Distribution, preference and seasonal emergence patterns of dragonfly species (Odonata: Anisoptera) of the Saco River, Maine, USA

Loyd, Ann E.
Tom Wessels, MA
Department of Environmental Studies
Exuvial collections were used to establish species presence, abundance, biotope, and microhabitat preference, and seasonal emergence patters of the Odonata (Anisoptera) of the Saco River for conservation purposes. All exuviae encountered were collected and recorded from six sites within a 37-mile stretch of the Saco River. Based on exuvial collections, there were significantly greater number of species and individuals found at the two upriver sites than any other site. Those same two sites also had the most significant finds of any site. In addition to one endangered species, one threatened species and three species of special concern were also recorded during the sampling season. The endangered species, Williamsonia lintneri and Ophiogomphus howei, a state threatened species, were both recorded from Site 2, Walker Falls. The three species of special concern, Boyeria grafina, Calopteryx amata, and Ophiogomphus anomalous were also recorded at Walker Falls. Although, statistical analysis was excluded due to low sample size, preference for biotope based on species relative abundance, suggests that there is a correlation between species abundance and biotope type. In addition, at the microhabitat level, there was a statistically significant correlation between abundance and bank type for three species. Based on the relative abundance of species, 70% preferred the Upriver sites to the Downriver or Tributary sites. In addition, most species appeared to prefer steep bank types for emergence than any other bank type, however, only three species, B. vinosa, G. adelphus, and O. carolus, exhibited a statistically significant preference. Emergence patterns were compared between abundant species and among sites. Most species in this study exhibited emergence patterns that were in accordance with “spring” species; emergence for such species were typically early, short in duration and had early distinguishable peaks. Emergence began a week earlier at Walker Falls (Site 2), than at any other site. Despite the earlier emergence however, most species did not emerge significantly different at other sites. The implications of these findings suggested that greater number of habitat conditions encourage a greater variety of rare and abundant species.

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