2.5 Asymmetry of the realized thermal niche
We extracted the mean, maximum, and minimum temperature values for the
five groups depending on the repository and depth (Bsurf, Bma, Bme, Bmi,
and Msurf) associated with each post processed presence record (see
above in “2.1 Presence records”) of each species at 5 and 10
arc-minutes of spatial resolution. For Bio-Oracle, we used directly the
mean, maximum, and minimum temperature variables in each depth. In the
case of MARSPEC, we used the surface temperature of the warmest month to
represent the maximum temperature and the surface temperature of the
coldest month to represent the minimum temperature. With those values,
we conserved and grouped the minimum and maximum value from each species
for characterized the lower and upper TNR limits
respectively.
Finally, we tested the asymmetry in TNR limits
hypothesis (asymmetry in the variances with more variance in lower
limit) by testing the homogeneity of variances between the lower and
upper realized thermal limits. This process was repeated for each
variable group on each temperature measurement at the three taxonomic
levels and two spatial resolution by applying a
non-parametric Fligner-Killeen
test (Fligner and Killeen 1976) (5 groups × 3 temperatures × 3 taxonomic
levels × 2 resolutions). Particularly, in genus level, we excluded the
genus Laticauda due to represent the same result at the
Laticaudinae subfamily, and Ephalophis andMicrocephalophis as a result of only have data for one species.