Title: Priority effects between annual and perennial plants,
Abstract: Dominance by annual plants has traditionally been considered a brief early
stage of ecological succession preceding inevitable dominance by competitive
perennials. A more recent, alternative view suggests that interactions between
annuals and perennials can result in priority effects, causing annual dominance
to persist if they are initially more common. Such priority effects would
complicate restoration of native perennial grasslands that have been invaded by
exotic annuals. However, the conditions under which these priority effects
occur remain unknown. Using a simple simulation model, we show that long-term
(500 years) priority effects are possible as long as the plants have low
fecundity and show an establishment-longevity tradeoff, with annuals having
competitive advantage over perennial seedlings. We also show that short-term
(up to 50 years) priority effects arise solely due to low fitness difference in
cases where perennials dominate in the long term. These results provide a
theoretical basis for predicting when restoration of annual-invaded grasslands
requires active removal of annuals and timely reintroduction of perennials.