Qualitative Analysis of the Pelagic Foodwebs of Three Acid‐impacted Lakes in Nova Scotia, Canada

Abstract

AbstractLoop analysis is a qualitative network technique which is useful for delineating pelagic foodwebs and for predicting production relationships. Loop models were fitted to data sets for three lakes in Kejimkujik National Park, Nova Scotia. Using qualitative correlation signs, there was 80–89 percent agreement of model predictions and data values. Individual networks were integrated by summarizing linkages between pairs of variables. The resultant core network is a three‐layered structure with 5 nutrient, 4 algae, 1 detritus and 10 zooplankton variables. The phytoplankton components utilize different types of nutrient complexes in each lake. Bluegreen algae have a special relationship to ammonia in Beaverskin Lake. Crustacean zooplankton consume phytoplankton directly whereas rotifers are connected to the foodweb via the detrital pool.In contrast to the multivariate statistical results reported by Blouin et al. (1984), loop analysis furnished some robust evidence of the inherent structure in these plankton communities. Qualitative methodology also helps identify casual pathways in the ecological networks. The analysis illustrated which links are oscillating the most and which are expected to remain resilient with increasing perturbation. The models suggest several aspects of these communities that could be verified experimentally.