The structural complexity of habitats and the distance from the dispersion source are considered important determinants of species diversity. The fractal dimensions of substrates are a strong alternative measure for quantifying the structural complexity. In this paper, we tested the hypothesis that structural complexity and distance from a dispersion source affect the density and diversity of macro-invertebrates on submersed macrophytes. To test this hypothesis, we used artificial substrates with different fractal dimensions, which were incubated at different distances from a dispersion source (a stand of macrophytes) in a Neotropical floodplain lake. The relationship between the structural complexity of macrophytes and the density and diversity of invertebrates attached to artificial substrates was positive and significant. On the other hand, distance from the dispersion source negatively affected both the density and diversity of the attached invertebrates. For Oligochaeta, however, there was a significant effect of structural complexity for the artificial plants positioned further away, but it was not significant in the plants positioned closer to the dispersion source. Thus, the effects of complexity depended on the distance from the dispersion source, at least for this specific group of macro-invertebrates. These results suggest that both structural complexity and distance from the dispersion source should be considered together to explain the diversity of invertebrates in river–floodplain systems. In addition, our results show that there is great potential for using fractal dimensions as a tool to quantify structural complexity in aquatic habitats, especially at the small spatial scales perceived by macro-invertebrates.
Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp.