Final Report - Center for Invasive Plant Management

CIPM Research Grants Final Report Suggested FormatFormat: 2-3 pages, single-spaced, Times New Roman, font size 12, left justifiedHeadings – boldFINAL REPORTGrant award year ___2007___Report submittal date 2/13/2009Title - Growth and Demography of the Newly Invasive False Brome*Investigators: Dr. Mitchell B Cruzan (replaced the original PI: David Rosenthal)Department of BiologyPortland State UniversityPO Box 751Portland, OR 97007*Title and original proposal are approximate since I do not have the final draft of theproposal available to me. It was originally submitted by David Rosenthal, who was apostdoc in my lab at the time. David has moved on to other projects and was notinvolved in this research.

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

challenges as rare species and / or isolated populations.Exotic plant range expansion may be characterized by three major steps:introduction, colonization, and naturalization with each step occurring at a successivelygreater spatial scale (Cousens & Mortimer 1995; Groves 1986; Radosevich et al. 2003).Each step is characterized by specific ecological and genetic phenomena (Fig. 1). Theinitial introduction involves the establishment and survival of a few individuals. At thebeginning of this “lag phase” (Primary Lag Phase, Fig. 1) these individuals becomeestablished, perhaps hybridize (i.e., interbreeding among genotypes from disparateportions of the native range), and produce offspring recruits. As the primary sourcepopulation(s) develops, these recruits are also subject to selection for adaptation to localconditions (Kliber & Eckert 2005). Over time, seeds from the founding source regionwill disperse, near and far, to form new satellite populations in peripheral regions (Fig. 1,Phase 2). The time necessary for a species to reach the next threshold (Fig. 1 Phase 3)may well be determined by the time required to recover from lower genetic diversityand/or inbreeding depression associated with colonizing populations (i.e., purging geneticlmillimeters (mm)Gene Diversity200180160140120100806040200CentralPeripheralPlant Height Leaf Length GrowthVegetative Biomass (g)8.50.0 0.1 0.2 0.3 0.4Gene Diversity (Hs)Figure 2. Size growth and biomass for central (putative source) and peripheral (sink) populations inOregon. Left panel: Bars are least square family means (n=8 to 16 families) nested in 7 central and 4peripheral populations (p< 0.01) indicating significant genetic variation for these traits. Right panel:Vegetative biomass harvested at the end of the second growing season for the same populations.1.41.21.00.80.60.40.20.0-0.2-0.4r 2 = 0.24 nsM14M11M6M3M8M1M16M50 20 40 60Reproductive Culms m -280 100Figure 3. Relationship between genediversity (Hs) and number of reproductiveculms per unit area for eight peripheralpopulations.12.011.511.010.510.09.59.0E4M1S2C6C7oad, Fig. 1, Phase 3) (Ellstrand &Schierenbeck 2000; Groves 2006; Lande& Schemske 1985; Sakai et al. 2001).Ultimately, the invading populations reachsome threshold genetic or demographiclevel and the species appears to spreadexponentially (Fig. 1, Phase 4).Unfortunately, little is known about howthese genetic and demographic processeswork in biological invasions.We have already found that populations inperipheral regions of the invasive range aregenetically depauperate and less vigorous(Fig. 2 left panel) and there appears to berelationship between genetic diversity andC1NC4E1C2C10E9CentralPeripheral

growth (Fig. 2 right panel). However these data are for greenhouse grown plants.Demographic field studies are necessary to determine if population growth rates exhibitsimilar trends in the field.We conducted a preliminary survey of a subset of 8 populations for plant number, densityand estimated reproductive output (number of reproductive culms per unit area). Wechose 8 populations to represent a continuum from genetically depauperate to relativelydiverse. Consistent with studies demonstrating a positive relationship between geneticdiversity and fitness within a species (Lienert et al. 2002; Lu et al. 2005), our preliminaryanalyses show a positive trend for plant density and population reproductive potential,suggesting a positive relationship between gene diversity and population growth (Fig. 5).Also note that one of the low genetic diversity populations that we sampled in 2004 nolonger existed in 2006. However, without growth, fecundity and recruitment data wecannot estimate which populations have higher intrinsic growth rates and consequentlypose a greater threat. Yearly monitoring of these and other peripheral regions coupledwith our proposed demographic and genetic studies will provide a powerful data set toclarify the roles population dynamics and metapopulation processes in a newly expandingspecies.Immediate Research objectives and HypothesesConduct field ecological surveys and demographic analyses of populations in the centerand at the edge of B. sylvaticum’s known invasive range to identify characteristic featuresof secondary source (high genetic diversity / high fitness) and sink (low genetic diversity/ low fitness) populations.Hypothesis 1a. Secondary sources have higher fitness (seed production) andperformance related traits (growth) under field conditions than sink (lowgenetic diversity) populations.Hypothesis 1b. Secondary source populations exhibit higher densities ofindividuals and reproductive culms than sink populations.Hypothesis 1c. Secondary source populations have higher intrinsic populationgrowth rates (λ) than sink populationsMethodsSite identification and mapping. At least five local clusters of populations willbe chosen for intensive study. There are a large number of suitable locations, so we willendeavor to distribute the clusters across the expanding periphery of B. sylvaticum’scurrent range. Candidate locations include The Blodgett Tract Forest, run by OregonState University but located NW of Portland, several locations in the Sweet Home regionto the east and SE of Corvallis, the Clackamas Watershed in Portland, the Pleasant Hillregion to the SE of Eugene, and in a recent area of introduction near the San FranciscoBay area of California. Local regions will be chosen for sampling based on the localdensity of populations, which should be high enough so that 25 to 30 populations can belocated along 3 to 5 km of contiguous roads.Demography. Ten populations (2 in each of the five local clusters defined above)with 80 to 100 plants will be monitored for changes in individual plant size, density,

seedling recruitment and fecundity. All individuals in each of these populations will bepermanently marked, and their locations mapped. Plants will be divided into four to sixsize classes based on the number of tillers and reproductive status. Size classes willinclude a seedling stage (single tiller), a juvenile stage (multiple tillers, no evidence ofpast or present sexual reproduction), and from one to three adult stages (sexualreproduction evident) that are based on estimated tiller number. Fecundity will beestimated for each adult size class based on the number of culms and florets per culm.Any seedling found in each delineated population area will be permanently marked,measured. Data for each population will be analyzed for the size classes described abovein Lefkovich transition matrices as described by Caswell (2000). Matrices will be used toestimate average transition probabilities, elasticities and sensitivity measures, and theaverage growth rate (λ) over the three seasons of this study. Average population growthrates will be tested using a paired t-test and a split plot ANOVA using the GLMprocedure of SAS (SAS 2001). The elasticity and sensitivity parameters will provide anassessment of the critical life history stages (i.e., that have the largest influence on λ:Caswell 2000), which will provide valuable information for targeted control measures.Once the source or sink status of each population is more firmly established from geneticdiversity and assignment tests, we will used pooled samples across populations of thesame type to obtain more robust estimates of the transition probabilities and growth rateparameters for each class of population.ResultsSynopsis of resultsSites were sampled for total density and reproductive effort per plant inpopulations that were central or peripheral to locations of the original introduction offalse brome in the Willamette valley. These same sites had previously been sampled forgenetic diversity at 10 microsatellite loci. Site location was not a very good predictor ofpopulation density or the reproductive effort per plant, but reproductive effort tended tobe higher for populations with higher genetic diversity.BackgroundGrasses make up a large proportion of invasive plants and are capable ofdisturbing ecological processes and native plant community structure (D'Antonio andVitousek 1992). A perennial bunch grass, Brachypodium sylvaticum, also known as falsebrome, was introduced into the Pacific Northwest in the early 1900’s. Within the lastfifteen years this species has rapidly become an aggressive invader in the Western US(Kaye 2003; Rosenthal et al. 2008 ; Ramakrishnan unpublished data). Previous work hasestablished that this species was introduced into two locations in the Willamette Valley ofOregon, and that invasive genotypes are hybrids from recombination of genotypesderived from several locations in Western Europe (Rosenthal et al. 2008). Due to therelatively recent introduction and spread of B. sylvaticum, its amenability to bothgreenhouse and genetic studies, and the large network of managers involved, this grass isan ideal system for assessing the ecological and genetic characteristics associated withinvasion.The goals of this project were two-fold: 1) to establish demographic plots forcharacterization of population size distributions and reproductive effort for sites having

different levels of genetic diversity; and 2) to measure early growth potential (relativegrowth rate) of plants derived from seeds from plants in populations having differentlevels of genetic diversity. These results are reported below along with a summary oftraining successes students that were involved in this research.I. Demographic PlotsWe established made measurements of plant size and reproductive effort for morethan 950 plants of the invasive Brachypodium sylvaticum (false brome) at 11 sitesin the Willamette Valley of Oregon. All sites had previously been sampled forgenetic diversity using microsatellite markers (Ramakrishnan et al. 2008). Siteswere chosen to represent areas close to, and peripheral to both originalintroduction locations near Eugene and Corvallis, OR (Rosenthal et al. 2008), andto represent a broad range of genetic diversity.A. MethodsThree to five one-meter square quadrats were established at each site and markedwith rebar stakes. Plants within each quadrat were mapped on a grid coordinatesystem and measured for the total number of culms and the number ofreproductive culms. Data were analyzed for differences in population size andreproductive effort with respect to location (near Corvallis or Eugene, or near therange perimeter) and level of genetic diversity within populations.B. ResultsPopulations of false brome varied for population size and the averagereproductive effort of individual plants. There were significant differencesamong sites for total number of plants and number of reproductive culms perplant (both P < 0.001, 10/37 df; Figs. 1, 2). There was a general trend forpopulations with higher genetic diversity to have Population size was notassociated with the level of genetic diversity (P > 0.37), but plants in populationswith higher genetic diversity tended to produce more reproductive culms (P =0.10; Fig. 1). Populations with higher genetic diversity were generally near areasof the original introductions, but some populations in peripheral regions also hadrelatively high diversity and rates of reproduction (Fig. 3). However, geneticdiversity was a better predictor of reproductive effort per plant than was the sitelocation (central or peripheral).

2520Plant Density151050C1 C11 C4 E4 E6 E9 M1 M16 M5 M7 S1C P C C C C P P P P PSite (region)Fig. 1. Number of plants per meter square for sites of false brome in theWillamette valley. Sites are divided into central (C) regions close to the originalintroductions, and peripheral (P) regions near the edge of the current range.0.70.6Reproductive Effort0.50.40.30.20.10C1 C11 C4 E4 E6 E9 M1 M16 M5 M7 S1C P C C C C P P P P PSite (region)Fig. 2. Number of sexual culms per plant for sites of false brome in theWillamette valley. Sites are divided into central (C) regions close to the originalintroductions, and peripheral (P) regions near the edge of the current range.

25Reproductive Effort2015105CP00 0.1 0.2 0.3 0.4Genetic DiversityFig. 3. The relationship between the proportion of sexual culms per plant andgenetic diversity (He) for sites of false brome in the Willamette valley. Sites aredivided into central (C) regions close to the original introductions, and peripheral(P) regions near the edge of the current range.Publications – list any publications (peer-reviewed or otherwise) produced from thework funded by this proposalLawson, J.L. , Rosenthal, D.R. and M.B. Cruzan. In revision*. Relative GrowthRate in the locally invasive grass Brachypodium sylvaticum*Will be submitted in the fall of 2009.Literature CitedAllendorf FW, Lundquist LL (2003) Introduction: Population biology, evolution, andcontrol of invasive species. Conservation Biology 17, 24-30.Buckley YM, Briese DT, Rees M (2003) Demography and management of the invasiveplant species Hypericum perforatum. I. Using multi-level mixed-effects modelsfor characterizing growth, survival and fecundity in a long-term data set. Journalof Applied Ecology 40, 481-493.California Invasive Plant Council (1999) Exotic pest plants of greater ecological concernin California (http://www.cal-ipc.org/file_library/4898.pdf).Caswell H (2000) Matrix population models: construction, analysis and interpretationSinauer, Sunderland, MA.Cousens R, Mortimer M (1995) The Dyamics of Geographic Range Expansion. In:Dynamics of Weed Populations, pp. 21-54. Cambridge University Press, NewYork.

Davis AS, Dixon PM, Liebman M (2004) Using matrix models to determine croppingsystem effects on annual weed demography. Ecological Applications 14, 655-668.Davis AS, Landis DA, Nuzzo V, et al. (2006) Demographic models inform selection ofbiocontrol agents for garlic mustard (alliaria petiolata). Ecological Applications16, 2399-2410.Dietz H, Edwards PJ (2006) Recognition that causal processes change during plantinvasion helps explain conflicts in evidence. Ecology 87, 1359-1367.Ellstrand NC, Schierenbeck KA (2000) Hybridization as a stimulus for the evolution ofinvasiveness in plants? Proceedings of the National Academy of Sciences of theUnited States of America 97, 7043-7050.Firbank LG, Watkinson AR (1986) Modeling the Population-Dynamics of an ArableWeed and Its Effects Upon Crop Yield. Journal of Applied Ecology 23, 147-159.Freckleton RP, Watkinson AR (1998) Predicting the determinants of weed abundance: amodel for the population dynamics of Chenopodium album in sugar beet. Journalof Applied Ecology 35, 904-920.Groves RH (1986) Invasion of mediterranean ecosytems by weeds. In: Resilience inMediterranean type ecosystems (eds. B. D, M. HAJ, Lamont BB), pp. 129-145.Junk, Dordrecht.Groves RH (2006) Are some weeds sleeping? Some concepts and reasons. Euphytica148, 111-120.Hanski I, Saccheri I (2006) Molecular-level variation affects population growth in abutterfly metapopulation. Plos Biology 4, 719-726.Kaye T (2003) Invasive Plant Alert: False-Brome (Brachypodium sylvaticum). Institutefor Applied Ecology, False Brome Working Group, Corvalis.Kliber A, Eckert CG (2005) Interaction between founder effect and selection duringbiological invasion in an aquatic plant. Evolution 59, 1900-1913.Lande R, Schemske DW (1985) The Evolution of Self-Fertilization and InbreedingDepression in Plants .1. Genetic Models. Evolution 39, 24-40.Lienert J, Fischer M, Schneller J, Diemer M (2002) Isozyme variability of the wetlandspecialist Swertia perennis (Gentianaceae) in relation to habitat size, isolation, andplant fitness. American Journal of Botany 89, 801-811.Lockwood JL, Cassey P, Blackburn T (2005) The role of propagule pressure inexplaining species invasions. Trends in Ecology & Evolution 20, 223-228.Lu YQ, Waller DM, David P (2005) Genetic variability is correlated with population sizeand reproduction in american wild-rice (Zizania palustris var. palustris, Poaceae)populations. American Journal of Botany 92, 990-997.Meimberg H, Hammond JI, Jorgensen CM, et al. (2006) Molecular evidence for anextreme genetic bottleneck during introduction of an invading grass to California.Biological Invasions 8, 1355-1366.Oostermeijer JGB, Luijten SH, den Nijs JCM (2003) Integrating demographic andgenetic approaches in plant conservation. Biological Conservation 113, 389-398.Oregon Department of Agriculture (2005) Noxious weed control policy andclassification. Oregon Department of Agriculture, Salem, OR.Parker IM (2000) Invasion dynamics of Cytisus scoparius: A matrix model approach.Ecological Applications 10, 726-743.

Radosevich SR, Stubbs MM, Ghersa CM (2003) Plant invasions-process and patterns.Weed Science 51, 254-259.Sakai AK, Allendorf FW, Holt JS, et al. (2001) The population biology of invasivespecies. Annual Review of Ecology and Systematics 32, 305-332.SAS (2001) SAS/STAT user's guide version 8.01 SAS institute, Carey, North Carolina.Shea K, Kelly D (1998) Estimating biocontrol agent impact with matrix models: Carduusnutans in New Zealand. Ecological Applications 8, 824-832.Shea K, Sheppard A, Woodburn T (2006) Seasonal life-history models for the integratedmanagement of the invasive weed nodding thistle Carduus nutans in Australia.Journal of Applied Ecology 43, 517-526.Smith GL, Freckleton RP, Firbank LG, Watkinson AR (1999) The population dynamicsof Anisantha sterilis in winter wheat: comparative demography and the role ofmanagement. Journal of Applied Ecology 36, 455-471.Tsutsui ND, Case TJ (2001) Population genetics and colony structure of the argentine ant(Linepithema humile) in its native and introduced ranges. Evolution 55, 976-985.Products – list any other products besides publications produced by this project1. Two students were trained on this grant.2. One Biology Honors Thesis was produced through support from this grant.3. Two proposals for federal funding (NSF and USDA/NRI) were enhanced bythis research. First-round reviews were generally positive and these proposalsare in revision for resubmission this spring and summer.Long-Term Goal/s and Continued Progress of ResearchRecent work has begun to quantify the relative roles that ecological andpopulation genetic processes play in plant invasions. However, as of yet, no clearecological process or evolutionary phenomena emerges as the Achilles heel of invasivespecies. Since it is becoming apparent we cannot prevent all exotic plant introductions ormake accurate predictions of which species will invade next, our best strategy may be todevelop practical science-based approaches to management. Newly invasive species arepromising research systems for this goal because they are subject to measurableecological (selection pressure (including pathogens and mutualists), and source/sinkeffects) as well as population genetic (inbreeding, bottlenecks, and drift) phenomena.Identifying how these processes affect metapopulation dynamics during range expansionwill facilitate the development of better management strategies for invasive species.We are using the newly invasive grass, Brachypodium sylvaticum, as a modelsystem to identify the processes responsible for rapid range expansion, and to developeffective methods for invasive species control. Our previous work on this speciesindicates that its current range expansion in Oregon is a consequence of at least twoindependent introductions in Oregon, one near Eugene and the second near Corvallis.The subsequent range expansion apparently ensued primarily via long distance dispersalevents, followed by local short-distance movement of seeds along dispersal corridors.Populations in peripheral regions are primarily genetically depauperate, and in general,genotypes from peripheral populations are less vigorous. The observation of low vigor inperipheral populations combined with the lower level of genetic diversity in these

populations suggests that some of these populations may be suffering from reduced vigordue to inbreeding depression (sink populations). However, a minority of peripheralpopulations have higher levels of genetic diversity, and results from assignment testsbased on microsatellite data indicate that these populations are acting as secondarysources for local invasion. Brachypodium is still in its initial stages of spread, andperhaps remains in a secondary lag phase. However, if a larger proportion of satellitepopulations become sources, then we expect this species will begin to spreadexponentially. This research will inform us about the population genetic processes atwork in newly colonizing populations and set the stage for the development ofmanagement strategies applicable to threatened as well as invasive species.The proposed studies have important implications for both applied and basicsciences. Our results will identify ecological, demographic and genetic data that are mostrelevant to population growth in this species. This will provide quantitative criteria bywhich land managers can identify specific invasive populations or sites for control oreradication.Benefits of Seed MoneyThis seed money established demographic plots, tested methodology, anddemographic data on central and peripheral populations of false brome. These data andmethods will be instrumental in our successful pursuit of federal funding for continuationof this research.Advancing This ResearchWe continue to work with managers and other researchers in Oregon to develop adata base for understanding the dynamics of the false brome invasion. We haveestablished a strong collaboration with Barbara Roy at Oregon State University and arecurrently collaborating on projects, manuscripts, and federal grant proposals.Our research was recently featured in the November 2008 issue of Molecular Ecology:*Dlugosch, K. M., and C. G. Hays. 2008. Genotypes on the move: some things old andsome things new shape the genetics of colonization during species invasions. MolecularEcology 17:4583-4585.*A review of the following paper that appeared in the same issue:Rosenthal, D. M., A. P. Ramakrishnan, and M. B. Cruzan. 2008. Evidence for multiplesources and intraspecific hybridization at early stages of the invasion of Brachypodiumsylvaticum (Hudson) Beauv. in North America. Molecular Ecology 17:4657-4669.Websitehttp://web.pdx.edu/~cruzan/Budget$200 - $300 was spent on suppliesThe remainder was spent on travel and student hourly wages for field andgreenhouse work.