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Small population size limits reproduction in an invasive grass through both demography and genetics

  • Population ecology - Original research
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Abstract

Small populations of founding individuals or survivors of incomplete management programs often represent critical transitions in biological invasions. Theory predicts that population size affects reproduction and, consequently, a population’s expansion, but there are few empirical tests, and fewer that account for the reduced genetic diversity that often accompanies small population size. We created experimental small populations of invasive ryegrass (Lolium multiflorum) with population size varying independently from genetic diversity. Treatment independence was achieved by cloning plants to increase population size without changing diversity. Plant fitness was measured as the proportion of florets producing a seed. We analyzed the effects of population size, genetic diversity, and their interaction using ANCOVAs, one of which accounted for variation in individual plant growth. As predicted, smaller populations produced significantly lower proportion seed set. Low genetic diversity also reduced seed set, but this was best interpreted as part of a significant interaction with population size. Specifically, the effect of population size on the proportion seed set was over five times larger for populations in the medium genetic diversity treatment than the highest diversity treatment, and 6.7 times larger for populations with the lowest level of diversity. Population size variation had biologically meaningful consequences, as the rate of seed set within the low diversity treatment increased by 80 % with increasing population size. The results indicate that both the demographics and genetics of populations can influence reproduction and invasive potential, and must be considered when assessing risk and designing management plans for invasive plants.

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Acknowledgments

J.L.F. was supported by a graduate student award from an endowment of the Department of Plant Sciences. Financial support for this research was provided by UC Davis departmental startup funds to M.J. We appreciate statistical help from Scott Steinmaus, and advice on the research and writing from Kevin Rice and Sharon Strauss. Jim Jackson’s field crew, Guy Kyser, Bill Pfender of the USDA Agricultural Research Service, and Pamela Riley ensured the survival of plants. Tom Lanini provided information on sampling locations. The Indiana Statistical Consulting Center clarified several points for us. Anonymous reviewers made important suggestions on an earlier version of the manuscript. The first author also thanks Dennis McFaden for training and inspiration. The authors declare that they have no conflict of interest and that experiments complied with the current laws of the country in which the experiments were performed.

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Authors and Affiliations

  1. Department of Plant Sciences and Graduate Group in Ecology, University of California, Davis, CA, 95616, USA

    Jeffrey L. Firestone & Marie Jasieniuk

  2. Department of Plant Sciences, MS 4, University of California, Davis, CA, 95616, USA

    Jeffrey L. Firestone

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  1. Jeffrey L. Firestone
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  2. Marie Jasieniuk
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Correspondence to Jeffrey L. Firestone.

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Communicated by Miguel Franco.

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Firestone, J.L., Jasieniuk, M. Small population size limits reproduction in an invasive grass through both demography and genetics. Oecologia 172, 109–117 (2013). https://doi.org/10.1007/s00442-012-2465-y

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  • DOI: https://doi.org/10.1007/s00442-012-2465-y

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