Nicoletiidae - Speleonycta anachoretes
Order Zygentoma (Thysanura)
Size: 12.7 mm (male); 15.0 mm (female)
Group Guild Status
Troglobiont Scavenger Common
One of the principle subjects of interest, and the catalyst for initiation of the recent macro-invertebrate study at Kartchner Caverns, was the resident population of the cave nicoletiid, a relative of the common silverfish. Cave adapted nicoletiids are currently known from only two disjunct cave populations in Arizona, the one at Kartchner Caverns, and the other at Arkenstone Cave in Colossal Cave Mountain Park 32 kilometers east of Tucson near Vail, Arizona.
It is currently not known whether the Arkenstone Cave population is a sister population to the one at Kartchner Caverns, or whether it represents a separate species. Our comparison of individuals from each site revealed that they are morphologically indistinguishable (Espinasa et al. 2012). DNA sequencing of fresh specimens from Arkenstone Cave will be required to make a final determination whether the populations represent one or two species. Unfortunately, Arkenstone Cave has been closed to research since 2004.
Only three nicoletiids were observed in Kartchner Caverns during the initial two-year study 20 years ago, and all three were found near the entrance to the Red River Passage. We have yet to observe a nicoletiid near the entrance to the Red River Passage, which is approximately 30 meters from the Jackrabbit Gallery, where we have identified the apparent center of the main contemporary population of the species in the cave. It may be coincidental that we have found none of the animals near or in the Red River Passage or, if the original sightings were peripheral individuals of the population centered in the Jackrabbit Gallery, the placement of the tour trail with its vertical curbs may have fragmented the habitat such that the animals no longer have easy access to that area. Nicoletiids are reasonably good climbers and are certainly capable of surmounting this barrier, but our observations of their behavior shows us that they typically crawl around on the floor and negotiate small objects on the floor, but seldom climb vertical faces such as cave passage walls.
The 34 individual observations we made of S. anachoretes during the recent two-year study consisted of 19 adults and 15 juveniles. Some of these observations may represent the same animals over a period of months, but in March of 2010 we confirmed at least 8 different individuals in the Jackrabbit Gallery. The animals have been observed in four rather widely separated areas of the cave during the recent study. The highest density occurs in the Jackrabbit Gallery (30 observations), with an apparently smaller population in Granite Dells (3 observations), and a single observation at the Big Room Overlook. Repeated searching at the Big Room Overlook did not produce additional sightings. This outlier sighting could either represent a vagrant animal from the Jackrabbit Gallery population, or there may be a smaller population at lower levels in the Big Room. A lack of observations of the species near the bottom of the large breakdown in the Big Room seems to make the vagrant hypothesis for this individual more likely. Subsequent to the field work for this study (on February 20, 2012) a juvenile nicoletiid was observed by Steve Willsey about 25 meters into the River Passage from its connection with the Big Room.
During the recent study individuals have been observed in all months except June. Primarily because of the spatio-temporal nature of our observations for the species in areas of suitable habitat within the cave, our current data is inadequate to comment on the population ecology of S. anachoretes. However, a plotted weighted average of observations and search effort does show an apparent peak of activity of the animals between November and March, and greatly reduced activity during the summer months. This data is preliminary and may or may not be an accurate representation of the activity of the species in the cave.
Habitat occupied by the nicoletiids in the Jackrabbit Gallery consists of two distinct types. In the front areas the floor is covered by an old (inactive), thin, brittle calcite flow, beneath which there is a maze of small, shallow, interconnected spaces that are occupied by the nicoletiids. Small portions of this calcite floor have been broken, and the nicloletiids have been located primarily by turning over these broken floor pieces. Based on observations of the sub-floor habitat where it is exposed reveals that the space beneath typically averages only a couple of centimeters in height at most. The substrate beneath this calcite “roof” typically consists of poorly-graded, coarsely granular, porous, off-white-colored, fine (sand-sized) calcite rubble. This material was likely derived from old calcite flow materials that have weathered to this fine material. In some places this material is apparently several centimeters deep. Where this layer is exposed, we have observed that the nicoletiids are easily able to penetrate down into the dry, loose material to an unknown depth. This sub-floor habitat of anastomosing spaces is apparently extensive in the main portion of the Jackrabbit Gallery. Occasionally an animal has been observed roaming openly across the calcite floor, but they typically wander the area for a short time and repeatedly re-enter the sub-floor area through natural openings or fractures in the flooring. At the rear of the Jackrabbit Gallery there is an upper, sloping, sub-parallel passage that has a substrate similar to the sub-floor of the main portions of the room. Within this dry, granular soil there are many very fine plant rootlets, reflecting the proximity of the entire Jackrabbit Gallery to the surface. Whether the presence of these roots in the area occupied by the nicoletiids has any ecological significance for the species is not known.
Each of the three nicoletiids observed in the Granite Dells area was found on a different substrate type. The only juvenile among them was found in soils very similar to that found in the rear section of the Jackrabbit Gallery. This location is drier than most sections of the Granite Dells area and is near a surface connection. The animal was found burrowed in the soil beneath a large (about 5 cm diameter) decaying velvet mesquite (Prosopis velutina) root that had penetrated the cave. One of the two adults was found beneath a small piece of debris atop a large calcite-covered breakdown block just before the main room in Granite Dells. The other adult was found walking in the open on a damp clay floor, habitat that is typical of that found near the entrance to the Red River Passage, where all three of the initial study observations were made. This is the only individual of 34 sightings during the recent study that occurred on this kind of substrate. However, a clayey floor substrate is a common habitat type for nicoletiids in Mexico (Luis Espinasa, personal observation).
Since the initial study only found three nicoletiids, and the dates for these records are unavailable, we cannot derive any ecological information from those records other than occupied habitat type based on the recorded locality of the observations. The low number of sightings during the initial study may simply be a matter of being in the right place at the right time or reflect the emphasis of efforts by researchers. The initial study considered the animal rare in the cave, which is not unreasonable considering the few observations recorded, both then and now. We suspect that the population has changed little in the intervening years. Based on the numbers of animals we have observed, we consider the species to be localized, but common in the cave, and the population to be healthy.
The Tarantula Tunnel and the tour trail were developed right through the heart of what we now recognize as the apparent center of the population of this species in the cave, the Jackrabbit Gallery, and the adjoining Red River Passage. While it is likely that some nicoletiid habitat may have been affected by this action, the species was either not significantly affected, or has managed to rebound within the intervening 20-year period (Espinasa et al. 2012). Regardless of any structural changes that may have been associated with tunnel development, the re-sealing of the tunnel and installation of a series of environmental doors to re-seal the cave likely minimized environmental changes that would have adversely affected the nicoletiids except for a relatively short period during construction. This may demonstrate that the species is relatively tolerant of disturbance.
ASP continues to monitor in-cave environmental conditions, and is proactive in its efforts to return the cave environment back to pre-development conditions. One of the planned mitigation measures is the replacement of the existing incandescent trail lighting with a lower temperature-emitting LED system. Implementation of this measure should have a significant effect on lowering the median ambient air temperature in the developed portions of the cave
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