Ant ecology and wood decomposition in a vertically stratified tropical ecosystem

Tropical forests are vertically stratified ecosystems with distinct abiotic and biotic gradients extending from below ground to the canopy. These vertical gradients are useful systems in which to study species distributions and ecosystem processes due to the large degree of variation found over a small spatial scale. Although our understanding of canopy biodiversity patterns has increased over the last 30 years, canopy access remains challenging and significant knowledge gaps remain. This thesis aims to understand better the abiotic and biotic factors that underpin patterns in ant species distribution and wood decomposition along a vertical gradient within tropical rainforest. First, the role of competition is explored by examining the impacts of suppressing the ground ant assemblage on the distribution of ant species in other strata. Second, patterns in protein preference with height are examined in arboreal ant assemblages. Third, a macroecological approach is taken to test hypotheses explaining patterns in the cuticle colour of ant assemblages along a vertical microclimatic gradient. And finally, the decomposition of dead wood over a vertical gradient is investigated and the relative contributions of biotic decay agents are quantified. These research aims were achieved through novel field experiments in Maliau Basin Conservation Area, Sabah, Malaysia that included: sampling 53,153 ants from four strata across eight experimental plots (four control plots and four ant suppression plots); identifying 318 morphospecies of ants belonging to 60 genera; collecting 5,212 morphological trait measurements; and, quantifying the decomposition of 148 wood blocks. Overall, this work advances our understanding of tropical rainforests as vertically stratified ecosystems. It empirically demonstrates that ant assemblages are stratified both taxonomically and according to functional traits. The findings challenge existing explanations for stratification and suggest that interspecific competition may play an important role in maintaining the vertical stratification of ant assemblages. Results also show that protein preference increases with height for the most abundant ant species and imply that nitrogen is a limiting resource for canopy ants. This thesis demonstrates that patterns in cuticle colour, normally detected along macroclimatic gradients, can also be detected along microclimatic gradients; darker ant assemblages in the canopy and understory can be explained by greater UV-B radiation and lower humidity. Finally, I show how the vertical stratification of communities influences important ecosystem processes; in particular, how dead wood decomposition is dependent on the vertical distribution of termites. This thesis emphasises how community structure and ecosystem processes are determined by complex abiotic and biotic interactions; further studies deciphering the relative influence of each are required if we are to predict or mitigate the impacts of anthropogenic change that continue to threaten tropical rainforests