The role of dispersal mechanisms in range shifts of plant species across sub-Antarctic Marion Island

Abstract

Dispersal is a key lifecycle event and is the means through which species spread geographically, across both fine and broad scales. Despite their ecological importance, dispersal events have proven challenging to quantify as they are often difficult to observe and measure accurately. An attempt to overcome this has been the use of mechanistic models and standardised experiments that combine theory and experimental data to simulate dispersal events that occur through wind, animals, water, and anthropogenic activity. The dispersal estimates obtained using such methods can be useful in multiple ways, including being incorporated into species distribution models to gain ecological and evolutionary insight into the current and future distributions of species across landscapes. Indeed, studies that include dispersal potential have developed more accurate predictions of how species and ecosystems respond to changing environmental conditions. Here, I use mechanistic modelling and standardised experiments to conduct the first quantification of the dispersal potential of the dominant vascular flora in the sub-Antarctic (via anemochory, thalassochory, zoochory, and anthropogenic activity) and test whether species’ dispersal capacity is correlated with inter-specific variation in recent changes in species’ ranges. My results show that species dispersal potential is not correlated with the magnitude of species range expansion for both native and alien species. Inter-specific variation in range expansion was also not related to species’ habitat specificity or functional traits, suggesting that other mechanisms (e.g. demography, competition, and/or the thermal requirements and nutrient demands of species) must be responsible for the variation observed in species range expansion rates. Since my findings contradict ecological theory and evidence from several other dispersal-focused studies, I conclude by reviewing the literature regarding methods for estimating dispersal and present suggestions about how these methods can be integrated to improve our understanding of the effects of dispersal at local scales. While there have been considerable advancements in methods for quantifying dispersal (especially where long-distance dispersal is concerned), this research shows that there is still room for improvement in how we study dispersal events and their effects at smaller scales.