Invasion biology: comparing scales of local genetic adaptation to exotic predators by prey with high and low dispersal potential

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Environmental change caused by human activities is allowing exotic predators and competitors to extend their geographical ranges into Canada. For example, increased sea surface temperatures during the 1997/98 El Niño allowed larvae of the subtropical lined shore crab to metamorphose on western Canadian shores and prey on four closely-related species of indigenous snails. These temperate snail species have shells that are vulnerable to the specialized shell-breaking appendages of predators from more tropical regions. Consequently, climate-driven range expansion of subtropical predator species may result in range contraction by temperate prey species unless they can quickly evolve thicker armour. This is an excellent system for studying the effect of prey migration on adaptation to subtropical predators. These four intertidal gastropods are ecologically similar but differ considerably in their dispersal potential: two species have a long-lived free-swimming larval stage and two species have lost the free-swimming larval stage and as a result disperse only by crawling.