Successful species invasions involve numerous ecological processes operating at multiple spatial and temporal scales. Sites must first meet basic physiological constraints; the boundaries of these suitable conditions are defined by the invader’s fundamental niche. If the invader is introduced into a highly suitable site, absent its natural enemies, invasion theory predicts a high probability of invasion success even in the face of low genetic diversity (enemy release). However, if sites are marginally suitable then multiple introductions may be necessary to provide the genetic diversity necessary for adaptation before successful invasion is possible, though exceptions appear to exist (genetic paradox). Successful biocontrol organisms that ultimately “escape”, such as the South American cactus moth (Cactoblastis cactorum (Berg)), provide well-documented invasions that can be used to evaluate the role that genetic diversity, environment, and biotic interactions play in invasion success.
Results/Conclusions
We have collected C. cactorum extensively in its native range and across Florida, and have obtained specimens from both Australia and South Africa to confirm the documented region from which the first 2,000 or so individuals were exported to Australia in the 1920s. Here we use habitat models constructed using MAXENT and published historical data to strongly suggest that the success of the original introduction in Australia was governed by biotic interaction with the specific cactus hosts in Queensland. Further, we demonstrate that while successful invasion in Australia (and likely South Africa) was determined by biological interactions, there is a strong signature of an environmental constraint in the North American invasion. Discovery of the degree to which this pattern represents the signature of constraints on the primary host, Opuntia stricta, along the Gulf coast in North America, versus constraints on the cactus moth itself will be critical to determining whether major determinants of invasion success can differ, even within a single species, among geographic regions.
