These projects are led by Aaron Bell

10,000 years ago, Lac la Ronge and the surrounding region were covered by Lake Agassiz, a massive glacial lake that formed as the Laurentide Ice Sheet retreated1. Today, Lac la Ronge is the fifth largest lake in Saskatchewan and home to more than 1300 islands of varying sizes and isolation. The geology of the lake is distinct, with rugged contours of Precambrian rock giving rise to a multitude of islands (and reefs) in the north, and sand and clay sediments that form the island-less basin in the south. The islands are heavily forested and except for a few summer cottages, are virtually untouched by human activity. Together, these features make Lac la Ronge and ideal location for studying island biogeography.

The islands were recently studied as part of Aaron Bell’s graduate work at the University of Alberta2,3. This work focused on ground beetles which, as their name suggests, occupy the surface of the forest floor, feeding on a variety of animal and plant materials. Ground beetles are model organisms for studying islands in part because dispersal ability varies widely between species: some species have functional wings for flight, while others are completely flightless, or in some cases individuals within a single species may or may not possess wings (wing-dimorphism). Dispersal from the mainland to islands or between islands varies depending on their wing morphology (and fully developed flight muscles to power those wings) and thus influences the colonization success and distribution of these beetles in an island landscape. But, wing morphology is just one trait – Aaron’s work has shown that body size and breeding season of the beetles are also important traits that determine which beetles are where and how ground beetle assemblages are structured on the islands.

Lac la Ronge is also located in the Boreal Shield ecozone which means that wildfire is common in the area, occurring roughly every 100 years on the mainland4. However, due to their isolation, wildfire behaves differently on islands. For example, frequency of wildfire on the islands is largely determined by size and distance from mainland: lightning strikes occur more often on larger islands owing to their larger surface area5, and the probability of embers from distant fires landing on an island decreases with isolation. This natural phenomenon creates a mosaic of islands on Lac la Ronge that are subject to varying frequencies of disturbance – a very interesting system for studying the interaction between disturbance and island ecology. Reconstruction of fire history on the islands of Lac la Ronge is ongoing.

References

1Teller, J. T. & Leverington, D. W. (2004) Glacial Lake Agassiz: a 5000 yr history of change and its relationship to the δ 18O record of Greenland. Geological Society of America Bulletin, 116, 729-742.

2Bell, A. B., Phillips, I. D., Nielsen, S. E., & Spence, J. R. (2017). Boreal ground-beetle (Coleoptera: Carabidae) assemblages of the mainland and islands in Lac la Ronge, Saskatchewan, Canada. The Canadian Entomologist, DOI: 10.4039/tce.2017.12

3Bell, A. B., Phillips, I. D., Nielsen, S. E., & Spence, J. R. (2017). Species traits modify the species-area relationship in ground-beetle (Coleoptera: Carabidae) assemblages on islands in a boreal lake. PLoS ONE, 12(12): e0190174. Available here: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0190174

4Parisien, M. A., Hirsch, K. G., Lavoie, S. G., Todd, J. B. & Kafka, V. G. (2004) Saskatchewan fire regime analysis. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta. Information Report NOR-X-394, 49 pp.

5Wardle, D. A., Zackrisson, O., Hӧrnberg, G. & Gallet, C. (1997) The influence of islands area on ecosystem properties. Science,277, 1296-1299.

Aaron Bell traveled to Georgia for the 4th International Symposium of Carabidology and presented this project. Below is the video of his lightning talk: Habitat diversity drives species-area relationships of ground beetles (Coleoptera: Carabidae) on boreal islands.