Author
David Ensing
david.ensing@agr.gc.ca
Summerland Research and Development Centre, Agriculture and Agri-Food Canada, Summerland, British Columbia, Canada
Coauthors
Robert Bourchier, Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada
Rosemarie De Clerck-Floate, Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada
Chandra E. Moffat, Summerland Research and Development Centre, Agriculture and Agri-Food Canada, Summerland, British Columbia, Canada
Abstract
Variable biological control of broadly distributed invasive species is a common pattern. In western North America, spotted knapweed (Centaurea stoebe ssp. micranthos) is a widespread and problematic invader of rangeland and urban areas and so has been subject to biocontrol since the 1970s. By the early 1990s, the North American knapweed biocontrol programme had led to the release of 13 insect agents. Integrating various long-term datasets on spotted knapweed density we found, on average, a long-term decline under biological control. Yet control remains variable among study sites and pockets of abundant spotted knapweed remain. Here we report on ongoing work exploring potential mechanisms for variability in biocontrol success, including incongruent range-limits between spotted knapweed and its biocontrol agents, population genetic diversity within and among populations, and inter-annual variation in climatic factors influencing knapweed success. Spatial environmental heterogeneity overlies all of these characteristics, and challenges biocontrol. Employing species range limit theory to clarify where and why biocontrol may be limited will be critical to achieve control when target populations are environmentally and spatially widespread.
keywords
range limits
population genetics
knapweed
Centaurea stoebe
long-term monitoring
Highlights
Biocontrol of widespread invasive plant species is often heterogeneous
Biocontrol of spotted knapweed has reduced density overall but control is highly variable
Population dynamic and population genetic range limit hypotheses may help explain variable control