Food web simplification driven by land use in lowland riverine wetlands

Abstract

Ecological interactions, such as food webs, are fundamental for predicting ecosystem responses to environmental changes and anthropogenic disturbances. With wetland ecosystems facing escalating threats from intensified land use, our study aimed to assess the effect of land use on macroinvertebrate food webs across four riverine wetlands situated in lowland streams of the Pampean ecoregion in Argentina. Two wetlands were situated in peri-urban agriculture areas, whereas the other two were located in rural areas with extensive livestock. Through macroinvertebrate sampling and gut content analysis, we present a general description of the diet and a classification of species on the basis of the proportion of different food items in their gut contents. Food webs were constructed for each wetland using the gut content data and structural attributes, such as food web size, number, complexity, and density of trophic links among others, were estimated. Our findings reveal that detritus is the primary resource in macroinvertebrate diets across all wetlands, followed by animal and plant remains. Peri-urban agricultural riverine wetlands exhibited simpler food webs compared to the rural ones, with smaller food web size and lower number, density, and complexity of trophic links. Rural wetlands were characterized by a higher degree of omnivory and proportion of top nodes, whereas peri-urban agricultural wetlands presented a higher number of basal nodes and resource: consumer index. These results suggest that land use may affect the structure of macroinvertebrate food webs in riverine wetlands, contributing to a better understanding of the functioning of these valuable ecosystems.