DOI: 10.5061/dryad.8931zcrrf
title: Niche conservation in copepods between ocean basins

description: This dataset provides the necessary data to test for niche
 conservatism as demonstrated in the article "Niche conservatism in
 copepods between ocean basins; 10.1111/ecog.05690".  Our
 study examined niche conservatism (i.e. a species' niche remains
 stable in space and time) between populations of the same species of
 marine copepod in different ocean basins. We used two approaches to test
 for niche conservatism which can be defined as a Princpial
 Component Analysis (PCA) and Environmental Niche Model (ENM) method.
 Niches may differ by virtue of the fact that the available environmental
 conditions do not overlap. This can be addressed by first establishing a
 baseline or a null model that quantifies how far a niche would be expected
 to differ by chance based on the environmental conditions in both areas.
 We used six environmental variables to define the environmental niche (sea
 surface temperature - SST °C, Salinity, mixed layer depth - MLD (m),
 bathymetric depth (m), chlorophyll-a - chl-a (mg m-3) and wind
 stress (N m-2). The PCA method uses the first 3 principal components to
 define the species niche in each population and the available background
 conditions in each area. If the niche distance between two populations is
 found to be significantly LESS than the distance in mean background
 conditions then the niches are judged to be conserved even if they are
 different. In contrast, if the niche distances are significantly different
 and MORE than the distance in mean background conditions then the niches
 are judges to be diverged.  The ENM method compares the niches of
 two populations by using Maximum Entropy modelling (MaxEnt) to first
 define each popultions distributions across the environmental gradients.
 The niche overlap between two different populations were quantified using
 the Schoener's D metric where 0 = no niche overlap to 1 = full niche
 overlap. To separate the effect of different background
 conditions on the level of niche overlap (D), a null distribution (H0) was
 generated for each population by calculating the differences between 100
 ENMs generated using the presence data of one population and random
 background samples from the other population. If  H0 &lt; D,
 the niches overlap greater than would be expected purely by chance and are
 therefore conserved. In contrast If 
 H0 &gt; D the niches overlap less than would be expected by
 chance and are therefore diverged. Of the 21 pairwise comparisons between
 populations of the same species a total of 10 showed evidence of
 niche divergence. The divergent popaultions belonged to 7 of the 15 marine
 copepod species with the majority belonging to the genus Pleuromamma. The
 findings have important implicatons on the use of  ecological
 models in defining the niche of marine copepods as regional
 populations may respond differently to environmental
 pressures. Evidence of strong genetic variation has been shown
 for many of these species with the potential for adaptive evolutionary
 response to regional pressures at a much faster rate than
 expected. Given this fact we encourage future studies to
 incorporate phylogenetic information into niche model analyses for
 plankton.
description: Both biological and environmental data are freely available for
 download. The copepod data were collected by the
 Continuous Plankton Recorder (CPR) and extracted from the Archive for
 Marine Species and Habitats Data (dassh.ac.uk).  The
 environmental data were extracted as monthly climatologies from the World
 Ocean Atlas while the bathymetric depth were extracted from GEBCO’s
 current gridded bathymetric data set (2020).
description: The readme files contains a description of the variables used in
 this work. The associated comma delimited files (.csv) provides the data
 for 1 of the species (<em>Nannocalanus minor</em>) to perform
 the PCA and ENM method used in this paper. An associated R script shows
 the procudure for the PCA method.  For further details
 please see the original paper.