Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Dr. Derek Gray

Advisor Role

Thesis Supervisor

Abstract

The North American Great Plains is home to thousands of closed-basin lakes that are sensitive to changes in hydrology. Climate change models predict increased aridity in this region over the coming century, which is expected to lead to higher salinity levels in many freshwater lakes. Increases in salinity levels may impact zooplankton communities, as laboratory experiments show that many freshwater species have a low tolerance for elevated salinity levels, and field data demonstrate that salinity is the primary factor structuring aquatic communities on the Great Plains. Changes to zooplankton communities could lead to a trophic cascade based on their important position in the lower food web, making it important to understand how they might respond. Zooplankton in lakes undergoing salinization may exhibit shifts in community structure toward salinity-tolerant species and a decrease in richness, diversity, and abundance. As a counter, the dispersal of zooplankton across the landscape from neighbouring water bodies may be able to compensate for the losses of sensitive zooplankton due to local adaptation to elevated salinities as well as taxonomic and functional redundancies in the regional species pool. For this study, I ran a field experiment at Kenosee Lake in southern Saskatchewan where salinities and zooplankton dispersal rates were artificially manipulated over six weeks. We found that increased salinities led to reduced zooplankton abundances and species richness levels, mainly due to a loss of cladocerans. However, enclosures with moderate salinities that received dispersers maintained a community composition similar to undisturbed control communities. The persistence of cladocerans in moderate salinity enclosures receiving dispersal may have been caused by a source-sink effect or the introduction of salinity-tolerant cladocerans. I ran laboratory toxicity assays using Daphnia collected from the plains and found that intraspecific variation in salinity tolerance exists, making the latter explanation plausible. My results indicate that dispersal could play an important role in determining how zooplankton communities respond to increased salinity levels, demonstrating the need to preserve biodiversity in the regional species pool and maintain the vectors and pathways that facilitate the dispersal of zooplankton among lakes on the Great Plains.

Convocation Year

2019

Convocation Season

Spring

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