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Harvard Forest REU Symposium Abstract 2005

  • Title: Ant interaction dynamics predict Formicinae species encroachment in aftermath of the Hemlock Woolly Adelgid
  • Author: Grace C Wu (Pomona College)
  • Abstract:

    Past studies of ant diversity in Southern New England revealed consistent correlations between ant species and forest type. One notable trend suggests that species of the genera Formica are virtually nonexistent in predominantly hemlock forests. However, the Hemlock Woolly Adelgid will provide openings for large-scale hardwood succession, possibly ensuing in simultaneous shifts in ant community composition. This shift prompted me to investigate a driving force in species composition determination: competition dynamics. To do so, I studied behavioral interaction of eight species, with representatives from hemlock and hardwood stands (Table 1). Of these eight, F. subsericea and F. subaenescens are primarily found only in hardwood forests. Different species were placed pair-wise in 0.25x3 cm tygon tubing for two minutes after initial interaction. I conducted ten trials for each pair and scored observations as dominance (bite, chase, open mandibles), subordination (avoidance, spasm), or coexistence (no apparent change). The dominance index, simply the percentage of the trials in which the particular species is dominant, revealed that four of five Formicinae species comprised the four highest indexes (Table 1). Chi-square analysis of coexistence: avoidance: attack ratios confirmed dominant behavioral similarity between species of Camponotus and Formica (Table 1). These results predict that with hardwood succession, Formicinae species would dominate in competitive behavior, possibly leading to a decline in the abundance of the subordinate Myrmicinae, most notably A. rudis. Further studies of interaction in a natural environment would be valuable, just as ecosystem-wide repercussions of A. rudis decline and Formica intrusion also warrant future investigation.

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