• Dispersal is a key ecological process that influences plant community assembly. Therefore, understanding whether dispersal strategies are associated with climate is of utmost importance, particularly in areas greatly exposed to climate change. We examined alpine plant communities located in the mountain summits of the tropical Andes across a 4000 km latitudinal gradient. We investigated species dispersal strategies and tested their association with climatic conditions and their evolutionary history.

• We used dispersal-related traits (dispersal mode and growth form) to characterize dispersal strategies for 486 species recorded on 49 mountain summits. Then we analysed the phylogenetic signal of traits and investigated the association between dispersal traits, phylogeny, climate and space using structural equation modelling and fourth-corner analysis together with RLQ ordination.

• A median of 36% species in the communities were anemochorous (wind-dispersed) and herbaceous. This dispersal strategy was followed by the barochory-herb combination (herbaceous with unspecialised seeds, dispersed by gravity) with a median of 26.3% species in the communities. The latter strategy was common among species with distributions restricted to alpine environments.

• While trait states were phylogenetically conserved, they were significantly associated with a temperature gradient. Low minimum air temperatures, found at higher latitudes/elevations, were correlated with the prevalence of barochory and the herb growth form, traits that are common among Caryophyllales, Brassicaceae and Poaceae. Milder temperatures, found at lower latitudes/elevations, were associated with endozoochorous, shrub species mostly from the Ericaceae family. Anemochorous species were found all along the temperature gradient, possibly due to the success of anemochorous Compositae species in alpine regions. We also found that trait state dominance was more associated with the climatic conditions of the summit than with community phylogenetic structure. Although the evolutionary history of the tropical Andean flora has also shaped dispersal strategies, our results suggest that the environment had a more predominant role.

• Synthesis: We showed that dispersal related traits are strongly associated with a gradient of minimum air temperatures in the Andes. Global warming may weaken this key filter at tropical alpine summits, potentially altering community dispersal strategies in this region and thus, plant community structure and composition.

We collected information of two traits associated with plant dispersal strategies, namely dispersal mode and growth form. These traits have been identified as key traits in determining plant dispersal distances (Tamme et al., 2014). Given that species could have more than one trait category (trait state), we built species vs traits matrix as multi-choice nominal variables for each trait (Pavoine, Baguette, & Bonsall, 2010).

Dispersal mode

Based on the morphology of their diaspores, we assigned each species a dispersal mode: (1) anemochory, (2) ballochory, (3) barochory, (4) endozoochory, (5) epizoochory, and (6) hydrochory. Dispersal mode was obtained from the literature and from direct observation of diaspores of herbarium specimens when fruits and seeds were available. We checked references where traits for different groups of high Andean species were studied (Cárdenas-Arévalo & Vargas, 2008; Frantzen & Bouman, 1989; Melcher, Bouman, & Cleef, 2000, 2004; Meneses, Beck, & Anthelme, 2016) but also original species descriptions, taxonomic publications, flora websites and flora publications (92 references).

We searched specimens of our species in five different herbaria:

• Universidad Nacional Mayor de San Marcos, Museo de Historia Natural (USM), Lima, Peru
• Universidad Nacional de Cajamarca (CPUN), Cajamarca, Peru
• Herbario Nacional de Bolivia, Universidad Mayor de San Andrés (LPB), La Paz, Bolivia
• Royal Botanic Gardens Kew (K), Richmond, UK
• Naturalis Biodiversity Center (AMD, L & U), Leiden, The Netherlands

We found 220 specimens representing 206 of our species that had fruits/seeds that were examined to obtain the morphological description and then assigned the correspondent dispersal mode category following Table 1 in the main text.

We chose to assign dispersal modes based on morphological characteristics of the diaspores to objectively assess all species. Therefore, we are excluding most observations from the field as this data was available for a reduced number of our species. In doing this, small seeds that are known to be dispersed by wind but lack any morphological adaptation for dispersal have been categorised as barochorous (unspecialized seeds) rather than anemochory. Previous studies have assigned these small seeds principally from the Poaceae family, as anemochorous (Frantzen & Bouman, 1989; Meneses, Beck, & Anthelme, 2016). In future studies, both seed size and morphological adaptations should be used to characterised dispersal modes, but currently we lack size/weight data for most of our species.

We couldn’t assign dispersal mode with certainty for 15 species. Given that they lack apparent morphological adaptations, or their congeneric species were mostly barochorous we assumed these species were barochorous as well. For 8 species (Bulbostylis juncoides, Oreobolopsis inversa, Oreobolus ecuadorensis, Oreobolus goeppingeri, Plantago orbignyana, Sisyrinchium hypsophilum, Sisyrinchium jamesonii, Trichophorum rigidum) no apparent morphological adaptation was found in their diaspore description. However, detailed microscopic studies of congeneric species show adaptations to other dispersal modes. A few Cyperaceae congeneric species have thick parenchymatous mesocarp layer that allows them to float (hydrochory) (Melcher et al. 2000). A few congenerics of P. orbignyana produce mucilage which indicates epizoochory (Melcher, personal observations), but this remains to be tested for P. orbignyana. A few species of Sisyrinchium have umbilicus forming an air bubble that helps them to float (Goldblatt, Henrich, & Keating, 1989). In the absence of such details studies for our species we consider it was safer to assume barochory for these species. For the other 7 species (Draba discoidea, Draba obovata, Draba pulvinata, Lachemilla moritziana, Poa glaberrima, Poa lepidula, Silene mandonii) there was a predominant lack of diaspore morphological adaptations among their congenerics, therefore we assigned them as barochorous as well.

Growth form

We used four growth form categories: (1) herb, (2) shrub, (3) tree, and (4) epiphyte based on the Tropicos database (www.tropicos.org). This classification was preferred over a more detailed classification of Andean alpine growth forms (e.g. Ramsay & Oxley, 1997) due to data availability and because it matches those used by dispersal studies (e.g. Thomson et al., 2010).

Description of the fields

family: species' family

sp_name_BIEN2017: species name used in this study

taxon_name_as_in_reference: taxon name for which trait data was collected as in the reference

trait: trait name

value_as_in_reference: trait data as in the reference

standardised_trait_value: categories of trait values defined for this study

main_reference: main reference from where the trait data was extracted.

Notes about data "in embargo"

Dispersal mode for 49 species is not give and is stated as "in embargo" in the field "standardised_trait_value" because the information is part of an unpublished on-going work (Melcher in prep.).

Notes about references

Only the main reference is provided in this dataset, secondary references (that include examination of herbarium specimens have not been provided).

Notes about missing values

We couldn’t assign dispersal mode with certainty for 15 species. Given that they lack apparent morphological adaptations, or their congeneric species were mostly barochorous we assumed these species were barochorous as well.  For 8 species (Bulbostylis juncoides, Oreobolopsis inversa, Oreobolus ecuadorensis, Oreobolus goeppingeri, Plantago orbignyana, Sisyrinchium hypsophilum, Sisyrinchium jamesonii, Trichophorum rigidum) no apparent morphological adaptation was found in their diaspore description. However, detailed microscopic studies of congeneric species show adaptations to other dispersal modes. A few Cyperaceae congeneric species have thick parenchymatous mesocarp layer that allows them to float (hydrochory) (Melcher et al. 2000). A few congenerics of P. orbignyana produce mucilage which indicates epizoochory (Melcher, personal observations), but this remains to be tested for P. orbignyana. A few species of Sisyrinchium have umbilicus forming an air bubble that helps them to float (Goldblatt, Henrich, & Keating, 1989). In the absence of such details studies for our species we consider it was safer to assume barochory for these species. For the other 7 species (Draba discoidea, Draba obovata, Draba pulvinata, Lachemilla moritziana, Poa glaberrima, Poa lepidula, Silene mandonii) there was a predominant lack of diaspore morphological adaptations among their congenerics, therefore we assigned them as barochorous as well.