Invasive species: “back-seat drivers” of ecosystem change?

Abstract

Invasive species are often assumed to be the cause (drivers) of declines in native species and alterations of native ecosystems. However, an alternative model suggests that many invasive plants are better described as passengers of altered disturbance regimes or other changes in ecosystem properties. Some species do seem to be easily categorized as passengers or drivers, but others may be better described as “back-seat drivers”. Back-seat drivers require or benefit from disruptions of ecosystem processes or properties that lead to declines of native species but also contribute to changes in ecosystem properties and further declines of native species. Among these possibilities, drivers are a direct cause of the decline of native species through the introduction of novel traits or functions to an ecosystem, whereas back-seat drivers interact with ecosystem change to cause native species declines. Passengers are better considered as a symptom of an underlying problem, rather than the cause of native species declines. Driver, back-seat driver and passenger models suggest different associations between invasive species, ecosystem change and native species declines, and these models provide a framework for predicting and understanding the response of native species to invasive species management.