Principal Investigator University of Alberta, Canada
Background/Question/Methods
As climate change drives biodiversity loss and transition of ecosystems, it is imperative to identify areas where cold-adapted species can persist. Climate refugia, or areas that are projected to remain relatively unchanged under climate change, can serve as remnant suitable habitat or as stepping stones as species disperse further north. Large, deep lakes provide climate refugia on their shorelines, due to upwellings of cold water and winds pushing cooler temperatures inland. Lake Superior serves as a model for cooling-mediated refugia, as its cold temperatures and wave action have maintained shoreline habitat suitable for disjunct populations of arctic-alpine plants since deglaciation. The objectives of our research were to explain patterns in the spatial distribution of disjunct species occurrence based on landscape and lake characteristics, and to predict the persistence of disjunct species under climate warming. We used logistic regression to predict disjunct arctic-alpine species distributions around Lake Superior’s shorelines using species occurrence data from provincial and state governments. Predictor variables were categorized into landscape variables, such as elevation and bedrock geology type, temperature variables such as land and water surface temperature, cold water variables such as depth offshore and annual circulation, and shoreline exposure variables.
Results/Conclusions
We found that bedrock type, elevation above the water, distance to shore, land surface temperature, and the depth of water within 10 km of shore were the best predictors of disjunct species occurrence (R² = 0.46, AUC = 0.93). We predicted refugia potential along the shoreline based on occurrence of disjunct species, and our model supported historical findings that colder, more exposed shoreline along the north shore and on islands further from shore were predicted to have high refugia potential, while warmer areas such as the southern shore of the lake and sheltered bays on the north shore were predicted to have low refugia potential. We also predicted persistence of refugia under moderate (3.5 °C) and a worst-case (5.7 °C) warming scenarios. We found that refugia potential was reduced to 25 % of its current extent under moderate warming, and to only 4 % of current refugia under the worst-case scenario. The identification of areas of shoreline best suited for the persistence of disjunct arctic-alpine species is key to conserving populations under climate change. The degree of isolation of populations at Lake Superior poses limitations on migration northward, and therefore in-situ conservation efforts will be necessary to ensure persistence.
