Florida harvester ant, Pogonomyrmex badius. Credit: Julian Resasco
What determines the composition of species at a given site? It’s determined in part by the environmental conditions of the site that affect which species can persist, for example variables like habitat structure and the abundance of competitors. It’s also determined in part by how spatially isolated the site is from other sites from which species could colonize.
Understanding the relative contributions of these spatial and environmental processes on community assembly is a central question in ecology. However, the apparent roles of spatial and environmental processes in community assembly may be sensitive to how variables are quantified. While spatial processes in community assembly are often quantified simply as geographic isolation, the growing understanding of the role that the matrix plays in mediating connectivity suggests that geographic isolation alone may be insufficient for quantifying the role of this process
In a recent study, we examined the roles of spatial and environmental processes on structuring assemblies of ants in 72 cleared patches embedded within a forested landscape in South Carolina, USA. To examine the role of spatial processes and how they may change if we consider connectivity, we contrasted the use of geographic distances between patches and effective distances estimated from connectivity modeling accounting for matrix vegetation structure hypothesized to be important for ant community assembly. To examine the role of environmental processes, we quantified patch age and abundance of a key competitor and invasive species, the fire ant Solenopsis invicta.
We found that both spatial and environmental processes were important for structuring ant communities. When spatial processes were quantified as geographic distance, environmental variables (fire ant abundance and patch age) were the predominant factors accounting for variation in ant community composition among patches.
However, accounting for connectivity with circuit-theoretic connectivity changed the primary variables accounting for that variation from environmental to spatial processes. Our findings show that accounting for connectivity through the matrix can be decisive in determining the primary drivers of community assembly. Therefore, connectivity mapping tools like circuit theory and related frameworks are promising and important to add to the community ecologist’s toolbox.
Resources
Resasco, J. and Fletcher, R.J. 2021. Accounting for connectivity alters the apparent roles of spatial and environmental processes on metacommunity assembly. Landscape Ecology. DOI: 10.1007/s10980-021-01203-z.
