Across-family analyses of ERR Slopes with respect to ecological,
evolutionary, and biogeographic correlates
For across-family analyses using phylogenetic independent contrasts
(PIC), we found that Malesian richness was not associated with
ERR slopes (Table 1). However, clustering of richness, based on thelocalized richness ratio , was positively associated with ERR
slopes (Table 1, Fig. 3a). Families with high localizedrichness ratio metrics and steeply positive ERR slopes included
Dipterocarpaceae (ratio of 0.82 and ERR slope of 0.53) and Anacardiaceae
(ratio of 0.84 and slope of 0.45). In contrast, families with low
localized richness ratio metrics and weaker positive ERR slopes
included Begoniaceae (ratio of 0.34 and slope of 0.24) and Gesneriaceae
(ratio of 0.35 and slope of 0.14). Similarly, the elevation with
peak in richness had a negative relationship with ERR slopes, with
higher ERR slopes when richness peaked at low elevations as compared to
high elevations (Table 1, Fig. 3b). For instance, the first quartile of
families (15 total) with low elevation peaks in richness (<
200 m a.s.l.) had an ERR slope average of 0.48, whereas those with peaks
within the last elevation peak quartile (avg. 1295 m a.s.l.) had an ERR
slope average of 0.09. Familial elevational extent also had a
negative relationship with ERR slopes (Table 1, Fig. 3c). Families
restricted to a narrow section of the gradient, either from ecological
specialization or geometric constraints (e.g. Burseraceae, familial
extent of ~ 2000 m and ERR slope of 0.55), had steeper
ERR slopes as compared to families with broad elevational occurrence
(e.g. Asteraceae, familial extent of ~ 4500 m and ERR
slope of -0.13). Average lower elevation limit and average
higher elevation limit metrics both had negative relationships with ERR
slopes (Table 1, Fig. 3d), with higher ERR slopes for families with
occurrence boundaries constrained to lower elevations. Counter to our
predictions, neither evolutionary age nor latitudinal
extent had a direct relationship with ERR slopes (results
insignificant). Consistent with our predictions, biogeographical
affiliation strongly influenced ERR slopes. Families with greater
westwardly skewed species occurrence (towards Sundaland) displayed a
strongly positive relationship with ERR slopes, whereas a negative
relationship emerged eastwardly (towards Sahul), with ERR slopes
becoming shallower, neutral, or negative (Table 1, Fig. 4a-d). The
spatially intermediate location, Wallacea, had mixed results when
comparing metrics of endemism or overlap (Table 1).Cosmopolitanism did not directly influence ERR slopes (Table 1,
Fig. 4d). The first pPCA component (pPC1, representing 43% of the
variance) had a positive relationship with ERR slopes (d.f. = 47,
F-statistic = 141.8, Adj. R2 = 0.75, P -value
< 0.001, Fig. 5). The observed dichotomy of range-size trends
for lowland Sundaland flora with concentrated centers of richness, with
low pPC1 scores and strongly positive ERR slopes, compared to montane
Sahul flora with distributed richness, with high pPC1 scores and weaker
ERR slopes (Table 1; see Supporting information). The second component
(pPC2, 19% of the variance) was non-significant.