The influence of vertebrate and invertebrate planktivores on zooplankton communities in lakes on the Avalon Peninsula of Newfoundland

Campbell, Christine Elaine (1990) The influence of vertebrate and invertebrate planktivores on zooplankton communities in lakes on the Avalon Peninsula of Newfoundland. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Predation by vertebrate and invertebrate planktivores in freshwater lakes can lead to decreases in total biomass of the pelagic zooplankton community and can alter zooplankton community structure (defined by species and size-class frequencies). However, the relative influence of predation on the zooplankton community as compared with the influence of lake productivity and physicochemical characteristics is unclear. Planktivore impact should be greatest in lakes such as those on the Avalon Peninsula of Newfoundland that have low faunal diversity, which may strengthen the intensity of predator-prey interactions, and low habitat heterogeneity, which may elevate species encounter rates. Vertebrate and invertebrate predation was assessed in 15 oligotrophic Avalon lakes through determination of planktivore distributions, abundances and prey selectivities, along with total biomass and species and size composition of the zooplankton community. Phytoplankton biomass and lake physicochemical characteristics were monitored to evaluate their influence relative to that of the predators. -- The major planktivores in the lakes are the vertebrate Gasterosteus aculeatus, the threespine stickleback, and the invertebrates Chaoborus punctipennis, Chaoborus trivittatus and Leptodora kindtii. Analysis of planktivore distribution patterns (presence/absence data) revealed that the distributions of both Chaoborus species were significantly and negatively related to the distribution of sticklebacks. 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. Examination of planktivore gut contents indicated that G. aculeatus selected mainly for large cladocerans (> 0.76 mm in length) while Chaoborus and Leptodora selected for rotifers and small cladocerans (<0.50 mm in length). Total zooplankton biomass was significantly and negatively related to stickleback catch (linear regression: r²= 0.40), suggestive of predator control limiting zooplankton populations, but was not significantly related to total invertebrate planktivore density. Zooplankton biomass was further related to a physicochemical principal component identified as increasing ionic strength (multiple linear regression: cumulative R² = 0.65). Multivariate analyses revealed that zooplankton community structure was related to factors describing ionic strength, lake size, nutrient concentrations, and watershed characteristics, as well as to stickleback catch. Hence, even in these shallow and oligotrophic lakes in which predation would be expected to have a major impact on the zooplankton community, planktivore abundance is not the primary influence on zooplankton biomass and community structure.

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