Distribution patterns of vertebrate and invertebrate planktivores in Newfoundland lakes with evidence of predator–prey and competitive interactions

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Abstract
The vertebrate Gasterosteus aculeatus, the threespine stickleback, and the invertebrates Chaoborus punctipennis, Chaoborus trivittatus, and Leptodora kindtii are the major predators of zooplankton in lakes on the Avalon Peninsula, Newfoundland. Predator–prey and competitive interactions among these planktivores are potentially strong. 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. Analyses of distributional patterns (presence or absence data) of the planktivores in 15 Avalon lakes indicated that the distributions of both Chaoborus spp. were significantly and negatively related to the distribution of sticklebacks. Chaoborus densities were significantly higher in the lakes without sticklebacks. Sticklebacks were observed to eat third and fourth instars of both Chaoborus species in laboratory experiments 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, however 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 (multiple linear regression, r2 = 0.71).