by Cameron Lukos
Global climate change is causing long lasting effects on all of Earth’s natural systems. A consequence of these changes is species range shifting. Accurately predicting these shifts is very difficult and many methods have been criticized. The standard bioclimate envelope models (BEMS) have been criticized as too simple because they do not incorporate biotic interactions or evolutionary adaptation. BEMs are widely used though. Kubish et al. (2013) wanted to determine the evolutionary conditions of dispersal, because local adaptation or interspecific competition may be of minor importance for predicting future shifts. They used individual-based simulations at two different temperatures as well as competing simulations. Their results show that in single-species scenarios excluding adaptation, species follow optimal habitat conditions or go extinct if their connection to the environment becomes too weak. With competitors, their results were dependent on habitat fragmentation. If a species was highly connected to its habitat, the range shifted as predicted; if a species was only moderately connected to its environment, there was a lag time, and with low connectivity to the environment, the result was extinction. Based on this work, Kubisch et al. determined that the BEMs may work well as long as habitats are well connected and there is no difficulty dispersing.
Kubisch et al. used simulations to simulate one species and two species interactions. The simulations are initialized with spatial separation of species. With two species scenarios, the colder half of the world is solely cold tolerant species and the warm half is solely warm tolerant species. In the single species scenarios they used only the warm adapted species restricted to their half. The experiments covered 3000 generations and each 1000 generations the temperature was increased. To test the influence of habitat connectivity the authors varied the dispersal mortality. For example, having high dispersal mortality means that the species has low habitat connectivity. The authors analyzed the data by calculating the range border position for the species and the number of occupied patches.
The authors determined that with their single species simulations that with low dispersal mortality the species will initially increase its range slightly and then follow the predicted shift. If the value for dispersal mortality is greater than 0.7 then the population completely collapses. The position of the range border is determined then by the niche width and the gradient. The authors then factored in mutations that would help adapt them to their temperatures and the resulting scenarios showed that with high connectivity the species takes over the whole range. With intermediate connectivity there was still an increase in expansion but not as quickly. The wide niches increased the survival of the populations even with a giant collapse at the same period of time. With two species systems the authors did not find any change in the speed of range shifts. By increasing the dispersal costs with this as well they saw an increased lag in the shift border.
Kubisch, A., Degen, T., Hovestadt, T. and Poethke, H. J. 2013. Predicting range shifts under global change: the balance between local adaptation and dispersal. Ecography, 36 873-882.