Use of Fractal Dimension to Assess Habitat Complexity and Its Influence on Dominant Invertebrates Inhabiting Tropical and Temperate Macrophytes

We evaluated the feasibility of using fractal geometry to measure the structural complexity innate to 11 species of temperate and tropical macrophytes. The efficacy of fractal dimension (D) as a surrogate of plant complexity was tested by using D values to predict the density of two dominant invertebrate taxa (Annelida and Odonata). Plants and invertebrates were collected from lagoons in the upper Paraná River, Brazil, and from a lake in central Minnesota, USA. Fractal dimensions varied from 1.16 (SD=0.03) in Potamogeton illinoiensis to 1.68 in Najas conferta (SD=0.07) and Myriophyllum spicatum (SD=0.02). Spatial scale did not affect D values, since the results obtained for pictures taken at 25 cm2, 100 cm2 and 600 cm2 did not differ for five tropical species. Using the results of D recorded at 100 cm2, a positive and significant relationship between plant complexity and Annelida and Odonata densities was observed. The biological significance of the positive correlations between D and invertebrate densities and the feasibility in calculating D make this method a potential candidate for measuring plant complexities at small scales.