A functional and trait-based approach in understanding ant community assembly in the Soutpansberg Mountains, South Africa

The concept of taxonomic diversity has been widely used to investigate diversity patterns and the mechanism underlying community assembly. However, functional and trait diversity can further explain the factors driving community assembly because they capture different aspects of species ecological roles such as habitat requirements and resource use. To investigate the factors shaping community assembly along the elevational Soutpansberg transect, ants were used as a model study organism because they are widely distributed geographically, ubiquitous and play several important roles in ecosystems. Functional and taxonomic diversity patterns along the elevation, their drivers (seasonality, soil properties, temperature and habitat structure) were examined using a long-term data set (8 years) collected seasonally. Morphological and physiological traits at a community level are quantified and their relationship to temperature, soil properties and habitat structure modelled. Traits were used to test the size-grain hypothesis, Janzen’s rule and Brett’s rule. Functional and taxonomic diversity had a humped-shaped pattern on the northern and a decreasing pattern on the southern aspect. However, taxonomic diversity did not decrease monotonically on the southern aspect. Functional diversity was mainly related to habitat structure and temperature while taxonomic diversity was explained by seasonality, soil properties and temperature. Functional and taxonomic diversity were positively related at a larger scale but habitat specific at a smaller scale. Taxonomic diversity explained more variation in functional diversity than habitat structure and their interactions. The results supported the size-grain hypothesis and Janzen’s rule but not the Brett’s rule. Patterns in taxonomic and functional diversity mirrored each other but were the result of different mechanisms. Temperature was however important for both measures. Incorporating functional diversity analysis into taxonomic diversity contributed significantly in understanding the different mechanisms underlying community assembly along the Soutpansberg transect. This together with trait responses to environmental variables such as a decrease in size with increased temperature could be used to model the responses of ant communities to global change drivers such as climate and land use change