Across the terrestrial landscape, animal movement is a latticework of suitable and unsuitable habitat patches. How plants and animals will move through this landscape under climate change has recently been detailed in several excellent movement maps, such as an animated map of animal migration from The Nature Conservancy, or a predicted movement route map for 3,000 species of the eastern United States.
Try to find a similar map for aquatic species, and you’ll be out of luck. For species that are restricted to river and streams, dispersal is limited to a single path from any given location and can be blocked by simple changes in structure and movement, such as a stream becoming too narrow or water flow becoming too fast. Few studies have been able to demonstrate how or if species will be able to shift ranges as a response to climate change in dendritic networks such as rivers and streams.
New research by Inoue and Berg takes a look at predicting shifts for one aquatic species, the freshwater spectaclecase mussel (Cumberlandia monodonta). It historically occupied the entire Mississippi River basin in the United States, but is currently restricted to a few locally abundant populations across approximately 20 large rivers. Populations are in danger of greater fragmentation if climate changes reduces habitat connectivity and prevents the species from shifting its range. The study included ecological niche modeling to examine future changes in habitat suitability under high and low emissions scenarios in 2050 and 2070, and a forward-time genetic simulation to predict potential changes in genetic diversity.
Results show that populations along the upper Mississippi River are currently panmictic, with stream connectivity existing between highly suitable habitat and more potential suitable habitat available. However, future climate change is likely to result in drastic range contraction northward and upstream, and panmixia will not be maintained. This decrease in connectivity will result in severe declines in genetic diversity, even in currently well-connected tributaries. While it is still possible that there are more undiscovered populations inhabiting the upper Mississippi River, population isolation seems inevitable under almost any emissions scenario. The study provides one more clue as to how species may fare under future climate conditions, although aquatic species such as C. monodonta will continue to provide a challenge for managers and conservation practitioners hoping to maintain population connectivity.
Inoue, K. and D. J. Berg. 2016. Predicting the effects of climate change on population connectivity and genetic diversity of an imperiled freshwater mussel, Cumberlandia monodonta (Bivalvia: Margaritiferidae), in riverine systems. Global Change Biology DOI: 10.1111/gcb.13369.