Dataset: Plant-plant facilitation increases with reduced phylogenetic relatedness along an elevation gradient

Environmental conditions can modify the intensity and sign of ecological
interactions. The stress gradient hypothesis (SGH) predicts that
facilitation becomes more important than competition under stressful
conditions. To properly test this hypothesis, it is necessary to account
for all (not a subset of) interactions occurring in the communities and
consider that species do not interact at random but following a specific
pattern. We aim to assess elevational changes in facilitation, in terms of
species richness, frequency and intensity of the interaction as a function
of the evolutionary relatedness between nurses and their associated
species. We sampled nurse and their facilitated plant species in two
1000-2000 m. elevation gradients in Mediterranean Chile where low
temperature imposes a mortality filter on seedlings. We first estimated
the relative importance of facilitation as a mechanism adding new species
to communities distributed along these gradients. We then tested whether
the frequency and intensity of facilitation increases with elevation,
taking into account the evolutionary relatedness of the nurse species and
the facilitated species. We found that nurses increase the species
richness of the community by up to 35%. Facilitative interactions are more
frequent than competitive interactions (56% vs. 44%) and facilitation
intensity increased with elevation for interactions involving distantly
related lineages. Our results highlight the importance of including an
evolutionary dimension in the study of facilitation to have a clearer
picture of the mechanisms enabling species to coexist and survive under
stressful conditions. This knowledge is especially relevant to conserve
vulnerable and threatened communities facing new climate scenarios, such
as those located in Mediterranean-type ecosystems.