Dominance by annual plants has traditionally been considered a brief early stage of ecological succession preceding inevitable dominance by competitive perennial plants. A more recent, alternative view suggests that interactions between annuals and perennials can result in priority effects, causing annual dominance to persist for decades if they are initially more common. Such priority effectswould 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 (equilibrium ) priority effects are possible only when the plants have low fecundity and show an establishment-longevity tradeoff, with annuals having competitive advantage over perennial seedlings . However, transient (but long-lasting over decades) priority effects are more likely and does not require the tradeoff. Our results provide a theoretical basis for predicting when restoration of annual-invaded grasslands requires active removal of annuals and timely reintroduction of perennials .
1. In many grassland communities, the identity of dominant species may be determined by initial frequency owing to priority effects. Yet , the conditions for these priority effects remain unclear. 2. Focusing on interactions between annual and perennial plants, we used a simulation model to investigate how longevity, fecundity, and the competitive ability of seedlings might affect the probability of equilibrium priority effects (alternative stable states) and transient priority effects (alternative transient states). 3. The model suggests that establishment-longevity tradeoff, in which annuals have competitive advantage over perennial seedlings , is a necessary condition for equilibrium priority effects. Equilibrium priority effects also require low fecundity in both annuals and perennials and small fitness differences, as determined by their relative fecundity, survival probability, and competitive ability at the seedling stage. 4. Transient priority effects need only small fitness differences. Furthermore, the model indicate that transient priority effects could last several decades under a range of the parameter space, exceeding the duration of typical experiments and observations. 5. Synthesis: Our results suggest that equilibrium priority effects driven by a life-history trade-off are possible but may be uncommon because they require unrealistically low fecundity. In contrast, transient priority effects should be more likely. Previous empirical findings of priority effects in grasslands may mostly indicate alternative transient, rather than stable, states, or other mechanisms than a life-history tradeoff .
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Dominance by annual plants has traditionally been considered a brief early stage of ecological succession preceding inevitable dominance by competitive perennial plants. A more recent, alternative view suggests that interactions between annuals and perennials can result in priority effects, causing annual dominance to persist for decades if they are initially more common. Such priority effectswould complicate restoration of native perennial grasslands that have been invaded by exotic annuals. However
1. In many grassland communities, the identity of dominant species may be determined by initial frequency owing to priority effects. Yet
R
under which
for
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occur remain unknown. Using a simple simulation model , we show that long-term (equilibrium ) priority effects are possible only when the plants have low fecundity and show an
remain unclear. 2. Focusing on interactions between annual and perennial plants, we used a simulation model to investigate how longevity, fecundity, and the competitive ability of seedlings might affect the probability of equilibrium priority effects (alternative stable states) and transient priority effects (alternative transient states). 3. The model suggests that
R
with annuals having
in which annuals have
R
. However, transient (but long-lasting over decades) priority effects are more likely and does not require the tradeoff. Our results provide a theoretical basis for predicting when restoration of annual-invaded grasslands requires active removal of annuals and timely reintroduction of perennials
, is a necessary condition for equilibrium priority effects. Equilibrium priority effects also require low fecundity in both annuals and perennials and small fitness differences, as determined by their relative fecundity, survival probability, and competitive ability at the seedling stage. 4. Transient priority effects need only small fitness differences. Furthermore, the model indicate that transient priority effects could last several decades under a range of the parameter space, exceeding the duration of typical experiments and observations. 5. Synthesis: Our results suggest that equilibrium priority effects driven by a life-history trade-off are possible but may be uncommon because they require unrealistically low fecundity. In contrast, transient priority effects should be more likely. Previous empirical findings of priority effects in grasslands may mostly indicate alternative transient, rather than stable, states, or other mechanisms than a life-history tradeoff