Ecoregion-scale variables
We tested whether tip-based metrics varied relative to ecoregion ecotone
and cores, as well as to other variables characterizing the ecological
and biogeographic context of ecoregions (Table 1). First, we
superimposed the points on the ecoregion shapefile (Olson et al. 2001)
to determine whether points were in ecoregion cores or ecotones, and
whether their habitat was either forested or open. The distinction
between forested and open habitats reflects broad differences in
vegetation structure and in the type of available niches and resources
(Vivo and Carmignotto 2004). Ecoregions belonging to forest, woodland,
and mangrove biomes were considered forested habitats, while ecoregions
belonging to grassland, shrubland, desert, savanna, inland-water, and
the rock and ice biomes were considered as open habitats.
We considered the predominant habitat type and number of neighboring
ecoregions in our analyses. Neighborhood can be important because an
ecotone assemblage can have values of tip-based metrics that resemble a
core assemblage when the ecotone lies between two ecoregions with
similar habitat. That ecotone assemblage is then expected to have lower
transition rates, higher stasis time, and longer last transition times
than an assemblage located in the ecotone between ecoregions with
contrasting habitats.
We considered the importance of the Central Andes and Atlantic Forest in
predicting aTR, aST, and aLT because sigmodontine diversification and
richness have a close relationship with these regions (Patton et al.
2015; Maestri and Patterson 2016; Maestri et al. 2019). We superimposed
ecoregions on the shapefiles of Central Andes (Löwemberg-Neto 2015) and
the Atlantic Rainforest (Muylaert et al. 2018, available at
https://github.com/LEEClab/ATLANTIC-limits) to distinguish their
ecoregions from others (Fig. S1, see Supplementary Results in Supporting
Information). We treated the southernmost portions of the Andean region
(mainly southern Argentina and Andean piedmont), as well as extreme
northern and southern portions of Atlantic Rainforest as belonging to
other regions (e.g., Uruguayan Savanna, Cerrado, Caatinga), not as
primary loci of sigmodontine diversification (Maestri et al. 2019).