Interplay of limiting factors explains context dependence in invader abundance
Using a grassland experiment, we show that the interplay of limiting factors can explain context dependence in plant invasions, including why relationships can oscillate between positive, negative and neutral depending on circumstances. Evidence suggested that seeds primarily limited fast invader cover in early and mid successional communities, resources limited invasion of both groups in late succession, and invader growth rate primarily limited slow invaders in early and mid succession (Fig. 5). The key limiting factor in each situation was only detectable, and a nuanced effect of each treatment only visible, when temporal trends and effects of the four treatments were collectively examined. For example, the strength of resource-limitation in late successional communities only became apparent through time, and the varied effects of disturbance illustrated changes in the relative importance of resource limitation with succession. By manipulating invader seed dose, imposing disturbance that altered resource availability and examining temporal trends of invaders with different growth rates, we were able to ascertain the hierarchy of limiting factors affecting cover abundance of two invader groups in three successional stages, and explain context dependence of the invasion relationships observed (Fig. 5).