Abstract

The drivers of phenotypic diversity have puzzled humanity for centuries. Functional trait approaches have helped advance the mechanistic understanding of the diversity of life forms. Previous work has shown that evolutionary history and environmental adaptation contribute to the observed diversity of phenotypes. However, most of our understanding comes from plants and studies that often neglect the influence of intraspecific variability. My thesis aims to investigate the drivers of phenotypic diversity across organizational levels using ants as study organisms. In Chapter 2, I examined the influence of evolutionary and environmental heterogeneity on the phenotypic diversity of ant lineages. I found a negative relationship between the diversity of climates occupied by ant genera and their phenotypic integration. This indicates that phenotypic integration may limit ant phenotypic diversification into new climatic zones. For Chapter 3, I examined geographic variation in community-wide patterns of phenotypic diversity, at different organizational levels (i.e., worker, colony, and species), along a 9° latitude gradient in Quebec, Canada. The results suggest that stressful environmental conditions typical of northern ecosystems exert a strong selection pressure on ant morphology causing shifts in optimal trait values of antennae length and eye size. Specifically, I found that shorter antennae and larger eyes possibly represent adaptations to cold, dry, and open habitats. In Chapter 4, I evaluated the impact of coffee plantation management practices on community-wide patterns of ant phenotypic diversity and composition. I found that intensified monocultures harbored phenotypically distinct ant communities. Moreover, community-wide phenotypic composition was more homogeneous in intensified plantations than in nearby forest patches or shade-grown plantations. This indicates that shade-grown strategies in coffee plantations buffer the impoverishment of ant phenotypic diversity following forest conversion, which could help preserve ecosystem services provided by ants. Overall, my thesis suggests that ant phenotypic diversity patterns are limited by phenotypic integration, vary among organizational levels (worker, colony, and species), and are influenced by anthropogenic disturbance across facets (taxonomic, phylogenetic, and functional). These findings have important implications for understanding how phenotypically complex organisms respond to climate change and provide guidance for conservation strategies targeting vulnerable lineages.