Niche conservation in copepods between ocean basins

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 < D,
the niches overlap greater than would be expected purely by chance and are
therefore conserved. In contrast If 
H0 > 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.