Final Report - Center for Invasive Plant Management

ProposalAbstractStudies integrating population genetic with demographic data are needed toaddress a fundamental paradox of biological invasions: if genetic bottlenecks are harmfulthen why do so many successful invaders have depauperate gene pools in the invadedrange when compared to their native range (Allendorf & Lundquist 2003)? Newlyinvasive species are particularly well suited to understand these phenomena aspopulations are expected to be highly genetically structured, with some harboring morevariation than others. In spite of overall reduced genetic diversity in the invasive range,some populations will harbor more variation than others. Our population genetic surveysof a newly invasive perennial grass Brachypodium. sylvaticum in Oregon confirm thisexpectation. The more genetically diverse invasive populations are expected to becomemore vigorous and produce more seeds. These populations would have greater intrinsicpopulation growth (λ) and increased propagule pressure contributing more to the invasion(Lockwood et al. 2005). This has not been tested in any invasive species. We propose toinitiate demographic surveys of invasive populations ranging in genetic diversity andspanning a range of regions with different invasion histories to identify the characteristicsof populations that make them a more imminent threat (i.e. higher genetic diversity,growth rate, and fecundity).Problem description and literature review and preliminary results.Demographic studies can help us model the spread of invasive species and informus about which life history stages should be targeted for management (Davis et al. 2006;Parker 2000; Shea et al. 2006). Population genetics studies demonstrate that successfulinvaders may have more (Lavergne & Molofsky), or less genetic diversity than in theirnative range (Meimberg etal. 2006; Tsutsui & Case2001, also see our databelow). However, we donot fully understand howgenetic diversity affectspopulation dynamics ininvasive species. This isprobably because studiesintegrating both approachesare less common in general(Hanski & Saccheri 2006)and more frequently calledfor in conservation of rareFigure. 1. A hypothetical scenario for range expansion in a newly-invasivespecies. Each dot represents an individual population. Darker dots indicate sourcepopulations. The model assumes that a secondary lag phase may be induced byinbreeding depression in newly established populations. Once the genetic load ispurged through population bottlenecks and inbreeding in small populations, the rateof range expansion is expected to increase dramatically. See Deitz and Edwards(Davis et al. 2006; 2006; Meimberg et al. 2006; Parker 2000; Shea et al. 2006) forpossible underlying dynamic ecological processes.or threatened species (e.g.,Oostermeijer et al. 2003)rather than in invasivespecies research. This issurprising since newlyintroduced species arelikely to face the same