A major factor influencing the success of particular plant species within ecological communities is the extent of herbivory. Herbivores rarely actually kill target plants, and so it is likely that their activities change the balance of competition between grazed species. Interest in the effects of herbivores on natural plant communities has largely focused on the consumption of leaves and stems. Now there is increasing interest in the ecological role of root herbivory by soil-dwelling invertebrates. Verschoor et al. studied the effects of root-feeding nematodes on the competitive ability of two grass species, Anthoxanthum odoratum and Holcus lanatus, grown on soil from a Netherlands nature reserve. Under natural conditions, A. odoratum, the stronger competitor for light, tends to replace H. lanatus, the stronger competitor for nutrients, in the course of vegetation succession. In a greenhouse experiment, nematode herbivores were found to hasten the replacement of H. lanatus by A. odoratum in the successional sequence. This effect was not the result of nematode preference for one plant species over another; rather, the stronger nutrient competitor was less vulnerable to the herbivores. These results suggest a mechanism by which the composition of managed grassland plant communities may be mediated by below-ground herbivores. -- AMS
J. Ecology 90, 753 (2002).
