Macroinvertebrates select complex macrophytes independently of their body size and fish predation risk in a Pampean stream

Macrophyte complexity has been associated with high abundance and richness of macroinvertebrates. While the effect on richness has been attributed to an increase in the number of niches, the effect on abundance has been explained by a higher availability of space for small individuals, refuge and/or food. For studying effects of complexity on macroinvertebrates we used complementary approaches of laboratory choice and field colonization experiments, with macrophytes (Egeria densa and Elodea ernstae) and plastic imitations of contrasting fractal dimension. We investigated whether macroinvertebrates may actively select complex habitats by Hyalella sp. choice experiments. Then, we tested effects of complexity on macroinvertebrate density, biomass, richness, diversity and body size using colonization experiments. Finally, a caging experiment was performed to study interacting effects of complexity and predation. The active choice of complex substrates by Hyalella sp., and the significant positive relationship between macrophyte fractal dimension and macroinvertebrate density supports the existence of a positive effect of complexity on abundance. As macroinvertebrate length was not associated with fractal dimension, such differences could not be attributed to a higher space available for smaller invertebrates in complex plants. Finally, neither macroinvertebrate density nor size were reduced by fish predation in the Las Flores stream.Fil: Ferreiro, Nicolas Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación En Biodiversidad y Medioambiente; Argentina. Universidad Nacional de Lujan. Instituto de Ecologia y Desarrollo Sustentable; Argentina. Universidad Nacional del Comahue; ArgentinaFil: Feijoó, Claudia Silvina. Universidad Nacional de Luján; ArgentinaFil: Giorgi, Adonis David Nazareno. Universidad Nacional de Lujan; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rosso, Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata; Argentin