Interação entre vertebrados e frutos/sementes em uma floresta de igapó na Amazônia central

Abstract

In igapó forests, water dynamics during river level recession is responsible for the seed patch formation. Animal-plant interactions that occur in that environment, as well as patches’ influence on frugivorous and granivorous vertebrates’ occurrence are unknown. This work is divided into two chapters and investigates i) the possible interaction between rodents and fruit/ seed, based on the bite sizes left in the fruits and ii) the role of seed patches in overall habitat use by vertebrate species in an igapó forest in Jaú National Park. Rodents have a highly specialized dentition, and incisor dimensions are very characteristic within each species. In chapter one, we field-tested a rarely-used methodology – using marks left by rodent incisors in fruits and seeds to identify the feeding species. The width of the incisors marks made in Plasticine™ blocks, using skulls in museum collections, were compared with the marks left on field-collected fruits and seeds. We confirmed the existence of an allometric relationship between incisors width and body size. Furthermore, larger and harder fruits showed larger bite marks compared with smaller and soft fruits/seeds, indicating the importance of fruit size and hardness in rodent food-plant selection. Based on tooth width measurements, the results also showed that smaller fruits/seeds are used by fewer rodent species, in comparison to fruits of larger size, these being more likely to be consumed and/or predated. Due to an overlap in body size between species, the method did not provide precise identifications of the rodent species consuming particular items, although it does reduced the likely suite of species in 46%. However, when used in conjunction to other methods, this is highly viable field technique due to its easy use and low cost. In chapter two we report on the deployment of camera traps in areas with and without the seed patches to examine the relation between these accumulation sites and birds and mammals species presence. It was recorded that vertebrates assemblage occurrence is not related to patch presence. However, there is a positive relationship between predator occurrence and spatial distribution of the vertebrate assemblage, indicating that predator species may be following their potential prey in unflooded igapó, and so possibly erasing granivore/seed associations that might otherwise occur. The widespread occurrence of these seed eaters animals throughout igapó, not only where are high density food resources, seems to be a compromise strategy that balances between selecting the most favorable food items with avoiding the higher predation risk of being foraging for prolongued periods at the seed patches. Our results underscore the potential importance of igapó forests as a key habitat for a variety of terra firme terrestrial taxa, and open the way for further studies.