DOI: 10.5061/dryad.d2547d8fh
title: Population density and size structure data for macroecology analysis on <em>Littorina littorea</em> from different locations along the Atlantic North American coast

description: Variation in abundance and size along environmental gradients provides
 insights into the capacity of species to adapt to changing environmental
 conditions and predict range expansions, this being particularly relevant
 for non-native species. Here, we evaluate how population density, shell
 height, and size structure vary in relation to environmental factors
 across a broad latitudinal gradient in the non-native Littorina littorea.
 We sampled ten locations, covering nearly the entire range of L. littorea
 in North America and measured snail density, shell height, substrate
 rugosity and algal biomass. We extracted other environmental factors from
 satellite data and used them to assess the influence of local
 characteristics and environmental gradients on mean snail density, mean
 shell height and size structure. We found evidence of a weak positive
 relationship between snail density and rugosity. Mean shell height showed
 a strong positive relationship with growing season length and a negative
 relationship with air temperature. We also found that high and variable
 temperatures during summer, length of the growing season, and high
 rugosity, negatively impacted the frequency of small individuals. Instead,
 high water temperature during the spawning period, low temperature
 variability during summer, and low substrate rugosity are positively
 associated with a higher frequency of small individuals. Our results
 indicated that substrate rugosity positively influenced the abundance of
 this non-native littorinid independent of the climatic conditions
 experienced. Instead, variation in shell height largely reflected the
 environmental gradient found throughout its range. In particular, we argue
 that the lower abundance of small snails in sites with high and variable
 summer temperatures reflects increased juvenile mortality, while the
 higher frequency of small snails in sites with warmer spawning periods and
 more stable summers indicates enhanced recruitment and population growth.
 These findings support the potential for L. littorea to expand its range
 poleward with the progression of climate warming.
description: # Population density and size structure data for macroecology analysis on
 *Littorina littorea* from different locations along the Atlantic North
 American coast The dataset regards measurements of density, body size, and
 size structure of L. littorea across 10 locations across Atlantic North
 America. Data include Population density and size measurements of
 Littorina littorea from 10 Locations along the North American Atlantic
 coast. Environmental variables extrapolated from satellite data for the 10
 locations are included, as well as rugosity and biomass data measured in
 situ. The R codes included were used for figure creation and statistical
 analysis. They can be used to reproduce the results of the paper using the
 raw datasets included. Data from this study can be used for other
 purposes, such as invasive species monitoring or species distribution
 modelling based on size and density. #### Description of the data and file
 structure This dataset is composed on 5 excel files and 2 csv file. Each
 of them contain the raw data used for the analyses of the paper. The
 analysed variable are Density Size and Size structure.
 "Density_and_size_data_for_PCA.xlsx" - Rows are the locations
 sampled Columns = Location, Density (ind./quadrat), Size (mm) Rugosity
 (a.u.) Biomass (g) Latitude (°) Longitude (°) SumSST (Summer sea surface
 temperature, °C) Seaslength (length of the growing season, °C) MaxSST
 (maximal sea surface temperature, °C) SpawnSST (Spawning sea surface
 temperature, °C) Sum75percSST (Summer 75th percentile sea surface
 temperature, °C) Sum90percSST (Summer 90th percentile sea surface
 temperature °C) SdSST (Standard deviation summer sea surface temperature,
 °C) Airtemp (Mean summer air temperature, °C) Density_m2 (ind/m2)
 "GeoDistanceMatrix.xlsx" - Geographical distance matrix of the
 ten location. Each values represent the distance from one location to
 another (km). Calculated tracing the most reasonable path.
 "Litto_locations.xlsx" - Full name and date of sampling of the
 ten locations. Columns = State/Province Location Date Code (code of the
 sampling sites) Code2 (simpler code)Latitude (°) Longitude (°)
 "Size_analysis.xlsx - Raw dataset presenting location, size and
 latitude of all the individuals measured in our sampling. Columns =
 Location Size (mm) Latitude (°)
 "PCA_scores_per_location_regressed_against_lat_and_long.csv" -
 PC1 and PC2 scores of the locations sampled, obtained from the
 environmental factors residual against latitude and longitude.
 "Residuals_against_lat_and_long_density.csv" -
 "Residuals_against_lat_and_long_for_PCA_SIZE.csv" - density and
 size data with "residualised" environmental factors against
 latitude and longitude. all columns represent the same variable in
 "Density_and_size_data_for_PCA.xlsx" but regressed, thus with
 arbitrary units. #### Code/Software The code files (.R) are:
 "AIC_selection_DENSITY.R" - the code used to select the best
 env. factor, run the model and create the figure for density - ,
 "AIC_selection_SIZE.R" - the code used to select the best env.
 factor, run the model and create the figure for size- ,
 "Mantel_test.R" - code used to perform mantel test - ,
 "Map_figure_1.R" - code used to generate Figure 1 -
 "PCA_analysis.R" - code used to run the PCA analysis and
 generate figures - , "Regression_lat___long.R" - code used to
 obtain regressed data against latitude and longitude - ,
 "Size_structure_analysis.R" - code used to run the size
 structure analysis and generate the figure - .