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T. Seaborn and K. Catley
22001166 SOUTHEASTERN NATURALIST Vo1l5.( 115):,6 N1–o7. 51
Abiotic Microhabitat Parameters of the Spruce–fir Moss
Spider, Microhexura montivaga Crosby and Bishop
(Araneae: Dipluridae)
Travis Seaborn1,2,* and Kefyn Catley1
Abstract - The Spruce–fir Moss Spider (Microhexura montivaga) is a federally endangered
species found only in the high-elevation southern Appalachian spruce–fir forests. Little is
known about the basic ecology of the spider. The goal of this project was to determine the
temperature and humidity parameters of the microhabitat around known spider locations.
iButton temperature and humidity data loggers were placed at sites on Mt. Lyn-Lowry,
Browning Knob, Whitetop Mountain, and Mt. Rogers (a range that encompasses all metapopulations).
No statistically significant (P > 0.05) differences in humidity between positive
and negative presence sites, among metapopulations, or individual sites were found. Temperature
data showed varied results. This research provides a number of applications for
the conservation and management of the Spruce–fir Moss Spider, such as understanding
metapopulation variation, better husbandry techniques, and using collected data to determine
conversion factors/models for temperature data between microhabitat measurements
and larger-scale measuring methods.
Introduction
The endangered southern Appalachian endemic Microhexura montivaga Crosby
and Bishop (Spruce–fir Moss Spider) is the world’s smallest and northernmost
member of the family Dipluridae, more commonly known as the funnel-web tarantulas.
Diplurids are generally found worldwide within the tropics, with most species
found in South and Central America and Australia, although they can also be found
in India and Africa. Microhexura is the northernmost genus found in the temperate
zone. There are a total of 24 genera with 181 species in Dipluridae (Platnick 2014).
Raven (1985) describes 3 diagnostic characters for the Dipluridae: lowered caput
and elevated thoracic region, elongated lateral spinnerets composed of 3 sections,
and widely separated sections of the spinnerets. Using Microhexura as an informative
outgroup to the rest of the diplurids may be indicated. However, due to the high
level of derived specialized characters and unique habitat requirements, its utility
as an outgroup is debatable (Coyle 1995). The Spruce–fir Moss Spider ranges in
size from 2.5 mm to 5.6 mm (Coyle 1981) and is restricted to the southern Appalachian
Mountains. Although listed as endangered since 1994 (Fridell 1994), minimal
research has been done on the basic ecology of the Spruce–fir Moss Spider. The
overarching purpose of this project was to define habitat correlates of the Spruce–fir
1Department of Biology, Western Carolina University, Cullowhee NC 28723. 2Current address
- School of Biological Sciences, Washington State University, Pullman, WA 99163.
*Corresponding author - travis.seaborn@email.wsu.edu.
Manuscript Editor: Richard Baird
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Moss Spider and fill in knowledge gaps that are preventing proper management of
this endangered species, such as proper husbandry techniques.
Spruce–fir Moss Spider webs of are confined to bryophyte mats and appear as
messy tangles of flat tubes and sheets in the interstitial space between the rock substrate
and the bryophyte mat. Although their diet has not been confirmed, springtails
(Collembola) and mites (Acari) are assumed to play a role due to their great abundance
in leaf-litter/bryophyte habitats in general (Coyle 1981) .
Spruce–fir Moss Spiders attain maturity in 2–3 years, with females laying eggs
in June and spiderlings emerging in September (Coyle 1981). Mating occurs in the
fall; once males have completed their last molt, they leave their webs in search of
females and die that winter (Coyle 1981). Male mating behavior is triggered by the
presence of a female’s web (Coyle 1985). Dispersal strategies, which might play
a vital role in the biology of this species, are still somewhat debated. Microhexura
idahoana Chamberlin and Ivie 1945, the sister species found in the western United
States, has been reported from snowfields, giving rise to the idea that ballooning
may occur (Coyle 1981). However, because millipedes have also been collected
from snowfields, presence there does not mean that aerial dispersal is required
(Crawford and Edwards 1986). If dispersal is not aerial, the very small size of
this animal suggests that movement, even across a single mountainside, or from
one rock outcrop to another, may prove very infrequent. Genetic flow among and
between metapopulations is currently being studied by Dr. Marshall Hedin of San
Diego State University. However, previous work from a small sample size suggested
that the metapopulations were in fact isolated populations with minimal gene
flow (Martens 2005). As part of its conservation efforts, the US Fish and Wildlife
Service (USFWS) would like to determine the validity of artificially increasing
gene flow either in the field or lab, but it is imperative to fully understand the habitat
requirements before moving any individuals to a new environment .
Originally collected and described by Crosby and Bishop (1925), the Spruce–fir
Moss Spider was added to the Federal List of Endangered and Threatened Wildlife
and Plants by the USFWS in 1994 (Fridell 1994). The reason was two-fold: the relatively
low abundance of the species and the rapid deterioration of suitable habitat.
The known Spruce–fir Moss Spider population is separated into 6 metapopulations:
Whitetop and Pine Mountains in Virginia, and Grandfather Mountain, Roan Mountain,
the Black Mountains, the Great Smoky Mountains, and the Plott Balsams of
North Carolina. The total number of mountain peaks the Spruce–fir Moss Spider
is known to inhabit is limited to 22, all in the southern Appalachians, resulting in
its endemic status. Although past surveys showed possible decreases in abundance
(US Fish and Wildlife Service 1998), it appears that all populations outside of
Clingman’s Dome (Coyle 2009) may be stable, but the total number of individuals
over all populations remains unknown, so final conclusions of population health
should be made with caution.
When dealing with such small organisms, it is important to consider the scale of
the landscape they experience; for example, when considering different species, the
characterization of the same habitat can shift from continuous to fragmented as body
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size shifts from large to small (Borthagaray et al. 2012). Research on soil-dwelling
spiders has found that environmental variables result in similar spider assemblages
across spatial scales (Ziesche and Roth 2008). In mite species, it has been shown that
particular microhabitats, such as the presence of dead wood, significantly increased
species diversity on the forest floor (Madej et al. 2011). Although the habitat of the
Spruce–fir Moss Spider appears well known, the actual parameters have yet to be
documented, which is one of the primary goals of this research.
The importance of recording microhabitat parameters and predictive mapping is
reflected in the goals of the Recovery Plan for the Spruce–fir Moss Spider (USFWS
1998). The current research contributes to task 1.3, characterization of the species’
habitat requirements, by collecting temperature and humidity data, and to task 2,
the search for additional populations and/or habitat suitable for reintroduction,
by providing abiotic guidelines for potential locations. If current populations become
more imperiled, it will be important to understand as much as possible to
decrease chances of mortality of individuals and increase overall success rates of
re-establishment. Description of the natural microhabitat also assists in developing
artificial holding and propagation techniques, which is task 3 of the Recovery Plan.
A clearer understanding of habitat requirements will enhance the effectiveness of
captive breeding efforts, which have proven problematic. At Louisville Zoological
Park, populations were maintained but not well enough for breeding activity to occur
(US Fish and Wildlife Service 1998). Knowledge of habitat requirements will
also aid in determining requirements for establishing new populations, which is
another important goal.
The endangered status of the Spruce–fir Moss Spider is one of the key driving
points of this research. More information will aid in bettering the future prospects
of the species. The species’ highly specific habitat requirements and loss of that
habitat makes conservation of this spider urgently important. The extensive loss
of Abies fraseri (Pursh) Poir. (Fraser Fir) in the spider’s habitat is a direct result
of infestation by Adelges piceae (Ratzeburg) (Balsam Woolly Adelgid), which is
an exotic species that was introduced in 1956. Mature Fraser Fir death within 5–7
years of infestation is possible though not inevitable (White et al. 1993), resulting
in loss of canopy, an increase in heat and light, decrease in moisture, and consequently
desiccation of the bryophyte mats that are vital for the Spruce–fir Moss
Spider (Coyle 1997).
It is anticipated that a decline of bryophyte mats would lead directly to a decline
in the spider population (US Fish and Wildlife Service 1998), and indeed the
entire and largely unknown high-elevation bryophyte-mat community. The loss of
Fraser Fir would not only be detrimental to the Spruce–fir Moss Spider, but also to
other southern Appalachian endemic arthropod species, such as Dasycerus bicolor
Wheeler and McHugh, a staphylinid beetle, and Sisicottus montigenus Crosby and
Bishop, a linyphiid spider, which have also shown sharp declines correlated with
declines of the fir (Sharkey 2001, Zujiko-Miller 1999). Declines of Fraser Fir due to
the Woolly Adelgid seem to have subsided, with some areas showing regeneration
(McManamay et al. 2011); however, some have postulated that a second wave of
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infestation is likely to occur (Moore et al. 2008). Climate change may also potentially
negatively influence the habitat, as a reduction in cloud cover would decrease
water availability (Berry et al. 2014). It is important to determine as much information
on the ecology of the Spruce–fir Moss Spider and the status of its current
populations as possible to aid in predicting the viability of current and future populations
in the face of the these 2 ecosystem stressors.
Field-Site Description
All metapopulations of the Spruce–fir Moss Spider are defined by some shared
characteristics. Populations are restricted to high elevations (1600–2042 m) in
spruce–fir forests (Coyle 1981). Spruce–fir forests in this area are dominated by
Fraser Fir and Picea rubens Sarg. (Red Spruce) (Spira 2011). In addition, the species
is only known from rock outcrops and boulders that serve as substrate for
bryophyte mats. These mats are generally 1–4 cm thick and moderately drained—
neither dry nor soggy. the Spruce–fir Moss Spider’s sensitivity to desiccation also
restricts it to north-facing slopes (Coyle 1981). The bryophyte genera most often
associated with the Spruce–fir Moss Spider include Bazzania (liverwort), Dicranodontium
(moss), and Polytrichum (moss).
Methods
We placed temperature and humidity data loggers at 2 sites at the farthest known
north and south metapopulations. The north metapopulation encompasses the Mt.
Rogers area, Grayson and Smyth counties, VA, and the southern metapopulation
encompasses the Plott Balsams area, Haywood and Jackson counties, NC (Fig. 1).
The distributions of these as metapopulations are presumed to be defined by limited
dispersal, not only between mountain slopes within a mountain range, but also
between appropriate microhabitats such as rock structures and bryophyte mats
on a single mountain. A positive presence location was chosen within each metapopulation:
Whitetop Mountain and Mt. Lyn Lowry, respectively. Known negative
presence sites were Mt. Rogers and Browning Knob, respectively. Exact GPS
points of positive and negative sites were provided by the USFWS. Surveys were
performed in 2009 by Dr. Fred Coyle.
We used iButton DS1920 loggers for humidity measurements and iBCod50
G loggers for temperature data at each site. We placed 3 iButton DS1920 and
4 iBCod50 G loggers at each site and averaged their data. Minimum and maximum
temperatures were recorded for each day at all sites for the period June 2013
to November 2013, and we calculated the daily average and difference of those
minimum and maximum temperatures. We read data from loggers in the field using
a USB clamp in September, November, and April. We set the data loggers to
record measurements every hour with a resolution of 0.5 for relative humidity
(% RH) and temperature (°C) for June through November. From November to
April, measurements were recorded every 1.5 hours. Due to the inaccessibility
of the sites during winter, we increased measurement increments to prevent data
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loss due to logger memory limitations. The time period of the study encompassed
the hottest months of the year, which may be a critical period given future climate
change. We used ANOVA with post-hoc Tukey’s pairwise comparison to analyze
the following variables: differences within metapopulations and between metapopulations,
presence of spiders, and difference between maximum and minimum
temperature (isothermality).
We incorporated 2 additional data sets in the final statistical analysis. These
were provided by the Mt. LeConte weather station and from a HOBO data logger
deployed at Mt. Lyn Lowry by the USFWS. Mt. LeConte is within the Great Smoky
Mountains National Park metapopulation. Data were provided through National
Oceanic and Atmospheric Administration (NOAA) and accessed through the National
Climatic Data Center for the same period of time as the iButton deployment.
The Mt. Lyn Lowry HOBO data logger was mounted in a tree near the iButton site
by USFWS throughout the duration of the iButton deployment. These 2 additional
data sets allowed for investigation of the effect of the bryophyte mats on humidity
and temperature. In addition to comparisons with all iButton loggers, modeling
analysis was used to determine correlation of the HOBO logger's measured daily
Figure 1. Distribution map of the 6 metapopulations of M. montivaga (Spruce–fir Moss
Spider). Zones created by buffering 7.5 km from known positive presence locations. Black
regions denote metapopulations for which we placed data-loggers, while the grey region,
represents the metapopulation for which data was obtained from the Mt. Leconte weather
station. Temperature data associated with the other metapopulations (white-filled regions)
that lie in the middle of the northeast–southwest georgraphic range of the species, were not
collected for this study.
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maximum and minimum temperature values and the iButton's measured temperature
values at the Mt. Lyn Lowry site.
Results
Temperature measurements
Temperatures were taken at both Whitetop and Mt. Rogers (274 measurements),
while 262 measurements were taken at both Lyn Lowry and Browning Knob. The
maximum temperature recorded was 19.8 °C, while the minimum temperature
recorded over the study period was -17.8 °C. ANOVA results show maximum
daily temperatures were significantly different for the pairwise comparison of Lyn
Lowry–Browning Knob (P < 0.01), Whitetop–Lyn Lowry (P < 0.01), Whitetop–Mt.
Rogers (P < 0.01), and Mt. Rogers–Lyn Lowry (P = 0.01), but not for Mt. Rogers–
Browning Knob (P = 0.77). Significant differences among maximum temperatures
within individual sites and within metapopulations were also indicated. Minimum
daily temperatures were significant for pairwise comparisons of Lyn Lowry–
Browning Knob (P < 0.01), Mt. Rogers–Browning Knob (P < 0.01), Whitetop–Lyn
Lowry (P < 0.01), and Whitetop–Mt. Rogers (P < 0.01), but not significantly different
for Whitetop–Browning Knob (P = 0.63) nor Mt. Rogers–Lyn Lowry (P =
0.99), indicating some differences of minimum temperatures within individual sites
or within metapopulations. Average minimum and maximum temperatures were
significant for pairwise comparisons of Lyn Lowry–Browning Knob (P < 0.01), Mt.
Rogers–Browning Knob (P = 0.01), Whitetop–Lyn Lowry (P < 0.01), and Whitetop–
Mt. Rogers (P < 0.01), but not significantly different for Whitetop–Browning
Knob (P = 0.27) or Mt. Rogers–Lyn Lowry (P = 0.76) (Fig. 2A). The average daily
maximum, average daily minimum, and daily average of minimum and maximum
temperatures varied by less than 25% within metapopulations (Table 1). The highest
percent change difference was between the averages of the daily minimum of
Lyn Lowry–Browning Knob, at 24.6%. It should be noted, however, that the average
of the minimums was 4.4 °C and 3.5 °C, respectively, so the percentage does
not reflect a large change in actual degrees. Isothermality, the difference between
the maximum and minimum temperatures, was significantly different (P < 0.03) for
all pairs except Lyn Lowry–Browning Knob (P = 0.99).
Table 1. Percent change comparison of temperature data averages within metapopulations, between
metapopulations, between presence status, and between all sites and USFWS logger on LynLowry and
the LeConte weather station. * indicates correlation is signific ant at 0.05 level (two-tailed).
Avg high Avg. low Avg. isothermality
temp. temp. Avg. temp. value
Lyn Lowry–Browning Knob -13.6%* -24.6%* 17.8%* 4.1%
Whitetop–Mt. Rogers 14.3%* 10.3%* -5.0%* -53.5%*
Plott Balsam–Virginia -13.9%* -0.4% -8.6%* -38.2%*
Positive–Negative Presence -12.8% -10.5% -6.2% -22.7%*
Lyn Lowry–USFWS -42.3%* 35.0%* -26.6%* -137.4%*
All–USFW -64.5%* 40.1%* 1.2%* -128.3%*
All–Leconte -86.4%* 103.9%* 12.0%* -265.9%*
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Maximum daily temperature was significantly different between the Virginia
(most northern) and Plott Balsams (most southern) sites ( -13.9%, P < 0.01).
Conversely minimum daily temperature was not significantly different between
the Virginia and Plott Balsams sites (-0.4%, P = 0.78). Average difference of the
minimum and maximum, the isothermality value, was also significantly different
(-8.6%, P = 0.03; Fig. 2B). Isothermality was significantly different (P < 0.01)
between metapopulations, with 38.2% change measured between the Plott Balsams
and Virginia sites (Table 1).
Figure 2. Temperature data logger summary: (A) Average of daily maximum and minimum
temperature for Browning Knob, Lyn Lowry, Whitetop, and Mt. Rogers; (B) Average of
daily maximum and minimum temperature for the 2 metapopulations studied, in the Plott
Balsams and Virginia; and (C) Average of daily maximum and minimum temperature for
positive- versus negative-presence sites. Positive-presence sites were Lyn Lowry and
Whitetop; negative sites were Mt. Rogers and Browning Knob.
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Daily maximum temperature values did not differ significantly between locations
for which the Spruce–fir Moss Spider has and has not been documented
(P = 0.41). Likewise, daily minimum temperature values did not differ significantly
between positive- and negative-presence sites (P = 0.88). Average of the minimum
and maximum daily temperature was also not different (P = 0.92; Fig. 2C).
Isothermality was significantly different (P < 0.01) between positive- and negativepresence
sites by -22.7%, equating to a dif ference of 0.5 °C.
Daily maximum and minimum temperature values differed significantly between
data loggers placed under the bryophyte mats, the HOBO logger in the tree, and the
LeConte weather station (P < 0.001). The average daily maximum and minimum
did differ significantly between our data loggers across all sites, the HOBO USFWS
data logger, and the Mt. LeConte weather station (P < 0.01; Fig. 3A). The difference
of the average of the maximum and minimum was 1.2% and 12% different
Figure 3. Comparisons with HOBO and weather station data. (A) Average of the daily
maximum and minimum temperature values from all iBCod50 G data loggers placed under
bryophyte mats at Mt. Rogers, Whitetop, Lyn Lowry, and Browning Knob (“All”) compared
to the values for the Leconte weather station and the USFWS HOBO logger mounted in
a tree near the Lyn Lowry iBCod50 G loggers. (B) Difference of the daily maximum and
minimum temperature values for the same scenarios as (A).
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between the iButton loggers and the HOBO logger and the LeConte weather station,
respectively. Overall, isothermality under bryophyte mats was, on average,
128.3% lower compared to the USFWS logger and 265.9% lower compared to the
LeConte weather station (Table 1, Fig. 3B). Direct comparisons of the iBCod50 G
data loggers found at Lyn Lowry to the tree-deployed USFWS data logger showed
significant differences in daily maximum (-42.3%), minimum (35.0%), average
of maximum and minimum temperature (-26.6%), and isothermality calculation
(-137.4%) (P < 0.001). A direct percent change between the Lyn Lowry iButton
loggers and the USFWS HOBO logger gave a difference in maximum temperature
of -14.8%, in minimum temperature of 8.4%, in average of maximum and minimum
of -4.2%, and in isothermality value of -136.6%.
Linear regression analysis of the temperature data collected from the iButton
data loggers and the HOBO logger at Lyn Lowry showed a significant relationship
(P < 0.001) between the recorded daily maximum and minimum temperature. Both
models reported an adjusted R2 value of 0.94. The equation for the daily maximum
was iButton = 0.968*HOBO - 2.1, while the equation for the daily minimum was
iButton = 0.82*HOBO + 1.7.
Humidity measurements
No loggers were recovered from Browning Knob; they all went missing (assumed
stolen). Three were recovered and still operational from Lyn Lowry for the period
of June to September, taking a total of 1808 measurements. Three were recovered
from Mt. Rogers: 1 for June–Sept (1808 measurements) and 2 for June–November
(3251 measurements). Three were recovered from Whitetop: 2 for June–September
(1808) and 1 for June–November (3559 measurements). The USFWS HOBO
logger recorded from June to November (6427 measurements). Primary cause
of failure for recovery was battery failure due to oversaturation. The majority of
measurements were greater than 100% RH, so percentage of measurements below
100 was used to calculate differences. Whitetop–USFWS were significantly different
(P = 0.04); all other pairwise comparisons were non-significant. There were
no significant differences between metapopulations (P = 0.13) or presence of the
Spruce–fir Moss Spider (P = 0.98) (Fig. 4).
Discussion
Previous research shows that microclimate is of great importance to a wide
range of taxa. For the spider Anelosimus studiosus (Hentz), temperature in the
web can drive the success of solitary or multifemale colonies and is also a key
factor in the maturation process (Jones and Reichert 2008, Jones et al. 2007). In
aquatic Diptera, emergence time and flight period are influenced by temperature
in the Plitvice Lakes (Cmrlec et al. 2013). In vertebrate taxa, microhabitat parameters
buffer and reduce vulnerability in frogs and determine growth and size in
avian offspring (Dawson et al. 2005, Scheffers et al. 2013a). In the Philippines,
microclimate habitats have been found to increase in temperature by a range of
0.11–0.66 °C while the macroclimate changes by 1 °C, also providing evidence
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that microclimates can buffer and ameliorate the ambient macro-level temperature
(Scheffers et al. 2013b).
Although daily maximum, minimum, and average of the maximum and minimum
may show small differences, the difference between the minimum and maximum
values remains much more stable under the bryophyte mats in the spruce–fir forest
when compared to ambient temperatures measured by the HOBO data logger on Mt.
Lyn Lowry and the Mt. LeConte weather station. This contrast was most apparent
Figure 4. Humidity data logger summary. (A) Percentage of days measured below 100%
RH for each site. Tukey’s pairwise comparison showed that Whitetop–USFWS were significantly
different (P = 0.04), but all other pairwise comparisons were not significant
(P > 0.05). USFWS logger was mounted in tree, whereas all other sites were iButton DS
1920 loggers placed down near bryophyte mats. (B) There were no significant differences
between metapopulations (P = 0.13) or (C) presence of M. montivaga (Spruce–fir Moss
Spider; P = 0.98). Bars are standard deviation. The USFWS logger data were not included
in the metapopulations and presence analysis.
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when considering data from loggers placed underneath bryophyte mats at Lyn Lowry
compared to data from the logger mounted up in a tree within 2 m of the same
mats. The difference between the LeConte weather station and the bryophyte mat
loggers and tree-mounted logger also brought to light the importance of realizing
that macroclimate records may not accurately reflect the microhabitat conditions
actually experienced by the Spruce–fir Moss Spider. Sequential differences were
observed as distance from the ground was increased. Although the LeConte weather
station was not located in the same range, it is expected that the increases in isothermality,
and similar average temperatures, would be observed elsewhere with
similar monitoring techniques. Isothermality, the difference between the maximum
and minimum temperature, was found to be 1 of the 5 most important variables
when creating distribution models of Procapra przewalskii Büchner (Przewalski’s
Gazelle; Hu and Jiang 2010). In addition, lower isothermality values correlate with
rates of spider endemism (Goncalves-Souza et al. 2014). Further research may
show, as in that study, that the fluctuation of the temperature over the course of the
day may be a key driver in the distribution patterns of the Spruce–fir Moss Spider.
Indeed, temperature stabilization provided by bryophyte mats, and especially the
reduction of maximum daily temperatures during summer, may in fact be 2 of
the defining features of the Spruce–fir Moss Spider ’s ecological requirements.
The minor differences in temperature and humidity between and among the
metapopulation sites, and between the positive and negative presence sites, are not
surprising. All sites were previously considered to be within the defined habitat of
the Spruce–fir Moss Spider; thus, general characteristics, such as slope, canopy
species, and aspect, were similar across all sites. However, such lack of differences
may be important in consideration of the USFWS stated goals, including identifying
potential locations of new populations and sites for future populations. It is
hoped that by knowing specific temperature and humidity ranges, potential artificial
migration events may be more successful. Temperature and humidity are also
very important in respect to captive-breeding conservation efforts. As stated previously,
Louisville Zoological Park successfully maintained populations, but not well
enough for breeding to occur (US Fish and Wildlife Service 1998). Hopefully, the
abiotic parameters of wild populations provided by this study will aid in the success
of potential breeding efforts. In conjunction with this, studies of captive maintained
populations could be informative on the thermal tolerances of the species, allowing
for more accurate monitoring in the wild by using thermal tolerances derived
from captive individuals as the bounds for potential new locations and assessing
the quality of current locations of populations.
Under bryophyte mats, the maximum temperature was lower, the minimum temperature
was higher, the average of the minimum and maximum values was lower,
and isothermality was lower. The percentages given in Table 1 should be used when
considering the habitat of the Spruce–fir Moss Spider. Areas of higher maximum
temperatures may be more vulnerable to climate change. The percentage conversion
factors and linear model could also provide a clearer understanding of the
potential effects of climate change, which are of particular concern to the spruce–fir
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forests (Spira 2011). Climate change may be buffered by certain microhabitats because
it appears that microclimates may moderate the macroclimate shifts recorded
in forests (De Frenne et al. 2013). Although large-scale climate models are convenient
and may enlighten general patterns, microclimates must still be considered if
accurate prediction of the imperiled status of a species is to be realized. However,
a large-scale monitoring goal can be achieved by using the calculated conversion
factors and the linear-model protocols to determine more accurate measurements.
Large-scale monitoring using the regression analysis for the temperature data can
be done without having to actually measure the temperatures underneath the bryophyte
mats. The feasibility of large-scale temperature monitoring with data loggers
under the bryophyte mats would be a massive undertaking from a financial and
labor stand point. This highlights the importance of the model, which allows for
more accurate monitoring while using preexisting infrastructure .
Although collecting data for the southern and northern metapopulations may
be a good starting point, future consideration should be given to all metapopulations
of the Spruce–fir Moss Spider to fully solidify the knowledge of this spider’s
ecology. These additional measurements across all metapopulations would also
help provide knowledge of the basic biology that is lacking for this endangered
species. Although new data presented here provide a strong baseline for conservation
efforts, there is still much work to be done. Temperature data from multiple
positive-presence sites within every metapopulation still needs to be collected.
Additional comparisons between iButton and HOBO data loggers may also add
support to the provided model as direct site comparisons are considered. A similar
methodology could use iButton loggers and the correlation of temperature data
with the Mt. LeConte weather station. It should also be noted that a single site was
used at each location; therefore, expansion to incorporate multiple rock outcrops
at each location would be helpful as well. Long-term monitoring will be key to ensuring
the survival of this species. In addition to using the linear model, it may be
beneficial to take the percent-change calculations between the Lyn Lowry iButton
loggers and the HOBO logger and use it as a conversion factor by multiplying the
percent change and non-microclimate measurements, allowing USFWS to use the
tree-mounted HOBO loggers; this would provide much more efficient data collection
due to increased storage capacity and durability. One fruitful area of research
could focus on the differences (both abiotic and biotic) between eastern and western
species of Microhexura. Microhexura idahoana is found in a greater range of habitat,
including an expanded elevation range and is not restricted to moss substrate
for web construction (Coyle 1981). If minimal differences are found, lab studies
on the non-endangered species may be helpful to better understand the physiology
and behavior of the Spruce–fir Moss Spider. Conversely, if differences are found, it
would provide justification for working directly on the endanger ed species.
Efforts to conserve nationwide biodiversity will need to be focused on those
ecosystems that harbor endemic species. The Spruce–fir Moss Spider may prove to
be very important in monitoring the system within which it is found. As a potential
key species within the microhabitat, the presence of the Spruce–fir Moss Spider
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could indicate the health of the bryophyte mats. In turn, these bryophyte mats may
well be indicators of the overall health of the high-altitude forest. As forest canopy
decreases, bryophyte mats also decline (Baldwin et al. 2011). The loss of an entire
ecosystem will not only endanger the known endemic spiders like the Spruce–fir
Moss Spider and S. montigenus that reside there, but also any other species that
may be adapted for that entire ecosystem. The potential for a complete loss of an
entire suite of taxa needs to be seriously contemplated and assessed to encourage
intensive conservation and habitat restoration.
Acknowledgments
T. Seaborn would like to express his deep gratitude to his thesis adviser and co-author
Dr. Kefyn Catley for introducing him to this fascinating little mygalomorph and giving him
copious advice over the course of his time at Western Carolina University; Dr. Beverly Collins
for her knowledge of the tools and ecological concepts of microhabitat research; and the
rest of his thesis committee: Dr. Ron Davis and Greg Adkison. Sue Cameron at USFWS also
deserves recognition for helping throughout the study. Last but most importantly, we thank
Dr. Fred Coyle for doing almost all previous research and surveys and for overall guidance.
We would are also grateful to our funding sources, the Western Carolina University Biology
Department, Western Carolina University Graduate School, and Highlands Biological
Station Grant in Aide of Research.
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