Niche specialization in dragonflies

Two organisms minimize competition and enable co-occurrence if they use their environmental requirements differentially. Niche specialization occurs at the interspecific but also at the intraspecific level, whereby we suggest that time, space and food are the three most important niche dimensions. A general aspect of the biology of dragonflies is that adults and larvae live in totally different habitats, and so they occupy different ecological niches. Climate, temperature and competition lead to different life-histories (e.g. duration of embryonic and larval development, diapause and larval growth rate) and to different diurnal and seasonal activity rhythms of adults. Spatial niche specialization occurs in all three dimensions with two-dimensional segregation being the most common one of these. It is shown that spatial niche segregation is highly dependent on the actual degree of competitive interactions. Temporal and spatial niche specialization, as well as the utilization of different diets or differentsized prey, reduce food competition. The impact of different predators (invertebrates and vertebrates) in larval habitats may be minimized by special antipredator defence strategies. Oscillating or stable predator dominances in the larval sites advance species with different migration tendencies.