Thermal niche traits of high alpine plant species and communities across the tropical Andes and their vulnerability to global warming

Aim The Climate Variability Hypothesis (CVH) predicts that locations with
reduced seasonal temperature variation select for species with narrower
thermal ranges. Here we (1) test the CVH by assessing the effect of
latitude and elevation on the thermal ranges of Andean vascular plant
species and communities, and (2) assess tropical alpine plants
vulnerability to warming based on their thermal traits. Location Tropical
Andes Taxon Vascular plants Methods Temperature data for 505 vascular
plant species from alpine communities on 49 summits, were extracted from
29,627 geo-referenced occurrences. Species thermal niche traits (TNTs)
were estimated using bootstrapping for: minimum temperature, optimum
(mean) temperature, and breadth (maximum-minimum). Plant
community-weighted scores were estimated using the TNTs of their
constituent species. CVH was tested for species, biogeographic species
groups and communities. Vulnerability to global warming was assessed for
species, biogeographic species groups and communities. Results Species
restricted to the equator showed narrower thermal niche breadth than
species whose ranges stretch far from the equator, however, no difference
in niche breadth was found across summits’ elevation. Biogeographic
species groups distributed close to the equator and restricted to alpine
regions showed narrower niche breadth than those with broader ranges.
Community weighted-scores of thermal niche breadth were positively related
to distance from equator but not to elevation. Based on their TNTs,
species restricted to equatorial latitudes and plant communities dominated
by these species were identified as the most vulnerable to the projected
1.5 °C warming, due to a potentially higher risk of losing thermal niche
space. Main conclusions Our study confirms that the CVH applies to high
tropical Andean plant species and communities, where latitude had a strong
effect on the thermal niche breadth. TNTs are identified as suitable
indicators of species’ vulnerability to warming and are suggested to be
included in long-term biodiversity monitoring in the Andes.