Riqueza e abundância de insetos galhadores associados ao dossel de florestas de terra firme, várzea e igapó da Amazônia Central

Abstract

Landscape mosaic found in the Amazonian region is enormous, as well as variation within habitats. This study focused distribution patterns of gall-forming insects, in three types of Amazonian vegetation: terra firme forests, vegetation which never suffer flooding, várzea forests and igapó forests, both seasonally flooded by water level fluctuation. In accordance with hypothesis of water and nutrient stress, plants that grow in poor soils and with shortage or excess of water are more sensitive to galling insect attack. It were sampled 50,238 insect galls in the two flooded forests, 246 gall morphospecies in the igapó and 302 morphospecies in the várzea forests. Of 250 igapó sampled trees, 229 presented insect galls. In the várzea forest, it was verified a higher number of non-attacked plants, 66 individuals of 312 trees. Gall-forming insect abundance did not present statistical differences between habitats or forest types. However, igapó forest showed a trend of lower number of tree species accumulates higher number of galling species. Then, trees of seasonally flooded forest can be more or less attacked by gall-inducing insects, depending on the nutrient availability in the system, corroborating the nutritional stress hypothesis. In the terra firme forest, size and isolation degree of forest fragments determine colonization and extinction rates, and then populations survival and maintenance. Small fragments are dominated by edge processes, presenting an increase in air temperature and soil/air moisture decrease, affecting local flora and fauna. In a total, 91,006 insect galls were collected in 503 continuous forests and fragments trees. Continuous forests and fragments did not exhibit significant differences in the abundance, richness and composition of galling species. Landscape configuration, secondary vegetation around fragments and similarity in the number of sampled trees in fragments and continuous forest can explain the obtained results. Comparisons among terra firme, várzea and igapó forests showed a differential abundance and richness due to variation on tree diversity in each landscape. Higher galling species richness and abundance were found on terra firme forest, compared to igapó and várzea forests. Besides, the ratio between gall- forming insect richness and sampled plant richness (GIR/SPR ratio) was significantly larger in igapó and terra firme forests, while várzea forest presented the lower values for this ratio. However, GIR/SPR ratio of várzea was approximately 2.5 higher than the greater value of this ratio on literature. In this sense, the poorest Amazonian vegetation (várzea) display one of the highest diversity of gall-forming insects, among all biogeographic realms already investigated. The results of this study corroborate Fernandes & Price (1988, 1991), Price et al. (1998) and Ribeiro (2003) hypotheses, once upper canopy represents a higrotermically stressed habitat, with higher sclerophylly levels, compared to a moist and non-scleromorphic understory environment of the Amazonian forests.