Invasion away from roadsides was not driven by adaptation to grassland habitats in Dittrichia graveolens (stinkwort)
Data files
May 30, 2024 version files 471.23 KB
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community_survey.csv
6.06 KB
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community_surveys_presence_absence_E.csv
2.29 KB
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cox_germ_constructionsoil8-2-21.csv
103.23 KB
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cox_germ_fieldsoil8-2-21.csv
89.94 KB
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cox_germ_filter_paper8-2-21.csv
77.93 KB
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dittrichia_graveolens_evolution.Rmd
66.10 KB
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field_relative_fitness_evolutionMS_2021.csv
58.54 KB
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greenhouse_competition_fieldsoil.csv
45.48 KB
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quadrat_data.csv
344 B
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README.md
21.32 KB
Abstract
Invasive plants along transportation corridors can significantly threaten ecosystems and biodiversity if they spread beyond anthropogenic environments. Rapid evolution may increase the ability of invading plant populations to establish in resident plant communities over time, posing a challenge to invasion risk assessment. We tested for adaptive differentiation in Dittrichia graveolens (stinkwort), an invasive species of ruderal habitat in California that is increasingly spreading away from roadsides into more established vegetation. We collected seeds from eight pairs of vegetated sites and their nearest (presumed progenitor) roadside population. We assessed differentiation between populations in roadside and vegetated habitat for germination behavior and for response to competition in a greenhouse experiment. We also tested for increased performance in vegetated habitat with a grassland field experiment including a neighbor removal treatment. Germination rates were slightly reduced in seeds from vegetated sites, which may indicate lower seed viability. Otherwise, plants did not show consistent differences between the two habitat types. Competition strongly reduced performance of D. graveolens in both the greenhouse and in the field, but plants originating from vegetated sites did not show enhanced competitive ability. Our findings show no evidence of adaptive differentiation between D. graveolens populations from roadside and vegetated habitats to date, suggesting that invasiveness in grasslands has not been enhanced by rapid evolution in the 40+ years since this species was introduced to California. Evolutionary constraints or potentially high levels of gene flow at this small scale may limit adaptation to novel habitats along roadsides.
README
1) Title of Dataset: Data from "Invasion away from roadsides was not driven by adaptation to grassland habitats in Dittrichia graveolens (stinkwort)"
https://doi.org/10.5061/dryad.wdbrv15wz
2) Author Information:
Principal Investigator Contact Information
- Name: Miranda Melen
- Institution: University of California, Santa Cruz
- Address: 130 McAllister Way, Santa Cruz, CA 9506
- Email: mkmelen@ucsc.edu
Associate or Co-investigator Contact Information
- Name: Ingrid Parker
- Institution: University of California, Santa Cruz
- Address: 130 McAllister Way, Santa Cruz, CA 9506
- Email: imparker@ucsc.edu
3) Year of data collection:
- community_survey.csv - 2020
- quadrat_data.csv - 2020
- community_surveys_presence_absence_E.csv - 2020
- cox_germ_filter_paper8-2-21.csv - 2021
- cox_germ_constructionsoil8-2-21.csv - 2021
- cox_germ_fieldsoil8-2-21.csv - 2021
- greenhouse_competition_fieldsoil.csv - 2021
- field_relative_fitness_evolutionMS_2021.csv - 2021
4) Geographic location of data collection:
- community_survey.csv - Santa Clara County, California, USA
- quadrat_data.csv - Santa Clara County, California, USA
- community_surveys_presence_absence_E.csv - Santa Clara County, California, USA
- cox_germ_filter_paper8-2-21.csv - University of California, Santa Cruz, California, USA
- cox_germ_constructionsoil8-2-21.csv - University of California, Santa Cruz, California, USA
- cox_germ_fieldsoil8-2-21.csv - University of California, Santa Cruz, California, USA
- greenhouse_competition_fieldsoil.csv - University of California, Santa Cruz, California, USA
- field_relative_fitness_evolutionMS_2021.csv - Blue Oak Ranch Reserve, Santa Clara County, California, USA
5) Dataset content
Community surveys of Dittrichia graveolens seed collection sites. Percent cover of Dittrichia graveolens, bare ground, and other vegetation, in addition to species abundance for each site.
- community_survey.csv
- quadrat_data.csv
- community_surveys_presence_absence_E.csv
Dittrichia graveolens seed germination on three substrates: filter paper, construction fill, and field top soil. Number germinated per dish, and data of germination is recorded.
- cox_germ_filter_paper8-2-21.csv
- cox_germ_constructionsoil8-2-21.csv
- cox_germ_fieldsoil8-2-21.csv
Greenhouse competition experiment with Dittrichia graveolens growing alone, or with a non-native grass species (Bromus hordeaceus or Festuca perennis). Plant aboveground biomass and height are recorded.
- greenhouse_competition_fieldsoil.csv
Field competition experiment with Dittrichia graveolens growing in an invaded annual grassland. Treatments included a grassland control where D. graveolen*s seedlings were planted into plots without manipulating the background vegetation, and biomass removal where *D. graveolens seedlings were planted into plots that were previously hoed to remove above and belowground competition and then kept bare for the remainder of the growing season.
- field_relative_fitness_evolutionMS_2021.csv
R code used for analyzing all datasets
- dittrichia_graveolens_evolution.Rmd
6) Description of the data and file structure:
*We used R version 4.2.2 (2022-10-31; R Core Team 2022) for all statistical analyses. Our general approach for each response variable (except the plant community survey) was to run mixed effects models with, at minimum, a fixed effect for habitat (roadside vs. vegetated) and a random effect for site. The site random effect takes into account the genetic similarity between the two nearby populations within a site, and captures landscape-scale variation between sites in, for example, elevation and roadside density.
Column headers for community_survey.csv
- Date - collection date
- Person - name of person that collected the data
- Habitat - two "habitats" identified in this dataset: vegetated (areas that are found in plant communities) and roadside (areas that are directly adjacent to paved roads)
- Site - name of site where data was collected, 8 sites total, each site has two paired habitats with populations of Dittrichia graveolens present
- Code - three letter code denoting the site name
- Latitude - latitude
- Longitude - longitude
- Elevation_ft - elevation recorded in feet
- Soil - soil was visually classified into three categories: soil, rock (natural), concrete/manmade material
- Site_Notes - notes about the site or soil
- Dittrichia_Notes - notes describing the substrate that the Dittrichia is growing out of
- Population_Shape - Dittrichia graveolens populations were categorized into two shapes: linear and polygon
- Phenology - plant phenology was recorded at time of data collection
- Est_number_population - Dittrichia graveolens population size was visually estimated into categories: 10, 50, 100, 1000, and 10000
- Q1_D_percent_cover - Quadrat 1 estimating percent cover of Dittrichia graveolens
- Q2_D_percent_cover - Quadrat 2 estimating percent cover of Dittrichia graveolens
- Q3_D_percent_cover - Quadrat 3 estimating percent cover of Dittrichia graveolens
- Total_D_percent_cover - Sum of percent cover of Dittrichia graveolens using data from Quadrat 1, 2, and 3
- Average_D_cover - Average percent cover of Dittrichia graveolens using data from Quadrat 1, 2, and 3
- Q1_Veg_percent_cover - Quadrat 1 estimating percent cover of vegetation (not Dittrichia graveolens)
- Q2_Veg_percent_cover - Quadrat 2 estimating percent cover of vegetation (not Dittrichia graveolens)
- Q3_Veg_percent_cover - Quadrat 3 estimating percent cover of vegetation (not Dittrichia graveolens)
- Total_Veg_percent_cover - Average percent cover of vegetation (not Dittrichia graveolens) using data from Quadrat 1, 2, and 3
- Average_Veg_cover - Average percent cover of vegetation (not Dittrichia graveolens)using data from Quadrat 1, 2, and 3
- Q1_Bare_percent_cover - Quadrat 1 estimating percent cover of bare ground
- Q2_Bare_percent_cover - Quadrat 2 estimating percent cover of bare ground
- Q3_Bare_percent_cover - Quadrat 3 estimating percent cover of bare ground
- Total_Bare_percent_cover - Average percent cover of bare groundusing data from Quadrat 1, 2, and 3
- Average_Bare_cover - Average percent cover of bare ground using data from Quadrat 1, 2, and 3
- Notes - notes about the data collection methods
Column headers for quadrat_data.csv
- quadrat_id - unique identifier for each quadrant in survey
- site - name of site where data was collected, 8 sites total, each site has two paired habitats with populations of Dittrichia graveolens present
- habitat - two "habitats" identified in this dataset: vegetated (areas that are found in plant communities) and roadside (areas that are directly adjacent to paved roads)
- species_count - number of unique species found in each quadrat
Column headers for community_surveys_presence_absence_E.csv
- Species - name of species identified. May be a genus, genus and species, or a category of unidentified genus that was seen repeatedly
- Baylands_Park_Roadside - site and habitat with presence (1) and absence (0) data for Species
- Baylands_Park_Vegetated - site and habitat with presence (1) and absence (0) data for Species
- Chesboro_reservoir_Roadside - site and habitat with presence (1) and absence (0) data for Species
- Chesboro_reservoir_Vegetated - site and habitat with presence (1) and absence (0) data for Species
- Guadalupe_reservoir_Roadside - site and habitat with presence (1) and absence (0) data for Species
- Guadalupe_reservoir_Vegetated - site and habitat with presence (1) and absence (0) data for Species
- Lexington_reservoir_Roadside - site and habitat with presence (1) and absence (0) data for Species
- Lexington_reservoir_Vegetated - site and habitat with presence (1) and absence (0) data for Species
- Oakridge_pond_Roadside - site and habitat with presence (1) and absence (0) data for Species
- Oakridge_pond_Vegetated - site and habitat with presence (1) and absence (0) data for Species
- Parkway_lakes_RV_Roadside - site and habitat with presence (1) and absence (0) data for Species
- Parkway_lakes_RV_Vegetated - site and habitat with presence (1) and absence (0) data for Species
- Penitencia_creek_Roadside - site and habitat with presence (1) and absence (0) data for Species
- Penitencia_creek_Vegetated - site and habitat with presence (1) and absence (0) data for Species
- South_San_Jose_VTA_Roadside - site and habitat with presence (1) and absence (0) data for Species
- South_San_Jose_VTA_Vegetated - site and habitat with presence (1) and absence (0) data for Species
Column headers for cox_germ_filter_paper8-2-21.csv
- Site - name of site where data was collected, but as a three letter code. 8 sites total, each site has two paired habitats with populations of Dittrichia graveolens present
- Habitat - two "habitats" identified in this dataset: vegetated (areas that are found in plant communities) and roadside (areas that are directly adjacent to paved roads)
- Population - a combination of Site using a three letter code followed by a "dash" (-) and the first letter of the habitat type (V = Vegetated, R = Roadside)
- Rep - there are 5 replications for each Population which are denoted using the first 5 letters of the English alphabet
- DishNum - there are 80 Petri dishes in this experiment and each dish was issued a number
- PopNum - there are 16 Populations and each Population was issued a number
- Treatment - this column identified that this treatment was using filter paper
- ID - a combination of the Rep and PopNum separated by an underscore (_)
- SurvivalID - a combination of the Treatment and Rep spearaed by an underscore (_)
- NoGermDish - number of seeds in the dish that did not germinate
- TotGermDish - number of seeds in the dish that did germinate
- PropGermDish - proportion of seeds in the dish that did germinate
- PlotPropGerm - proportion of seeds in the dish that did not germinate
- Label - each dish had 10 seeds, so each seed was given a number (1-10) and labeled as "Seed[number]Date"
- PlantDate - date that the seed was placed in the dish
- GermDate - date that the seed germinated, blank if it did not germinate
- Censor - Censor = 1 if the seed germinated, Censor = NA if the seed did not germinate
- Census - date of the most recent census to determine if seeds had germinated
- DaysCensus - given a zero to help calculate DaysToGerm
- DaysToGerm - GermDate minus PlantDate. If calculation throws an error because the seed did not germinate (GermDate = blank), then it displays DayCensus (0)
Column headers for cox_germ_constructionsoil8-2-21.csv
- Site - name of site where data was collected, but as a three letter code. 8 sites total, each site has two paired habitats with populations of Dittrichia graveolens present
- Habitat - two "habitats" identified in this dataset: vegetated (areas that are found in plant communities) and roadside (areas that are directly adjacent to paved roads)
- Population - a combination of Site using a three letter code followed by a "dash" (-) and the first letter of the habitat type (V = Vegetated, R = Roadside)
- Rep - there are 5 replications for each Population which are denoted using the first 5 letters of the English alphabet
- DishNum - there are 80 Petri dishes in this experiment and each dish was issued a number
- PopNum - there are 16 Populations and each Population was issued a number
- Treatment - this column identified that this treatment was using construction soil (construction fill)
- ID - a combination of the Rep, PopNum, and Treatment separated by an underscore (_)
- SurvivalID - a combination of the Treatment and Rep spearaed by an underscore (_)
- NoGermDish - number of seeds in the dish that did not germinate
- TotGermDish - number of seeds in the dish that did germinate
- PropGermDish - proportion of seeds in the dish that did germinate
- PlotPropGerm - proportion of seeds in the dish that did not germinate
- Label - each dish had 10 seeds, so each seed was given a number (1-10) and labeled as "Seed[number]Date"
- PlantDate - date that the seed was placed in the dish
- GermDate - date that the seed germinated, blank if it did not germinate
- Censor - Censor = 1 if the seed germinated, Censor = NA if the seed did not germinate
- Census - date of the most recent census to determine if seeds had germinated
- DaysCensus - number of days between PlantDate and Census
- DaysToGerm - GermDate minus PlantDate. If calculation throws an error because the seed did not germinate (GermDate = blank), then it displays 0
Column headers for cox_germ_fieldsoil8-2-21.csv
- Site - name of site where data was collected, but as a three letter code. 8 sites total, each site has two paired habitats with populations of Dittrichia graveolens present
- Habitat - two "habitats" identified in this dataset: vegetated (areas that are found in plant communities) and roadside (areas that are directly adjacent to paved roads)
- Population - a combination of Site using a three letter code followed by a "dash" (-) and the first letter of the habitat type (V = Vegetated, R = Roadside)
- Rep - there are 5 replications for each Population which are denoted using the first 5 letters of the English alphabet
- DishNum - there are 80 Petri dishes in this experiment and each dish was issued a number
- PopNum - there are 16 Populations and each Population was issued a number
- Treatment - this column identified that this treatment was using field soil (field top soil)
- ID - a combination of the Rep, PopNum, and Treatment separated by an underscore (_)
- SurvivalID - a combination of the Treatment and Rep separaed by an underscore (_)
- NoGermDish - number of seeds in the dish that did not germinate
- TotGermDish - number of seeds in the dish that did germinate
- PropGermDish - proportion of seeds in the dish that did germinate
- PlotPropGerm - proportion of seeds in the dish that did not germinate
- Label - each dish had 10 seeds, so each seed was given a number (1-10) and labeled as "Seed[number]Date"
- PlantDate - date that the seed was placed in the dish
- GermDate - date that the seed germinated, blank if it did not germinate
- Censor - Censor = 1 if the seed germinated, Censor = NA if the seed did not germinate
- Census - date of the most recent census to determine if seeds had germinated
- DaysCensus - number of days between PlantDate and Census
- DaysToGerm - GermDate minus PlantDate. If calculation throws an error because the seed did not germinate (GermDate = blank), then it displays 0
Column headers for greenhouse_competition_fieldsoil.csv. Empty cells represent no data available and remain empty for use with the accompanying code.
- Pot ID - a unique three digit number given to each pot for identification
- Soil - Field Soil was used for this experiment
- Site - name of site where data was collected, but as a three letter code. 8 sites total, each site has two paired habitats with populations of Dittrichia graveolens present
- Block - 8 blocks using numerical numbers (1-8)
- Habitat - two "habitats" identified in this dataset: vegetated (areas that are found in plant communities) and roadside (areas that are directly adjacent to paved roads)
- Competition - three types of competition for a pot: None = D. graveolens growing by itself in the pot (1 plant per pot), Bromus = D. graveolens growing with Bromus hordeaceus (2 plants per pot), Festuca = D. graveolens growing with Festuca perennis (2 plants per pot)
- Population - a combination of Site using a three letter code followed by a "dash" (-) and the first letter of the habitat type (V = Vegetated, R = Roadside)
- Biomass_date - date that biomass was harvested from plant
- Dittrichia_biomass - mass of D. graveolens biomass (mg)
- LRR_All - Log response ratio is manually calculated for proof on concept. Calculation = ln (competition/D. graveolens)
- Grass_biomass - mass of grass species biomass (mg)
- MeasurementDate_2 - all plant height was measured twice. MeasurementDate_2 is the first date of measuring plant height
- MeasurementDate_3 - second date of measuring plant height
- GrassHeight_cm_2 - height measurement of grass in cm on date MeasurementDate_2
- GrassHeight_cm_3 - height measurement of grass in cm on date MeasurementDate_3
- GrassGrowth - calculation of overall grass growth using GrassHeight_cm_3 minus GrassHeight_cm_2
- DittrichiaLLL_mm_2 - D. graveolens longest leaf length in mm on date MeasurementDate_2
- DittrichiaLLL_mm_3 - D. graveolens longest leaf length in mm on date MeasurementDate_3
- DittrichiaGrowth - calculation of overall D. graveolens growth using DittrichiaLLL_mm_3 minus DittrichiaLLL_mm_2
Column headers for field_relative_fitness_evolutionMS_2021.csv. Empty cells represent no data available and remain empty for use with the accompanying code.
- Block - Treatments are in a Blocked design, with 5 treatments in each Block, 10 Blocks total (A,B,C,D,E,F,G,H,I,J)
- Plot - Treatments are applied to each Plot. There are 5 Plots in each Block (1,2,3,4,5), 10 Plots of each Treatment.
- Flag - Each Plot has a Flag in the southwestern corner denoting the Block letter and Plot replicate
- Pos - Pos = Position of the plant. Each Plot was planted from the south to north and from west to east. There are 16 plant positions in a 4x4 grid
- Flag_Pos - Each plant position within a plot was given a unique code combining the Flag and Pos separaed by an underscore (_)
- Population - a combination of Site using a three letter code followed by a "dash" (-) and the first letter of the habitat type (V = Vegetated, R = Roadside)
- Site - name of site where data was collected, but as a three letter code. 8 sites total, each site has two paired habitats with populations of Dittrichia graveolens present
- Habitat - two "habitats" identified in this dataset: vegetated (areas that are found in plant communities) and roadside (areas that are directly adjacent to paved roads)
- Treatment - this experiment had two treatments: Biomass Removal and Grassland Control. Biomass Removal had all plant competitors removed from the plot by hoeing prior to planting D. graveolens and then weeded throughout the growing season. Gassland Control allowed the resident grassland species to naturally grow and D. graveolens was planted into the vegetation.
- HabitatTreatment - a combination of Habitat and Treatment separated by a forward slash (/)
- PlantDate - the date the D. graveolens seedling was planted into the field
- LeafMeas1 - Measurement of the length of the longest leaf (mm) at transplantation date
- LeafMeas2 - Measurement of the length of the longest leaf (mm) during May
- Growth - calculation of overall D. graveolens growth using LeafMeas2 minus LeafMeas2
- MortDate - date of D. graveolens mortality during mortality survey
- MortHarvDate - date of D. graveolens mortality if it began reproducing or if it was dead during the mortality survey
- CensorAll - set to 1. Initially used while surveys were ongoing.
- DaysMort - calculated number of days that the plant was alive
- Census - date of last plant survey
- DaysCensus - calculated number of days since the plant was planted
- NumDaysAlive - calculated number of days that the plant was alive before dying or harvest
- HarvDate - date of biomass harvest
- CensorBiomass - A binary code for stating whether biomass was recorded for the plant
- BudDate - The date when buds were first identified on the plant starting on July 2, 2021
- CensorReproduction - A binary code for stating whether the plant reproduced. 0 = failure, 1 = reproduction
- SurvToRepro - A binary code for stating whether the plant reproduced. 0 = failure, 1 = reproduction
- CensorTest - A binary code for stating whether the plant reproduced. Inverse of CensorReproduction and SurvToRepro 1 = failure, 0 = reproduction
- PropBud - proportion of plants that reached the budding stage of phenology
- PropBudSite - proportion of plants that reached the budding stage of phenology by site
- Phenology - date buds appeared or date of death
- DaysToPheno - calculated number of days from planting to Phenology
- CensorPheno - A binary code for stating whether the plant
- Height - The height (cm) of the plant from the crown (root/stem boundary) to the tallest leading leaf
- Biomass - The dry aboveground biomass (g) of the plant
- Biomass date - The date the aboveground biomass was weighed
Sharing/Access information
- Links to publications that cite or use the data: [WILL ADD LINK TO PUBLICATION ONCE AVAILABLE]
- Recommended citation for this dataset: [WILL ADD LINK TO PUBLICATION ONCE AVAILABLE]
Methods
Plant community survey: Data was collected at 8 sites of Dittrichia graveolens in Santa Clara County, CA, USA, from July 1st through August 14th, 2020. Each site had a roadside and vegetated population pair. At each population, we laid a 50 m transect tape along the longest axis of the population (for roadsides, transects were always parallel to the road) and placed a 0.5 x 0.5 m quadrat at three equidistant points along the axis. We visually estimated percent cover within each quadrat for D. graveolens, other vegetation, and bare ground (sum equaling 100%). We identified species within the three quadrats for each population and then walked the area to search for additional rare species. Taxa were identified to species when possible using The Jepson Manual: Vascular Plants of California (Second Edition). We calculated the average percent cover of bare ground, D. graveolens, and other vegetation per population by taking the mean of the three quadrats along each transect. Species richness was the total number of species found at a population (the three quadrats + surrounding rare species survey). We evaluated differences in percent cover and species richness between source habitats (roadside and vegetated) using paired t-tests (N = 8 sites with pairs of roadside and vegetated populations at each site).
Dittrichia graveolens seed collection for lab, greenhouse, and field experiments: In September and October of 2020, we sampled seeds from each of the 16 populations. We collected from at least 10 individuals, 3 m apart, for each population, along a randomly-placed transect. We combined seeds from all individuals in a population.
Lab - seed behavior: In the summer of 2021, we compared germination behavior of seeds from roadside and vegetated habitat types. We did three studies on different substrates: moist filter paper, engineered fill, and field topsoil (collected from a site on the UC Santa Cruz campus). We germinated 50 seeds from each population in Petri dishes (80 Petri dishes; 5 replicates with 10 seeds each) for each substrate (filter paper, engineered fill, and field topsoil). Seeds were visually inspected beforehand to ensure that only fully developed seeds were used for all experiments. Petri dishes were sealed with Parafilm M ™ and placed in a randomized block design in an incubation chamber with a daytime temperature of 23 ºC from 0900 - 0100 h and a nighttime temperature of 19 ºC from 0100 - 0900 h. We scored germination daily until no further germination was observed, then 7 more days (a total of 23 d on filter paper, 12 d on engineered fill, and 11 d on field topsoil). Signs of germination included the first emergence of the root radical or the cotyledon. Petri dishes were misted with DI water, and germinated seeds were removed once scored. We also took one homogenized sample of 30 seeds from each of the 16 populations and weighed them to the closest 0.001 g. We analyzed the germination rate on each of the three substrates (filter paper, engineered fill, and field topsoil) using a mixed-effects Cox proportional hazards model (coxme and survival packages), with source habitat as a fixed effect and site, population, and dish number as nested random effects. We evaluated the main effect of source habitat using a Type II partial-likelihood-ratio test (car package). We calculated average seed mass for each source habitat using a Welch Two Sample t-test.
Greenhouse - response to competition: We quantified response to competition in a greenhouse experiment with three treatments: D. graveolens grown alone, with Bromus hordeaceus, or with Festuca perennis. We collected B. hordeaceus seeds from Blue Oak Ranch Reserve and F. perennis seeds from the Terrace Lands of Younger Lagoon Reserve on the UC Santa Cruz Coastal Science Campus. We germinated D. graveolens seeds in the conditions described in Lab - seed behavior. We germinated grasses in trays with potting mix and placed them under fluorescent light banks for 16-hour length days and 8-hour length nights. Once radicles and cotyledons emerged, seedlings were transplanted in sets of three (one for each treatment). We grew plants in D16 Deepots (5 cm diameter, 18 cm height) in the greenhouse using field topsoil collected from a UC Santa Cruz campus site. Pots were then randomized into a blocked design with each block consisting of one D. graveolens seedling from each of the 16 populations for each of the three competition treatments, N = 48 per block x 8 blocks (384 total). After 4 months, we harvested D. graveolens aboveground biomass at the crown and dried it in a 60 ºC oven for 3 days before weighing it. We calculated response to competition as the log response ratio (LRR) of the aboveground biomass, LRR = ln(biomass with competitor / biomass alone), on a per-block basis (N = 8 blocks) for each of the 16 seed origins (vegetated or roadside habitat at each of the 8 sites). Therefore, each seed origin had 8 replicate LRR estimates for each competitor grass (Bromus hordeaceus and Festuca perennis). We fit a linear mixed effects model for each competitor with LRR as the response variable, source habitat as a fixed effect, and random effects for population nested in site, and block (lme4 package). Block was removed from the B. hordeaceus model because it did not explain sufficient variance, causing a singular fit. We tested for differences between source habitats using Type II Wald F-tests with Kenward-Rogers degrees of freedom (car package). To evaluate whether each competitor grass affected the biomass of D. graveolens, we tested whether the LRR intercept was significantly different from zero using t-tests with Kenward-Rogers degrees of freedom (pbkrtest and lmerTest packages).
Field - relative fitness: The field experiment was conducted at Blue Oak Ranch Reserve, San Jose, California, USA (37°22'54.89"N, 121°44'10.55"W). We tested whether rapid evolution during invasion into vegetated sites has enhanced fitness in the presence of grassland competitors. We established a 10 m x 26 m fenced field site and used a randomized block design with 10 blocks of 1.5 m2 plots. We had two treatments: grassland control (high competition) and complete competitor removal (no competition). We left the previous year’s thatch for the grassland control treatment and allowed vegetation to grow throughout the experiment. For the competitor removal treatment, we tilled the soil to completely remove below and aboveground biomass in December 2020 and then weeded to remove aboveground biomass throughout the growing season. In January 2021, we germinated seeds in Petri dishes in incubation chambers before transplanting them into soil collected in late December 2020 from Blue Oak Ranch Reserve. After about eight weeks, we planted seedlings into each plot from February 27 - March 24, 2021 (20 plots total). Each plot included one D. graveolens individual from each of the 16 populations, in a 4 x 4 grid centered on the plot. During the first month of growth, we replaced any D. graveolens that died. We surveyed plants weekly to assess D. graveolens survival and bud initiation until all plants had either produced buds or perished. We terminated plants at the first sign of budding to prevent reproduction of a noxious weed. As proxies for reproductive output, we measured height and biomass. We harvested aboveground biomass by cutting at the root crown and drying in a 60 ºC oven for three days before weighing. Height and biomass were strongly correlated (r = 0.74, N = 157), and results for the two response variables were similar. Therefore we present only the results for final biomass.
The field experiment had four response variables: survival (assessed both as total proportion surviving and time to death), final biomass at budding, and phenology (the survey date buds first appeared). We used a similar statistical approach for all response variables, fitting mixed effects models with source habitat, competition treatment, and their interaction as fixed effects; and initially including random effects for site, population nested in site, and block. Random effects that explained very low amounts of variance, causing singular fits, were removed. When interaction terms were not significant, they were removed and models were re-run with main effects only. Here we describe the structures of the final models. We compared total survival to budding with a generalized linear mixed model using a binomial family with a logit link function; fixed effects were source habitat and competition treatment, and random effects were population nested in site, and block (glmmTMB package). We evaluated the main effect of source habitat using a Type II Wald Chi-Square test (car package). Second, we analyzed survival using a mixed-effects Cox proportional hazards model (coxme and survival packages); fixed effects were source habitat and competition treatment, and random effects were population nested in site, and block. We evaluated the main effects of source habitat and competition treatment using likelihood ratio tests. We analyzed final biomass at the time of bud production using a linear mixed effects model (lme4 package); fixed effects were source habitat, competition treatment, and their interaction, and the only remaining random effect was site. We evaluated the main and interaction effects using Type II Wald F-tests with Kenward-Rogers degrees of freedom (car package). We used a log transformation of the biomass data to improve homoscedasticity. To assess changes in phenology, we compared the timing to bud for those plants that reached the reproductive state, using a mixed-effects Cox proportional hazards model (coxme and survival packages); fixed effects were source habitat and competition treatment, and random effects were population nested in site, and block. We evaluated the main effects using likelihood ratio tests.