Ecological traps in changing environments: Ecological and evolutionary consequences of a behaviourally mediated Allee effect

Species usually have to use indirect cues when assessing habitat quality. T his means that it is possible for humans to alter habitats in a way that ca uses a discrepancy between the cues and the true quality of different habit ats. This phenomenon is called an 'ecological trap'. Here we show that the trap may lead to a behaviourally mediated Allee effect, where population gr owth is reduced because of non-ideal choices of individuals. The reduction is greatest at low densities because more individuals can choose their pref erred habitat when competition for breeding sites is reduced. An ecological trap may lead to multiple equilibria in population dynamics and cause dete rministic extinction in habitats that are capable of sustaining a viable po pulation. We also study the efficiency of three mechanisms that may rescue a population from this extinction trap: natural selection acting on habitat preferences and two forms of phenotypic plasticity, experience-based learn ing and a philopatric preference for the natal habitat. Selection is most e fficient in short-lived species with large heritable variation in habitat p references, whereas in long-lived species, plastic traits outperform geneti cally determined preferences. The simple philopatric strategy generally pro duces the most favourable outcome. It hardly differs from the optimal strat egy that assumes perfect and immediate knowledge of habitat change, and is very robust to non-ideal variation in the strength of habitat preferences. We conclude that conservation biologists need to ensure that cues for habit at choice correlate with habitat quality.