The effect of consumers and mutualists of Vaccinium membranaceum at Mount St. Helens: dependence on successional context.
In contrast to secondary succession, studies of terrestrial primary succession largely ignore the role of biotic interactions, other than plant facilitation and competition, despite the expectation that simplified interaction webs and propagule-dependent demographics may amplify the effects of consumers and mutualists. We investigated whether successional context determined the impact of consumers and mutualists by quantifying their effects on reproduction by the shrub Vaccinium membranaceum in primary and secondary successional sites at Mount St. Helens (Washington, USA), and used simulations to explore the effects of these interactions on colonization. Species interactions differed substantially between sites, and the combined effect of consumers and mutualists was much more strongly negative for primary successional plants. Because greater local control of propagule pressure is expected to increase successional rates, we evaluated the role of dispersal in the context of these interactions. Our simulations showed that even a small local seed source greatly increases population growth rates, thereby balancing strong consumer pressure. The prevalence of strong negative interactions in the primary successional site is a reminder that successional communities will not exhibit the distribution of interaction strengths characteristic of stable communities, and suggests the potential utility of modeling succession as the consequence of interaction strengths.
School of Biological Sciences, Washington State University, Pullman, Washington, United States of America. suy14@psu.edu
Suann
S
Yang
Eelke
E
Jongejans
Sylvia
S
Yang
John G
JG
Bishop
D000818:Animals; D058448:Biota; D004175:Diptera; D055669:Ecological and Environmental Phenomena; D060434:Herbivory; D054817:Pollination; D012098:Reproduction; D012639:Seeds / Q000254:growth & development; D013269:Stochastic Processes; D029796:Vaccinium / Q000254:growth & development / Q000382:microbiology / Q000502:physiology; D014861:Washington