Trait correlations equalize spread velocity across plant life histories

Aim: Forecasting species migration with climate change and the advance of biological invasions requires a better understanding of species' relative migration capacity. Although theory predicts that species combining high fecundity and dispersal with early maturation should spread the fastest, possible correlations between these traits greatly complicate predictions of species' relative spread velocity. We asked whether the demographic and dispersal rates controlling plant population spread are correlated across species, and which observed association of these traits leads to the fastest spread. Location: Worldwide. Time period: Current. Major taxa studied: Eighty species of herbaceous and woody plants from 35 families and 64 genera. Methods: We examined the relationships between age at maturity, dispersal and fecundity for 80 plant species, ranging from annual herbs to trees. We incorporated these rates into a model predicting spread velocities, in order to estimate species' spread capacity as a function of their life history. Results: Across species, age at maturity was positively associated with both dispersal and fecundity. Given that these traits have opposing effects on spread, our models predict that species widely spaced along an age-at-maturity gradient should spread at comparable rates. This result was driven by variation between rather than within life-forms; the traits controlling spread were not correlated within annual herbs, perennial herbs or trees. The predicted spread velocities for these plant life-forms overlapped considerably, although on average, trees were predicted to spread faster than herbaceous species. Main conclusions: Our results suggest that very different plant life histories allow for similar rates of biological invasion or native species migration under climate change. Determining where species fall within the correlated suite of traits controlling spread might provide the most effective way to predict relative spread velocities.