Mammalian herbivores (e.g. cattle, sheep, deer, rabbits) can affect plant diversity, vegetation structure and ecosystem productivity. The changes in vegetation characteristics may in turn affect abundance and diversity of many invertebrates, depending on the intensity, timing, duration of grazing and the productivity of the habitat.
According to a new study published in Oikos, the strength of the cascading effects of mammalian herbivores on invertebrates depends also on the body size of the mammalian herbivore as well as on the functional traits of the invertebrate.
In this new study, Dr. WANG Xiaowei of the Institute of Applied Ecology of the Chinese Academy of Sciences and his international colleagues (AC Risch et al.) at the Swiss Federal Institute for Forest, Snow and Landscape Research assessed how the progressive exclusion of mammals of different body size affected the community structure and functional traits of ground beetles (Coleoptera, Carabidae) in two subalpine grassland vegetation types (short- and tall-grass vegetation).
The study showed that the exclusion of large herbivores (e.g. red deer, chamois) had the strongest effects on carabid beetles, but at the same time highlighted the ecological significance of smaller herbivorous mammals (e.g. alpine marmot, mountain hare and mice).
The researchers found that mammalian grazing not only altered carabid community composition, but also caused community-wide functional trait shifts. Carabids with specific functional traits (e.g. dispersal ability, trophic level, visual acuity) differed in their responses to grazing of different sized mammals. Total carabid biomass, the activity densities of short-winged beetles and small-eyed beetles were significantly higher when certain mammals were excluded compared to when all mammals had access. At least in this study area, the researchers revealed that the changes in aboveground plant biomass, rather than that of plant diversity or vegetation structural heterogeneity, were key drivers of mammalian grazers’ influence on carabids.