Consequences of leaf-cutting ants on plant fitness: integrating negative effects of herbivory and positive effects from soil improvement
- 331 Downloads
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. To estimate the negative and positive effects on plants, we sampled 7000 plant fragments carried by the ants and analyzed the nutrient contents of refuse dumps in 15 ant nests. We estimated plant fitness measuring ~10,000 flowers and ~3600 fruits of 122 individuals from 7 of the most common plant species within the ant foraging area. First, we compared the fitness between plants growing on the nutrient-rich refuse dumps and co-specifics 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. To explain this pattern, we discuss the role of plant compensation to foliar damage, the limited plant response to soil nutrients due to water stress and the potential high abundance plant consumers on ant refuse dumps. Our results illustrate the complexity of herbivore-plant interactions emphasizing the need of measuring direct and indirect effects of herbivory in field conditions to validate greenhouse experiments.
KeywordsAcromyrmex lobicornis Ant foraging Indirect effects Monte desert Nest effects Patagonia Plant fitness Structural equation models
This work was partially funded by CONICET, Argentina (PIP 1320) and FONCyT, Argentina (PICT 1406). The comments of three anonymous referees greatly improved earlier versions of this manuscript.
- Correa MN (1969) Flora Patagónica. Instituto Nacional de Tecología Agropecuaria, Buenos AiresGoogle Scholar
- Farji-Brener AG, Ghermandi L (2008) Leaf-cutting ant nests near roads increase fitness of exotic plant species in natural protected areas.Proc R Soc Ser B 275:1431–1440Google Scholar
- Hölldobler B, Wilson EO (2011) The leafcutter ants. Civilization by instinct. WW Norton & Company, New YorkGoogle Scholar
- Mazzarino MJ, Bertiller MB, Schlichter T, Gobbi M (1998) Nutrient cycling in Patagonian ecosystems. Ecol Austral 8:167–181Google Scholar
- Rojas P (1989) Entomofauna asociada a los detritos de Atta mexicana (Hymenoptera) en una zona árida del centro de México. Acta Zoológica Mexicana 33:1–51 Google Scholar
- Sparks D, Page A, Helmke P, Loeppert R, Soltanpour P, Tabatabai M, Johnston C, Sumner M (eds) (1996) Methods of soil analysis. SSSA, ASA, Madison, Wisconsin, E.E.U.UGoogle Scholar
- R Core Team (2013) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0. http://www.R-project.org
- Vasconcelos HL, Fowler HG (1990) Foraging and fungal substrate selection by leaf-cutting ants. In: Vander Meer R, Jaffe K, Cedeno A (eds) Applied myrmecology—a world preview. Westview Press, Boulder, pp 411–419Google Scholar
- Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM (2009) Mixed effects models and extensions in ecology with R. Statistics for biology and health. Springer Science + Business Media, LLCGoogle Scholar