Is evolution faster at ecotones? A test using rates and tempo of diet
transitions in Neotropical Sigmodontinae (Rodentia, Cricetidae)
We evaluated whether evolution is faster at ecotones as niche shifts may
be needed to persist under unstable environment. We mapped diet
evolution along the evolutionary history of 350 sigmodontine species.
Mapping was used in three new tip-based metrics of trait
evolution–Transition Rates, Stasis Time, and Last Transition
Time–which were spatialized at the assemblage level (aTR, aST, aTL).
Assemblages were obtained by superimposing range maps on points located
at core and ecotone of the 91 South American ecoregions. Using Linear
Mixed Models, we tested whether ecotones have species with more changes
from the ancestral diet (higher aTR), have maintained the current diet
for a shorter time (lower aST) and have more recent transitions to the
current diet (lower aLT) than cores. We found higher aTR, aST and aLT at
ecotones than at cores. Although ecotones are more heterogeneous, both
environmentally and in relation to selection pressures they exert on
organisms, ecotone species change little from the ancestral diet as
generalist habits are necessary toward feeding in ephemeral
environments. The need to incorporate phylogenetic uncertainty in
tip-based metrics was evident from large uncertainty detected. Our study
integrates ecology and evolution by analyzing how fast trait evolution
is across space.