Oecologia

, Volume 145, Issue 1, pp 153–164

Invasive annual grasses indirectly increase virus incidence in California native perennial bunchgrasses

  • Carolyn M. Malmstrom
  • April J. McCullough
  • Hope A. Johnson
  • Linsey A. Newton
  • Elizabeth T. Borer
Global change ecology

DOI: 10.1007/s00442-005-0099-z

Cite this article as:
Malmstrom, C.M., McCullough, A.J., Johnson, H.A. et al. Oecologia (2005) 145: 153. doi:10.1007/s00442-005-0099-z

Abstract

In California valley grasslands, Avena fatua L. and other exotic annual grasses have largely displaced native perennial bunchgrasses such as Elymus glaucus Buckley and Nassella pulchra (A. Hitchc.) Barkworth. The invasion success and continued dominance of the exotics has been generally attributed to changes in disturbance regimes and the outcome of direct competition between species. Here, we report that exotic grasses can also indirectly increase disease incidence in nearby native grasses. We found that the presence of A. fatua more than doubled incidence of infection by barley and cereal yellow dwarf viruses (B/CYDVs) in E. glaucus. Because B/CYDV infection can stunt E. glaucus and other native bunchgrasses, the indirect effects of A. fatua on virus incidence in natives suggests that apparent competition may be an additional mechanism influencing interactions among exotic and native grasses in California. A. fatua’s influence on virus incidence is likely mediated by its effects on populations of aphids that vector B/CYDVs. In our study, aphids consistently preferred exotic annuals as hosts and experienced higher fecundity on them, suggesting that the exotics can attract and amplify vector populations. To the best of our knowledge, these findings are the first demonstration that exotic plants can indirectly influence virus incidence in natives. We suggest that invasion success may be influenced by the capacity of exotic plant species to increase the pathogen loads of native species with which they compete.

Keywords

Invasive speciesAphidsBarley yellow dwarf virusApparent competitionAvena

Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Carolyn M. Malmstrom
    • 1
  • April J. McCullough
    • 1
    • 2
  • Hope A. Johnson
    • 1
    • 3
  • Linsey A. Newton
    • 1
  • Elizabeth T. Borer
    • 4
  1. 1.Department of Plant BiologyMichigan State UniversityEast LansingUSA
  2. 2.College of Arts and SciencesCornell UniversityIthacaUSA
  3. 3.Registration Division (7505C)U.S. Environmental Protection AgencyWashingtonUSA
  4. 4.Department of ZoologyOregon State UniversityCorvallisUSA