The effects of myrmecochore species abundance, diversity, and fruiting phenology on Aphaenogaster (Hymenoptera: Formicidae) nesting and foraging in southern Appalachian rich cove forests

Background/Question/Methods

In Southern Appalachian forests, myrmecochory, or ant-mediated seed dispersal, is a diffuse mutualism between more than 42 plant species and ants of the genus Aphaenogaster.  Myrmecochores produce lipid-rich appendages on their seeds called elaiosomes, a reward that attracts Aphaenogaster ants and facilitates dispersal.  Myrmecochorous species vary in the timing of seed set, which generally occurs between March and September depending on species.  Accordingly, forests with higher myrmecochore species diversity may provide a more continuous source of elaiosomes, which could affect foraging and nesting behavior.  I compared myrmecochore abundance and diversity among young, middle-aged, and mature forests at nine sites in western North Carolina, and tested for correlations between herb community characteristics and Aphaenogaster foraging behavior, nest colonization, and elaiosome availability.  I examined colonization of artificial ant nests paired with bait stations that were provisioned with tuna in temporal patterns of continuous and interrupted availability.

Results/Conclusions

The best-fit generalized linear model showed Aphaenogaster foraging increased in sites with higher myrmecochore abundance and higher soil temperature.  Myrmecochore species diversity did not differ among forest ages, and varying bait availability did not affect foraging or nesting behavior.  Most colonized nests were in mature forests, which had higher soil moisture.  Elaiosomes were more abundant and more consistently available in middle-aged forests, which did not correlate with myrmecochore species diversity or abundance, and did not affect Aphaenogaster nesting or foraging.  My results suggest Aphaenogaster nesting and foraging are influenced more by moisture and temperature than by resource availability.  The lack of significant differences in diversity among forest ages precludes measuring the effects of myrmecochore species diversity on either elaiosome availability or on Aphaenogaster dynamics.  However, my results support current research that shows elaiosomes provide a supplement to resources preferred by Aphaenogaster ants, and that myrmecochory is a facultative, not obligate, mutualism for Aphaenogaster.