ARE INVASIVE SPECIES MORE GENERALIST THAN NATIVE SPECIES? A study on Swedish vascular plants

Abstract

Invasive species are a threat to biodiversity and the economy. Despite this, there is currently no simple method to predict whether an alien species will become invasive. Are invasive species more generalist than native species, and if so, can generalist tendency be used to predict whether an alien species can become invasive? The hypothesis is that invasive species are more generalist because a broad niche is advantageous in a new environment, where they can either outcompete native species or occupy empty niches. In this project, data from Tyler et al. (2020) was used, containing the occurrence of species in 38 different vegetation types, along with an index of invasive concern for all Swedish vascular plants. Generalist tendency was calculated through niche width, representing the number of vegetation types each species is present in. The relationship between invasive concern and generalist tendency was examined. The most invaded vegetation types were also identified. The results indicate a negative relationship between niche width and the probability that a species is alien, meaning that generalist species are more likely to be native. Among alien species, there was no significant relationship between niche width and how invasive a species is. The most invaded vegetation types included ruderal; base-rich wasteland; arable land: hedgerows, thickets, wood-margins and groves, and intermediate deciduous forest. The results suggest that a high generalist tendency cannot be used to predict invasiveness. This may be because invasive species have not had time to spread to multiple vegetation types and become generalist in Sweden, even though they have the potential to do so; or because generalist tendency is not related to whether a species becomes invasive or not.