Fern Cave: A Hotspot of Subterranean Biodiversity in the Interior Low Plateau Karst Region of Alabama in the Southeastern United States

Abstract

The Fern Cave System, developed in the western escarpment of the Southern Cumberland Plateau of the Interior Low Plateau karst region in Northeastern Alabama, USA, is a global hotspot of cave-limited biodiversity as well as home to the largest winter hibernaculum for the federally endangered Gray Bat (Myotis grisescens). We combined the existing literature, museum accessions, and database occurrences with new observations from bioinventory efforts conducted in 2018–2022 to generate an updated list of troglobiotic and stygobiotic species for the Fern Cave System. Our list of cave-limited fauna totals twenty-seven species, including nineteen troglobionts and eight stygobionts. Two pseudoscorpions are endemic to the Fern Cave System: Tyrannochthonius torodei and Alabamocreagris mortis. The exceptional diversity at Fern Cave is likely associated with several factors, such as the high dispersal potential of cave fauna associated with expansive karst exposures along the Southern Cumberland Plateau, high surface productivity, organic input from a large bat colony, favorable climate throughout the Pleistocene, and location within a larger regional hotspot of subterranean biodiversity. Nine species are of conservation concern, including the recently discovered Alabama cave shrimp Palaemonias alabamae, because of their small range sizes, few occurrences, and several potential threats.

Global Subterranean Biodiversity: A Unique Pattern

“…Lukić et al [36] reported that almost all information for the fauna of the Lukina Jama-Trojama Cave System in Croatia dates from the 1990s or later. The same is true for Fern Cave in Alabama [44], Hon Chong in Vietnam [46], and the Água Clara Cave System in Brazil [27,28]. Sampling effort is therefore a major determinant of the richness of species in these caves.…”

“…They point out that the ridge is the area of highest secondary productivity in Europe. Such a ridge of high biodiversity does not occur in North America, but there is a small area near the combined border of Tennessee, Alabama, and Georgia of similarly high biodiversity and presumed high secondary productivity [15,43,44]. More generally, a difference between Europe and North America is that European mountain ranges are often oriented east-west while North American mountains are north-south in orientation.…”

“…(i) Table S2 in[42]; (j) aquifer is greater than 2500 km 2 so single points used; (k) Crystal and Wonder Caves connected by 91 m long surface stream, therefore combined; (l) all taxa considered from the two columns "Historical" and "This Study" of Table1in Niemiller et al[44]; (m) taxa considered from the column "This Study" of Table1in Niemiller et al[45].…”

The Crystal-Wonder Cave System: A New Hotspot of Subterranean Biodiversity in the Southern Cumberland Plateau of South-Central Tennessee, USA

“…The cave-limited fauna of the Crystal-Wonder Cave System is remarkably diverse with 31 troglobionts and stygobionts, making it the most diverse cave system in the southern Cumberland Plateau region, and one of the most diverse cave systems in all of North America. With 31 cave-limited species, the Crystal-Wonder Cave System trails only the San Marcos artesian Well in central Texas (55 species; [85]) and the Mammoth Cave System in central Kentucky (49 species; [86]) and ranks ahead of the Fern Cave System in Alabama (27 species; [10]) and Sistema Huautla in Oaxaca, Mexico (27 species; [87]). In particular, the terrestrial fauna is exceptionally rich with 23 species, trailing only the Mammoth Cave System (32 troglobionts; [86]) and Sistema Huautla (27 species; [87]) in North America.…”

“…Several cave systems support a significant biodiversity at the local scale, including 19 caves with >12 cave-limited (i.e., permanent inhabitants of subterranean habitats) species documented [2,8], Niemiller and Zigler, unpublished data]. In particular, two cave systems in the southern Cumberland Plateau region have been recognized as hotspots for cave-limited biodiversity [sensu 9]: Shelta Cave in Madison County, Alabama with 24 species [9], and Fern Cave in Jackson County, Alabama with 27 species, respectively [10]. Here, we add a third cave system-the Crystal-Wonder Cave System in Grundy County, Tennessee-that is the most speciose cave system with respect to the cave-limited fauna in the southern Cumberland Plateau.…”