DOI: 10.5061/dryad.r4xgxd2r1
title: A test of the abundant-center hypothesis for stream fishes

description: The abundant-center hypothesis (ACH) provides a conceptual model for
 predicting range-wide distributions of species abundance, suggesting that
 abundance peaks in the center of the geographic range and declines towards
 range edges. Empirical studies testing the ACH and its subsequent
 derivations predominantly occurred in terrestrial systems and reported
 mixed support. Moreover, none of these models consider the possibility of
 multiple geographic areas of elevated abundance (which we refer to as
 abundant cores). Naturally, dispersal limited species may exhibit multiple
 abundant cores, requiring refinement of the ACH. We used fish species
 abundances from 29,206 community monitoring surveys and weighted
 geospatial kernel density estimation to identify the number of abundant
 cores for 64 freshwater fish species. We regressed the number of abundant
 cores against range size and body size to test if larger geographic
 distributions and body sizes contain more abundant cores than smaller
 distributions and body sizes. The two predictors are surrogates for
 evolutionary age and dispersal ability, respectively, because older
 species are generally associated with larger ranges, and large-bodied
 fishes have greater dispersal ability than small-bodied fishes in
 dendritic networks. For studied species, 43 exhibited multi-core
 distributions, and 21 exhibited a single-core distribution. Species range
 size, but not body size, was significantly and positively associated with
 the number of abundant cores. The ACH was not a good descriptor of the
 abundance patterns of most stream fishes we studied, suggesting that an
 abundant center model may not be well-suited for freshwater fishes. Recent
 geo-climatic events in evolutionary time have isolated populations of the
 same species by a matrix of unsuitable habitat and/or hard dispersal
 barriers, providing the basis for multi-core distributions. Biogeographic
 and ecological mechanisms likely underpin observed multi-core patterns,
 and our work indicates that the ACH and related concepts still present
 opportunities for testing and refinement.
description: # A test of the abundant-center hypothesis for stream fishes Dataset DOI:
 [10.5061/dryad.r4xgxd2r1](10.5061/dryad.r4xgxd2r1) ## Description of the
 data and file structure The following files include data and code for
 running analyses in the associated study. The study hinges on the KDE
 (kernal density estimates) that inform the distribution modeling.  ###
 Files and variables #### File: Ecography\_Rproject.Rproj
 **Description:** R Project file for the analysis #### File: ACH\_code.R
 **Description:** R script for running the abundance center hypothesis
 analysis #### File: KDEcoreResults\_Ecography.csv **Description:** CSV
 data for the kernal density data ##### Variables * Scientific_Name:
 Scientific name of stream fishes in study * Common_Name: Common name of
 stream fishes in study * avg.c10: average number of c10 cores estimated *
 sd.cores10: standard deviation of c10 core estimates * c10_SE: standard
 error of c10 core estimates * c10_2.5: 2.5% quantile of c10 core estimates
 * c10_97.5: 97.5% quantile of c10 core estimates * avg.cores25: average
 number of c25 cores estimated * sd.cores25: standard deviation of c25 core
 estimates * c25_SE: standard error of c25 core estimates * c25_2.5: 2.5%
 quantile of c25 core estimates * c25_97.5: 97.5% quantile of c25 core
 estimates * totalCoverage: Percent coverage area of species in study
 (compared to total species range) * sampleRangeSize: Range size (km^2)
 included in the study for the species * MAXTL: maximum total length
 estimate (cm) * distribution: species distribution information (MCH =
 multicore hypothesis; SCH = single core hypothesis) * Family: Taxonomic
 family * Order: Taxonomic order #### File: ACHtest\_distanceData.csv
 **Description:** CSV data for species distance from center ##### Variables
 * Scientific_Name: Scientific name of stream fishes in study *
 Common_Name: Common name of stream fishes in study * relAbund: Species
 relative abundance (proportion, 0–1) * distance_km: Distance (km) from
 center of distribution ## Code/software R is required to run the code, and
 R Studio would be preferable or required to use the R project file. CSV
 files are loaded into R and do not need to be otherwise opened, but can be
 done so in Excel or even a text editor.  ## Access information Other
 publicly accessible locations of the data: * None