Population dynamics and potential for biological control of an exotic invasive shrub in Hawaiian rainforests

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31 Scopus citations

Abstract

Introduction of biological control agents to reduce the abundance of exotic invasive plant species is often considered necessary but risky. I used matrix projection models to investigate the current population dynamics of Clidemia hirta (Melastomataceae), an invasive shrub, in two rainforest stands on the island of Hawaii and to predict the efficacy of hypothetical biological control agents in reducing population growth rates. Stage-structured matrix models were parameterized with field data collected over 3 years from 2906 C. hirta plants in a recently invaded forest with an open overstory (Laupahoehoe) and 600 plants in a less recently invaded forest with a closed canopy (Waiakea). Asymptotic population growth rates (λ) for both populations in all years were greater than one, demonstrating that both populations were growing. Composite elasticities were high for the seedling life-history stage and fecundity, and near-term demographic elasticities suggested that changes in seedling survival would have the largest effect on population size in the short term. However, simulations showed that almost 100% of seedlings or new recruits produced per reproductive adult would have to be destroyed to cause populations to go locally extinct under current environmental conditions. Herbivores or pathogens that decrease survival across all vegetative stages by 12% at Waiakea and 64% at Laupahoehoe were projected to cause the populations to decline. Thus, biocontrol agents that reduce survival of multiple life-history stages rather than seed production should be pursued to control C. hirta in Hawaiian rainforests.

Original languageEnglish (US)
Pages (from-to)1145-1158
Number of pages14
JournalBiological Invasions
Volume8
Issue number5
DOIs
StatePublished - Jul 2006
Externally publishedYes

Bibliographical note

Funding Information:
I am grateful to Roddy Nagata, Gareth DeWalt, Kalan Ickes, and Bob Cabin for field assistance. Julie Denslow, Jack Ewel, Jim Hamrick, and two anonymous reviewers provided helpful comments on the manuscript. This research was supported by a USDA Forest Service Pacific Southwest Research Station Internal Competitive grant, Sigma Xi Grants-in-Aid-of-Research, and a Board of Regents’ fellowship from Louisiana State University.

Keywords

  • Biological control
  • Clidemia hirta
  • Demography
  • Elasticity analysis
  • Invasive species
  • Matrix models
  • Near-term dynamics

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