Original paper
Distribution of the grappletail dragonfly (Octogomphus specularis), a lake outlet stream specialist at its northern range limit
Chalmers, Paulina; Melchers, Grace; Tikka, Kelsey; Richardson, John S.
Fundamental and Applied Limnology Volume 197 Nr. 1 (2023), p. 1 - 8
16 references
published: Sep 14, 2023
published online: Mar 7, 2023
manuscript accepted: Feb 12, 2023
manuscript revision received: Feb 12, 2023
manuscript revision requested: Jan 14, 2023
manuscript received: Oct 31, 2022
ArtNo. ESP141019701000, Price: 29.00 €
Abstract
The grappletail dragonfly Octogomphus specularis (Gomphidae) reaches the northern end of its range in Canada and has only seven known occurrences within British Columbia, where its larvae are known only from lake outlet streams. Lake outlet streams provide a unique lotic environment with water from lakes providing high quality seston to filter feeders, favourably warmer water in summer, buffering from variation in discharge, and more stable substrates, in comparison to streams uninfluenced by lakes. We investigated factors that might explain why the distribution of larval grappletails appears to be restricted to lake outlet streams. We sampled the larvae from two outflow streams over one summer to determine their number of age classes and estimate their abundances relative to distance from the lake outlets. We characterized the thermal regime of each lake outlet stream, and quantified the temperature differences between lake outlets and inflow streams. The two lake outlet streams were on average 37 % warmer (4.4 °C and 7.2 °C) higher than the inflow streams. We found three groupings of larval sizes, indicating a life cycle of three years. In one stream, larval abundance decreased with increasing distance from the lake, but in the other stream there was no pattern of decrease. Our results are consistent with the theory that warmer thermal conditions throughout summer at lake outflow streams provide sufficient degree-days to support development of this species’ larvae at the northern end of their global range.
Keywords
distribution • lake outlet • Odonata • range limit • stream • temperature