Interações entre aranhas, formigas e plantas com nectários extraflorais: redes ecológicas e efeitos recíprocos

Abstract

Ecological interactions, such as those established between extrafloral nectary-bearing plants and predator arthropods, are very important for the maintenance of species diversity and structure of food webs in ecosystems. In this context, this study aimed to know and characterize the interactions involving extrafloral nectary-bearing plants, spiders and ants. We also verify the impacts of these predators on plant s herbivores and herbivory. We aimed still, by laboratory tests, to prove nectar consume by wandering and web weaver spiders. All studies took place in cerrado sensu stricto area in Clube de Caça e Pesca Itororó, located in Uberlândia County, Minas Gerais State, Brazil, between August 2012 and February 2014. In an initial survey, we found 35 ant species and 74 spider species associated to 19 extrafloral nectary-bearing plant species. The interaction networks between spiders and plants and ants and the same plants were significantly nested and with low specialization, as in other facultative mutualistic systems. This pattern of interactions occurred in the diurnal and nocturnal period, despite changes in the composition and position of species in the networks. We found an emergent impact of spiders and ants on herbivores in two plant species with high importance index in the studied community, Heteropterys pteropetala (Malpighiaceae) and Ouratea spectabilis (Ochnaceae), by experiments of exclusion of predators. However, the herbivory in these species were only reduced in the presence of spiders. We found that about 88% of collected spiders in extrafloral nectary-bearing plants consume nectar, by chemical analyses in laboratory. The positive results covered adults and immatures, wandering and web weaver spiders. This study highlights the importance of studying ecological interactions in broader perspective, in the community level, in order to know general patters and processes inherent to the interactions.