A study of páramo plant-pollinator interactions on the sky islands of Colombia: specialization, modularity, and species roles

Plant-pollinator interactions are crucial for reproduction of both angiosperms and their pollinators, and consequently influence ecological and evolutionary dynamics of diverse ecosystems globally. These interactions range from specialized (involving few species) to generalized (involving many species), with the former being more vulnerable to disturbances because the loss of one member can lead to the disappearance of its mutualist. Thus, understanding the relationships of plant-pollinator interaction networks provide information about ecosystem resilience. It has been hypothesized that the tropics will have specialist pollination systems because of their higher diversity. However, little is known about pollination systems in the tropics, especially at high altitudes. We examined the plant-pollinator network within a Colombian páramo—an alpine tropical ecosystem—through a phytocentric sampling strategy spanning 22 months, including 305 h of direct observation and 3689 h of camera trapping, focusing on 36 common plant species. A total of 90 pollinator morphospecies were documented, including hummingbirds, bats, hymenopterans, dipterans, lepidopterans, coleopterans, and hemipterans. The network was modular (8 modules) and moderately specialized (H2′ = 0.45), yet with many generalist species (pollinator d′ = 0.36; plant d′ = 0.43), but low connectivity (0.10) and low nestedness (9.2). Modularity analysis identified 19 morphospecies pivotal to the network`s integrity including Bombus rubicundus as a network hub. Comparisons with Venezuelan and Costa Rican páramos suggest that the Colombian páramo's higher pollinator diversity may confer greater stability, though the potential loss of any of the hub and connector species could have cascading effects on extinction processes, making their conservation a priority.