatively affect their growth or survival, but at the same time, they can help plants via pollination or seed dispersal.

On the other hand, there are huge differences in study characteristics (exclosure size and duration) and site conditions (biome, temperature, precipitation, and primary productivity) between studies, which frequently create statistical noise to draw conclusions. 

By performing the meta-analysis using data from 123 animal exclusion experiments in natural terrestrial ecosystems, Dr. JIA Shihong and Prof. WANG Xugao, two researchers from the Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences (CAS), together with their international colleagues from the Smithsonian Tropical Research Institute, concluded that top-down regulation by herbivores was also a 'pervasive process' shaping terrestrial plant communities at the global scale. 

The researchers found that herbivores significantly reduced plant survival, biomass, abundance and reproduction and increased species evenness.  

They also concluded that the strength of top-down regulation in terrestrial ecosystems was highly site specific and not predicted by basic site conditions because they didn’t find significant relationship between the magnitude of herbivore effect size and study site characteristics (e.g., primary productivity), or body size of herbivores (small vs. large vertebrates).  

The study highlights the roles of top-down regulation in shaping properties in plant communities, which provides an important scientific impetus for scientists to plant communities, and for ecosystem managers to protect and manage terrestrial ecosystems.  

The results, entitled "Global signal of top-down control of terrestrial plant communities by herbivores", have been published in a paper in PNAS.  

The study is financially supported by the Strategic Priority Research Program of CAS and the National Natural Science Foundation of China.