Effects of littoral habitat complexity on trophic structure

The functional importance of habitat complexity and heterogeneity has wide-ranging implications for the restoration and protection of wetland habitats. The loss of littoral complexity due to shoreline modifications, water level fluctuations or invasive species may have negative consequences not only for biodiversity but also for ecosystem processes; however, little is known about the role of macrophyte complexity and bathymetric heterogeneity in supporting diverse food webs. To address this knowledge gap, we used stable isotopes to characterize the trophic niche of macroinvertebrate predators across a gradient of macrophyte complexity. Our results show a wide range in individual isotopic signatures within what is commonly averaged out as one minor trophic level of macroinvertebrate predators. Trophic position had a complex relationship with habitat attributes but was not strongly correlated with macrophyte canopy cover, and that deep and shallow vegetated areas only a few meters apart had distinctly different integrated food webs based on predator isotopic niches. Maximum trophic position and predator niche overlaps were not correlated with the coarse measures of complexity, potentially because of the truncated complexity gradient and lack of predators in the lowest-complexity habitats. These findings underscore the need to consider more individuals to capture the intra-guild variation in food web studies and are potentially transformative for interpreting foods webs constructed with the commonly used replication of three samples per guild (or major habitat). This study can also inform the design of future research aimed at advancing functional assessments of complex habitats increasingly threatened by anthropogenic stress.