Résumé
Theory suggests that the structure of evolutionary history represented in
a species community may affect its functioning, but phylogenetic diversity
metrics do not allow for the identification of major differences in this
structure. Here we propose a new metric, ELDERness (for Evolutionary
Legacy of DivERsity) to estimate evolutionary branching patterns within
communities by fitting a polynomial function to lineage-through-time (LTT)
plots. We illustrate how real and simulated community branching patterns
can be more correctly described by ELDERness and can successfully predict
ecosystem functioning. In particular, the evolutionary history of
branching patterns can be encapsulated by the parameters of third-order
polynomial functions and further measured through only two parameters, the
“ELDERness surfaces.” These parameters captured variation in productivity
of a grassland community better than existing phylogenetic diversity or
diversification metrics and independent of species richness or presence of
nitrogen fixers. Specifically, communities with small ELDERness surfaces
(constant accumulation of lineages through time in LTT plots) were more
productive, consistent with increased productivity resulting from
complementary lineages combined with niche filling within lineages.
Overall, while existing phylogenetic diversity metrics remain useful in
many contexts, we suggest that our ELDERness approach better enables
testing hypotheses that relate complex patterns of macroevolutionary
history represented in local communities to ecosystem functioning.