Acaridae - Sancassania sp.
Size: 0.82 mm
Group Guild Status
Eutroglophile Scavenger Abundant
The initial study reported Sancassania as the most abundant mite species on the fresh bat guano deposits. Even though there have apparently been significant changes to the ecology of the fresh bat guano deposits subsequent to the initial study twenty years ago, Sancassania remains a significant element, and is seasonally the most populous arthropod species present. Various life stages of this mite are present in the guano throughout the year. Due to excluded access when the bats have their young in July, we do not have records of the species for that month for the recent study. The initial study documented the peak activity period of Sancassania as occurring in June and July each year. Sancassania are fungivorous, but also feed on insect eggs and larvae, and occasionally on nematodes (Welbourn 1999).
The peak activity for Sancassania below the two major bat roost sites, the earlier-occupied Lunch Spot site, and the subsequently occupied Maternity Roost, should chronologically follow the activity pattern of the bats. Earlier in the year, before they have their young, the bats are dispersed in several small to medium-sized roosts in several areas of the Big Room (including the Lunch Spot). Once the bats near parturition, they relocate to the Maternity Roost site, which is higher in the Big Room. Micro-environmental conditions at this location are apparently more favorable for birthing. Because of this the peak of the mite activity at the Maternity Roost site should occur slightly later than at the Lunch Room site. Welbourn’s discussion of this in his paper agrees with this intuitive chronology.
We repeated the mite sampling using the same methodology employed during the initial study, and found some significant differences. During the initial study the bat population in the cave was reported at between 1,000 and 2,000 bats (Buecher and Sidner 1999). During the study the peak of the bat population was about 518 bats in 2010 and 882 in 2011. Whether the lower numbers of bats significantly affected the results is not known for certain, but it likely depressed the populations somewhat.
Since some Sancassania species can complete their life cycle in as little as 8 or 9 days (Welbourn 1999), comparison of populations between years can potentially be greatly affected by sampling times. Complicating a comparison between the studies is the lack of actual sampling dates for each month for the initial study. Because of this, population comparisons are not temporally comparable, but should still be comparable for peak values. Additionally, there is some variability in the occupancy and breeding times of the bat population in the cave from year to year. In the past few years the bats have been late arriving at the cave. This also complicates temporal comparisons of data between years.
The most obvious difference in the Sancassania ecology was a much higher density of deutonymphs recorded at both sites during the recent study. Our data for June 2010 was eight times that of the initial study for the Lunch Spot and 18 times the density at the Maternity Roost. We also registered a spike of the deutonymph population at the Maternity Roost site in April 2010 that was four times the value recorded for the initial study. This “early” spike in deutonymphs is not understood. And, the numbers of post-deutonymphs during 2010 were considerably lower than the densities found by Welbourn. However, the 2010 data does not include larvae, which were part of the totals reported by Welbourn. We do not know what percentage of the initial study data are represented by larvae.
The data from the initial study showed an inverse relationship between the numbers of deutonymphs and non-deutonymphs throughout the year, with the deutonymph population being high when the non-deutonymph numbers were low, and the number of deutonymphs tapering off as the post-deutonymph forms increased. This pattern appears to be repeated in the 2010 data, with the possible exception of the June value at the Lunch Spot site. However, without data for July this is inconclusive. The numbers of post-deutonymphal stages at both sites seems low, but lacking the July data, this is also inconclusive, and may actually not be statistically significant.
The 2010 data appears to show the post-deutonymphal stages peaking later at the Maternity Roost site. At the Lunch Spot site post-deutonymphal stages begin appearing in late May or early June and are gone by the middle of August, while at the Maternity Roost site they do not appear until at least the middle of June and are present well into August.
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