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Discussion
Our experimental results demonstrate that space- and
propagule-limitation both regulate S. muticum recruitment.
Our finding that S. muticum recruitment was positively
related to propagule input is similar to those of two previous
studies (Parker 2001; Thomsen et al. 2006), in which the pro-
pagule input of invasive plants was manipulated. In our control
d
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Disturbance, Propagule input and invasion

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© 2007 The Authors. Journal compilation © 2007 British Ecological Society, Journal of Ecology, 96, 68–77
treatment space was limiting, a result that has also been found
in previous studies of S. muticum recruitment (Deysher &
Norton 1982; De Wreede 1983; Sanchez & Fernandez 2006).
Consequently, increasing propagule pressure had a relatively
weak effect on recruitment in undisturbed plots (Fig. 1a).
However, when space limitation was alleviated by disturbing
the plots, increasing propagule pressure caused a dramatic
increase in recruitment (Fig. 1a). This suggests that in the
presence of adequate substratum for settlement, propagule
limitation becomes the primary factor controlling S. muticum
recruitment. These results indicate that S. muticum recruit-
ment under natural field conditions will be determined by the
interaction between disturbance and propagule input.
Only a few previous studies have investigated the effect
of resource supply on the relationship between propagule
pressure and recruitment of an introduced species. Although
disturbance generally increases invasion success by increasing
resource availability (Richardson & Bond 1991; Bergelson