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Fiddler Overlap Data Levinton 2023 -- Description of Data Files

These data come from a GIS study of geographic ranges of fiddler crabs throughout the world, analyzed in 2019. They consist of (1) GIS files: .shp and related files usable as GIS source material in the ESRI data software system; (2) Range length data for all species studied in km of coastline; (3) Centroid data for all species, given as latitude and longitude; (4) Overlaps of all species, given as number of species overlapped within a biogeographic zone (Indo-West Pacific IWP, Eastern Pacific EPAC, and Western Atlantic WATL.

1. GIS files: Source geographic ranges of fiddler crab species came from fiddlercrab.info. We digitized ranges from the fiddler crab website as of July, 2019 (http://www.fiddlercrab.info.) Coastline data was extracted from https://www.ngdc.noaa.gov/mgg/shorelines/ and was extracted using ArcMap v 10.6 (Environmental Systems Research Institute Corporation, Redlands, California - Esri), at the "intermediate" resolution shapefile to an ocean base map provided by Esri. Range maps were projected to World Mercator using coastline data and digitized coastal species ranges.
2. Range Length Data. These are extracted range lengths in km using the data from GIS files and extracted coastline data. They are in the file FIDDLER CRAB RANGES.csv, organized by biogeographic region, genus and species name.
3. Centroid Data. Centroids for all species are given as latitude and longitude. The ArcMap 10 centroid tool was calculated to provide a measure of the center of species ranges. The centroid is a geometric center of a polygon determined by the range boundaries. Centroids for each species are organized by Biogeographic region (IWP, EPAC, WATL), genera within regions.
4. Overlap data. These data give the number of species overlapped within a biogeographic region (IWP, EPAC, WATL). Absolute number of species overlapped and relative overlap measure is given for each species within a region. Absolute number of species is the raw number of species overlapped (Number Overlapped) by a focal species. Relative Range (RR), which is the range of a given species in km divided by the range of the species with the largest range within a given biogeographical region, or subgenus, where appropriate. RR allows comparisons of range and overlap between regions with very different geographic scales or average ranges. Since the size of each region differs, RR provides a comparative scale of biogeographic coverage, ranging between 0 and 1. Proportional Overlap is given, which is the number of species a focal species overlaps within its biogeographic realm divided by the total number of species in that biogeographic realm. These consist of three files: OVERLAP DATA IWP.csv, OVERLAP DATA EPAC.csv, OVERLAPS DATA WATL.csv. These data can also be used to calculate overlaps by genus.