Data from: Species richness and interacting factors control invasibility of a marine community

Anthropogenic vectors have moved marine species around the world leading
to increased invasions and expanded species' ranges. The biotic
resistance hypothesis of Elton (in The ecology of invasions by animals and
plants, 1958) predicts that more diverse communities should have greater
resistance to invasions, but experiments have been equivocal. We
hypothesized that species richness interacts with other factors to
determine experimental outcomes. We manipulated species richness, species
composition (native and introduced) and availability of bare space in
invertebrate assemblages in a marina in Monterey, CA. Increased species
richness significantly interacted with both initial cover of native
species and of all organisms to collectively decrease recruitment.
Although native species decreased recruitment, introduced species had a
similar effect, and we concluded that biotic resistance is conferred by
total species richness. We suggest that contradictory conclusions in
previous studies about the role of diversity in regulating invasions
reflect uncontrolled variables in those experiments that modified the
effect of species richness. Our results suggest that patches of low
diversity and abundance may facilitate invasions, and that such patches,
once colonized by non-indigenous species, can resist both native and
non-indigenous species recruitment.