Ontogenetic Diet Shifts among Neotropical Stream Macroinvertebrates

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Size-dependent dietary shifts, which are often linked to gape-size limitation and intraspecific competition, are common among vertebrates. However, few studies have examined these patterns in aquatic macroinvertebrates. We examined gut contents, tissue chemistry, and excretion of different size classes of dominant macroinvertebrate taxa in a Panamanian headwater stream. As they grew, non-predatory taxa and predatory midges increased consumption of vascular plant material and amorphous detritus and decreased consumption of non-algal biofilm. Predatory taxa shifted from high degrees of omnivory to more carnivorous diets during later instars, likely due to gape limitation. Nitrogen (N) and phosphorus (P) excretion rates decreased with increasing size, suggesting reduced nutritional demands of later instars. Also, P content of macroinvertebrate tissues decreased with size, suggesting ontogenetic shifts from smaller, nutrient-rich foods to larger, nutrient-poor food types with increasing individual size. More nutritious resources are essential for growth during early instars, while later instars may switch to detrital resources due to higher availability and lower nutritional demands. Our results suggest generalist feeding patterns are prevalent among tropical stream macroinvertebrates, which may facilitate coexistence in biologically diverse regions.


Society for Freshwater Science Annual Meeting (SFS)


Louisville, KY