The Overlooked Link Between Different Resource Partitioning Strategies and Plant Species Richness in Tropical Alpine Ecosystems

ABSTRACT Aim Species coexistence is based on resource partitioning and modulates biodiversity patterns across climates, latitudes and altitudes. Resource partitioning can occur via niche size or separation in the geographic range or ecological niche. While resource partitioning promotes biodiversity, the impact of different partitioning strategies on species richness remains largely unexplored. Location Two ecosystems with similar climates and ages are the species‐rich tropical alpine ecosystem in the South American Andes and the more species‐poor tropical alpine ecosystem in the eastern African mountains. Time Period Present‐day distribution and climatic conditions, integrating phylogenetic information extending back to the last 7 million years maximum. Major Taxa Studied Six lineages from the Asterales; three in each ecosystem, respectively. Methods We test whether geographic range and climatic niche partitioning strategies may explain differences in species richness between two ecosystems. We combine phylogenomic data with occurrence records and estimate metrics of size and overlap for climatic niche and geographic range. Results We show that the Andean species have larger climatic niches than the African species, suggesting that niche size is not explaining higher species richness in the Andes. Instead, a striking pattern for species with overlapping geographic ranges emerged: the Andean species show less climatic niche overlap than the African species, indicating more effective niche separation among Andean species. Main Conclusions We hypothesise that differences in resource partitioning, specifically increased niche separation among geographically overlapping species in the Andes compared to the eastern African mountains, contribute to the species richness difference between these tropical alpine biodiversity hotspots.