Firestone, Jeffrey , Jasieniuk, Marie .
Small population size reduces the rate of seed set in an invasive grass (Lolium multiflorum).
Invasive species are well known for their large populations. Small populations, however, can be very important by founding new invasions, expanding the invaded range or surviving control programs, and theory shows that they can affect invasion probability and dynamics. Surprisingly, there have been few studies of small population size and plant invasions in the wild. To elucidate the effects of population size on plant reproduction and potential invasiveness, we identified 21 naturally-occurring small populations of the invasive annual ryegrass Lolium multiflorum. We compared seed production on focal plants to three attributes of the population: population size, a focal plant's floret neighborhood (a measure of the size and pollen production of nearby potential pollen donors), and focal plant size. Both floret neighborhood and population size were weighted by the distance between plants so that these measures took into account plant density, spatial arrangement and pollen dispersal. The rate of seed set (per floret) was explained by the population size and the floret neighborhood, but not by the focal plant's size. Thus, the size of the population in terms of individuals or pollen production, and the proximity of plants within the population, are positively correlated with reproduction. Aborted seed were also found; the rate of aborted seed production was significantly related to maternal resources, inbreeding, and/or a decrease in the genetic quality of pollen received. For viable and aborted seed, our results are consistent with recent studies suggesting that population size and genetic diversity can both affect reproduction even in invasive plants. Reduced reproduction resulting from reduced size and/or density of a population (while accounting for maternal size) is an Allee effect, which may limit our ability to predict invasion risks and rates, particularly if the effect is not recognized. This study is one of few that measure the effects of natural variation in population size upon plant invasions and introductions
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1 - University of California, Davis, Plant Sciences / Ecology, 1 Shields Avenue, Davis, CA, 95616, USA
2 - University of California, Davis, Plant Sciences & Ecology, 1 Shields Avenue, Davis, CA, 95616, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 9th, 2012
Time: 9:15 AM