The factors driving the assembly of communities along spatial and environmental gradients are actively debated among ecologists. Using an ant assemblage in a spatially heterogeneous region in Florida, we analyzed evidence for species segregation along spatial, temporal, and dietary axes that potentially promote species coexistence. We first examined species and functional group spatial co-occurrence patterns at local and regional scales, utilizing null models that incorporate abundance data and spatial/environmental constraints. To complement null model analyses, we analyzed ant species-environment relationships to examine whether habitat suitability represents a potential mechanism underlying regional co-occurrence patterns. To examine temporal segregation at the local scale, we assessed a suite of interspecific trade-offs associated with resource use and temperature stress in habitats spanning a temperature gradient. Finally, we used stable-isotope analysis to investigate potential dietary differences among ant assemblages associated with different habitats. Our study delimits a myriad of processes enforcing resource partitioning that, as a whole, seeks to demonstrate how the mechanisms regulating species interactions and coexistence change with scale and environmental context.
Results/Conclusions
At the regional scale we found segregated co-occurrence patterns when abundance data were used and habitat suitability was controlled for, indicating competition may drive these patterns. The species-environment relationship showed ants partition shrub and forest habitat; vapor pressure deficit, surface temperature, and groundcover were significant predictors of assemblage composition. Thus regional spatial partitioning promotes ant coexistence and results from a combination of habitat suitability and competitive effects.
At local scales random co-occurrence patterns indicate spatial partitioning does not promote coexistence in either habitat. Both shrub and forest ant assemblages were arranged in dominance hierarchies, with dominants consistently defeating subordinates at resources. In shrub habitat, subordinate ants foraged at higher temperatures, foraged closer to “risky” temperatures, and increased foraging efficiency at higher temperatures. Thus ant coexistence in the hotter shrub habitat is temperature mediated, enforcing temporal segregation of resource acquisition. In the thermally moderate forest, ants do not trade-off between the ability to dominate resources and discover resources nor is there evidence for temperature mediated effects. However, δ15N ratios of ants in forest were significantly more dispersed than in shrub habitat, suggesting trophic segregation between species is greater in forest. Thus dietary segregation may contribute to species coexistence in forest habitat.
