Habitat effect on assemblage-level tip-based metrics
We found that the type of ecoregion habitat —and therefore a broader
environmental context— has a large influence on the time of diet
evolution. Species from the ecotone of forest ecoregions had higher aTR,
and higher aST and higher aLT than the core of forest ecoregions, the
core of non-forest ecoregions, and the ecotone of non-forest ecoregions.
Stability of forest regions can explain high stasis time and prolonged
transition times. Available evidence show that cores were more stable
over time than ecotones, at least for forested regions (Mayle et al.
2004; Mayle and Powell 2008; Costa et al. 2017). This stability can be
traced back to the Eocene, which had forests that resemble forests today
in terms of vegetation structure and taxonomic composition (Burnham and
Johnson 2004). However, the ecotones of forest ecoregions considerably
changed over time and repeatedly expanded over savannas and grasslands
over time (Behling and Pillar 2007; Costa et al. 2017). Rodent feeding
strategies may have changed due to ecotone dynamics, then resulting in
diet transitions to track variation in available resources. In the same
line of evidence, we find that trait evolution is faster at the ecotone
of non-forested ecoregions. Such open-habitat ecoregions, which are the
result of long periods of cold and dry climate, were much more extensive
in the past than they are today (e.g., Behling and Pillar 2007). The
expansion of forests over non-forested regions could therefore have
demanded more recent adaptations of sigmodontine rodents to persist in
the more forested landscapes of South America.