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

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.Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorDoutor em Ecologia e Conservação de Recursos NaturaisInterações ecológicas, como aquelas estabelecidas entre plantas com nectários extraflorais e artrópodes predadores, são muito importantes para a manutenção da diversidade de espécies e estrutura das teias tróficas nos ecossistemas. Nesse contexto, este estudo se propôs a conhecer e caracterizar as interações envolvendo plantas com nectários extraflorais, aranhas e formigas. Buscamos também verificar os impactos desses predadores sobre os herbívoros e a herbivoria das plantas. Objetivamos ainda, por meio de testes em laboratório, comprovar o consumo de néctar por aranhas errantes e construtoras de teia. Todo o estudo foi conduzido em área de cerrado sentido restrito no Clube de Caça e Pesca Itororó em Uberlândia, Minas Gerais, no período de agosto de 2012 a fevereiro de 2014. Em um levantamento inicial, nós encontramos 35 espécies de formigas e 74 espécies de aranhas associadas às 19 espécies de plantas com nectários extraflorais avaliadas. As redes de interações entre aranhas e plantas e entre formigas e as mesmas plantas foram significativamente aninhadas e com baixa especialização, como em outros sistemas mutualísticos facultativos. Esse padrão se manteve no período diurno e noturno, apesar das mudanças na composição e posições das espécies nas redes. Por meio de experimentos de exclusão de predadores, nós constatamos que houve um impacto emergente de aranhas e formigas sobre herbívoros em duas espécies com alto índice de importância na comunidade estudada, Heteropterys pteropetala (Malpighiaceae) e Ouratea spectabilis (Ochnaceae). No entanto, a herbivoria nessas espécies foi reduzida somente na presença de aranhas. Por meio de análises químicas em laboratório, constatamos que cerca de 88% das aranhas coletadas em plantas com nectários extraflorais consomem néctar. Os resultados positivos abrangeram adultos e imaturos, aranhas errantes e construtoras de teia. Esse estudo realça a importância de estudar interações ecológicas em uma perspectiva mais ampla, em nível de comunidade, a fim de conhecermos padrões e processos gerais inerentes às diversas interações

Limited effects of fire disturbances on the species diversity and structure of ant-plant interaction networks in Brazilian Cerrado.

Fire is one of the main natural disturbances in Tropical Savannas, changing the diversity of species, altering the structure of species interactions, and driving the evolution of adaptations. Here, we investigated the effects of fire disturbance on interactions between ants and plants with extrafloral nectaries in Cerrado (Brazilian Savanna). We carried out the study in two different ecosystems of Brazilian Cerrado 700 km apart; Woody Cerrado and Rupestrian Grasslands. We conducted a Before-After-Control-Impact (BACI) experiment, in which the impact was the disturbance caused by fire. In Woody Cerrado, we found no evidence of fire affecting the diversity and composition of plants or its interactions. Fire also did not affect ant diversity but changed the interaction pattern of its interactions by reorganizing the paired interactions between species (i.e., rewiring). However, this effect did not result in changes on the overall structure of the network. In Rupestrian Grasslands, fire also did not affect the diversity and composition of plant species or its interactions, but it did increase the number of ant species and change its composition, leading to a reorganization of the its paired interactions. However, these fire disturbances in the ant level did not affect the overall structure of the network. Our findings indicate that the structure of ant-plant interaction networks is robust to fire disturbances, more in Woody Cerrado than Rupestrian Grasslands, confirming our hypothesis that ant-plant interactions in Cerrado are adapted to fire disturbances. In sum, our study enhances the understanding of the effects of environmental disturbances and the stability of the ant-plant interactions in fire-adapted ecosystems such as Brazilian Cerrado