| Most herbivores do not have exclusive use of their environments---they must share resources with other herbivores. A fundamental set of questions in ecology involves understanding whether these species interact with each other, and, if so, to what degree. In a large-scale, long-term study area in a bushed grassland in East Africa, cattle caused compositional changes within the grasshopper assemblage. In the presence of cattle, the number of grasshopper individuals increased by approximately 17%, and the individuals tended to be smaller---mean adult grasshopper mass was 23% less. The decrease in mean size of adult grasshoppers where cattle were present could be mostly explained by an increase in small-bodied grasshopper species and a decrease in medium-bodied species. In a similar study in an adjacent, low-productivity habitat, grasshopper biomass increased by 277% in glade habitats in the absence of cattle and native ungulate herbivores. In addition, grasshoppers consumed up to 0.71 kg/ha/day more grass biomass in glade habitats where ungulates were removed. Thus, although grasshoppers did not compensate completely following the removal of ungulates, large mammalian herbivores may have an even larger effect on the structure and biomass of the vegetation than previously realized because small herbivores may compensate for them to some degree when they are removed. A final, preliminary study demonstrated that grasshoppers and other small herbivores might also be capable of affecting large mammalian herbivores, by consuming tree seeds and seedlings. Four months after experimental burns, the biomass of grasshoppers was reduced by 77% and the biomass of the dominant rodent Saccostomus mearnsi was reduced by 43% in burned plots relative to unburned control plots. Acacia seeds were up to ∼15 times more likely to escape predation in burn plots than control plots. Acacia drepanolobium seedlings retained 1.4 times more growing tissue in burned plots than in control plots. Therefore, under certain conditions, fire may not only reduce the density of adult trees, but at the same time increase the recruitment of young trees by suppressing seed and seedling consumers, especially grasshoppers and rodents. |
