DISTRIBUTION PATTERNS OF VERTEBRATE AND INVERTEBRATE PLANKTIVORES IN NEWFOUNDLAND LAKES WITH EVIDENCE OF PREDATOR PREY AND COMPETITIVE INTERACTIONS

Gasterosteus aculeatus (threespine stickleback), Chaoborus punctipennis, Chaoborus trivittatus and Leptodora kindtii are the major predators of zooplankton in lakes on the Avalon Peninsula. Low faunal diversity in the lakes limits the number of interacting species, which may increase the intensity of the interactions, while the low habitat heterogeneity of the lakes decreases the probability of spatial separation of species to increase rates of species encounters. Distributions and densities of both Chaoborus spp. were significantly and negatively related to the distribution of sticklebacks. Sticklebacks are 3rd and 4th instars of both Chaoborus species and hence, through predation, may be able to exclude these species from some lakes. There was no significant relationship between the distributions of Leptodora and sticklebacks or between Leptodora and C. punctipennis, though the distributions of Leptodora and C. trivittatus were significantly and negatively related, indicating a possible competitive interaction. Environmental factors also influence planktivore distribution and abundance: a principal components factor derived from planktivore density data was significantly correlated with cyclopoid copepod biomass, lake SO4 levels, and lake surface area. -from Authors