Scale dependence in abundance-environment relationships
Since FIA is a systematic survey program, we considered the absence of a
species’ record in a plot as a true absence. Thus, we analyzed whether
there is scale-dependence in tree abundance-environment relationships,
that is, whether models for species with wide geographical or
environmental range are better than models for species with narrower
environmental or geographical range. To do that, we calculated Spearman
correlations between model´s ∆AIC and species’ area of occupancy, extent
of occurrence, and environmental breadth. The area of occupancy was
estimated as the number of plots occupied by the species divided by the
total number of plots in the database (89,369 plots). The extent of
occurrence was calculated as the minimum convex polygon of all
occurrences (MCP - IUCN, 2019) and given as the proportion of the extent
occupied by each species divided by the total available geographical
space.
Finally,
we calculated the environmental breadth as the proportion of the
environmental space occupied by the species in relation to the total
available environmental space by applying the Schoener’s D index
(Schoener, 1974; Broennimann et al. , 2012; Ronquillo et
al. , 2020).