Beyond Species Diversity: Functional Approaches Reveal Consistent Fauna Community Responses to Exotic Grass Invasion...

Fauna communities respond to exotic plant invasions through multiple pathways, including via changes to habitat structure and food resources and depending on the scale at which fauna access these resources. To assess whether such multi-dimensional impacts on fauna can be generalised across taxa, we developed and empirically tested a conceptual framework to predict how fauna communities respond to exotic grass invasion in open arid ecosystems. We predicted the greatest impact on combinations of lower trophic levels or diet-specialists, ground-active fauna, including open habitat specialists, and species that operate over smaller spatial scales. We further proposed that functional analysis would more readily detect impacts than total taxon abundance, diversity or taxonomic composition. Replicated across two regions of arid central Australia, we sampled birds, reptiles and ants at native sites and paired sites invaded by exotic buffel grass (Cenchrus ciliaris). Results largely validated our predictions. Bird and ant communities showed significant functional homogenisation or restructuring at invaded sites, respectively (PERMDISP or PERMANOVA p ≤ 0.005), with some functional differences also evident for reptiles (p = 0.02), despite low captures of this group with dry conditions. Ground-active reptiles, birds and ecologically dominant ant groups, especially those that use open microhabitats, were less characteristic of invaded sites. Diet specialists were less associated with invaded sites, including insectivorous birds, and granivorous ants and birds, except where granivores operated at landscape scales. Whilst ant abundance was reduced by 50% (0.41 [0.25-0.68, 95% CI]) and bird communities showed taxonomic homogenisation in invaded sites (PERMDISP p = 0.005), no impacts on taxonomic diversity were detected. Functional responses provided the clearest and most consistent detection of community-level impacts in a multi-taxa context. This validates key aspects of our conceptual framework and offers a robust, transferrable approach for analysing exotic grass invasions and other drivers of ecological change.