A better understanding of plant–herbivore relationships should integrate negative and positive effects of consumers on plant fitness.
We studied the effect of a major insect herbivore (leaf-cutting ants, LCA) on plant fitness in
several species of Monte Desert, assessing both the direct negative effect of ant defoliation and the indirect positive role of ants as soil improvers. First, we compared the fitness between plants growing on the nutrient-rich refuse dumps and cospecifics on adjacent non-nest soils. Second, using hierarchical confirmatory path analysis model, we analyzed how
herbivory and nutrient content of refuse dumps affected plant fitness.
We found that the fitness of plants growing on refuse dumps (a) was similar than those growing on adjacent
non-nest soils, and (b) was unaffected by ant harvesting or
by increments in nutrient content in a consistent way. In this
dry habitat, the effect of LCA on plant fitness was complex
and species-dependent.
Our results illustrate the complexity of herbivoreplant interactions emphasizing the need of measuring direct and indirect effects of herbivory in field conditions to validate
greenhouse experiments
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