Ecological consequences of pathogen and insect invasions

Abstract

The introduction and successful establishment of nonnative species poses a significant threat to the function and structure of native ecosystems and biodiversity. Forest ecosystems are especially threatened due to the worldwide importance of wood packaging material universally used in global trade, the importation of lumber and wood products, and the importation of live trees for planting. This collectively enables a number of invasion pathways that facilitate the introduction of forest insects and pathogens. Consequently, forest ecosystems worldwide are under threat from nonnative forest pest species, many of which pose little concern in their native habitats due to the checks and balances associated with natural enemies and host plant defensive responses. Unfortunately, the lack of concern for many species in their native habitats leads to a significant knowledge gap when such species are introduced into a new environment and begin to pose negative ecological consequences. In this review, I discuss variation in establishment success and ecological consequences exerted by nonnative forest insects and pathogens, define characteristics of high-impact species, and review recent research on the ecological consequences of these highimpact species in forest ecosystems. Although specific insect and pathogen examples are drawn from invasions in North American forest ecosystems, the concepts of habitat invasibility, species invasiveness, and the ecological consequences expressed by nonnative forest species are not unique to North America.