Rates of species turnover across elevation vary with vertical stratum in rainforest ant assemblages

Climatic variation at local scales can influence both exposure and sensitivity of organisms and thereby scale up to influence population persistence and community composition across broader geographic extents. Tropical forest canopies are more climatically dynamic than the understorey. Consequently, the niche space of forest canopies has higher overlap in thermal conditions along elevation gradients, which imposes less of a climatic barrier to arboreal species than their ground-dwelling counterparts. We use ant communities of the Australian Wet Tropics to test the prediction that ground communities should have higher rates of species turnover over elevation compared to arboreal communities. We sampled ground and arboreal ants along elevation gradients at a bioregional scale that includes four mountain sub-regions. We assessed community composition at three spatial resolutions (regional, elevation, vertical) and then calculated beta diversity (species turnover) over elevation for ground and arboreal communities using null modelling procedures to compare different-sized species pools. Vertical niche affinity was a strong contributor to overall biogeographic patterns; indicated by a strong interaction between vertical niche and elevation in beta diversity models. On average, the ground community exhibited a pronounced elevational distance-decay pattern while the arboreal community showed no pattern. Mean species turnover was 36% higher in ground than arboreal communities. Our findings suggest that the vertical niche has a pronounced effect on biogeographic patterns which has important implications for understanding the role of local scale climate conditions in shaping communities and for potential responses to future climate change.

Methods
Ants were sampled at 15 elevation sites at four mountain sub-regions in the Australian Wet Tropics Bioregion. Ants were collected using tuna baits with 5 vials placed every three metres in vertical height from the ground to the canopy at mutliple trees per site. Survey height varied between 15–27m. 

Leahy_etal_WFCA_Ant_Data.csv

The main data file. A site by species matrix. Cells show counts of individuals of each species per vial. This file is read in to the three R scripts in the folder.

Leahy_etal_beta_div.csv

The file produced from the R script "Leahy_etal_Ant_Beta_Diversity.R" that is read in for the models R script, "Leahy_etal_Models"