DOI: 10.5061/dryad.3r2280gbv
title: Thermal niche traits of high alpine plant species and communities across the tropical Andes and their vulnerability to global warming

description: 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.
description: Thermal niche traits (optimum temperature, minimum temperature
 and niche breadth) were estimated for each species. We used all available
 geo-referenced records of each species to extract monthly mean
 temperatures for each location record. We collected 29,627 species records
 from on-line databases and South American herbaria, including 1,388
 records from the summit sites. Mean monthly temperature maps were obtained
 from WorldClim gridded datasets (Hijmans, Cameron, Parra, Jones, &
 Jarvis, 2005) and then were downscaled to a 90 m pixel resolution. For
 this we used the Shuttle Radar Topography Mission Digital Elevation Model
 (SRTM DEM; http://www2.jpl.nasa.gov/srtm/) with a lapse rate of 0.54 °C 100 m<sup>-1 </sup>(Bush, Silman, & Urrego, 2004). To estimate the species TNTs, we first calculated the mean, minimum and maximum temperature of each location record only using the months of the growing period. The length of the growing period (active season) varies along the latitudinal gradient (Körner, Paulsen, & Spehn, 2011). Around the equator the growing season is all year round. Moreover, significant inactive seasons in terms of prolonged periods with low temperatures are exceptional for most of the entire tropical area involved. For transitional areas (i.e. 15-18 °N; 23-27 °S) and outside of the tropics (&gt; 27 °S), the ‘inactive season’ was defined here as the months where mean air temperature is equal or below 0 °C. Second, we used the estimated values of mean, minimum and maximum temperatures of all records per species to obtain 1,000 bootstrapped observations of the mean, minimum and maximum temperatures per species. Then we estimated the mean of the bootstrapped observations to obtain unique values for each of the three temperature values per species and obtained the following species thermal niche traits: optimum temperature (mean), minimum temperature and niche breadth (maximum – minimum temperature).