Preformed Scour Holes Associated with Road Building May Maintain Anuran Diversity in Urbanizing Areas
Andrew J.B. Jennings1 and Stanley H. Faeth1,*
1Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27402. *Corresponding author.
Urban Naturalist, No. 1 (2014)
Abstract
To mitigate erosion and stream pollution from road runoff, the North Carolina Department of Transportation implemented new stormwater-control structures: preformed scour holes (PSH). PSH may also provide habitat for amphibians in the urbanizing southeast United States. We surveyed anuran species in PSH in the Piedmont region of North Carolina and correlated species richness with local and regional factors associated with PSH. Degree of urbanization was negatively associated with total species richness, and PSH surface area and the presence of riparian vegetation were positively associated with total species richness. Our results suggest that PSH and similar stormwater-control measures may help to mitigate anuran diversity loss due to urbanization. Further study is warranted to determine if PSH act positively or negatively (e.g., as ecological traps) on amphibian diversity in urbanizing areas.
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A.J.B. Jennings and S.H. Faeth
22001144 URBAN NATURALIST No. 1:N1–o1. 51
Preformed Scour Holes Associated with Road Building May
Maintain Anuran Diversity in Urbanizing Areas
Andrew J.B. Jennings1 and Stanley H. Faeth1,*
Abstract - To mitigate erosion and stream pollution from road runoff, the North Carolina
Department of Transportation implemented new stormwater-control structures: preformed
scour holes (PSH). PSH may also provide habitat for amphibians in the urbanizing southeast
United States. We surveyed anuran species in PSH in the Piedmont region of North Carolina
and correlated species richness with local and regional factors associated with PSH. Degree
of urbanization was negatively associated with total species richness, and PSH surface area
and the presence of riparian vegetation were positively associated with total species richness.
Our results suggest that PSH and similar stormwater-control measures may help to
mitigate anuran diversity loss due to urbanization. Further study is warranted to determine
if PSH act positively or negatively (e.g., as ecological traps) on amphibian diversity in
urbanizing areas.
Introduction
Human populations are rapidly becoming more urban and less rural. Currently,
more than 50% of the world’s population lives in urban areas, and that fraction is
expected to rise to over 60% by 2035 (UN 2012). In the United States, over 80%
of the population now lives in cities, with increases to over 85% anticipated by
2025 (UN 2012). Habitat fragmentation and loss (McKinney 2006), hydrographic
changes (Walsh et al. 2005), changes in nutrient availability (Lewis et al. 2006),
and introduction of non-native species (McKinney 2008) are very often coupled
with increasing urbanizing populations and expanding cities. One consequence
of changes attributable to urbanization is the loss of diversity of native flora and
fauna (e.g., Faeth et al. 2011). As the degree of urbanization increases, native biodiversity
usually decreases (Faeth et al. 2011; Hamer and McDonnell 2008, 2009;
McKinney 2008).
Urban declines in native diversity have been documented for plants (e.g., Faeth
et al. 2011), birds (e.g., Chace and Walsh 2006, McKinney 2008), arthropods (e.g.,
Faeth et al. 2011, Raupp et al. 2010), mammals (e.g., Wenguang et al. 2008), and
reptiles and amphibians (e.g., Hamer and McDonnell 2008, Mitchell et al. 2008).
Explanations for observed declines in biodiversity include local abiotic factors
such as altered temperature (e.g., Brazel et al. 2000), hydrography (e.g., Walsh et
al. 2005), and nutrient availability (e.g., Kaye et al. 2006, Shochat et al. 2006),
and regional factors such as increased isolation and decreased connectivity due to
fragmentation (e.g., Faeth and Kane 1978, Leibold et al. 2004).
1Department of Biology, University of North Carolina at Greensboro, Greensboro, NC
27402. *Corresponding author - shfaeth@uncg.edu.
Manuscript Editor: Travis Ryan
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Similar to other taxonomic groups, the biodiversity of anurans (frogs and toads)
also usually decreases with urbanization (Dodd and Smith 2003, Hamer and Mc-
Donnell 2008, Knutson et al. 1999, Scheffers and Paszkowski 2012). Scheffers and
Paszkowski (2012) reviewed 24 studies of North American anuran responses to
urbanization. Each study included more than one species, allowing Scheffers and
Paszkowski (2012) to examine 144 responses to urbanization. Each response was
defined by abundance, species occurrence (presence or absence), mortality, and/
or recruitment. As an example, a negative response would be “characterized by
having higher abundances, greater occurrence, higher species richness, lower mortality,
and greater recruitment at non-urban (i.e., native habitat) over urban sites”
(Scheffers and Paszkowski 2012). Many anurans had negative responses (31%), a
few had positive responses (4%), and others had either a neutral response (17%) or
an unknown response (48%) to increasing urbanization. The underlying causes of
these responses were not identified.
The most commonly proposed cause for these declines are local processes related
to habitat loss and degradation (Hamer and McDonnell 2008, Ostergaard et al.
2008). Anurans are sensitive to alterations to hydrography, pollutants, temperature,
and habitat fragmentation, and thus are often used as indicators of environmental
health (Brand et al. 2010, Lips et al. 2008). Whereas most taxa suffer some losses
in diversity due to habitat loss, anurans are especially affected relative to other terrestrial
animals due to their complex life cycle. Most anurans require two different
habitats, terrestrial and aquatic, and the quantity and quality of both impact anuran
biodiversity (Hamer and McDonnell 2008). Adults require suitable terrestrial habitat
during the nonbreeding season for survival prior to dispersal to aquatic habitats
during the breeding season (Semlitsch and Bodie 2003). Most anurans, and all
those in the southeastern United States, require aquatic habitats for breeding and
larval survival. The declining quantity and quality of terrestrial and aquatic habitats
coupled with increases in temperature, due to the urban heat-island effect (Brazel et
al. 2000), and noise pollution that affects the efficacy of mating calls (e.g., Kaiser
and Hammers 2009) have been linked to reductions in anuran biodiversity in urban
areas (Hamer and McDonnell 2008).
At the regional level, the connectivity of, and dispersal among, terrestrial and
aquatic patches is critical in determining anuran biodiversity. This connectivity is
often disrupted in urban environments due to construction of buildings and roads.
Indeed, intensity of urbanization is often measured by density of roads (McIntyre
et al. 2000). Even non-urban roads can have negative effects on dispersal because
roads are often implicated in direct mortality of adult anurans (van der Ree et al.
2011). As the connectivity between patches decreases, the persistence of a species
within an area decreases due to less likelihood of rescue effects following a
local extinction event (Leibold et al. 2004, Parris 2006). This isolation of adult
upland forest and aquatic habitat used for breeding can lead to declines in anuran
biodiversity within the highly fragmented urban environment. Correlative studies
suggest that anuran biodiversity changes are due to both local (habitat quality
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2014 No. 1
and patch size) and regional (habitat quantity and connectedness) processes (Barrett
and Guyer 2008, Birx-Raybuck et al. 2009, Ficetola and De Bernardi 2004,
Gagné and Fahrig 2007, Parris 2006, Scheffers and Paszkowski 2012).
Although the overall effects of urbanization on anuran diversity are negative,
some features of urbanization may promote diversity. For example, anthropogenic
ponds associated with roadways and urbanization may indirectly but positively
affect anuran diversity by providing habitat for survival and breeding. These
ponds are primarily built for retention and erosion control, usually with little
consideration of possible ecological cost or benefits. Brand and Snodgrass (2010)
found a general decline in anuran diversity along an urban–rural gradient, but also
showed that anthropogenic ponds had a higher level of anuran biodiversity when
compared to naturally formed ponds with the same level of urbanization. These
results suggest that human-made stormwater controls (i.e., retention ponds) may
lessen anuran biodiversity loss caused by urbanization as anthropogenic ponds
tend to retain more water for a longer period of time than natural ponds (Brand
and Snodgrass 2010).
The most common type of stormwater control used in studies of urban anuran
diversity is the retention pond (e.g., Birx-Raybuck et al.2009, Brand and
Snodgrass 2010, Ostergaard et al. 2008). While conspicuous and fairly common,
retention ponds are but one of many types of stormwater control used by cities,
counties, and states. The North Carolina Department of Transportation (NCDOT)
recently implemented a new stormwater control: preformed scour holes (PSH).
PSH are pre-shaped basins that are located downhill from a stormwater outflow
with permanent soil-reinforcement matting to prevent erosion (NCDOT 2008).
The main purpose of PSH is to minimize erosion caused by roadside scour and
secondarily to promote runoff infiltration (NCDOT 2008). Design features that
address this secondary purpose, promoting runoff infiltration, allow stormwater
to gather and form temporary pools that may provide habitat for pond breeding
amphibians. PSH are ideal stormwater-control structures for the study of amphibian
diversity because they are associated with new road construction and are
found along an urban to rural gradient. The use of PSH by anurans has not been
previously examined.
We examined the anuran biodiversity associated with PSHs and determined
which local and regional-level factors associated with PSHs are correlated with
changes in anuran biodiversity. Based on previous studies (Ficetola and De Bernardi
2004, Parris 2006), we predicted that PSH surface area would be positively
correlated with anuran diversity and urbanization would be negatively correlated
with anuran diversity. Although previous studies have shown that urbanization
has a negative impact on anuran biodiversity (e.g., Barrett and Guyer 2008, Bunnell
and Zampella 1999, Delis et al.1996, Hecner and M’Closkey 1997, Parris
2006), fewer studies have statistically modelled multiple possible explanatory
factors that affect anuran biodiversity in urban environments, and none have
specifically examined PSH. Similar to Ficetola and De Bernardi (2004), we
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examined local and regional factors to build an explanatory model that may be
useful as a baseline for future studies on PSH and similar stormwater controls in
the urbanizing southeastern United States.
Field-site Description
A PSH is a “structural stormwater control designed to dissipate energy and
promote diffuse flow” (NCDOT 2008). Each PSH is pre-shaped, stabilized with
filter fabric, and lined with rip-rap, medium-sized stones around 20 cm in diameter
(NCDOT 2008). PSH mimic natural scour holes that prevent road run-off erosion
from point discharges. The intended water-quality benefits of PSH are to “reduce
the amount of end-of-pipe erosion by eliminating unabated scour” and “promote
runoff infiltration and reduce downgrade erosion” (NCDOT 2008). To date, no one,
including the NCDOT, has conducted any studies of the potential effects of PSH on
the diversity of urban flora and fauna.
The NCDOT provided access to PSH erosion-control sites throughout central
North Carolina. Greensboro, the urban center for this research, is located in the
Piedmont region of North Carolina and is typified by temperate deciduous forests.
All of the PSHs in Guilford, Alamance, Randolph, and Caswell counties were
considered candidates and screened on the basis of holding water for at least two
months during the anuran breeding season (February to June). After being initially
screened in February 2012, each PSH was re-examined in early May 2012, and of
the 54 PSH found in the study area, 21 PSH held water for longer than two months
(Fig. 1, Table1).
Figure 1. The four North Carolina counties and locations of PSHs. Top: Caswell County
(n = 1), middle: Guilford County (n = 18), Alamance County (n = 1), and bottom: Randolph
County (n = 1).
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Methods
Study organisms
In the study area, there are 12 species of anurans: Anaxyrus americanus (Holbrook)
(American Toad), Anaxyrus fowleri (Hinckley) (Fowler’s Toad), Acris
crepitans (Baird) (Northern Cricket Frog), Hyla chyrsoscelis (Cope) (Cope’s Gray
Treefrog), Hyla versicolor (LeConte) (Gray Treefrog), Gastrophryne carolinensis
(Holbrook) (Eastern Narrowmouth Toad), Pseudacris feriarum (Baird) (Upland
Chorus Frog), Pseudacris crucifer (Wied-Neuwid) (Spring Peeper), Lithobates
sphenocephalus (Cope) (Southern Leopard Frog), Lithobates palustris (LeConte)
(Pickeral Frog), Lithobates clamitans (Latreille) (Green Frog), and Lithobates
catesbeianus (Shaw) (Bullfrog) (Dorcas and Gibbons 2008). Each of these species
has a unique and distinct call that is typically heard only during the breeding season,
and thus, calling activity indicates reproductive activity and not simply migration.
Our sampling was based on detecting calls and therefore coincided with the breeding
season for all species.
We identified and recorded all species in situ. Recorded calls were listened
to again for confirmation using the database created and managed by Davidson
Herpetology (Price and Dorcas 2011). Visual inspections confirmed species presence
when and where possible. If an individual (or individuals) of a species was
detected calling from a PSH, then the species was considered present. We sampled
PSH from late February 2012 to late June 2012. Each site was visited once every
Table I. Study site locations in decimal degrees organized by year of construction. Included is county
of site location, year of site construction, and government-determined identification number (ID #).
This ID Number was the designation used by the researchers to identify sites.
ID # County Year built Latitude (°N) Longitude (°W)
1344 Caswell 2009 36.39833069 79.19750214
2059 Guilford 2009 35.99288940 79.94513702
2276 Guilford 2010 36.05199814 79.91819763
2278 Guilford 2010 36.04610825 79.90554810
2283 Guilford 2010 36.03264999 79.88883972
2284 Guilford 2010 36.03192902 79.88761139
2286 Guilford 2010 36.00239944 79.84303284
2287 Guilford 2010 36.00251007 79.84217834
2288 Guilford 2010 36.00262833 79.84185791
2289 Guilford 2010 36.00308990 79.83764648
2290 Guilford 2010 36.00313187 79.83676147
2487 Guilford 2011 36.00294113 79.91243744
2492 Guilford 2011 36.00217056 79.91074371
2493 Guilford 2011 36.00201035 79.91059875
2494 Guilford 2011 36.00196075 79.91027832
2495 Guilford 2011 36.00175095 79.91001892
2496 Guilford 2011 36.00151062 79.90959167
2500 Guilford 2011 36.00503922 79.9149704
2501 Guilford 2011 36.00566864 79.91606903
2505 Randolph 2011 35.75416183 79.81050110
2532 Alamance 2011 36.13832855 79.51278687
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two weeks from 1 March 2012 to 24 April 2012, and each site was visited once a
week from 30 April 2012 to 28 June 2012, for a total of 12 site visits for each site
throughout the breeding period of 2012. Due to the frequency of site visits, it is
unlikely that any species went undetected at a given site (see Appendix 1).
Our auditory survey based on presence/absence identification utilized the
manual calling surveys (MCS) approach (Wright and Wright 1949). In addition to
presence, we assigned a relative abundance category using the MCS abundance
one, two, three classification system (1 = a single calling individual; 2 = multiple,
distinct individuals; and 3 = multiple, indistinguishable individuals or a chorus;
Dorcas et al. 2009)). If a species was observed visually within 1 m of the bank of
the PSH but not recorded calling, that species was given an MCS number of one.
Explanatory factors
Following Ficetola and De Bernardi (2004), we performed a study that examined
environmental (local-level) factors (Table 2) and isolation or dispersal (regional-
Table 2. Values of local-scale factors that were measured in the study. Preformed scour holes (PSH)
are identified using the number assigned by the NCDOT. Area = PSH surface area (m2), Depth = depth
at center of each PSH (m), Angle = angle in degrees of the incline of the bank of each PSH, Wetland
= presence (1) or absence (0) of an additional man-made drainage area less than 10 m from each
PSH, Soil = presence (1) or absence (0) of soil in each PSH, SubVeg = presence (1) or absence (0)
of submerged terrestrial vegetation in each PSH, Float = presence (1) or absence (0) of floating nonalgal
vegetation in each PSH, Rip = presence (1) or absence (0) of riparian (aquatic) vegetation in
each PSH, Surround = the type of terrestrial vegetation surrounding each PSH (1 = grass, 2 = scrub,
nonwoody vegetation, 3 = woody forest), and Shade = shade covered at each PSH during solar noon
in May (0 = full sun/no shade, 1 = less than 25% shade, 2 = 25–50% shade, 3 = 50–75% shade, 4 =
more than 75% shade). Area was log-transformed for statistical analysis.
PSH Area Depth Angle Wetland Soil SubVeg Float Rip Surround Shade
2284 3.60 0.27 14.93 0 1 1 1 0 1 4
2278 30.55 0.04 1.32 1 0 0 0 0 1 1
2276 12.57 0.58 16.28 0 1 1 1 0 2 1
2283 4.52 0.27 12.53 0 0 0 0 0 3 3
2059 4.00 0.33 18.27 0 0 0 0 0 3 4
2487 37.11 0.17 6.97 1 1 0 1 0 1 2
2492 10.40 0.38 10.79 0 1 0 1 0 1 0
2493 4.91 0.17 7.52 0 0 0 1 0 1 0
2494 6.61 0.19 7.48 0 0 0 0 0 1 1
2495 16.15 0.23 7.66 1 1 0 1 0 1 0
2496 7.07 0.13 4.84 0 0 1 0 0 1 0
2500 16.80 0.13 5.64 1 1 1 0 0 1 2
2501 12.50 0.37 16.49 0 1 1 0 0 1 1
2286 18.86 0.56 12.85 0 1 1 1 1 1 3
2287 13.85 0.13 3.46 0 1 0 0 0 3 3
2288 18.10 0.24 5.74 0 0 0 0 0 3 3
2289 13.20 0.51 14.08 0 0 0 0 0 2 0
2290 19.15 0.27 7.24 1 0 0 1 0 2 1
2505 3.46 0.25 13.27 0 0 0 0 0 1 0
2532 51.70 0.25 11.66 1 0 0 0 0 1 0
1344 11.34 0.20 8.75 1 0 1 1 1 2 2
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level) factors (Table 3) that may explain patterns of anuran diversity in PSH. The
local-level factors were: presence or absence of 1) human-made additional wetland
at the PSH, 2) submerged nonaquatic vegetation (including detritus), 3) floating
non-algal vegetation, 4) riparian vegetation (common riparian species such as cattails),
and 5) soil in PSH (categorized as no soil if the bottom of PSH was rip-rap or
stone), as well as 6) surrounding vegetation, 7) shade percentage, 8) PSH surface
area, 9) depth at center of PSH, and 10) angle of the slope of the bank of the PSH
(Table 2).
Regional or landscape-level factors (see Table 3) include 1) an estimate of the
degree of urbanization, 2) distance from a riparian zone, 3) distance from road,
4) distance to nearest upland forest patch, and 5) distance from nearest PSH.
Impervious cover was chosen as the estimate of urbanization to ensure consistency
for each PSH. Impervious cover increases with urbanization (Pauleit and
Breuste 2011), has been used as an indicator of urbanization (Pauleit and Breuste
2011), and allows for a quantitative comparison of sites. We estimated the percent
of impervious cover surrounding each site at a radius of 1000 m using the
Table 3. Values of regional-scale factors measured in the study. Preformed scour holes (PSH) are
identified using the number assigned by the NCDOT. UTM North, East, and Zone are location data
provided by the NCDOT. County = county each PSH is located in, Road = distance (in meters)
from center of each PSH to the nearest edge of the road, Patch = distance (in meters) from center
of each PSH to the nearest patch of forest, H2O = distance (in meters) from center of each PSH to
the nearest riparian zone, DistPSH = distance (in meters) from center of each PSH to the center of the
nearest PSH, and Urb1000 = percent of impervious cover within a 1000-m radius of each PSH. Road,
Patch, H2O, and DistPSH were all log-transformed for statistical analysis.
UTM UTM UTM
PSH North East Zone County Road Patch H2O DistPSH Urb1000
2284 3988064 600221 17 Guilford 15.70 2.22 29.93 136.13 78.09
2278 3989615 598585 17 Guilford 16.70 17.49 28.05 1221.31 91.16
2276 3990256 597436 17 Guilford 20.60 30.89 417.42 1221.31 73.20
2283 3988140 600107 17 Guilford 8.90 1.00 90.65 136.13 77.92
2059 3983680 595081 17 Guilford 17.00 1.00 29.74 3007.53 52.57
2487 3984830 598022 17 Guilford 18.40 3.61 63.71 171.28 62.51
2492 3984741 598169 17 Guilford 13.00 11.41 103.43 22.06 75.00
2493 3984729 598190 17 Guilford 12.30 16.33 120.48 22.06 75.00
2494 3984715 598209 17 Guilford 11.80 6.91 149.76 24.60 75.00
2495 3984692 598240 17 Guilford 11.40 31.98 189.23 36.86 75.00
2496 3984665 598274 17 Guilford 10.70 75.79 229.61 41.32 75.00
2500 3985052 597787 17 Guilford 23.10 5.12 304.95 41.31 54.32
2501 3985080 597753 17 Guilford 21.40 4.74 266.44 41.31 54.32
2286 3984832 604274 17 Guilford 30.70 1.00 64.73 77.17 66.06
2287 3984842 604352 17 Guilford 26.10 1.00 7.45 30.11 65.89
2288 3984858 604379 17 Guilford 23.80 1.00 25.75 30.11 65.89
2289 3984915 604757 17 Guilford 9.10 16.01 4.47 78.08 63.40
2290 3984919 604838 17 Guilford 9.00 10.28 7.76 78.08 63.40
2505 3957333 607539 17 Randolph 11.50 5.44 15.60 27,389.29 56.15
2532 4000325 633813 17 Alamance 7.00 9.42 15.22 32,744.82 11.14
1344 4029610 661645 17 Caswell 15.30 13.33 60.62 40,302.57 8.45
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most recent data on impervious cover from the National Land Cover Database
(USGS 2006) using ArcMap (ArcGIS version 10.1). Percent of impervious
cover was measured as the number of 30 m x 30 m pixels within 1000 m that
were covered in impervious cover divided by the total number of pixels in each
circle. Pixel size used was the smallest pixel size available for the National Land
Cover Database (USGS 2006). We defined upland forest patches as any patch of
canopy-producing trees that covered a minimum of 450 m2, and riparian zones as
areas surrounding permanent flowing or standing water; these zones include, but
are not limited to, streams, rivers, and lakes. Distance from each PSH to road,
forest patch, riparian zone, and next PSH was determined using Google Earth®
and the most recent satellite image.
Statistical analysis: diversity
To determine which of the local and regional factors were associated with species
diversity, we used a step-wise linear regression model (R version 2.15.1) with
species richness and relative abundance (as estimated by MCS) as the dependent
variable. PSH surface area, distance from riparian zone, distance from upland forest
patch, distance from road, and distance from nearest PSH were log-transformed to
ensure normality. We used BIC criteria to create a model that employed forward/
backward stepwise linear regression to determine which variable should be added
to the model (see Ficetola and De Bernardi 2004 for details).
Results
Species presence
The species richness of the 21 PSH ranged from one to six species (mean = 3
± 1.10 SD, median = 3). One species (Cope’s Gray Treefrog) was detected at all
21 sites, and two species (Fowler’s Toad and the Southern Leopard Frog) were not
detected at any site (Appendix 1).
Species richness model
The best-fit stepwise linear regression model to explain species richness (as
measured using the maximum MCS abundance number for each species) included
urbanization, log surface area of each scour hole, and the presence of riparian vegetation.
This model began with all available explanatory factors minus urbanization
and no interactions to determine which non-urban factors affect diversity. Following
the step-wise regression, urbanization was introduced to the model (Table 4).
Table 4. The stepwise linear regression model for the diversity of anuran species in PSHs. logArea
= log transformed surface area of PSH, RipVeg = the presence of riparian vegetation, and Urb100 =
urbanization at 100-m radius. Adjusted R2 = 0.7003.
Estimate Std. Error t value Pr(>|t|)
Intercept 5.996 1.548 3.873 0.001
logArea 1.487 0.459 3.241 0.005
RipVeg 4.069 1.191 3.416 0.003
Urb100 -0.050 0.013 -3.815 0.001
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Presence of riparian vegetation had the strongest positive effect on amphibian
richness followed by surface area of the PSH. In contrast, urbanization had a significant,
but weaker, negative effect on richness compared to vegetation presence
and area.
Discussion
Preformed scour holes associated with road building may provide habitat for
anuran species and may help maintain some of the regional biodiversity in the
face of urbanization. Our findings are consistent with other studies showing that
stormwater controls can provide habitat for anurans in urban areas. For example
Parris (2006) found 10 species of anurans using stormwater controls for breeding
in Melbourne, Australia, and Birx-Raybuck et al. (2009) showed five species used
stormwater controls for breeding in the western Piedmont of North Carolina. Most
PSHs harbored more than one species during the breeding season (with a mean
of three species), indicating that PSH have features that are attractive to breeding
males of multiple species of anurans.
The suitability of PSHs as breeding habitats appeared to vary among anuran
species. For example, Cope’s Gray Treefrog was found at all sites. Cope’s Gray
Treefrog is a fairly common anuran species that is tolerant of a variety of conditions
at both the local and landscape scales (Brand and Snodgrass 2010, Brand et
al. 2010). Seven of the other 10 species were found at multiple sites, and only three
species were observed at a single site. Of the probable regional pool of anuran species,
only Fowler’s Toad and the Southern Leopard Frog were not observed.
Our predictions concerning the relationship between PSH surface size and anuran
diversity were supported. Overall anuran species diversity was positively related to
PSH area. The presence of riparian vegetation was also positively correlated with anuran
diversity. We expected that larger PSHs with riparian vegetation should support
higher diversity of anurans than smaller habitats with less vegetation (e.g., Ficetola
and De Bernardi, 2004; Parris 2006; Shulse et al. 2010, 2012). Larger sites may
support higher population sizes and thus reduce local extinction. Larger and more
vegetated sites also provide more structural and habitat complexity for breeding and
sustenance that support a wider diversity of species. All the anurans in the study area
are herbivorous until metamorphosis. Many adult anurans use riparian vegetation as
oviposition sites. In addition, Hyla and Pseudacris species use vegetation to avoid
predation and as vertical calling structures so their calls carry over a large area. However,
larger non-PSH sites may also be riskier than smaller sites because large pools
support aquatic predators such as fish (Ficetola and De Bernardi 2004). However, the
PSH in our study are separated from larger water bodies and are ephemeral pools, and
therefore usually do not harbor fish.
Urbanization effects on anuran diversity
Whereas anuran diversity was positively correlated with size and vegetation,
diversity was negatively correlated with degree of urbanization, as we predicted.
However, although significant, urbanization had weaker effects in the model than
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vegetation or area. Urbanization was the only regional factor to remain in the bestfit
regression model. Urbanization was measured as percent of impervious surfaces
and is thus likely an indirect measure of other regional factors such as reduced
connectivity due to upland forest loss and increased impediments to dispersal.
Urbanization may also be associated with local factors such as increased mortality
from air and water pollutants, altered climate (i.e., heat-island effects), and reduced
reproduction due to elevated noise or light pollution that interferes with mating
(Kaiser and Hammers 2009). These results are consistent with previous research
showing that urbanization generally has a negative effect on anuran biodiversity
(Birx-Raybuck et al. 2009, Brand and Snodgrass 2010, Ficetola and De Bernardi
2004, Parris 2006, Scheffers and Paszkowski 2012). For example, Parris (2006)
found that as road cover (or degree of urbanization) increased in proximity to
stormwater controls, anuran biodiversity decreased.
Our results are similar to those found by Parris (2006) in that a model that
includes two local factors and one regional factor best explains the trends in biodiversity.
In fact, the model proposed by Parris (2006) included two of the same
three factors found in our model of anuran biodiversity: surface area of stormwater
control and degree of urbanization as measured by amount of impervious surface
cover. Because our study was correlational, the specific local and regional factors
that affect anuran diversity associated with PSHs cannot be disentangled without
further studies and controlled experiments. Nonetheless, there was strong evidence
that patch-specific factors as well as connectivity affects anuran biodiversity. Thus,
metacommunity theory (Liebold et al. 2004), which incorporates both local and
regional factors and processes may be a good framework to examine anuran biodiversity
in human-dominated environments (Birx-Raybuck et al. 2009, Ficetola and
De Bernardi 2004, Parris 2006).
Stormwater controls and ecological reconciliation
Many anuran species are declining due to habitat loss and other factors, and
the creation of anthropogenic ponds and stormwater controls may mediate,
and possibly halt, some of the loss in biodiversity due to urbanization. Thus, as
advocated by Rosenzweig (2003), anthropogenic habitats can be designed so that
they are compatible with use by a broad array of species. Because similar stormwater
and erosion-control structures are employed by multiple states in the US,
these structures may serve a meaningful ecological purpose as habitats for aquatic
and amphibious species.
Our results suggest that stormwater controls should be designed to be as large
as possible and contain riparian vegetation to promote anuran use of stormwater
controls for breeding. Our results did not ascertain if there is a threshold size for
stormwater controls, a size where biodiversity either increases or declines, as has
been found for wetland areas in general (Ficetola and De Bernardi 2004).
There are limitations of our study. The study was observational and correlational;
thus, the causes that underlie patterns of anuran diversity cannot be understood
without additional studies. This study encompassed only one field season and was
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A.J.B. Jennings and S.H. Faeth
2014 No. 1
limited to 21 sites. Therefore, caution is required in extrapolating to different urban
environments, larger spatial scales, and longer time frames. Also this study did not
address fitness of anurans. Although it appears that PSHs can provide breeding
habitat, and possibly mediate anuran biodiversity loss, our study cannot exclude
the possibility that PSHs act as ecological traps (e.g., Battin 2004). Stormwater
controls in general, and PSHs in particular, need to be examined for fitness effects
before any one type of stormwater control is endorsed to mediate biodiversity loss.
Nonetheless, our study indicates that PSHs may be effective, especially with modifications,
to mitigate anuran diversity loss in urbanizing areas .
Acknowledgments
We thank M. Kalcounis-Ruppell, G. Wasserberg, and two anonymous reviewers for
comments on the manuscript; R. Deustch for statistical assistance; and M. Dorcas, J. Beene,
and S. Price for their anuran expertise. We thank the NCDOT for providing study sites and
D. Hayes, R. Baron, N. Owens, L. Fondario, A. Craven, M. Schwartz, A. Speen, and R. Jennings
for assistance in the field season. UNCG Biology Department and NSF GK 12 grant
DGE-0947982 provided funding for this research.
Literature Cited
Barrett, K., and C. Guyer. 2008. Differential responses of amphibians and reptiles in riparian
and stream habitats to land-use disturbances in western Georgia, USA. Biological
Conservation 141:2290–2300.
Battin, J. 2004. When good animals love bad habitats: Ecological traps and the conservation
of animal populations. Conservation Biology 18:1482–1491.
Birx-Raybuck, D.A., S.J. Price, and M.E. Dorcas. 2009. Pond age and riparian-zone proximity
influence anuran occupancy of urban retention ponds. Urban Ecosystem 13:181–190.
Brand, A.B., and J.W. Snodgrass. 2010. Value of artificial habitats for amphibian reproduction
in altered landscapes. Conservation Biology 24:295–301.
Brand, A.B., J.W. Snodgrass, M.T. Gallagher, R.E. Casey, and R. Van Meter. 2010. Lethal
and sublethal effects of embryonic and larval exposure of Hyla versicolor to stormwater
pond sediments. Archives of Environmental Contamination and Toxicology 58:325–331.
Brazel, A., N. Selover, R. Vose, and G. Heisler. 2000. The tale of two climates: Baltimore
and Phoenix urban LTER sites. Climate Research 15:123–135.
Bunnell, J.F., and R.A. Zampella. 1999. Acid-water anuran pond communities along a regional
forest to agro-urban ecotone. Copeia 1999:614–627.
Chace, J.F., and J.J. Walsh. 2006. Urban effects on native avifauna: A review. Landscape
and Urban Planning 74:46–69.
Delis, P.R., H.R. Mushinsky, and E.D. McCoy. 1996. Decline of some west-central Florida
anuran populations in response to habitat degradation. Biodiversity and Conservation
5:1579–1595.
Dodd, C.K., and L.L. Smith. 2003. Habitat destruction and alteration: Historical trends
and future prospects for amphibians. Pp. 94–112, In R.D. Semlitsch (Ed.) .Amphibian
Conservation. Smithsonian Institution, Washington, DC, USA.
Dorcas, M.E., and J. W. Gibbon. 2008. Frogs and Toads of the Southeast. University of
Georgia Press, Athens, GA.
Urban Naturalist
A.J.B. Jennings and S.H. Faeth
2014 No. 1
12
Dorcas, M.E., S.J. Price, S.C. Walls, and W.J. Barichivich. 2009. Auditory monitoring of
anuran populations. Pp. 281–298, In C.K. Dodd (Ed.). Conservation and Ecology in
Amphibians. Oxford University Press, Oxford, UK. 464 pp.
Faeth, S.H., and T.C. Kane. 1978. Urban biogeography: City parks as islands for Diptera
and Coleoptera. Oecologia 32:127–133.
Faeth, S.H., C. Bang, and S. Saari. 2011. Urban biodiversity: Patterns and mechanisms.
Annals of the New York Academy of Science 1223:69–81.
Ficetola, G.F., and F. De Bernardi. 2004. Amphibians in a human-dominated landscape: The
community structure is related to habitat features and isolation. Biological Conservation
119:219–230.
Gagné, S.A., and L. Fahrig. 2007. Effect of landscape context on anuran communities in
breeding ponds in the National Capital Region, Canada. Landscape Ecology 22:205–215.
Hamer, A.J., and M.J. McDonnell. 2008. Amphibian ecology and conservation in the urbanizing
world: A review. Biological Conservation 141:2432–2449.
Hamer, A.J., and M.J. Mcdonnell. 2009. The response of herpetofauna to urbanization:
Inferring patterns of persistence from wildlife databases. Austral Ecology 35:568–580.
Hecner, S.J., and R.T. M’Closkey. 1997. Spatial scale and determination of species status
of the Green Frog. Conservation Biology 11:670–682.
Kaiser, K., and J. Hammers. 2009. The effect of anthropogenic noise on male advertisement
call rate in the neotropical treefrog Dendropsophus triangulum. Behaviour
146:1053–1069.
Kaye, J.P., P.M. Groffman, N.B. Grimm, L.A. Baker, and R.V. Pouyat. 2006. A distinct
urban biogeochemistry? Trends in Ecology and Evolution 21:192–199.
Knutson, M.G., J.R. Sauer, D.A. Olsen, M.J. Mossman, L.M. Hemesath, and M.J. Lannoo.
1999. Effects of landscape composition and wetland fragmentation on frog and toad
abundance and species richness in Iowa and Wisconsin, USA. Conservation Biology
13:1437–1446.
Leibold, M.A., M. Holyoak, N. Mouquet, P. Amarasekare, J. M. Chase, M.F. Hoopes, R.D.
Holt, J.B. Shurin, R. Law, D. Tilman, M. Loreau, and A. Gonzalez. 2004. The metacommunity
concept: A framework for multi-scale community ecology. Ecology Letters
7:601–613.
Lewis, D.B., J.P. Kaye, C. Gries, A.P. Kinzig, and C.L. Redman. 2006. Agrarian legacy in
soil-nutrient pools of urbanizing arid lands. Global Change Biology 12:703–709.
Lips, K.R., J. Diffendorfer, J.R. Mendelson III, and M.W. Sears. 2008. Riding the wave:
Reconciling the roles of disease and climate change in amphibian declines. PLoS Biology
6(3):e72.
McIntyre, N.E., K. Knowles-Yanez, and D. Hope. 2000. Urban ecology as an interdisciplinary
field: Differences in the use of “urban” between the social and natural sciences.
Urban Ecosystem 4:5–24.
McKinney, M.L. 2006. Urbanization as a major cause of biotic homogenization. Biological
Conservation 127:247–260.
McKinney, M.L. 2008. Effects of urbanization on species richness: A review of plants and
animals. Urban Ecosystem 11:161–176.
Mitchell, J.C., R.E.J. Brown, and B. Bartholomew. 2008. Urban Herpetology. Society for
the Study of Amphibians and Reptiles. Salt Lake City, UT, USA. 608 pp.
North Carolina Department of Transportation (NCDOT). 2008. Stormwater best management
practices toolbox. NCDOT Hydraulics Unit, Raleigh, NC, USA.
Urban Naturalist
13
A.J.B. Jennings and S.H. Faeth
2014 No. 1
Ostergaard, E.C., K.O. Richter, and S.D. West. 2008. Amphibian use of stormwater ponds in
the Puget lowlands of Washington, USA. Pp. 259–270, In J.C. Mitchell, R.E.J. Brown,
and B. Bartholomew (Eds.). Urban Herpetology. Society for the Study of Amphibians
and Reptiles, Salt Lake City, UT, USA. 608 pp.
Parris, K.M. 2006. Urban amphibian assemblages as metacommunities. Journal of Animal
Ecology 75:757–764.
Pauleit, S., and J.H. Breuste. 2011. Land-use and surface-cover as urban ecological indicators.
Pp. 19–30, In J. Niemela (Ed.). Urban Ecology. Oxford University Press, Inc., New
York, NY, USA. 392 pp.
Price, S.J., and M.E. Dorcas. 2011. The Carolina Herp Atlas: An online, citizen-science
approach to document amphibian and reptile occurrences. Herpetological Conservation
and Biology 6:287–296.
Raupp, M.J., P.M. Shrewsbury, and D.A. Herms. 2010. Ecology of herbivorous arthropods
in urban landscapes. Annual Review of Entomology 55:19–38.
Rosenzweig, M.L. 2003. Reconciliation ecology and the future of species diversity. Oryx
37:194–205.
Scheffers, B.R., and C.A. Paszkowski. 2012. The effects of urbanization on North American
amphibian species: Identifying new directions for urban conservation. Urban Ecosystem
15:133–147.
Semlitsch, R.D., and J.R. Bodie. 2003. Biological criteria for buffer zones around wetlands
and riparian habitats for amphibians and reptiles. Conservation Biology 17:1219–1228.
Shulse, C.D, R.D.Semlitsch, K.M. Trauth and A.D. Williams. 2010. Influences of design
and landscape-placement parameters on amphibian abundance in constructed wetlands.
Wetlands 30:915–928.
Shulse, C.D, R.D. Semlitsch, K.M. Trauth and J.E. Gardner. 2012. Testing wetland features
to increase amphibian reproductive success and species richness for mitigation and restoration.
Ecological Applications 22:1675–1688.
Shochat, E., P.S. Warren, S.H. Faeth, N.E. McIntyre, and D. Hope. 2006. From patterns
to emerging processes in mechanistic urban ecology. Trends in Ecology and Evolution
21:186–191.
United Nations Population Division (UN). 2012. World urbanization prospects. UN Department
of Economic and Social Affairs, New York, NY, USA.
United States Geological Survey (USGS). 2006. Multi-resolution land characteristics
consortium (MRLC). Available online at http://www.mrlc.gov/index.php. Accessed 23
January 2012.
van der Ree, R., J.A.G. Jaeger, E.A. van der Grift, and A.P. Clevenger. 2011. Effects of
roads and traffic on wildlife populations and landscape function: Road ecology is moving
toward larger scales. Ecology and Society 16:48–48.
Walsh, C.J., A.H. Roy, J.W. Feminella, P.D. Cottingham, P.M. Groffman, and R.P. Morgan
III. 2005. The urban stream syndrome: Current knowledge and the search for a cure.
Journal of the North American Benthological Society 24:706–723.
Wenguang, Z., H. Yuanman, H. Jinchu, C. Yu, Z. Jing, and L. Miao. 2008. Impacts of
land-use change on mammal diversity in the upper reaches of Minjiang River, China:
Implications for biodiversity conservation planning. Landscape and Urban Planning
85:195–204.
Wright, A.H., and A.A. Wright. 1949. Handbook of Frogs and Toads of the United States
and Canada, 3rd Edition. Comstock Publishing Associates, Ithaca, NY, USA. 248 pp.
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Appendix 1. Species presence and activity level for each site for each sampling period in 2012. Preformed scour holes (PSH) are identified using the number
assigned by the NCDOT. Activity level is shown using the 1, 2, 3 MCS abundance level (1 = single individual calling/visual of adult/visual of distinct
egg-mass, 2 = multiple distinguishable individuals calling, 3 = multiple indistinguishable individuals calling) Hc = Hyla chrysoscelis, Pf = Pseudacris feriarum,
La = Lithobates catesbeianus, Lc = Lithobates clamitans, Pc = Pseudacris crucifer, Ba = Anaxrynus americanus, Gc = Gastrophyrne carolinensis,
Lp = Lithobates palustris, Hv = Hyla versicolor, Ac = Acris crepitans, Bf = Anaxrynus fowleri, and Ls = Lithobates sphenocephalus.
Sampling period
PSH March 1–7 March 21–30 April 11–24 April 30 – May 3 May 7–10 May 14–17
2284
2278 Pf (1), Pc (1) Pc (2)
2276 Pf (1), Pc (1) Hc (2), La (1)
2283 Pf (2) Hc (2), La (1) Hc (1)
2059
2487 Pf (2) Lc (1) La (1), Lc (1) La (1), Lc (1) Hc (3), La (1), Lc (1)
2492 Lc (1) La (1) La (1), Lc (1) Lc (1) Hc (2), Lc (1)
2493 Pf (1) Lc (1) Pf (2), Hc (2)
2494 Lc (1) Lc (1) Hc (1) Hc (3), Lc (1)
2495 Pf (1) La (1) Hc (1) Hc (2), La (1)
2496 Hc (2)
2500 Pc (3) Hc (2), Lc (1) Lc (1) Hc (3), Lc (1)
2501 Pf (1) Pc (3) Pc (2) Hc (1), Lc (1) Hc (3), Lc (2)
2286 Pf (2), Pc (3) Aa (1) Gc (1), Hc (3)
2287 Pf (3) Hc (1) Pf (2), Hc (3)
2288 Pf (1) Pf (1)
2289 Lc (1)
2290 Pf (1) Pc (3) Hc (2) Hc (2)
2505 Pc (1), Aa (1) Hc (3) Lc (1) Hc (3)
2532 Pf (1), Pc (1) Pf (1), Pc (3), Ac (1), La (1) Ac (1), Hc (3), La (1) Hc (3), La (1) Ac (3), Hc (3)
1344 Pf (1) Pf (3), Pc (3) Hc (3), Hv (2) Pc (1), Hc (3), Hv (3)
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Sampling period
PSH May 21–24 May 28–31 June 4–7 June 11–14 June 18–21 June 25–28
2284 Hc (3), La (1) Hc (3), Lc (1) Hc (1), La (1)
2278 Hc (2) Hc (2)
2276 Hc (2) La (1) Hc (2), Lc (1) Hc (1), Lc (1) Lc (1)
2283 Hc (3) Hc (2), La (1), Lp (1) La (1) Hc (3) La (1)
2059 Hc (3) Hc (2), La (1) Hc (2), La (1) Hc (1)
2487 Hc (3), Lc (1) Hc (2), Lc (1) Lc (1) Hc (1*) Lc (1) La (1), Lc (1)
2492 Hc (2), Lc (2) Hc (2), Lc (2) Lc (1) Hc (1*) La (1), Lc (1) La (1)
2493 Hc (2) Hc (2) Hc (1*) La (1)
2494 Hc (3) Hc (1*) Hc (1)
2495 Hc (2) Hc (2) Hc (1*) Lc (1)
2496
2500 Hc (3), Lc (2) Hc (3), La (1), Lc (1) La (1), Lc (1) Hc (1*) Lc (1) La (1), Lc (1)
2501 Hc (3), Lc (1) Hc (1), Lc (1) Lc (1) Lc (1*) Lc (3) Lc (1)
2286 Gc (3), Hc (3) Hc (1)
2287 Hc (2)
2288 Hc (2) Hc (2) Hc (1)
2289 Lc (1) Gc (3), Hc (2), Lc (1) Lc (1) Gc (2), Lc (1) Gc (1), Lc (1) Lc (1)
2290 Lc (1) Lc (1) Hc (3) Hc (2), Lc (1) Hc (2)
2505 Hc (2) Hc (2) Dry Dry
2532 Ac (1), Hc (1) Ac (2) Lc (1) Ac (3), Hc (2), La (1) Hc (1)
1344 Hc (1)