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.