Mitigating exotic impacts: restoring deer mouse populations elevated by an exotic food subsidy

• Published in: Ecological applications 2008-03, Vol.18 (2), p.321-334
• Main Authors: Pearson, D.E, Fletcher, R.J. Jr
• Format: Article
• Language: English
• Subjects: Animal traps; Animals; Applied ecology; biological control agents; Centaurea - drug effects; Centaurea maculosa; Centaurea stoebe subsp. stoebe; community ecology; Conservation of Natural Resources; demography; Depopulation; Ecological invasion; Ecosystem; exotic species; Food; Food Chain; food limitation; Food movements; food resources; Food security; Food supply; Herbicides; Herbicides - pharmacology; Insecta - physiology; invasive species; Mice; movement; Natural resources; Peromyscus - physiology; Peromyscus maniculatus; Pest Control; population biology; Population Dynamics; population ecology; spotted knapweed; survival; Time Factors; Urophora; Urophora spp; weed control; weeds; wildlife food habits; wildlife management
• ISSN: 1051-0761; 1939-5582
• DOI: 10.1890/07-0766.1

The threat posed by exotic organisms to native systems has led to extensive research on exotic invaders, yet management of invasives has progressed relatively slowly. This is partly due to poor understanding of how exotic species management influences native organisms. To address this shortfall, we experimentally evaluated the efficacy of an invasives management tool for restoring native deer mouse (Peromyscus maniculatus) populations elevated by exotic species. The exotic insects, Urophora spp., were introduced in North America for biological control of the Eurasian invader, spotted knapweed (Centaurea maculosd), but instead of controlling C. maculosa, Urophora have become an important food resource that doubles P. maniculatus populations, with substantial indirect effects on other organisms. We hypothesized that herbicide suppression of Urophora's host plant would reduce the Urophora food resource and restore P. maniculatus populations to natural levels. Prior to treatment, mouse populations did not differ between controls and treatments, but following treatment, P. maniculatus were half as abundant where treatment reduced Urophora. Peromyscus maniculatus is insensitive to direct herbicide effects, and herbicide-induced habitat changes could not explain the P. maniculatus response. Treatment-induced reductions of the Urophora food resource offered the most parsimonious explanation for the mouse response. Multistate mark-recapture models indicated that P. maniculatus survival declined where Urophora were removed, and survival rates were more correlated with variation in population size than movement rates. Other demographic and reproductive parameters (sex ratios, reproductive status, pregnancy rates, and juvenile recruitment) were unaffected by treatment. These results suggest the Urophora biocontrol elevated P. maniculatus survival, and the herbicide treatment restored mouse populations by removing the exotic food and reducing survival. This work illustrates the importance of mechanistic understandings of community and population ecology for improving invasive species management.