Historical land use change reduces habitat availability for keystone seeding-dispersing ant, Aphaenogaster sp.

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Carly L. Gerth, Carmela M. Buono and John A. Santare, Department of Biological Sciences, Binghamton University (SUNY), Binghamton, NY, Kirsten M. Prior, Biology, Binghamton University, NY

Background/Question/Methods
In northeastern North America, most forests are “secondary,” meaning they were previously cleared and allowed to regenerate. Historical land use change could influence habitat availability and quality for forest organisms, including functionally important species. Aphaenogaster sp. ants are common in northeastern forests and are the primary seed dispersers of 30-40% of understory herbs adapted to dispersal by ants (“myrmecochores”). Myrmecochores have not recovered well in secondary forests, likely due to several factors. Previously, we found a reduction in seed dispersal by ants of myrmecochores in secondary forests compared to primary forests, which may contribute to poor regeneration. Here, we examine a putative mechanism for this loss of function - the impact of land use history on ant habitat availability. We established 3 50 m transects in 20 paired primary and secondary forests in three regions in the northeast. We assessed ant habitat as the availability of potential nest sites for Aphaenogaster sp. by measuring the volume of leaf litter, rocks, and logs in 5m2 plots along transects. We also measured the level of decay of logs. We recorded the presence of Aphaenogaster ants in each ant habitat type and estimated Aphaenogaster abundance in plots using pitfall traps.
Results/Conclusions
We examined if ant habitat varied between primary and secondary forests and was related to Aphaenogaster sp. presence and abundance. We found that Aphaenogaster sp. abundance was higher in primary forests than secondary forests, and variation in abundance was also explained by region. We also found that log volume was greater in primary forests, but that leaf and rock volume did not differ between forest type or region, with high variation among sites. Logs were the preferred nesting habitat for Aphaenogaster sp., and we found that secondary forests reduced the quantity of favorable nesting sites to nearly one third of primary forests. We will further explore this habitat type by performing regressions between the level of log decay and Aphaenogaster sp. presence and abundance. Primary forests had more canopy cover, and our results suggest that primary forests with more intact structure may provide higher habitat availability for the functionally important seed-disperser, Aphaenogaster sp. A better understanding of land use history impacts on forest habitat availability may help in conservation and restoration of key species interactions in forest ecosystems.