Herbivores are important agents in driving plant population dynamics, but plants are also regulated by a diverse array of other fauna that can impose indirect filters. Few studies, however, have investigated how herbivores and other fauna groups can interactively affect the performance of plants. In semi-arid grasslands of northeastern China, large vertebrate herbivores (such as cattle) are regarded as a major driver of plant population dynamics, while the potential impacts of smaller, more cryptic fauna groups (such as ants) have largely been ignored. We conducted a three-year large-scale cattle and ant manipulative experiment to quantify how these animals can independently and interactively control the population performance of a dominant plant species, Leymus chinensis grasses.
Results/Conclusions
We found that cattle and ants have a significant but oppose effect on plant growth and reproductive success. Cattle grazing significantly decreased population growth and biomass of L. chinensis grasses, the most-preferred food plants of these grazers, but such effects occurred only when the ants were suppressed. In the presence of ants, cattle grazing failed to affect Leymus grass growth, even though they tend to feed on more frequent on these grasses compared to the ant suppression sites. Ants also tend to mitigate the negative effects of cattle on flower and seed production of Leymus grass in the grazed areas. The presence of ants led to a 25% increase in soil total available nitrogen (N) compared to ant removal sites in the grazed areas, either due to ant activities themselves or the higher visiting frequency of cattle that allow more feces and urine inputs to the soil, potentially benefiting plant growth of Leymus grass in the sites. Our results suggest that invertebrates have the potential to modify large herbivores’ top-down effects on plants. Considering not only the conspicuous large herbivores, but also their interactions with co-occurring fauna, may help us better understand the role of these mammals in structuring plant populations and communities.