Biological control as an invasion process: disturbance and propagule pressure affect the invasion success of Lythrum salicaria biological control agents
- 532 Downloads
Understanding the mechanisms behind the successful colonization and establishment of introduced species is important for both preventing the invasion of unwanted species and improving release programs for biological control agents. However, it is often not possible to determine important introduction details, such as date, number of organisms, and introduction location when examining factors affecting invasion success. Here we use biological control introduction data to assess the role of propagule pressure, disturbance, and residence time on invasion success of four herbivorous insect species introduced for the control of the invasive wetland plant, Lythrum salicaria, in the Columbia River Estuary. Two sets of field surveys determined persistence at prior release sites, colonization of new sites, and abundance within colonized sites. We quantified propagule pressure in four ways to examine the effect of different measurements. These included three measurements of introduction size (proximity to introduction site, introduction size at a local scale, and introduction size at a regional scale) and one measure of introduction number (number of introduction events in a region). Disturbance was examined along a tidal inundation gradient (distance from river mouth) and as habitat (island or mainland). Statistical models and model averaging were used to determine which factors were driving invasion success. In this study we found: (1) sparse evidence for the positive influence of propagule pressure on invasion success; (2) disturbance can negatively affect the invasion success of herbivorous insects; (3) the effects of disturbance and propagule pressure are species specific and vary among invasion stages, and (4) not all measures of propagule pressure show the same results, therefore single measures and proxies should be used cautiously.
KeywordsGalerucella calmariensis G. pusilla Hylobius transversovittatus Introduced alien species Nanophyes marmoratus Purple loosestrife
We thank J. Kooser, L. Moore, and E. Thompson for laboratory and field assistance. G. Dorsey, E. Coombs, P. McEvoy, F. Grevstad, L. Wunder, D. McLain, and M. Magruder provided valuable support and advice. Special thanks to A. Bourne, S. Burgess, and J. Dwyer for statistical advice. R. Van Klinken and three anonymous reviewers provided constructive reviews. Funding for this project was provided to S. Schooler and R. Garono by the Oregon Department of Agriculture and the Oregon State Weed Board, to A. Yeates through an Australian Postgraduate Award, and to Y. Buckley by an ARC Australian Research Fellowship (DP0771387).
- Burnham KP, Anderson DR (2002) Model selection and multimodel inference: a practical information theoretic approach, 2nd edn. Springer, New YorkGoogle Scholar
- Gelman A, Hill J (2007) Data analysis using regression and multilevel/hierarchical models. Cambridge University Press, New YorkGoogle Scholar
- Piper GL, Coombs EM, Blossey B, McEvoy PB, Schooler SS (2004) Purple loosestrife. In: Coombs EM, Clark JK, Piper GL, Cofrancesco AF (eds) Biological control of invasive plants in the United States. Oregon State University Press, Corvallis, pp 281–292Google Scholar
- Pyšek P, Jarošík V (2005) Residence time determines the distribution of alien plants. In: Inderjit S (ed) Invasive plants: ecological and agricultural aspects. Birkhäuser Basel, Switzerland, pp 77–96Google Scholar
- Pyšek P, Jarošík V, Müllerová J, Pergl J, Wild J (2008) Comparing the rate of invasion by Heracleum mantegazziam at continental, regional, and local scales. Divers Distrib 14:355–363Google Scholar
- R Development Core Team (2008) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, http://www.R-project.org
- Turner MG, Gardner RH, O’Neill RV (2001) Landscape ecology in theory and practice: pattern and process. Springer-Verlag, New YorkGoogle Scholar