Aboveground (AG) and belowground (BG) organisms interact using plants as mediators. These interactions have important implications for plant community structure and dynamics. Spatial scales on which AG and BG organisms act differ largely due to limited mobility belowground, which may affect the outcome of AG-BG interactions. For example, small patches created by BG organisms may be homogenized by large AG herbivores. In contrast, small AG herbivores may promote BG driven heterogeneity. Consequences of AG-BG scale differences, particularly in field situations, are still poorly understood. We explore how disparities between AG-BG scales affect plant community patterns. In a field experiment we investigate plant community patches created by BG organisms (subterranean yellow meadow ants) in the presence of small (European brown hares) or large (cattle) AG vertebrate herbivores. Hares represent AG organisms acting at a small scale matching the scale at which ants operate, while cattle act at a large scale. We hypothesize two different mechanisms that may drive plant community patches as a result of AG-BG interactions: (1) changes in soil abiotic and biotic properties by BG organisms and (2) selective grazing by small AG herbivores.
Results/Conclusions
We found that hares promote plant community heterogeneity initially created by yellow meadow ants, whereas, cattle homogenized plant community differences between ant mounds and their surroundings. Hares showed a preference for larger ant mounds and vegetation on mounds was increasingly converted to palatable plant species. Most soil biotic and abiotic properties did not explain plant community patterns observed. However, preliminary results indicate that plant nutrient content may be enhanced on ant mounds. Higher nutrient quality probably attracts small herbivores that choose foraging patches more selectively because they depend on higher food quality than large herbivores. We found increased grazing pressure of small AG herbivores on ant mounds, which confirms that selective grazing may be one of the mechanisms driving plant community patches. We conclude that AG-BG interactions are important in determining plant community patterns and that the outcome of these interactions is dependent on AG herbivore size.
