How do native species respond to invaders? Mechanistic and trait-based perspectives

Adaptive responses of native species are important in enabling their persistence in the face of unprecedented biotic exchange. In the present paper I discuss how native species respond to invasive species both from a mechanistic and trait-based perspective. An earlier review by Strauss et al. (Ecol Lett 9:357-374, 2006) discussed a conceptual model of native species evolution in which the likelihood of an evolutionary response to an invader is dependent upon the strength of the selective pressure imposed (degree of variation in fitness between genotypes) and the adaptive capacity of the native (extent of pre-adaptation or genetic diversity). I aim to update and build upon this framework in light of new information on the interaction of phenotypic plasticity and evolutionary processes in adaptive responses of native species. Phenotypic plasticity can be a precursor to or an inhibitor of evolutionary responses and, under conditions of strong selection, phenotypic plasticity may enable adaptation where natives have a low evolutionary capacity. Based on current evidence, it is likely that phenotypic plasticity is the first front in native species adaptation, after which genetic changes occur via a genetic accommodation mechanism. Lastly, I review the literature on behavioural, morphological, physiological and life history trait changes of responding native species in light of this framework. Knowledge of the genetic and physiological underpinnings of adaptive responses in native species is limited and would aid in distinguishing the contributions of phenotypic plasticity and evolutionary change in future studies.