Apparent competition: an impact of exotic shrub invasion on tree regeneration
Invasion of habitats by exotic shrubs is often associated with a decrease in the abundance of native species, particularly trees. This is typically interpreted as evidence for direct resource competition between the invader and native species. However, this may also reflect indirect impacts of the exotic shrubs through harboring high densities of seed predators––known as apparent competition. Here I present data from separate seed predation experiments conducted with two shrub species exotic to North America; Rosa multiflora, an invader of abandoned agricultural land, and Lonicera maackii, an invader of disturbed or secondary forest habitats. Both experiments showed significantly greater risks of seed predation for tree seeds located under shrub canopies when compared to open microhabitats within the same site. These results indicate the potential importance of indirect impacts of exotic species invasions on native biota in addition to the direct impacts that are typically the focus of research.
KeywordsExotic shrubs Habitat selectivity Lonicera maackii North America Rosa multiflora Seed predation Survival analysis
Douglas-Hart Nature Center
Hutcheson Memorial Forest Center
- L. maackii
- P. leucopus
- R. multiflora
I thank G. M. Groves and P. Forsythe for assistance in the field, T. A. Nelson for providing data on the seed predator assemblage at DHNC, the 2001 Plant Ecology class at EIU for conducting the species removal, and L. C. Miramontes, B. E. Wachholder, and K. A. Yurkonis for comments on previous versions of this manuscript. Work at HMFC was supported by a Summer Research Fellowship from Rutgers University. Work at DHNC was supported by Wildlife Preservation Fund Grant #02–002W from the Illinois Department of Natural Resources and a Redden Fund grant from the Eastern Illinois University Foundation.
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