Evidence of range contraction and increased metapopulation patchiness of the rare eastern Nearctic Karst Snowfly Allocapnia cunninghami Ross & Ricker, 1971

Abstract

The distribution of the rare Karst Snowfly, Allocapnia cunninghami Ross & Ricker, 1971, was assessed during winters of 2019 and 2020. This species has been assigned a NatureServe ranking of G1 (= Critically Imperiled) and was recently included in a Center for Biological Diversity petition to the U.S. Fish and Wildlife Service as potentially threatened or endangered. Sampling for adult A. cunninghami occurred in 45 unique localities in central Kentucky and middle Tennessee, USA, mainly within the known historical range of this species. This species was found in winters of 2019 and 2020 in very low numbers compared to regional Allocapnia and the winter-emergent fauna in general. Allocapnia cunninghami was collected at only five unique localities and comprised only 1.1% and 1.0% of all Allocapnia and the total winter-emergent fauna individuals collected, respectively. By comparison, the widespread species A. rickeri Frison, 1942 was collected from 41 of 45 unique localities and comprised 70% of all individual adults collected. Despite the difficulties of interpreting historical locality data from 1964 to 1966, A. cunninghami appears to now be present in fewer stream sites and distributed more patchily compared to ca. 55 years ago. A confounding biological factor for A. cunninghami is that Allocapnia adults in general have poor dispersal capacity, making natural colonization and potential recolonization events substantially more problematic for what appears to be a rare species in slow decline within an already small native geographic range. By including positive collection data from 1999–2012, increasing the number of known contemporaneous sites to nine, predictive distributional models can now be generated to allow for more focused searching for previously undetected populations and potentially expand the known geographic range of this rare species.