BOX 1. Emergence of traits × environment correlations at the
community level
Community-level traits are a useful starting point linking environmental
properties and traits of organisms even when we cannot easily sample
individuals in nature, as is the case for microorganisms. Here, I
present a simplified community assembly scenario showing how traits ×
environment correlations emerge at the community level under an
environmental filtering / species sorting paradigm. Assume an
environmental gradient consisting of 5 distinct environmental patches
with contrasted conditions for an environmental parameter x(i.e., the red-blue scale in the large squares in the figure). Also
assume a pool of 5 species with given values for a trait y ,
exemplified in the figure using a similar red-blue color scale, such
that low values for trait y translates into high reproductive
success in environments with a low value for parameter x . We
start (t = 1, first row of panels in the figure) by randomly
drawing 100 individuals from the species pool and placing them in each
local community. Then, we simulate the extinction of a given number of
individuals (here, 5 per time step) and replace them based on the
reproductive success of the remaining species in the local community, as
opposed to a zero-sum ecological drift assumed by a neutral model. This
is rather in line with a species sorting paradigm where local community
dynamics are assumed to reach an equilibrium faster than the
environmental properties change, and with little/no impact of dispersal
from neighbouring communities (i.e., source-sink dynamics) (Leibold et
al., 2004). If, at each time step, we compute a community-weighted mean
(CWM) trait y for each local community, and correlate CWM and
local environmental property x , we see that community-levels
traits rapidly mirror local environmental conditions (right panel).