Insetos sobre plantas: efeito do estágio de desenvolvimento de Anadenanthera macrocarpa (mimosaceae) sobre assembleias de formigas e insetos herbívoros

Abstract

Growth and ontogeny are important processes in plant development. The first is related with the plant physiology and consists in the increment in crown height and in complexity without change in the plant’s gene expression. The second consists of a special case of plant development that is generated by a change in gene expression, occurring mainly in the meristem, and which results in abrupt changes in the vegetative structures throughout the plant. The processes of tree development can influence the distribution of insects in crowns, although studies on this are scarce. Therefore, the aim of this work was to determine the effect of the developmental stage of Anadenanthera macrocarpa (a mirmecophilous and homoblastic plant) on ant and herbivore insect assemblages, and their consequences for plant herbivory. The study was conducted between January and February 2004 in the Rio Doce State Park (PERD). Ants and insect herbivores were sampled in 30 individuais of A. macrocarpa from different developmental stages, from young individuais (> 3 m in height) to emergent trees (up to 40 m). Ants were collected using pitfall traps and beating, while insect herbivores with beating only. Among several other measures of plant structure, the variable height was chosen as the best representative of A. macrocarpa development stage and then it was used in all analyses. Larger individuais presented a greater tree trunk, a larger crown and a more complex architecture. There was a significant increase in both the abundance and species richness of ants and herbivore insects with an increase in plant height. In addition, plant height had a significant effect on the species composition of ants and herbivore insects. In general, the species found in small- and medium-sized trees consisted of a subset of the species found in larger, canopy trees. There was a negative effect of ant abundance on herbivory leveis, which was independent of the plant height, suggesting that ants act as biotic defense agents of A. macrocarpa. Although ants and herbivore insects had different biology, they responded in a similar way, although with different intensities, to the changes generate by the plant’s development. It is likely that the observed increase in the abundance and species richness of ants and herbivores is related to the greater heterogeneity of the crown and surrounding environment in the canopy habitat