DOI: 10.5061/dryad.83bk3jb3k
title: Data from: Applying invasion biology frameworks to predict impacts of range-expanding predators

description: Aim: Global change is driving many species to expand their geographic
 ranges into novel communities. The impacts of range expansions on
 recipient populations and communities, which remain uncertain, might be
 anticipated using frameworks derived from invasion biology. Our goal,
 therefore, is to test whether two frameworks developed in invasion
 theory—that impacts of expanding predators on prey and community diversity
 would be nonlinear (negatively density-dependent) and greatest in novel
 (i.e, expanded) ranges—can be used to predict the impacts of two
 range-expanding predators. Location: The Pacific coasts of California,
 USA, and Baja California, Mexico. Time Period: 2022-2023. Major Taxa
 Studied: Two species of intertidal carnivorous snail, the whelks
 Acanthinucella spirata and Mexacanthina lugubris. Methods: We conducted
 observational surveys and manipulative experiments in the historic and
 expanded ranges of both predators. We assessed how impacts on prey (acorn
 barnacles and mussels) and community diversity scale with predator density
 and compared per capita impacts between regions. Results: As with
 non-native invasive predators, we found that both range-expanding
 predators reduced the abundance of prey species. However, our results
 supported a linear relationship and no decrease in per capita effect on
 prey with increasing abundance of the shifting predator, and we did not
 observe consistent impacts of range-shifting whelks on community
 diversity. Finally, impacts in whelks’ expanded ranges were generally
 consistent with those in historic ranges, with some potential for
 increased impact in the expanded range. Main Conclusions: Our results
 provide empirical evidence that frameworks developed in invasion biology
 can be used to predict the impacts of future range expansions, allowing us
 to anticipate impacts based on those in the species’ historic ranges and
 indicating a linear increase in impacts with range expander abundance.
description: **Overview:  ** There are two main data
 sources in this dataset: (1) observational survey data collected from
 2022-2023, spanning 23 intertidal sites from Baja California, Mexico,
 through northern California, USA, and (2) manipulative density data from 6
 sites in Baja California, Mexico, and northern California USA. These
 geographic ranges compromise the historic and expanded ranges of the two
 range-expanding intertidal whelks, Acanthinucella spirata and Mexacanthina
 lugubris.   **Observational Data: **
 To assess the current distributions and abundances of
 <em>Acanthinucella</em> and <em>Mexacanthina</em>,
 as well as <em>in situ</em> associations with abundances of
 prey species and community diversity metrics, we conducted field surveys
 at 23 sites across California, USA and Baja California, Mexico between
 April 2022 and October 2023. Sites in northern California, USA, and Mexico
 were surveyed once per year in the spring (2 surveys per site), and sites
 in southern California, USA, were surveyed in the spring and fall each
 year (4 surveys per site). In addition, to ensure we included the most
 recent range information for these species, we conducted a single, partial
 survey (timed count only, using methods as described below) at the Santa
 Monica Pier and Venice Breakwater in March 2024, following recent reports
 posted on iNaturalist.com.  At each site, we laid a 25
 m horizontal transect at the top of the intertidal (i.e., parallel to the
 water at the top of the barnacle zone) and 5 vertical transects
 (perpendicular to and extending toward the waterline) at random locations
 along the horizontal transect. Along each vertical transect, we placed
 0.25 m × 0.25 m (0.0625 m<sup>2</sup>) quadrats every 0.25 m
 drop in vertical elevation. Within each quadrat, we conducted community
 diversity surveys where we assessed the relative abundance of all species,
 both mobile and sessile, as percent cover. To estimate the relative
 abundance of each expanding whelk species, we conducted an additional,
 1-hour timed search for <em>Acanthinucella</em> and
 <em>Mexacanthina</em> individuals following the diversity
 surveys; any individual whelks found during timed counts were associated
 with a shore height using an Apache Tools Mesa SL101 laser level and local
 tide predictions (https://tidesandcurrents.noaa.gov/tide_predictions.html). **Manipulative Density Experiment: ** To test the relationship between the abundance of range-expanding whelks and impacts on (a) prey abundance and (b) community diversity, as well as compare impacts across historic and expanded regions, we conducted a manipulative caging experiment from May to September in 2023 at a subset of our survey sites. We identified two <em>Acanthinucella</em>-expanded sites in northern California (Mendocino North and Mendocino South) and two *Acanthinucella-*historic sites in southern California (Dana Point and Scripps Reserve). Similarly, we identified two <em>Mexacanthina</em>-expanded sites in southern California (Dana Point and Scripps Reserve; at a different elevation than <em>Acanthinucella</em>-historic plots) and two <em>Mexacanthina</em>-historic sites in Baja California, Mexico (Punta Morro and Campo Kennedy). At each site, we identified seven 33 × 33 cm (0.1 m<sup>2</sup>) plots parallel to the water line at shore heights of greatest focal whelk abundance, as determined by survey data from 2022 (~0.5 m above MLLW for <em>Acanthinucella</em> plots [mean plot shore height = 0.56 m, range = 0.28-0.81 m] and ~1.0 m above MLLW for <em>Mexacanthina</em> plots [mean plot shore height = 0.87 m, range = 0.65-1.13 m]). <em>Mexacanthina</em> plots contained at least two of these three target prey groups: acorn barnacles (<em>Chthamalus</em> & <em>Balanus</em> spp.), gooseneck barnacles (<em>Pollicipes polymerus</em>), and/or mussels (<em>Mytilus</em> spp*.*). Gooseneck barnacles and mussels were rare at <em>Acanthinucella</em>’s most common shore height, where plots contained primarily acorn barnacles, shown by previous studies to be their main prey. We randomly assigned a treatment to each of the seven plots: one of two controls—no cage or partial cage (where a cage was deployed but two of the sides are left open)—or one the following density treatments: 0, 1, 3, 6, or 12 whelks added per cage. Thus, the whelk-addition plots represented densities of 0, 10, 30, 60, or 120 individuals per m<sup>2</sup>, spanning a range of densities encountered in field surveys. We occasionally observed higher densities of <em>Mexacanthina</em> when they were aggregated at sites in Mexico (commonly 100-300 whelks per m<sup>2</sup>), so we established an additional 24 whelk-addition plot (representing 240 individuals per m<sup>2</sup>) in both <em>Mexacanthina</em>-historic sites. To control for potential differences in feeding rates between whelks of various sizes within a site, we put equal numbers of small, medium, and large whelks in each plot (e.g., four small, four medium, and four large whelks in the 12-whelk plot), except the 1-whelk plot, which received a single medium individual. Size classes were defined at the site level based on the population structure of the whelks we encountered at each site. We removed all other whelk species from the whelk-addition plots, so cages contained only one focal whelk species. All cages were constructed of welded stainless steel mesh cloth (Master-Carr part ID: 9322T64).                                                 After we established the plots, we monitored (via community surveys, focal whelk measurements, and archival photographs) and maintained cages (cleaned and whelks replaced as needed to maintain density treatments) every 2 weeks for 8 weeks. Any focal whelks lost from the cages were replaced with medium-sized individuals. We initially conducted all community counts in the field and later verified or corrected counts from archival photographs. <em>Mexacanthina</em> cages were deployed from May to August 2023, and <em>Acanthinucella</em> cages were deployed from late June through September 2023.
description: # Data from: Applying invasion biology frameworks to predict impacts of
 range-expanding predators This README file was generated on 2024-01-26 ##
 Data Collection Period Spring (Apr-June) and Fall (Sept-early Nov),
 2022-2023. ## Files and Description ### Data and Metadata Files
 **ExptCommunityData (.csv)** Provides community data from the manipulative
 experiment. Data were collected in approx. 2 week intervals (see Methods
 for additional details). Rows correlate to individual observations of each
 plot. Columns provide plot identifying information and community data.
 **ExptData_Metadata (.csv)** Provides the metadata for all columns in the
 ExptCommunityData file, including all abbreviations and codes.
 **SurveyCommunityData (.csv)** Contains all observational community survey
 data. Rows correspond to individual quadrats, and columns provide quadrat
 identifying data and community information. **SurveyTransectData (.csv)**
 Contains information about each vertical transect from the observational
 data. Rows correspond to individual transects, and columns are used to
 calculate shore height at the top of each transect (relative to mean lower
 low water, MLLW). **SurveyWhelkLengthData (.csv)** Contains information
 about the size of all whelk individuals captured in the observational
 data. Rows correspond to individual whelks. **SurveyData_Metadata (.csv)**
 Provides the metadata for all observational survey ("Survey")
 sheets, including all abbreviations and codes. ### Script Files
 **Cage_Predation_Cleaned.R** This script can be used to generate the
 statistical analysis of all predation rates and predation figures derived
 from the manipulative cage experiment. Figures are named according to
 their placement in the manuscript. **Cage_Diversity_Cleaned.R** This
 script can be used to generate the statistical analysis of all changes in
 diversity and diversity figures derived from the manipulative cage
 experiment. Figures are named according to their placement in the
 manuscript. **Survey_Analysis_Cleaned.R** This script can be used to
 generate the statistical analysis of all data and figures generated from
 the observational study. Figures are named according to their placement in
 the manuscript. ## Recommended Workflow Download all datafiles, R scripts,
 and the R project. In addition to statistical analysis and figure
 creation, data cleaning and manipulation is performed within each script.
 Each script will call the necessary packages and, if open in R studio,
 will prompt the installation of said packages. Each script is broken into
 sections of analysis (delineated by "## [Description]
 ------------"). Each analysis and associated figures can be generated
 by running all code within a section. Both "Cage" scripts rely
 on the same data (ExptCommunityData.csv). Scripts are intended to be run
 linearly from top to bottom. "Cage" scripts call the
 experimental manipulation data and are broken into sections for each type
 of analysis. Within each section, linear models are built and then
 checked, and then the results are stored to an item in the workspace. To
 replicate these results, run all code to the "Model Outputs"
 section. Each line in the Model Outputs can be run to print the results of
 the statistical test. Figures presented in the manuscript text are
 produced at the end of the script. The "Survey" is similarly
 broken into sections. Sections approximately follow the order of
 presentation in the manuscript. Unlike the "Cage" scripts,
 analyses and figures are produced next to each other.