Virus infection and grazing exert counteracting influences on survivorship of native bunchgrass seedlings competing with invasive exotics
Article first published online: 30 JAN 2006
Journal of Ecology
Volume 94, Issue 2, pages 264–275, March 2006
How to Cite
MALMSTROM, C. M., STONER, C. J., BRANDENBURG, S. and NEWTON, L. A. (2006), Virus infection and grazing exert counteracting influences on survivorship of native bunchgrass seedlings competing with invasive exotics. Journal of Ecology, 94: 264–275. doi: 10.1111/j.1365-2745.2006.01101.x
- Issue published online: 30 JAN 2006
- Article first published online: 30 JAN 2006
- Received 8 June 2005 revision accepted 8 November 2005 Handling editor: Jeremy Burdon
- apparent competition;
- barley yellow dwarf virus;
- invasive species;
- 1Invasive annual grasses introduced by European settlers have largely displaced native grassland vegetation in California and now form dense stands that constrain the establishment of native perennial bunchgrass seedlings. Bunchgrass seedlings face additional pressures from both livestock grazing and barley and cereal yellow dwarf viruses (B/CYDVs), which infect both young and established grasses throughout the state.
- 2Previous work suggested that B/CYDVs could mediate apparent competition between invasive exotic grasses and native bunchgrasses in California.
- 3To investigate the potential significance of virus-mediated mortality for early survivorship of bunchgrass seedlings, we compared the separate and combined effects of virus infection, competition and simulated grazing in a field experiment. We infected two species of young bunchgrasses that show different sensitivity to B/CYDV infection, subjected them to competition with three different densities of exotic annuals crossed with two clipping treatments, and monitored their growth and first-year survivorship.
- 4Although virus infection alone did not reduce first-year survivorship, it halved the survivorship of bunchgrasses competing with exotics. Within an environment in which competition strongly reduces seedling survivorship (as in natural grasslands), virus infection therefore has the power to cause additional seedling mortality and alter patterns of establishment.
- 5Surprisingly, clipping did not reduce bunchgrass survivorship further, but rather doubled it and disproportionately increased survivorship of infected bunchgrasses.
- 6Together with previous work, these findings show that B/CYDVs can be potentially powerful elements influencing species interactions in natural grasslands.
- 7More generally, our findings demonstrate the potential significance of multitrophic interactions in virus ecology. Although sometimes treated collectively as plant ‘predators’, viruses and herbivores may exert influences that are distinctly different, even counteracting.