The foraging behavior of seed-harvesting ants can facilitate plant dispersal and recruitment, thereby impacting local patterns of plant diversity. However, the manner in which agricultural legacies alter the strength and direction of consumer effects on plant diversity is largely unknown. Here, we evaluate differences in the abundance and diversity of plants growing on mounds of seed-harvesting Pogonomyrmex badius at 20 remnant and post-agricultural sites located in longleaf pine savannas at Fort Bragg, North Carolina. At each site, we surveyed vegetation on a pair of active and abandoned Pogonomyrmex badius mounds to evaluate the effects of mound abandonment on plant recruitment in both remnant and post-agricultural habitat. Further, we compared the composition of plant species growing on abandoned Pogonomyrmex badius mounds with that of the surrounding vegetation to evaluate the manner in which seed-harvesting ant foraging behavior shapes local patterns of plant diversity. We determined if these consumer effects on plant diversity are contingent on agricultural land-use history.
Results/Conclusions
Vegetation surrounding Pogonomyrmex badius mounds differed substantially between the two land-use categories. Specifically, local plant species diversity and abundance were greater among remnant than post-agricultural sites. For both land-use categories, plant density was greater on abandoned mounds than on active mounds. Likewise, plant species richness was greater on abandoned mounds in both remnant and post-agricultural habitat. However, the composition of plants growing on abandoned mounds differed substantially between the two land-use categories. At remnant sites, abandoned mounds largely yielded species indicative of undisturbed plant communities, whereas ruderal species indicative of disturbed habitats were more abundant among mounds at post-agricultural sites. These results indicate that the accumulation of seeds by harvester ants can profoundly influence local diversity patterns following mound abandonment. Further, for each land-use category, mound germinant composition differed substantially from that of the surrounding vegetation, suggesting that Pogonomyrmex badius foraging behavior can affect local diversity patterns and that the nature of these effects are contingent on historical land-use activities. Evaluating the role of historical land use in mediating consumer effects on diversity can provide novel insight into the factors shaping plant communities in human-modified landscapes.