PS 19-21
Changes in species richness, abundance, and community composition of arboreal twig-nesting ants along an elevational gradient
The distribution, diversity, and assembly of tropical insects has long intrigued ecologists, and for tropical ants, can be affected by competitive interactions, microhabitat requirements, dispersal, and availability and diversity of nesting sites. Arboreal twig-nesting ants are limited by number of hollow twigs available for colonies, especially in intensive agricultural systems. Elevation may also impact ant diversity and abundance, but no studies have examined if nest-site limitation or richness of twig-nesting ants varies with elevation. In coffee agroecosystems, twig-nesting ants provide important ecosystem services as predators of important pests, such as the coffee berry borer and the coffee leaf miner. Yet, there is still much to learn about these ants. We examined communities of twig nesting ants to answer the following questions: (1) Does nest-site limitation change with elevation? (2) Do species richness and colony abundance change with elevation? (3) Does community composition change with elevation? We collected data in 2013 across several farms of a coffee landscape in Chiapas, Mexico. We surveyed 42 10x10m plots from 500-1500m elevation with two plots every 50m along the gradient. We checked every dead twig on each coffee plant for ants and recorded vegetation data, including canopy cover, coffee density, and tree richness.
Results/Conclusions
Overall, we sampled a total of 2211 hollow coffee twigs, 77.3% of which were occupied by one of 33 species of ants collected. The number of available hollow twigs did not change with elevation, however, both the percent of hollow twigs that were occupied and twig-nesting ant species richness peaked at mid-elevations (between 800-1050m). Among common ant species, some had higher numbers of colonies at intermediate elevations (e.g. Nesomyrmex echinotinodus). Others were more common within a specific range along the gradient. For example, Pseudomyrmex simplex and P. filiformis occupied a wide range of elevations, but were more common at lower elevations (together accounting for 90% of colonies). Cephalotes minutus was only found below 950m, whereas Procryptocerus hylaeus was only found above 750m. Pseudomyrmex ejectus dominate in the highest elevations (representing >70% of colonies). The composition of twig-nesting ant species thus strongly changes along an elevational gradient. In sum, we found that nest-site limitation (% of occupied hollow twigs), richness, abundance, and composition changes with elevation in coffee agroecosystems. This information may be important in maintaining and understanding the role of these ants as predators in the complex coffee insect food web.