Variation in diurnal primate biomass at different altitudinal levels in the Eastern Andes of Colombia: the role of fruit productivity.

Altitudinal variation plays a key role in structuring ecological communities, as increasing elevation leads to lower temperatures and reduced ecosystem productivity. These environmental constraints can be particularly limiting for species with low thermal tolerance, restricting resource availability and influencing species persistence, distribution, and population densities. Several models describe the relationship between species richness and altitude, with the monotonic decreasing and the Intermediate Domain Model being the most reported. However, the extent to which these patterns apply to different primate species and regions remains poorly understood. Here, we evaluated how primate abundance and species richness vary at different altitudinal levels in the Eastern Andes of Colombia and analyzed the relationship between fruit productivity and primate biomass. We used line transects to estimate the density of diurnal primates at three altitudinal levels (low: 800-1300 m, medium: 1300-1800 m, and high: 1800-2300 m), from which we calculated primate biomass. We measured fruit productivity for 1 year using 50 hanging mesh traps per altitudinal level along transects. We found that primate biomass and fruit productivity were higher at low and medium elevations compared to high elevations, although no significant differences were observed between the first two. Our results do not fully align with commonly reported patterns in the literature based on gradual changes with altitude. In our study system, habitat productivity was associated with primate distribution and biomass. Our results highlight the importance of long-term studies across multiple mountainous sites to better understand the mechanisms shaping primate communities.