Long-term shifts in the functional composition of
communities
After the taxa had obtained coordinates in the PCoA, the functional
composition was described by the position of the community in the PCoA
plot. The position of the community was calculated as a mean position of
the taxa in the sample with respect to A1 and A2, weighted by their
relative abundances. Long-term trends (explanatory variable year) were
then visualized and quantified by Generalized Additive Model (GAM)
smooth functions (family Gaussian, link identity), using the community
coordinates A1 or A2 in May or August as response variables. Models were
fitted to A1 and A2 separately, since it is more difficult to visualize
and interpret the temporal trends on a 2D surface. To analyse the trends
in A1 and A2 independently was also meaningful, because the distribution
of trait values along A1 and A2 is straightforward (feeding type varies
along A1, complexity and body size vary along A2).