Limitations
Environmental variation unrelated to the distance from ecotones could
alternatively explain the lower transition rates and higher stasis time
and last transition times we find for ecotone species. For instance,
ecotones of many ecoregions may be formed by other environmental factors
(e.g., soil moisture and type) rather than climate, which might make
them temporally more stable than the ecotones formed by climate
(Cantidio and Souza 2019). In addition, patches of stable habitat
currently found at ecotones could rather be at the core of ecoregions in
the past. Thus, shifts in ancestral area could alternatively influence
trait evolution. Combining the tip-based metrics we developed here with
approaches that incorporate shifts in ancestral area (e.g., Maestri and
Duarte, 2020) can help to show whether trait evolution is produced by
shifts in distribution.
We used diet because it varies across sigmodontine species (Paglia et
al. 2012) and habitat types (de Vivo and Carmignotto 2004), and is
available for virtually all species (e.g., Wilman et al. 2014). In
addition, each diet type is subjected to a particular set of selection
pressures and presents different probabilities of transition and speeds
of evolution (Price et al. 2012; Maestri et al. 2017). Although other
important traits like life-mode could produce different results, we
believe our results are robust to trait choice as diet and life-mode
were shown to produce similar macroevolutionary patterns of
morphological disparity in sigmodontine rodents (Maestri et al. 2017).
Results were mostly robust when considering small-ranged species, whose
rates and time of diet transition respond to the position x habitat type
interaction —similarly to overall results. The location of species
assemblages in Andean and Atlantic Rainforest ecoregions has a large
influence on its tip-based metrics. This result is largely expected as
most of their small-ranged species both speciated and subsequently
evolved within these regions (D’Elia and Pardiñas 2015).