The ecology of fear and anti-predator behavior in species invasions

We present a general framework for understanding how antipredator behavior and the ecology of fear might help to answer major questions in invasion ecology.  One hypothesis (the 'naïve prey' hypothesis) is that an exotic predator will more likely invade successfully and have major impacts on prey if the new predator is fundamentally different from predators that co-occur with the prey; i.e., if the exotic predator is functionally novel.  We clarify how one might define 'functionally novel' and report on the results of a meta-analysis addressing the naïve prey hypothesis.  Other hypotheses posit that the success of an invasion depends on 'enemy release' which might then free the invader to evolve superior competitive abilities (EICA).  Enemy release and EICA can also hinge on behavior and lack of evolutionary history - here, the naivety of the invader's predators and competitors.  Due to this naivety, enemies in the invaded community might not recognize or respond adaptively to an invader.  We discuss the synergistic inter-relationships among these three hypotheses.  Note that while an invader's predators, competitors and prey might be naïve to the invader, the converse is also true. When and why do invasive species gain a 'novelty advantage' over the members of the invaded community?  We discuss a theoretical scenario revolving around initial advantages of novelty and subsequent predator-prey evolution that could help to explain both the immediate success of some invasions, as well as the mystery of why other invasions take off decades after an initial invasion.