Biological invasions and the spatial ecology of genes

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Invasive species are plants and animals that are introduced to regions outside their natural range, and subsequently spread out and dominate native habitats.  Because they are a major threat to biodiversity, and can also greatly reduce agricultural productivity, billions of dollars are spent each year fighting invaders.  However, we cannot successfully repel invaders until we have a better understanding of just what makes some introduced species invasive while others remain stable.  With this goal in mind, I am concentrating on the common reed (Phragmites australis), a species that is well known for the reed beds that it forms in freshwater sites round the world including North America and Europe.  In both continents, native reed populations have been stable for thousands of years, but this all changed in North America more than a century ago when a European strain of the common reed was introduced.  This strain is now invasive in North America, where populations are spreading rapidly and taking over estuaries, lakes, ponds, streams, and other habitats that were previously home to a wide range of species.  Invasive reeds are now such a problem that they have been identified as one of the most destructive plants in Canadian natural habitats.  I aim to find out just why it is that reed populations that remain stable in their native range become invasive and destructive when they move to new regions.  I will do this through a detailed analysis of the ecology of both invasive and stable reed populations, paying particular attention to whether the invasive strain can tolerate a much broader range of habitats in North America compared to its native Europe.  I will then investigate whether movement of invasive reeds across North America has been accompanied by genetic changes within populations that allow reeds to become better adapted to their new environments.  This direct comparison of reeds in their native and invaded habitats, combined with a search for adaptive genes, will help us to better understand invasions and therefore target future potential invaders.