Abiotic drivers of consumer foodweb structure in lakes

The effects of the combined roles of abiotic and biotic factors defining foodweb structure are often ignored. In aquatic systems, abiotic variables can regulate food webs through bottom-up effects, but abiotic settings also can have indirect effects on aquatic food webs that are mediated through shifts in the magnitudes of top-down and bottom-up effects. We used link-and-chain properties (LCP) and stable-isotope community metrics (SIM) to assess the trophic structure of consumers in 10 world lakes. Our goal was to identify the key abiotic variables driving these metrics through multivariate regression trees (MRTs). Food-chain length in the lakes did not depend on any LCP metric and was controlled mainly by resource availability and foraging biology of top generalist (omnivore) species. Variances explained by abiotic variables used in MRT models on LCP and SIM were high (71-74%) and showed that altitude, followed by water temperature, was the main factor of dissimilarity among lake food webs. This result implies that abiotic variables other than those related to water quality were accountable for some variance of the lake foodweb structure. MRT results showed that these abiotic variables exerted a common pattern of influence among foodweb size and trophic redundancy in food webs of lakes. The physical environment was the main driver of abiotic variables on trophic structure in pristine lakes, whereas effects of water quality (which include most human effects) were restricted to lakes at the lower part of river basins.