Habitat Assessment and Range Updates for Two Rare
Arkansas Burrowing Crayfishes:
Fallicambarus harpi and Procambarus reimeri
Cody M. Rhoden, Christopher A. Taylor, and Brian K. Wagner
Southeastern Naturalist, Volume 15, Issue 3 (2016): 448–458
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2016 Vol. 15, No. 3
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2016 SOUTHEASTERN NATURALIST 15(3):448–458
Habitat Assessment and Range Updates for Two Rare
Arkansas Burrowing Crayfishes:
Fallicambarus harpi and Procambarus reimeri
Cody M. Rhoden1,*, Christopher A. Taylor1, and Brian K. Wagner2
Abstract - The Ouachita Highlands Freshwater Ecoregion harbors the 6th-highest native
crayfish species density in the US and Canada. Many of these species are understudied,
and the burrowing crayfishes of this region are of particular interest. We conducted field
surveys in the spring of 2014 and 2015 to assess the range and habitat preferences of 2 of
Arkansas’ rarest burrowing crayfishes: Fallicambarus harpi (Ouachita Burrowing Crayfish)
and Procambarus reimeri (Irons Fork Burrowing Crayfish). Both crayfishes are currently
of conservation concern—F. harpi is vulnerable and P. reimeri is endangered according to
the American Fisheries Society. Our surveys detected new populations of both species and
documented marginal and wider range expansions for F. harpi and P. reimeri, respectively.
The preferred habitat for both species was characterized as wet seepage areas with an open
canopy, low grasses, and abundant sedges. Our surveys support prior observations that these
species are geographically constrained; however, the new populations and range expansion
of P. reimeri suggest the American Fisheries Society Endangered Species Committee should
reevaluate the conservation status of this species.
Introduction
North America harbors the highest diversity of crayfishes worldwide (Taylor
et al., 2007). Within North America, 22% of the species listed as endangered or
threatened in a conservation review (Taylor et al. 2007) were primary burrowing
crayfishes. Primary burrowing crayfishes differ from stream-dwelling crayfishes
in their life-history traits; they spend most of their life cycle underground, leaving
their burrows only to forage and find a mate (Hobbs 1981). The Ouachita
Highlands Freshwater Ecoregion is the 6th-most diverse freshwater ecoregion for
native crayfishes in the US and Canada (Moore et al. 2013). Within the Ouachita
Highlands Freshwater Ecoregion, the Ouachita Mountains Ecoregion (OME;
Woods et al. 2004) of southwestern Arkansas harbors the highest diversity of primary
burrowing crayfishes in the state with 6 species: Fallicambarus harpi Hobbs
& Robison (Ouachita Burrowing Crayfish), F. jeanae Hobbs (Daisy Burrowing
Crayfish), F. strawni (Reimer) (Saline Burrowing Crayfish), Procambarus liberorum
Fitzpatrick (Osage Burrowing Crayfish), P. parasimulans Hobbs & Robison
(Bismark Burrowing Crayfish), and P. reimeri Hobbs (Irons Fork Burrowing
Crayfish) (Hobbs 1989).
1Illinois Natural History Survey University of Illinois Urbana-Champaign, 607 East Peabody
Street, Champaign, IL 61820. 2Arkansas Game and Fish Commission, 915 East Sevier
Street Benton, AR 72015. *Corresponding author - codyrhoden@gmail.com.
Manuscript Editor: Bronwyn Williams
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The narrowly endemic nature of North American crayfishes is well documented
(Morehouse and Tobler 2013, Page 1985, Simmons and Fraley 2010, Taylor et al.
2007), and Robison et al. (2008) specifically addressed the primary burrowing crayfishes
in Arkansas. Endemic species are vulnerable to extirpation because they occur
at such a constrained geographic scale; thus, it is important to accurately describe
their habitat preferences and range to ensure the persistence of local populations
through management of suitable habitat and monitoring of existing populations.
Two primary burrowing crayfishes in Arkansas in need of these conservation assessments
are Fallicambarus harpi and Procambarus reimeri.
Little information has been published regarding the habitat preferences and
range assessments of F. harpi and P. reimeri since the species were first described.
Both crayfishes are endemic to the OME in southwestern Arkansas. These species
were assessed as endangered (P. reimeri) and vulnerable (F. harpi) based on vulnerability
to habitat modification or reduction and because of their restricted range
(Taylor et al. 2007). The conservation categories of endangered and vulnerable are
based upon determinations by the American Fisheries Society Endangered Species
Committee, which followed Williams et al. (1993). These species were included
in a recent petition filed by the privately funded Center for Biological Diversity
(Tuscan, AZ) for protection under the Federal Endangered Species Act. To assess
these conservation concerns, we developed a study with the following objectives:
(1) determine the holistic range of F. harpi and P. reimeri within the OME of Arkansas,
and (2) refine the description of suitable habitat for b oth species.
Target species accounts
Fallicambarus (Fallicambarus) harpi. The Ouachita Burrowing Crayfish
was described from 2 locations in Pike County, AR, in 1985 by H.H. Hobbs Jr.
and H.W. Robison (Hobbs and Robison 1985). Robison and Crump (2004) reviewed
and updated the status of this endemic crayfish, and documented 12 new
populations in Montgomery, Hot Spring, Garland, and Pike counties, AR. No
information has been published relating to the range or habitat requirements of
this crayfish since 2004. F. harpi is known from wet seepage areas with abundant
sedges, such as roadside ditches and other rights of way (Robison and Crump
2004). Fallicambarus harpi most-closely resembles F. strawni and F. jeanae, but
differs by possessing a free, never adnate, cephalic process on the first pleopod of
the first-form male (Hobbs and Robison 1985).
Procambarus (Girardiella) reimeri. The Irons Fork Burrowing Crayfish was
described from 6 locations in Polk County, AR by H.H. Hobbs Jr. in 1979 (Hobbs
1979). Robison (2008) reviewed and updated the status of this Arkansas endemic
and determined that the species only occurred in Polk County, in the vicinity
of Mena, AR. No other information has been published relating to the range or
habitat requirements of this species since 2008. This primary burrowing crayfish
constructs relatively simple burrows in sandy clay soil in wet seepage areas and
roadside ditches (Hobbs 1979, Robison 2008). Procambarus reimeri most closely
resembles P. gracilis (Bundy) (Prairie Crayfish) and P. liberorum, but differs from
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both by possessing a broader areola and lacking tubercles on the annulus ventralis
(Hobbs 1979).
Methods
We conducted field surveys for these 2 primary burrowing crayfishes in southwestern
Arkansas during the spring of 2014 and 2015. We sampled in the spring
of both years because this is the time of peak activity for both species (Robison
2008, Robison and Crump 2004) and, thus is the time with the greatest likelihood
of species detection. In 2014, we sampled historic locations listed in the Illinois
Natural History Survey Crustacean Collection (Champaign, IL), National Museum
of Natural History Invertebrate Zoology Collection (Washington, DC), and
Arkansas Department of Natural Heritage (Little Rock, AR) records. For each
species, we selected historical localities that were accessible and could be validated
with geographic positioning information. These searches resulted in 20 unique
and accessible locations for F. harpi and P. reimeri. We sampled 13 counties encompassing
the known range of both species. From east to west, those counties
were Pulaski, Saline, Perry, Garland, Hot Spring, Clark, Yell, Montgomery, Pike,
Scott, Howard, Polk, and Sevier in western Arkansas. We predicted the historical
and current range of both species using minimum-bounding convex polygons
around all localities from historical museum records and new captures from 2015
in ArcMap using the minimum-bounding geometry toolset.
In 2014, we set up three to six 50-m transects at and near each historic locality
(Rhoden et al. 2016). We placed the first transect at each sampling site where burrows
were present, ensuring the first transect was situated at the historic location.
After we obtained a GPS location and azimuth at the 0-m mark, we placed a 1-m2-
PVC quadrat over the linear transect every 10 m, for a total of six 1-m2 quadrats
per 50-m transect. We completed 2–5 additional transects in adjacent habitat at the
sampling site. We determined the number of transects sampled at each site based
on habitat heterogeneity. We placed fewer transects in homogeneous sites; thus,
sampling took less time and we were able to increase the number of sampling sites
we could visit during the sampling window. We conducted supplemental sampling
in the vicinity (less than 100 m) of each sampling site to verify non-detection observations
from transect collections. We used our 2014 capture records to develop species-distribution
models (SDMs). The SDMs were constructed with Maxent (Phillips et al.
2006), a presence-only modeling algorithm used to predict the relative occurrencerate
of a focal species across a predefined landscape (Fithian and Hastie 2013). In
2015, we sampled a semi-random group of sites based on SDMs for F. harpi and for
P. reimeri (Rhoden 2016). The environmental variables used for the SDM analysis
consisted of canopy cover, elevation, distance to nearest waterbody, compound
topographic-index value (CTI), and solar-radiation value (Table 1). We determined
canopy and herbaceous cover with a spherical densiometer (Model-C; Robert E.
Lemmon Forest Densiometers, Bartlesville, OK), elevation from the USGS National
Elevation dataset (http://nationalmap.gov/elevation.html), and distance to
nearest waterbody from the National Hydrology dataset (http://nhd.usgs.gov/). We
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followed Evans et al. (2010) to determine CTI and used the National Elevation dataset
and ESRI spatial analyst tools to determine solar-radiation values. Our Maxent
models were constructed with 30-m-resolution rasters following Peterman et al.
(2013) for model construction and evaluation.
We thoroughly searched each quadrat along each transect for the presence of
burrows and collected the following habitat variables within each 1-m2 quadrat:
percent tree-canopy cover, percent herbaceous groundcover, stem density (count
of stems within a 100-cm2 quadrat placed within the upper right-hand corner of
each 1-m2 quadrat), number of burrows, and the presence or absence of hydrophilic
sedges (presence or absence of herbaceous plants having 3-ranked leaves, an angular
stem, and a spiked fruiting body; Rhoden et al. 2016) (Table 1). We used a
soil probe (AMS 2.2 cm [7/8 in] diameter open-end probe, AMS, Inc., American
Falls, ID) to collect 3 evenly spaced soil samples on each transect. We analyzed
the soil samples with laser diffraction on a Malvern Mastersizer 3000 (Malvern
Instruments, Malvern, UK) to obtain percent composition of sand, silt, and clay for
each sample. We analyzed habitat variables using generalized linear mixed models
(package lme4; Bates et al. 2014, R Development Core Team 2014) to determine
the fine-scale habitat preferences of both burrowing crayfish species (Table 2).
The response variable in each model was the number of burrows within each 1-m2
Table 1. Habitat variables, description of each variable, source of each habitat variable, and general
statistics from a study of habitat associations of 2 primary burrowing crayfishes in western Arkansas.
F. harpi P. reimeri
Variable Description Min/max(unit) (μ [sd]) (μ [sd])
Canopy Percent tree-canopy cover 0/100 (% cover) 22.5 (32.5) 22.5 (32.8)
Herb Percent herbaceous groundcover 0/100 (% cover) 66.6 (32.4) 71.7 (31.0)
Stem Number of stems per 100-cm2 0/169 (number 22.7 (19.7) 25.4 (20.7)
sub-quadrat of stems)
Sedge Presence of hydrophilic sedge in 1/0 (binary: yes/no) - -
quadrat (binary: yes/no)
Soil 1, Transformed soil variables - -
Soil 2
Elevation Digital elevation model of the study 50.50/818.96 (m) 189.3 (32.8) 304.4 (59.7)
site
Water dist Euclidean distance to nearest 0/1740.26 (m) 176.3 (118.5) 157.2 (138.0)
permanent waterbody across the
study site
CTI A function of slope and the upstream 2.67/27.58 (index 8.4 (1.7) 8.4 (1.5)
contributing area per unit width value)
orthogonal to the flow direction
(Evans et al. 2010)
Solar Incoming solar radiation value (watt 3542.41/64134 6062.9 (105.3) 6071.3 (42.0)
h per m2) based on direct and diffuse (watt h/m2)
insolation from the unobstructed sky
directions
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quadrat modeled with a Poisson error distribution and log link. To account for
potential site effects, we modeled transects nested within sites as a random effect
in each model. We scaled and centered all habitat variables by subtracting the variable
mean from each respective value and dividing by the standard deviation of
that variable. We compared candidate models with Akaike’s information criterion
corrected for small sample sizes (AICc; Table 3; Akaike 1974). We examined the
relative support for each model and calculated unbiased model-averaged parameter
estimates from the top models (ΔAICc < 4) with the package MuMIn (Barton 2014)
by means of model selection and averaging methods described by Burnham and
Anderson (2002) and Luckacs et al. (2009).
We hand-excavated a subset of burrows at each sampling site and along each
transect to confirm the identity of the burrow occupant in each occupied quadrat.
Table 2. Candidate models and hypotheses tested in the generalized linear mixed-model analysis for
Fallicambarus harpi and Procambarus reimeri in Arkansas. The response variable used in each model
was burrow abundance in each 1-m2 quadrat. See Table 1 for variable names.
Model Variables Hypothesis
Mod 1(global) Sedge + canopy + herb + stem Crayfish selection based on quadrat-level wetness
+ elevation + solar + water_dist characteristics, canopy cover, herbaceous
+ CTI + soil1 + soil2 community, erosion potential, topographic
position, and soil cues
Mod 2 Canopy + sedge Crayfish selection based on canopy cover and
quadrat-level wetness
Mod 3 Sedge + solar + water_dist Crayfish selection based on quadrat-level wetness
characteristics and topographic position
Mod 4 Sedge + CTI Crayfish selection based on quadrat-level wetness
characteristics and topographic position
Mod 5 Water_dist + CTI Crayfish selection based on topographic position
Mod 6 Solar + CTI Crayfish selection based on topographic position
Mod 7 Elevation + water_dist Crayfish selection based on topographic position
Mod 8 Sedge + stem Crayfish selection based on herbaceous community
Mod 9 Canopy + herb Crayfish selection based on canopy and herbaceous
community
Mod 10 Herb + soil1 + soil2 Crayfish selection based on herbaceous community
and soil cues
Mod 11 Canopy + soil1 + soil2 + sedge Crayfish selection based on canopy cover, soil cues,
and quadrat-level wetness
Mod 12 Canopy + solar + soil1 + soil2 Crayfish selection based on canopy cover, solarradiation
potential, and soil cues
Mod 13 Canopy + sedge + stem Crayfish selection based on canopy cover, quadratlevel
wetness, and erosion potential
Mod 14 Soil1 + soil2 Crayfish selection based on soil cues
Mod 15 Canopy Crayfish selection based on canopy cover
Mod 16 Solar Crayfish selection based on solar-radiation potential
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Hand excavation consisted of using a hand shovel to slowly dig around the burrow
entrance to follow the main burrow-tunnel, feeling for crayfish as we worked
our way through the burrow complex. We chose this method because of its high
success-rate and the limited amount of time required at each burrow location (Ridge
et al. 2008). We collected, preserved in 70% ethanol, and deposited in the Illinois
Natural History Survey Crustacean Collection voucher specimens of all crayfish
species detected from all occupied sites with burrows present.
Results
During the 2014 and 2015 field surveys for F. harpi and P. reimeri, we sampled
1392 quadrats across 232 transects at 180 sites in western Arkansas (Fig. 1). All
of the historical localities sampled were less than 50 m from primary, secondary, and
tertiary roadways. In 2014, we sampled adjacent habitat less than 100 m from the historiccollection
sites and out of the right of way in an attempt to survey different habitat
types spatially available to individuals at each site. In 2015, all of the sites sampled
were in the rights of way of primary, secondary, and tertiary roadways. We
found F. harpi in 79 quadrats across 16 sites and P. reimeri in 90 quadrats across
24 sites. During the field sampling we encountered 14 other crayfish species:
Cambarus ludovicianus Faxon (Painted Devil Crayfish), F. fodiens (Cottle) (Digger
Crayfish), F. jeanae, F. jeanae x F. strawni, F. strawni, P. (Girardiella) sp., P.
acutus (Girard) (White River Crayfish) P. curdi Reimer (Red River Burrowing
Crayfish), P. liberorum, P. parasimulans, P. regalis Hobbs & Robison (Regal Burrowing
Crayfish), P. simulans (Faxon) (Southern Plains Crayfish), P. tenuis, and
P. tulanei Penn (Giant Bearded Crayfish).
Fallicambarus harpi
Of the 91 sites sampled for F. harpi, we found the species at all historical sites
(n = 11) and 6% of selected sites sampled in 2015 (n = 5) (Fig. 2). The longest-
Table 3. Model name, number of model parameters (K), Akaike’s information criterion adjusted for
small sample size (AICc), difference in AICc (ΔAICc), Akaike weights (wi), and log liklihood (LL)
for the top habitat models (ΔAICc < 4) from a suite of variables modeled with a generalized linear
mixed-model analysis for 2 primary burrowing crayfish species, Fallicambarus harpi and Procambarus
reimeri in Arkansas. See Tables 1 and 2 for a description of each model and the variables
included.
Species/model K AICc ΔAICc wi LL
Fallicambarus harpi
Mod 12 7 469.67 0.00 0.35 -227.80
Mod 3 6 470.32 0.65 0.25 -229.10
Mod 16 4 471.28 1.61 0.15 -231.60
Mod 6 5 471.66 1.99 0.13 -230.80
Mod 1 13 473.36 3.70 0.05 -223.40
Procambarus reimeri
Mod 2 5 543.56 0.00 0.62 -266.74
Mod 13 6 545.59 2.03 0.22 -266.73
Mod 11 7 546.59 3.03 0.14 -266.21
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persisting population of F. harpi was first discovered in 1982. We captured F. harpi
along 1 transect with P. parasimulans present and 1 transect with P. simulans; both
transects were removed from the dataset prior to the final statistical analysis. We
calculated a historical range of 147 km2 and a current range of 265 km2 for F. harpi.
The modeling analysis showed that the number of burrows in a quadrat was negatively
associated with canopy cover (Table 4). Burrows were generally present in
quadrats with little to no canopy cover (n = 79, μ = 4.8%, σ = 18.7). The presence
of hydrophilic sedges and amount of solar radiation were positively associated with
the number of burrows in a quadrat (Table 4). Sedges were present in 76% of the
quadrats with burrows present (n = 60) and 40% of quadrats where burrows were
absent (n = 247).
Procambarus reimeri
Of the 89 sites sampled for P. reimeri, we found the species at all but one historical
site sampled (n = 8) and 20% of the selected sites sampled in 2015 (n = 16)
(Fig. 2). The oldest resampled site continuing to harbor populations of P. reimeri
was first discovered in 1973. We captured Procambarus reimeri along 1 transect
where P. tenuis was present; this transect was removed from the dataset prior to the
final statistical analysis. We calculated a historical range of 80 km2 and a current
Figure 1. Sampling locations for 2 species of primary burrowing crayfish, Fallicambarus
harpi and Procambarus reimeri, in western Arkansas in the spring of 2014 and 2015.
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Figure 2. Historical and current capture locations of Fallicambarus harpi (right) and Procambarus
reimeri (left) in western Arkansas.
Table 4. Unbiased model-averaged parameter estimates of the top models (Table 3) for 2 primary burrowing
crayfish species (Fallicambarus harpi and Procambarus reimeri) in Arkansas. See Table 2 for
a description of the variables included. Sedge1 = presence of sedge in quadrat, CL = confidence limits.
Variable Model-averaged estimate (SE) 95% CL
Fallicambarus harpi
Canopy -0.84 (0.38) -1.59, -0.10
Sedge1 0.43 (0.21) 0.03, 0.83
Solar 2.24 (0.68) 0.91, 3.57
Stem 0.07 (0.14) -0.21, 0.35
Herb -0.05 (0.20) -0.44, 0.34
Soil1 0.06 (0.50) -0.93, 1.04
Soil2 -0.48 (0.36) -1.19, 0.24
Water_dist -0.37 (0.52) -1.39, 0.64
CTI 0.12 (0.10) -0.07, 0.30
Elevation -0.72 (0.70) -2.10, 0.65
Intercept -6.27 (1.05) -8.33, -4.21
Procambarus reimeri
Canopy -0.83 (0.26) -1.34, -0.32
Sedge1 2.24 (0.47) 1.33, 3.15
Stem 0.01 (0.12) -0.23, 0.25
Soil1 -0.01 (0.55) -1.01, 1.08
Soil2 0.51 (0.61) -0.68, 1.70
Intercept -5.54 (0.85) -7.21, -3.88
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range of 1467 km2 for P. reimeri. Modeling revealed that the number of burrows
in a quadrat was negatively associated with canopy cover (Table 4). Burrows were
generally present in quadrats with little to no canopy cover (n = 90, μ = 4.1%, σ =
12.8). The presence of hydrophilic sedges was positively associated with the number
of burrows in a quadrat (Table 4). Sedges were present in 94% of the quadrats
with burrows present (n = 85) and present in 44% of quadrats where burrows were
absent (n = 269).
Discussion
Our study assessed the range and habitat of 2 primary burrowing crayfish species
in southwestern Arkansas. We recorded F. harpi at all of the historical sites
sampled and P. reimeri at all but one historical site. Although we did not visit all
historical locations, historical sites sampled encompassed the (then) known range
of both species. Our sampling scheme resulted in most (91% and 93% for F. harpi
and P. reimeri, respectively) of the sampling sites to be near or in the rights of way
of primary, secondary, and tertiary roadways. Although we conducted most of our
sampling in these highly altered habitats, our field surveys revealed new populations
of both species. Both species showed common patterns of habitat preference,
which correspond with early descriptions of the habitats preferred by both species
(Hobbs 1979, Hobbs and Robison 1985). Based on our findings, we recommend
that F. harpi retain its conservation-status category of vulnerable and that scientists
re-evaluate the conservation category of endangered for P. reimeri.
Our samples documented a marginal range expansion for F. harpi of ~118 km2
and 5 new populations, including 1 found in a county (Clark) not previously documented
within the species’ range (Fig. 2). Our records document a greater range
expansion for P. reimeri of ~1387 km2, including 16 new populations. We discovered
1 of these populations in a county (Montgomery) previously not considered
in the range of P. reimeri (Fig. 2). Despite our findings, the documented ranges for
F. harpi and P. reimeri are relatively small compared to most of the other primary
burrowing crayfishes in the OME (e.g., F. jeanae, F. strawni, P. liberorum, and
P. parasimulans; Taylor et al. 2007). Although new populations of both species may
be discovered on the periphery of the range reported here, we believe the updated
range extent is accurate based on the breadth of sites sampled across the OME
(Fig. 1). We captured P. reimeri in Arkansas less than 1 km from the Oklahoma state line
(Fig. 2), a discovery which led us to suspect that P. reimeri may occur in Oklahoma;
however, more field surveys are needed to assess this possibility .
Our modeling and field observations revealed both F. harpi and P. reimeri
showed common patterns of habitat preference. These burrowing crayfishes were
most abundant in treeless, wet seepage areas with an abundance of low grasses and
sedges. The soil composition at 92% and 94% of quadrats occupied by F. harpi and
P. reimeri, respectively, was loam and silt loam (Soil Survey Division Staff 1993).
The burrows of F. harpi and P. reimeri that we excavated in the field were complex,
0.5–1-m deep, and connected to groundwater. Our results highlight the importance
of these wet, open-canopy habitats as a preferred environment f or both species.
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Our success in finding F. harpi at all of the historical sites sampled and 5 new
populations indicates that this crayfish is geographically constrained, but continuing
to persist. Its total range is estimated to be 265 km2. These results suggest
F. harpi should remain categorized as vulnerable due to its restricted range (Taylor
et al. 2007). Our documentation of P. reimeri at all but one historical site and
16 new populations, one of which was >50 km away from the previously known
range, indicates this crayfish is somewhat geographically constrained, but is more
widespread than originally thought. We estimate its total range at ~1467 km2. This
finding suggests that a re-evaluation of the conservation status given by Taylor et
al. (2007) is warranted for P. reimeri.
Acknowledgments
We thank Josh Seagraves, Andrea Daniel, Allison Fowler, Benjamin Thesing, and Justin
Stroman for permitting and field assistance, with special appreciation to Sarah Tomke and
Dan Wylie for field assistance. This work was funded with a State Wildlife Grant from the
Arkansas Game and Fish Commission. Thanks to Mike Dreslik, Robert Schooley, and Bill
Peterman for help with initial study design and analysis, and Henry Robison for his extensive
collections of these species that formed the basis for our study.
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