Invasive species are a major driver of global biodiversity loss. Now researchers have developed a simple model that can quickly predict which species are likely to become established outside their native environment. The team recently reported in the Proceedings of the Royal Society B that the model could streamline existing laborious risk assessments, and possibly help protect ecosystems from further harm.
According to the International Union for Nature Conservation—a science-based environmental network—up to 20% of all alien species become invasive and harm local biodiversity. Current approaches to predicting problematic species tend to focus on organisms that have already become invasive. Researchers look for traits that might have given invasive species an edge. In the case of plants, for example, species’ capacity to adapt rapidly to new environments. But these indicators are complicated and time-consuming to evaluate, relying on measuring indirect characteristics such as seed size, growth rate, and water use efficiency, notes coauthor David Richardson, an invasion ecologist at Stellenbosch University in South Africa.
“It’s very important to be able to predict which species will become invasive,” he says. But it’s not feasible to undertake the research needed to characterize the traits of the thousands of alien species that could be problematic, Richardson adds. “We were looking for a short-cut.”
Richardson’s group worked with species of two well studied plant clades native to Australia—acacias and eucalypts. They screened data freely available on the Australasian Virtual Herbarium on the ecology and evolutionary history of 259 species of acacias and 317 eucalypts species. Using additional open-access data, they also took into account other environmental factors such as climate.
The team then developed four indicators to gauge how easily species successfully establish themselves in new environments: niche characteristics such as breadth (related to the range of environmental conditions in which the species can survive); species’ global range size (to indicate how likely species are to find suitable conditions elsewhere); the extent to which a species’ niche overlaps with human-disturbed environments (invasive plants tend to be successful in areas with human activity); and two proxies to indicate the capacity for becoming established in a new environment (the number of biogeographic regions that species’ ancestors successfully colonized over evolutionary history and species’ ability to dominate local environments). For example, to estimate niche breadth, they used climate and rainfall data to define the array of conditions that characterize where a species is distributed in an area.
The researchers validated the model by fitting it to one group of data they collected, then showing, using a separate group of data collected, that the model could predict the likelihood of acacia and eucalypts species becoming established. They did this a total 50 times (part of a statistical method called “area under the curve”).
The researchers also found that the best indicator for both plant clades is species global range size, which accounted for 76% and 61% of the variable importance in predictive power compared to the other indicators for acacias and eucalypts respectively. “The models could be used for all kinds of animals, plants and microbes to assess their potential for invasion,” Richardson says.
The findings are “novel and brave,” says Christoph Kueffer an ecologist at the ETH Zurich University in Switzerland, who was not involved in the study. But he notes that the models don’t reveal whether the alien species are likely to harm the environments they invade. And Kueffer questions how useful the models are for risk assessments. “We need to be able to predict which species will have a negative impact, particularly in environments that have yet to be disturbed by human activity,” he says.
Richardson counters that all acacias and eucalypts that have become invasive have had negative impacts. A robust protocol for assessing risk of establishment “is a crucial first step” in developing risk assessments, says Richardson. He notes that all established alien plants have an impact in the environments in which they occur, for example by changing networks of pollination or seed dispersal. Whether such changes translate into harmful impacts can be extrapolated from past experience with invasions of similar species. “It’s is very clear that many potentially invasive and harmful species are waiting in the wings and could invade and cause harm if given the opportunity,” Richardson says.