Structure and dynamics of food webs in Andean lakes

Abstract

Food webs from oligotrophic Andean lakes of Bariloche region (41°S) are described. Their peculiarities in comparison with Northern Hemisphere studies are noted. The endemic species composition, the extended euphotic zone, and the oxygenated bottom allow a particular structure of the pelagic and benthic food webs. Experimental work with pelagic communities indicates that models based only on zooplankton body size are questionable and that nutrient enrichment does not necessarily lead to a positive effect on herbivorous populations. Invertebrate predation effects depend on the lake and type of predator, while vertebrate predation does control crustacean populations. The characteristic low species richness of top predators is likely to change following the introduction of exotic salmonids. The benthic food web is quite distinctive with a slow rate of decaying organic matter and easily altered by the introduction of exotic tree species.