Consequences of leaf-cutting ants on plant fitness: integrating negative effects of herbivory and positive effects from soil improvement

A. G. FARJI-BRENER; M. TADEY

INSECTES SOCIAUX

BIRKHAUSER VERLAG AG

Lugar: BASEL; Año: 2016 vol. 64 p. 45 - 54

0020-1812

Abetter understanding of plant-herbivore relationships should integrate negativeand positive effects of consumers on plant fitness. We studied the effect of a majorinsect herbivore (leaf-cutting ants, LCA) on plant fitness in several speciesof Monte Desert, assessing both the direct negative effect of ant defoliation andthe indirect positive role of ants as soil improvers. To estimate the negative andpositive effects on plants, we sampled 7,000 plant fragments carried by theants and analyzed the nutrient contents of refuse dumps in 15 ant nests. Weestimated plant fitness measuring ~10,000 flowers and ~3,600 fruits of 122individuals from seven of the most common plant species within the ant foragingarea. First, we compared the fitness between plants growing on thenutrient-rich refuse dumps and co-specifics on adjacent non-nest soils. Second,using hierarchical confirmatory path analysis model, we analyzed how herbivory andnutrient content of refuse dumps affected plant fitness. We found that the fitnessof plants growing on refuse dumps (a) was similar than those growing on adjacentnon-nest soils, and (b) was unaffected by ant harvesting or by increments innutrient content in a consistent way. In this dry habitat, the effect of LCA onplant fitness was complex and species-dependent. To explain this pattern, wediscuss the role of plant compensation to foliar damage, the limited plant responseto soil nutrients due to water stress and the potential high abundance plant consumerson ant refuse dumps. Our results illustrate the complexity of herbivore-plantinteractions emphasizing the need of measuring direct and indirect effects ofherbivory in field conditions to validate greenhouse experiments