Predicting species invasions is hard enough, but how can we accomplish this for non-native species with little history of misbehaving? New research published in the journal Global Ecology and Biogeography by Eric Larson and Julian Olden from the University of Washington suggests that borrowing the experience of a known invasive species – an ‘avatar’ species – may be useful in identifying where emerging invaders can establish.
Although avatars largely breached public consciousness through a 2009 film of the same name, the utility of a virtual or remote entity to test or play out scenarios is well recognized (e.g., the basis of many video games).
Ecologists have long sought to predict which species are likely to be invasive and where they will spread. Predictive models are typically based on information about a species in its native region. For example, a plant or animal that occurs only in warm or humid areas is not expected to establish where conditions are cooler or drier. The problem is this method doesn’t consistently pan out, with native range models often underestimating where new species actually establish or spread.
Lead author Larson says, “Managers often base decisions to prohibit import of species on whether they are expected to establish in a particular climate. But we’ve seen enough species live in climates quite different from their native ranges to suggest that’s not a safe assumption.” So the authors applied information from avatars – in this case, two species of crayfish which are already widely invasive – to predict potential establishment of a new invader.
The new invader is the red-claw crayfish (Cherax quadricarinatus, pictured above), a native of northern Australia becoming increasingly popular in the global aquarium trade, a trend which equates to increased danger of accidental introductions. To apply avatar information to the predicted establishment of red-claw, Larson first examined the distribution of two well-documented, globally invasive species – the signal (Pacifastacus leniusculus) and red swamp (Procambarus clarkii) crayfish. Using a temperature based model, he compared the native range predictions for these species to the locations where they actually ended up surviving in nature. When this difference was modeled for red-claw crayfish, the avatar model approximately doubled the potential range, which means managers in more watersheds might have cause to be concerned about this species.
The research is a case study, prompting an important question: can avatars improve models for any emerging invader? The approach is probably more appropriate for some species than others. According to Larson, “In the paper we say maybe some species of plants or birds don't really need this approach, because the native range is largely determined by climate. On the other hand, we think it may be a particularly good approach for freshwater species, which are often limited in their dispersal by geographic features like rivers or mountains.”
Larson adds, “I think a question we need to be asking is when are native ranges reliable predictors of invasive ranges, and when aren't they?”
The question of which invaders need avatars is being addressed in a follow up paper. Avatar 2? Well, even James Cameron is making a sequel.
Photo: Herwig Ster