Life history trade-offs affect the invasion velocity of spreading plant populations

Background/Question/Methods
The spread velocity of invading plant populations depends on seed dispersal ability, fecundity and the age of maturity, according to theoretical models. Plants have evolved a great variety of life cycles and dispersal strategies, and life history theory predicts that there may be trade-offs between dispersal ability and other life history traits. However, previous studies of these trade-offs have shown mixed results and are mostly based on indirect measures of dispersal ability, such as the terminal velocity of seeds. Furthermore, it is unknown how life history trade-offs may affect the spread velocity of invading populations.
We collected data from the literature on the age of maturity, fecundity and dispersal ability of 63 plant species from North and South America, Eurasia and Australia, ranging from herbaceous annual species to trees. The rate at which seed dispersal declines with distance from the parent was used as a direct measure of dispersal ability. We then used a furthest-forward individual model of plant population spread to estimate where along the possible trade-off axes the spread velocity was maximized.

Results/Conclusions
The dispersal ability of species rapidly increased with the age of maturity. However, while tall, late-maturing species all dispersed very well, there was a large variation in dispersal ability among short, early-maturing species. In particular, a few early-maturing species also had a high dispersal ability. Similar spread velocities were predicted for plant species on both sides of the general dispersal/age at maturity trade-off. Because of this trade-off, annual herbs and trees on average reached the same spread velocity and may shift their range at the same rate. The fastest spread velocities were found for the early-maturing species with high dispersal ability, which may be potential invaders. Our results improve our understanding of how life history traits affect the spread velocity of natural plant species.