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

FARJI-BRENER, ALEJANDRO GUSTAVO; TADEY, MARIANA

INSECTES SOCIAUX

BIRKHAUSER VERLAG AG

Lugar: BASEL; Año: 2017 vol. 64 p. 45 - 54

0020-1812

A better understanding of plant?herbivore relationshipsshould integrate negative and positive effects ofconsumers on plant fitness. We studied the effect of a majorinsect herbivore (leaf-cutting ants, LCA) on plant fitness inseveral species of Monte Desert, assessing both the directnegative effect of ant defoliation and the indirect positiverole of ants as soil improvers. To estimate the negative andpositive effects on plants, we sampled 7000 plant fragmentscarried by the ants and analyzed the nutrient contents ofrefuse dumps in 15 ant nests. We estimated plant fitnessmeasuring *10,000 flowers and *3600 fruits of 122individuals from 7 of the most common plant species withinthe ant foraging area. First, we compared the fitness betweenplants growing on the nutrient-rich refuse dumps and cospecificson adjacent non-nest soils. Second, using hierarchicalconfirmatory path analysis model, we analyzed howherbivory and nutrient content of refuse dumps affectedplant fitness. We found that the fitness of plants growing onrefuse dumps (a) was similar than those growing on adjacentnon-nest soils, and (b) was unaffected by ant harvesting orby increments in nutrient content in a consistent way. In thisdry habitat, the effect of LCA on plant fitness was complexand species-dependent. To explain this pattern, we discuss the role of plant compensation to foliar damage, the limitedplant response to soil nutrients due to water stress and thepotential high abundance plant consumers on ant refusedumps. Our results illustrate the complexity of herbivoreplantinteractions emphasizing the need of measuring directand indirect effects of herbivory in field conditions to validategreenhouse experiments.