Land use extent and intensity affect the trophic structure of apex fish in neotropical lagoons

Abstract

The conversion of natural ecosystems to human land use is a primary cause of worldwide biodiversity loss and trophic structure changes in ecosystems. We investigated the effect of human land use at different spatial extents and aquatic trophic state on basal energy sources, food chain length (FCL), and the isotopic niche of apex fish in four large neotropical wetlands. We had two hypotheses. (i) Increased regional human land is negatively associated with the contributions of allochthonous energy sources, FCL, and isotopic niche. (ii) Trophic state is directly associated with FCL, autochthonous energy source, and niche area. We found that C₃ riparian vegetation was the primary energy source for apex consumers. Human land uses in a 5000 ​m buffer were directly associated with allochthonous basal-energy source assimilation and niche area and indirectly with FCL. FCL was shorter in environments with more human land use and allochthonous energy source assimilation had an important role on FCL. Therefore, conserving riparian vegetation surrounding water bodies is a crucial protective factor for waters, as it serves as a primary energy source for food webs. Decreased FCL with increased human activity demonstrated the sensitivity of these environments to trophic-link losses from human invasion. Conversely, increased isotopic niche areas in environments with high human activities may be attributed to the introduction of new energy sources from those activities. Hence, the loss of natural cover resulting from human activities is an important factor in aquatic trophic structure changes.