The Macroecology of Biological, Life History and Ecological Traits of Invasive and Threatened Marine Invertebrates

Global environmental change is accelerating both species extinctions and species invasions, with extinction risk and invasion success thought to be mediated by biological, life history and ecological traits. It is, therefore, important to understand how traits, phylogeny and environmental factors interact to characterise imperilment and invasiveness and to determine the vulnerability of species to climate change. In this thesis I aim to determine the key traits of invasive, native, and threatened marine invertebrates and to provide a framework for predicting native species likely to become invasive and for determining the life-history and environmental traits correlated with extinction risk and invasiveness. I compile trait datasets for 2,322 invertebrate species and use multivariate analysis to identify the discriminating traits between non-indigenous and native species and to propose a list of ‘potentially invasive’ native species. I further show that species from different risk categories display contrasting, although not opposite, life-history traits and that the risk status of marine molluscs is largely driven by
phylogeny, with invasiveness and extinction risk not randomly distributed across families. I then combine species-trait data with environmental data to show that there is a strong phylogenetic signal in species’ realised thermal niches. The relationship between the range of temperatures a species experiences (thermal tolerance breadth) and the maximum temperature to which it is exposed is stronger in shallow-water invasive species than other risk categories. Finally, I show that life-history variation across marine molluscs is largely consistent with Thorson’s rule that in lower latitude environments species are typically small-bodied, early maturing and highly fecund, while the reverse is true in higher latitude environments. This thesis provides a foundation for future comparative macroecological studies investigating invasive and threatened species and makes a unique contribution to understanding the traits of marine invertebrates across multiple risk categories and their likely response to environmental change.