BOX 5-1 Impacts of Invasive-Species Management Efforts
In the rush to control invasive species, we sometimes create long-term problems that are harder to address. Importation of nonindigenous predators, parasitoids, or pathogens to control invasive pests can have long-term deleterious effects on native, nontarget species. Compsilura concinnata was intentionally established for gypsy moth control in North America. This parasitic fly is known to parasitize over 180 native lepidopteran species; it might be responsible for dramatic declines of large attractive species, such as the cecropia moth (Boettner et al. 2000), and it has expanded well beyond the range occupied by gypsy moths.
Similar examples of unanticipated effects on nontarget species have been documented for insects introduced for biological control of undesirable plants. The European weevil Rhinocyllus conicus, introduced in 1968 to control weedy thistles, now affects native nontarget plants, including rare species of Californian Cirsium (Ehler 1991, Louda et al. 1997). An Argentine moth, Cactoblastis cactorum, was introduced into the Caribbean in 1957 to control undesirable Opuntia species. Its unanticipated arrival in Florida in 1989, however, has generated concern about its impacts on five native Opuntia species, including a rare, protected cactus. Continued range expansion threatens the diverse guild of Opuntia in Mexico (Johnson and Stiling 1996, Pemberton 1995, Simberloff 1992, Strong and Pemberton 2000). Two immigrant ladybird beetles, Coccinella septempunctata (L) and Harmonia axyridis (pallas), originally imported for biological control, are suspected of displacing native ladybird beetle species (Colunga-Garcia and Gage 1998), and H. axyridis is now considered an annoying pest because it aggregates in masses on homes.
A further complication arises when an invasive species is deemed a curse by one segment of society and a salvation by another. That possibility is well illus
We are unlikely to obtain such quantitative information on patterns of variation and correlation among abundances of species in a community, so it is reassuring that simple qualitative analysis and modeling can further our understanding of potential ecological effects of nonindigenous species and serve as a practical tool for adaptive management (Li et al. 1999). A community matrix can be constructed by representing relationships between the species (or variables) in a community with scores of positive (+1), negative (-1), or zero values, signifying the effect of one species or variable on another. Mathematical tools can be applied to determine the presence of equilibrium and its stability, as well as the effect of input into the system. This approach has led to important policy and management recommendations in agriculture, and fisheries, and has been useful in risk analysis of species introductions.