Species response to rapid environmental change in a Subarctic pond
Lemmen, Kimberley Dianne
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Unprecedented rates of anthropogenic environmental change have resulted in dramatic decreases in biodiversity worldwide. In order to persist during changes in both the abiotic and biotic environment resulting from anthropogenic stressors such as climate change and habitat degradation, populations must be able to respond or face extirpation. Predicted population-level responses to environmental change include i) range shifts as individuals disperse into more suitable regions, ii) phenotypic plasticity allowing for shifts in the mean phenotype of the population or iii) microevolution resulting from a genetic change within the population. The goal of this thesis is to assess how species within a community respond to a dramatic change in the environment. This study used the sediment record of a Subarctic pond to investigate the impacts of a rapid increase in salinity on two species of the crustacean zooplankton Daphnia. One species, Daphnia tenebrosa, was unable to persist in the high salinity conditions and is believed to have been extirpated from the system. The other species, Daphnia magna, was tolerant of the new environmental conditions and was present throughout the sediment record. To investigate the changes in life history of D. magna, resting eggs from the sediment were hatched to compare iso-female lines from pre- and post-disturbance time periods. No differences were observed between the clone lines, suggesting that phenotypic plasticity allowed D. magna to persist despite the rapidly changing environmental conditions, and that microevolution in salinity tolerance may not have occurred in this population. This study suggests that, in environments with moderate levels of post environmental change, pre-existing phenotypic plasticity may play a greater role than microevolution in species response to environmental changes. However, not all species from a community display the same response to environmental changes, as seen in this study with the extirpation of D. tenebrosa. To better understand how communities will be affected by future environmental change, further investigations need to be made on what factors influence species response. Identifying species response may allow conservation efforts to focus on species that are unlikely to adapt to environmental change, and are most at risk.