Distribution, abundance, and ecology of the threatened Gibson’s Big Sand Tiger Beetle (Cicindela formosa gibsoni Brown) in the Elbow Sand Hills of Saskatchewan

Abstract

Gibson’s Big Sand tiger beetle, Cicindela formosa gibsoni Brown, occurs primarily in the Saskatchewan sand hills and was recently listed as threatened in Canada due to habitat loss caused by dune stabilization. Herein, we report on a 3-year population study initiated in 2016 to better understand the distribution, abundance, and ecology of C. f. gibsoni in the Elbow Sand Hills, a large active dune complex in southern Saskatchewan. Estimated adult population size for the dune complex varied from a low of 1106 (95% confidence interval (CI) 975–1237) to a high of 1474 (CI 1350–1598), possibly due to inter-annual variation in May–June rainfall. Adult abundance varied substantially between interdunal swales (0–137 individuals), with the highest numbers occurring in sparsely-vegetated habitats on the stoss side of the dune complex where the rate of encroachment by vegetation is highest. Approximately a third of the total population is concentrated within a relatively small area (~ 6 ha) in the northwestern region of the dune complex, although the specific cause for this localized distribution is not clear. Our findings suggest that the distribution of C. f. gibsoni within the dune complex is not limited by prey availability or larval habitat quality but is instead related to the amount of sparsely-vegetated habitat. We hypothesize that sparsely-vegetated areas allow beetles to shuttle between exposed and shaded microhabitats, thereby assisting in thermoregulation and maintenance of high body temperatures that are optimal for foraging.