Effects of historical land use and forest patch size on myrmecochores and ant communities

We studied the effects of patch size and historical land use on woodland ants and myrmecochores (plant species that have their diaspores dispersed by ants) in mesic forests of the southern Appalachian Highlands. Our purpose was to examine a potential mechanism, the presence and diversity of seed-dispersing ants, that might explain the reduced abundance and diversity of myrmecochores in small forest patches with high intensities of past land use. Small patches (<25 ha) of forest harbored a greater abundance and diversity of myrmecochorous ants, but a lower abundance and species richness of myrmecochores than large patches (>200 ha) with minimal past land use. Overall, sites with greater myrmecochore species richness and abundance had less diverse ant communities and a lower abundance of ants. However, ant species composition varied with patch size. Large patches with low historical land-use intensity were dominated by one ant species, Aphaenogaster fulva, whereas small patches supported higher numbers of Aphaenogaster rudis and two Camponotus species. The abundances of immature myrmecochores were more strongly related to land-use history, forest patch size, and the abundance of mature conspecifics than to ant variables. An absence of seed-dispersing ants cannot explain the reduced numbers of myrmecochores in small patches with high past land use because seed dispersal by ants still appears to be available in those patches. Land-use legacies or fragmentation effects may be overriding any advantages offered by the increased diversity and abundance of ants at those sites.