Figure 6 . Summary of climatic niches and elevational
distributions of Climatically-Similar Non-Alpine (CSNA) species, defined
here as non-alpine species whose ranges encompassed the same temperature
and precipitation conditions as alpine taxa. (a ) Phylogeny of
alpine (blue tips ) and CSNA (brown tips ) species. At this
broad scale, no clear phylogenetic separation of the two groups exists,
and both groups are distributed broadly across the seed plant phylogeny.
However, at the genus level, substantial taxonomic differences were
observed, and these differences persisted at both the familial and
ordinal levels (see Table 1 and main text). (b-c ) Density
histograms of the occupied climatic niche space and niche breadth,
respectively, of CSNA species, showing good overlap between their
climatic conditions and those of true alpine species (compare with
panels d in Fig. 2-3). (d ) Elevational distribution of
CSNA (brown bars ), compared to the elevational distribution of
all species in our dataset (“All Sp.”, grey bars ). Compared
with the American seed plant species pool overall, CSNA species tended
to have ranges that included a higher proportion of mountain foothills
(with frost exposure) and, to a lesser extent, lower montane, habitat.
Additionally, a lower proportion of their ranges were found in
exclusively frost-free or lowland areas. (Up. Mon: upper montane;
Lw. Mon.: lower montane; alpine elevational categories omitted here for
clarity. ) (e ) Scatterplot showing a strong
(R2=0.68) and significant (p<0.001) positive
correlation between species richness at Mexican sites where alpine
richness was lowest and CSNA richness was highest, indicating that sites
which support higher richness for one group likely do so for the other
group was well.