Thursday, August 9, 2007 - 10:50 AMOOS 36-9: The consequences of anthropogenic impact on the disruption of biotic interactions in tropical dry forest ecosystems
Rodolfo Dirzo, Stanford University
In comparison to tropical rain forests, seasonally dry tropical dry forests have been poorly studied, particularly from the perspective of plant-animal interactions. However, some pioneer and some recent studies show that the diversity, complexity and exuberance of plant-herbivore interactions can be similar in both forest types. In this presentation I describe some representative case studies of intricate plant-herbivore interactions, and document the general patterns of herbivory in Mexican tropical dry forests, comparing herbivory regimes in trees from hill-sides and from riparian habitats. Trees in the hillsides are deciduous while those of riparian habitats are evergreen. I hypothesized those trees from riparian habitats, because they are exposed to herbivores throughout the year, should be better defended and should sustain lower levels of herbivory. The comparison shows that rates of herbivory are significantly lower in evergreen plants and that these have higher concentrations of defensive metabolites and tougher leaves than deciduous species. I interpret these patterns as the result of selective pressure due to continuous exposure to herbivory, given that several species of phytophagous insects migrate to riparian habitats during the dry season. The intricate specific interactions I used as examples and the described patterns of herbivory are likely to be disrupted with the current anthropogenic impact which is characterized by higher deforestation rates in the riparian habitats than in hillsides. Over the long-term this might have repercussions not only in terms of the alteration of herbivory regimes, but also in terms of the survival of insects that depend on the riparian trees during the dry season