Elucidando a competição intra e interespecífica em ninfas de libélulas neotropicais

Abstract

Understanding the processes that structure natural communities is one of the ultimate goals of ecology. Among these processes, competition is fundamental to maintaining biodiversity. According to the Coexistence Theory, for two or more species to coexist, it is necessary to follow the criterion of invasibility, when they are capable of invading a community and increasing their abundance when rare. Thus, one of the mechanisms that can favor coexistence is to make intraspecific competition greater than interspecific competition, so that each population self-regulates before competitively excluding the other. However, when the invasibility criterion is not met, species can co-occur in the long term when they have no ecological differences (equivalent) and their populations are simply affected by neutral demographic processes (independent of the species). Dragonfly nymphs are organisms that are potentially affected by neutral processes, as they are opportunistic generalists, with similar sit-and-wait strategies. Thus, to test the ecological equivalence of dragonfly nymphs, competition experiments were conducted in microcosms under controlled conditions. Our experiments manipulated total abundances in monocultures and relative abundances in pairs of species of Libellulidae and Coenagrionidae, with the aim of quantifying the intra- and interspecific per capita effect on mortality, spatial distribution, number of emergences and ecdyses. The results revealed that there is strong intraspecific competition compared to interspecific competition, leading to higher mortality in situations with higher intraspecific densities for both species. Our calculations of the coexistence mechanisms suggest a high spatial niche differentiation and small differences in fitness, leading to a potential stabilization in the coexistence of dragonfly nymphs of the two families.