Data from: Zoogeographic patterns of pelagic oceanic cephalopods along the eastern Pacific Ocean

Aim: To analyse the diversity and distribution of oceanic pelagic
cephalopods along the Eastern Pacific Ocean, assessing the existence of
biogeographic structuring, and the role of physical variables in
generating geographical patterns. We hypothesized that the control by
environmental factors, and the effect of geometric constraints, determine
the range size and limits of distribution of oceanic cephalopods along the
eastern Pacific Ocean, generating a latitudinal gradient in species
richness. Location: Eastern Pacific Ocean (60°N – 60°S), from the Gulf of
Alaska to the Southern Ocean. Methods: Based on a literature review and
>5,000 records obtained from collections, we constructed a
presence-absence matrix including 61 latitudinal bands (2° each) along the
Eastern Pacific, and estimated species richness and range endpoints at
each band. Biogeographic units were determined by means of multivariate
analyses. Species richness was compared with null model predictions in
order to test for the existence of geometric constraints using the
Mid-Domain Null model. The effects on species richness of environmental
variables (temperature, salinity and oxygen) were evaluated separately for
surface and depth (0-1,000 m) data, by means of ordinary least squares
regression and simultaneous autoregressive models. Rapoport’s pattern was
assessed by applying the Stevens’ method and the range midpoint method.
Results: Species richness was high across the tropics and decreased
towards the both poles. We identified five biogeographic units,
highlighting two major distribution breaks at 40°N and 42°S. Species
richness was strongly related with environmental variables, although the
combined variables accounted for a large fraction of the variance between
0-1,000 m (R2 = 0.99), while temperature was the best single predictor at
the surface (R2 = 0.98). Species richness curves showed a mid-domain
effect (MDE), and the mean latitudinal range was higher in the tropics and
at warm latitudes, generating an inverse Rapoport’s pattern. Main
conclusions: Along the Eastern Pacific Ocean, oceanic cephalopods exhibit
both a clear biogeographic patterning and an interhemispheric (poleward
decreasing) diversity gradient, which appear strongly related with
physical factors and external forcing, as well as with a MDE as a
seemingly consequence of the naturally bounded domain of the Eastern
Pacific.