Content uploaded by Travis J. Ryan
Author content
All content in this area was uploaded by Travis J. Ryan on Feb 28, 2019
Content may be subject to copyright.
Urban
Naturalist
No. 21 2019
Diet of Trachemys scripta (Red-
eared Slider) and Graptemys
geographica (Common Map Turtle)
in an Urban Landscape
Jessica D. Stephens and Travis J. Ryan
The Urban Naturalist . . .
♦ A peer-reviewed and edited interdisciplinary natural history science journal with a
global focus on urban areas ( ISSN 2328-8965 [online]).
♦ Featuring research articles, notes, and research summaries on terrestrial, fresh-water,
and marine organisms, and their habitats. The journal's versatility also extends to pub-
lishing symposium proceedings or other collections of related papers as special issues.
♦ Focusing on field ecology, biology, behavior, biogeography, taxonomy, evolution,
anatomy, physiology, geology, and related elds. Manuscripts on genetics, molecular
biology, anthropology, etc., are welcome, especially if they provide natural history in-
sights that are of interest to eld scientists.
♦ Offers authors the option of publishing large maps, data tables, audio and video clips,
and even powerpoint presentations as online supplemental les.
♦ Proposals for Special Issues are welcome.
♦ Arrangements for indexing through a wide range of services, including Web of
Knowledge (includes Web of Science, Current Contents Connect, Biological Ab-
stracts, BIOSIS Citation Index, BIOSIS Previews, CAB Abstracts), PROQUEST,
SCOPUS, BIOBASE, EMBiology, Current Awareness in Biological Sciences
(CABS), EBSCOHost, VINITI (All-Russian Institute of Scientific and Technical
Information), FFAB (Fish, Fisheries, and Aquatic Biodiversity Worldwide), WOW
(Waters and Oceans Worldwide), and Zoological Record, are being pursued.
♦ The journal staff is pleased to discuss ideas for manuscripts and to assist during all
stages of manuscript preparation. The journal has a mandatory page charge to help
defray a portion of the costs of publishing the manuscript. Instructions for Authors are
available online on the journal’s website (www.eaglehill.us/urna).
♦ Co-published with the Northeastern Naturalist (Print ISSN # 1092-6194, Online ISSN
# 1938-5307), the Southeastern Naturalist (Print ISSN # 1528-7092, Online ISSN #
1938-5412), and Caribbean Naturalist (ISSN # 2326-7119 [online]). Together these
journals provide an integrated publishing and research resource for all of eastern main-
land North America and the offshore waters and islands from Canada south to the Ca-
ribbean region, as well as urban areas worldwide.
♦ Available online in full-text version on the journal's website (www.eaglehill.us/urna).
Arrangements for inclusion in the BioOne database (www.bioone.org, a collaborative
effort of Allen Press, AIBS, et al.), EBSCOhost product line, and the Proquest Informa-
tion and Learning databases (www.il.proquest.com) are being pursued.
♦ May be ordered through any major subscription service.
Cover Photograph: Basking adult Trachemys scripta (Red-eared box turtle). Photograph © Todd
Pierson.
URBAN NATURALIST
Board of Editors
Myla Aronson, Rutgers University, New Brunswick, NJ, USA
Joscha Beninde, University of Trier, Trier, Germany
Andrea Larissa Boesing, Universidade Estadual de Londrina, Parana, Brazil
Sabina Caula, Universidad de Carabobo, Naguanagua, Venezuela
Sylvio Codella, Kean University, Union New Jersey, USA
Julie Craves, University of Michigan-Dearborn, Dearborn, MI, USA
Ana Faggi, Universidad de Flores/CONICET, Buenos Aires, Argentina
Leonie Fischer, Technical University of Berlin, Berlin, Germany
Keith Goldfarb, GoldRush Science Services, Steuben, ME, USA ... Editor-in-Chief
Chad Johnson, Arizona State University, Glendale, AZ, USA
Kirsten Jung, University of Ulm, Ulm, Germany
Madhusudan Katti, North Carolina State University, Raliegh, NC, USA
Erik Kiviat, Hudsonia, Bard College, Annandale-on-Hudson, NY, USA
Sonja Knapp, Helmholtz Centre for Environmental Research–UFZ, Halle (Saale), Germany ...
Managing Editor
David Krauss, City University of New York, New York, NY, USA
Mark Laska, Great Ecology, San Diego, CA, USA
Zdenka Lososova, Masaryk University, Brno, Czechia
Joerg-Henner Lotze, Eagle Hill Institute, Steuben, ME, USA ... Publisher
Kristi MacDonald, Hudsonia, Bard College, Annandale-on-Hudson, NY, USA
Ian MacGregor-Fors, Insituto de Ecología Mexico, Veracruz, Mexico
Tibor Magura, University of Debrecen, Debrecen, Hungary
Brooke Maslo, Rutgers University, New Brunswick, NJ, USA
Mark McDonnell, Royal Botanic Gardens Victoria and University of Melbourne, Melbourne,
Australia
Mike McKinney, University of Tennessee, Knoxville, TN, USA
Desirée Narango, City University of New York, New York, NY, USA
Mitchell Pavao-Zuckerman, University of Arizona, Tucson, Arizona, USA
Joseph Rachlin, Lehman College, City University of New York, New York, NY, USA
Travis Ryan, Center for Urban Ecology, Butler University, Indianapolis, IN, USA
Michael Strohbach, Technische Universität Braunschweig, Institute of Geoecology, Braunsch-
weig, Germany
Katalin Szlavecz, Johns Hopkins University, Baltimore, MD, USA
Paige Warren, University of Massachusetts, Amherst, MA, USA
Jill Weber, Eagle Hill Institute, Steuben, ME, USA ... Production Editor
Alan Yeakley, Portland State University, Portland, OR, USA
Iriana Zuria, Universidad Autónoma del Estado de Hidalgo, Hidalgo, Mexico
The Urban Naturalist (ISSN # 2328-8965) is published by the Eagle Hill Institute, PO Box 9, 59 Eagle Hill Road, Steuben, ME
04680-0009. Phone 207-546-2821, FAX 207-546-3042. E-mail: office@eaglehill.us. Webpage: www.eaglehill.us/urna. Copyright
© 2019, all rights reserved. Periodical postage paid in Steuben, ME and additional mailing offices. Special issue proposals are
welcome. On-line secure subscription ordering: rate per year - $20 regular, $15 students, $80 organizations. Authors: submission
guidelines are available at www.eaglehill.us/una. Co-published journals: The Northeastern Naturalist (ISSN 1092-6194 [print],
ISSN 1938-5307 [online]), the Southeastern Naturalist (ISSN 1528-7092 [print], ISSN 1938-5412 [online]), and the Caribbean
Naturalist (ISSN 2326-7119), journals with separate Boards of Editors. The Eagle Hill Institute is a tax exempt 501(c)(3) nonprofit
corporation of the State of Maine (Federal ID # 010379899).
Urban Naturalist
1
J.D. Stephens and T. J. Ryan
2019 No. 21
URBAN NATURALIST
2019 No. 21:1–11
Diet of Trachemys scripta (Red-eared Slider) and Graptemys
geographica (Common Map Turtle) in an Urban Landscape
Jessica D. Stephens1,2 and Travis J. Ryan1,*
Abstract - Urban environments present many challenges for aquatic turtle species. Here,
we investigated whether the diets of Trachemys scripta (Red-eared Slider) and Graptemys
geographica (Common Map Turtle) may help explain the spatial ecology of these 2 species
in a pair of constructed aquatic habitats in Indianapolis, IN, USA. We conducted stomach
ushings on 43 turtles from 2 sites (Central Canal, n = 33; IMA Lake, n = 10). Common
Map Turtles from the Central Canal (n = 27) consumed mostly mollusks and craysh,
which comprised ~86% of the volume of stomach contents. We captured no adult Common
Map Turtles at IMA Lake, likely due to the lack of mollusks within this habitat. There was
considerable variability in the diet of Red-eared Sliders between the 2 habitats, with 98.8%
of the diet contents comprised of plant material in the Central Canal (n = 6) and only 67%
plant material in IMA Lake (n = 10). This difference in diet may have been due to the lower
abundance of vegetation found in IMA Lake compared to the Central Canal, or possibly a
diversication of diet in response to decreased interspecic competition in IMA Lake. Diet
comparison between species in the Central Canal shows almost no overlap, which may
partially explain habitat association and movement differences between the 2 species docu-
mented in a previous study. The descriptions of Red-eared Slider and Common Map Turtle
diets presented here are the rst to be described from an explicitly urban landscape. Further
understanding of the ecology of these species in urban habitats can aid city planners and
managers with the goal of maintaining species diversity in urban landscapes.
Introduction
Aquatic systems are extremely sensitive to urbanization. These systems are
challenged by surface runoff (via impervious infrastructure), bank erosion, and
changes in nutrient loads, while also supplying cities with potable water (Faulkner
2004, Paul and Meyer 2001). These apparent threats to aquatic ecosystems have
prompted rigorous research in riparian systems examining microbial (Gibson et
al. 1998, Zuma 2010), algal (Patrick 1973), and invertebrate (Thorne et al. 2000,
Wright et al. 1995) responses as indicators of water quality and measures of biodi-
versity declines. Underrepresented in riparian urban ecology, however, is research
examining community interactions, population dynamics, habitat distribution, and
behavioral ecology of larger-bodied taxa (discussed in Walsh et al. 2005, but see
Mitchell et al. 2008). This gap in understanding is dismaying given that larger
animals are thought to be more susceptible to the negative effects of urbanization
because of their larger ranges (Ryan et al. 2008, 2014), smaller population sizes
(Woodroffe and Ginsberg 1998), and road fatalities (Steen and Gibbs 2004).
1Department of Biological Sciences and Center for Urban Ecology, Butler University, 4600
Sunset Avenue, Indianapolis, IN 46208, USA. 2Atlanta Botanical Garden, Atlanta, GA
30309, USA. *Corresponding author - tryan@butler.edu.
Manuscript Editor: Iriana Zuria
Urban Naturalist
J.D. Stephens and T. J. Ryan
2019 No. 21
2
In recent years, ecological investigations of freshwater turtle responses to ur-
banization have provided new insight. These studies have documented skewed
sex ratios resulting from road mortality (Gibbs and Steen 2005), changes in nest
distribution (Marchand and Litvaitis 2004a), and non-random spatial distribution
along aquatic gradients with varying degrees of urbanization (Harden et al. 2009,
Marchand and Litvaitis 2004b). Similar patterns have been detected in turtles within
human-made habitats located in Indianapolis, IN, USA. Ryan et al. (2008) noted
non-random habitat association and hibernacula selection across the Central Canal
within Indianapolis for both Trachemys scripta elegans Wied-Neuwied (Red-eared
Sliders) and Graptemys geographica Le Sueur (Common Map Turtles). In addition,
there were differences in spatial ecology between the 2 species, with females of
these species exhibiting similar distances for daily movements, although the female
Common Map Turtles had signicantly larger home ranges. Furthermore, Conner et
al. (2005) noted a difference in the relative abundance of these species in the Central
Canal and a human-made lake located ~165 m away, with Common Map Turtles the
most abundant species in the canal and Red-eared Sliders the most abundant species
in the lake.
Although these differences in movement and relative abundance may be at-
tributed to a variety of factors, chief among them may be contrasting feeding
preferences between the 2 species (Conner et al. 2005, Ryan et al. 2008). In par-
ticular, the Central Canal supports a more robust population of several aquatic snail
species and aquatic vegetation than the lake habitat, potentially inuencing turtle
assemblages (Conner et al. 2005, Ryan et al. 2008). Previous studies of chelonian
diets have suggested that food preference can impact species’ habitat selection (Hart
1983, Plummer and Farrar 1981) and can inuence how species respond to habitat
alteration (Lindeman 2013, Richards-Dimitrie et al. 2013). Given habitat variability
in prey items, our aim in this study was to describe the diets of Red-eared Sliders
and Common Map Turtles in Indianapolis, IN, across these 2 human-made aquatic
habitats in the context of the hypothesis presented in Conner et al. (2005) and Ryan
et al. (2008), that food availability may be a contributing factor inuencing differ-
ences in habitat association, movement, and turtle assemblages.
Methods
Study area
We conducted our fieldwork at 2 sites in the northwest corner of Marion
County (Fig. 1), which is home to Indiana’s largest city, Indianapolis, and is in the
top 2% of most populated counties in the US (human-population density = 857
inhabitants/km2; US Census 2018). The Central Canal is a human-made water-
way created in the 1830s, originating at the White River and extending 11.2 km
before it enters a water-treatment facility. The Central Canal provides the city of
Indianapolis with ~60% of its annual water use, and therefore, efforts are made to
control water level, flow rate, vegetation, and debris. The banks of the canal vary
considerably, with turf grass, riprap, native plantings, and forest edge as the most
common groundcovers. The canal is no more than 25 m wide and 2 m deep and is
Urban Naturalist
3
J.D. Stephens and T. J. Ryan
2019 No. 21
bordered by a habitat matrix composed of commercial, residential, and recreation-
al areas (Ryan et al. 2008, 2014).
The Virginia B. Fairbanks Art and Nature Park, owned by the Indianapolis
Museum of Art (IMA), is adjacent to the Central Canal. It comprises 40.5 ha of
woodlands, lake, and mown lawn ~30 m from the White River on the northern edge
and 165 m from the Central Canal on the southern edge. The park was an agricul-
tural eld in the 1920s and was later converted into a gravel pit used to excavate
material for the construction of an interstate in the 1960s. The resulting borrow
pit was then converted into IMA Lake, which is roughly 14.7 ha in size with a
maximum depth of more than 15 m. Narrow strips of wooded areas surround the
lake along most of its shoreline. There has been recent effort to inventory taxa and
promote reestablishment and restoration of native species (Dolan et al. 2011).
Turtle capture and diet assessment
Although there are 6 species of turtles in the Central Canal and IMA Lake (Con-
ner et al. 2005), we conducted diet assessments on 2 of the largest and most com-
mon species, the Common Map Turtle and the Red-eared Slider. We captured turtles
used for this study between July and August 2004 with aquatic hoop traps (76.1-
cm–diameter hoops, 30 cm x 30 cm coated nylon mesh with a funnel at one end
and a closed bag at the other) baited with sardines as part of a co-occurring study of
population and community ecology in both the canal and lake habitats; see Conner
et al. (2005) for additional details regarding trapping. The turtle assemblages within
Figure 1. Urban-land use in northwest corner of Marion County, Indianapolis, IN, USA.
Turtles were collected along the Central Canal and Indianapolis Museum of Art (IMA) Lake.
Urban Naturalist
J.D. Stephens and T. J. Ryan
2019 No. 21
4
these habitats are described in further detail in earlier papers (Conner et al. 2005;
Peterman and Ryan 2009; Ryan et al. 2008, 2014). We opened sardine cans <1 cm to
ensure that turtles would not ingest the bait and skew analyses of stomach contents.
We checked traps daily, refreshed bait every few days, and relocated traps weekly.
Although the sampling period represented only a portion of the active period of
Red-eared Sliders and Common Map Turtles, previous diet studies have relied on a
similar temporal range (e.g., Demuth and Buhlmann 1997), and the diet of female
Common Map Turtles seems to vary little across a wider range of the active period
(Richards-Dimitrie et al. 2013).
Turtles collected from traps were immediately taken to the lab to be measured and
marked (see Cagle 1939), and we placed those to be used for the stomach-ushing
procedure (≥15 cm in carapace length) in a cold room (~2 °C) in order to slow di-
gestion and allow for easier manipulation (Ford and Moll 2004). Common Map
Turtles demonstrate strong sexual size dimorphism (Lindeman 2013); thus, only
females were large enough to be included in our analysis. We followed the procedure
described by Legler (1977) to ush the stomach contents of collected turtles. This
procedure has been successful in a number of studies on diets (Fields et al. 2003,
Legler and Sullivan 1979) with a very low risk of harm or death (Legler 1977, but see
Lindeman 2006). We returned all turtles to their collection sites within 48 h of cap-
ture. We collected stomach contents in a 0.5-mm–mesh sieve and preserved them in
70% ethanol. We examined stomach contents under a dissecting microscope to iden-
tify food items to the lowest taxonomic level possible. Plant material was difcult to
distinguish, except for Lemna (duckweed), therefore we used plant-anatomy catego-
ries (e.g., owers, seeds, bark) for all plant material other than duckweed.
We used frequency of occurrence (% FO) for each identication level to describe
diets, which is presented as the number of turtles that contained a given item (Bow-
en 1983). We also measured the abundance of each food item in diet by measuring
the total volume of each diet item using water displacement for all samples from
each site/species divided by total volume across those samples. We determined
diet-taxon richness for each location and turtle species. We used the vegan package
(Oksanen et al. 2010) in R v2.6.2 statistical software environment (R Development
Core Team 2008) to calculate diversity of prey taxa in each sample using the Simp-
son (D') and Shannon diversity (H') indices, which account for the number of taxa
and abundance of each species. We calculated Horn–Morisita dissimilarity indices
in the vegan package (Oksanen et al. 2010) to compare how similar the diets were
between the same species across location and different species within location. The
Horn–Morisita dissimilarity index varies between 0 and 1, with values close to 1
indicating no overlap in diet and values close to 0 indicating no difference in diet.
We chose this index over others because the Horn-Morisita dissimilarity index is
better suited to handle differences in sample sizes and diversity (Wolda 1981).
Results
We obtained stomach contents from 43 turtles from the 2 sites (Central Canal,
n = 33; IMA Lake, n = 10). We captured a total of 6 Red-eared Sliders from the
Urban Naturalist
5
J.D. Stephens and T. J. Ryan
2019 No. 21
Central Canal and 10 from IMA Lake, while all the Common Map Turtles (n = 27)
were from the Central Canal. We captured only juvenile Common Map Turtles at
IMA Lake, which were not of sufcient size to conduct stomach ushings. The
average carapace length of Common Map Turtles and Red-eared Sliders was 160.8
mm and 133.4 mm, respectively.
Stomach contents displayed a wide variety of prey, comprising 7 phyla and 5
classes. We were also able to identify taxa belonging to 6 orders, 4 families, 2 gen-
era, and 1 species (Table 1). Two-thirds of Common Map Turtle samples from the
Central Canal contained snails (Gastropoda), whereas we found no snails within
the stomach contents of Red-eared Sliders in either the Central Canal or IMA Lake.
Red-eared Sliders consumed large amounts of plant material, with 100% of indi-
viduals in the Central Canal and 60% in IMA Lake consuming plants. Although
Table 1. Stomach contents of Common Map Turtles and Red-eared Sliders from the Central Canal
and IMA Lake, Indianapolis, IN. Only Common Map Turtle juveniles were captured in IMA Lake,
and therefore, were not of sufcient size to conduct stomach ushings. Sample size is indicated by n;
%FO is the percent frequency of occurrence of each respective taxon.
Central Canal IMA Lake
Common Map Red-eared Red-eared
Turtle (n = 27) Slider (n = 6) Slider (n = 10)
Prey taxon n %FO n %FO n %FO
Plantae
Total plant material 8 30 6 100 6 60
Duckweed 4 15 3 50 0 0
Flowers 0 0 2 33 0 0
Seeds 0 0 0 0 3 30
Bark 0 0 0 0 1 10
Animalia
Gastropoda (snails) 18 67 0 0 0 0
Decapoda
Cambaridae (craysh) 8 30 2 33 0 0
Odonata
Total Anisoptera 0 0 2 33 0 0
Larvae 0 0 1 17 0 0
Adult dragonies 2 7 1 17 1 10
Zygoptera nymphs 1 4 0 0 0 0
Nematoda 2 7 1 17 7 70
Arachnida (spiders) 2 7 0 0 0 0
Annelid (Hirudinea) 1 4 0 0 0 0
Hemiptera (Corixidae) 1 4 0 0 0 0
Diptera (Culicidae larvae) 5 19 0 0 0 0
Ephemeroptera (Baetidae) 3 11 0 0 0 0
Coleoptera (Popillia japonica) 2 7 0 0 5 50
Osteichthyes 0 0 0 0 1 10
Styrofoam 0 0 1 17 0 0
Unidentiable 4 15 0 0 1 10
Unidentiable animal 2 7 0 0 2 20
Urban Naturalist
J.D. Stephens and T. J. Ryan
2019 No. 21
6
some Common Map Turtle samples contained vegetable matter, it may have been
coincidental by-catch, as it was exclusively duckweed, a small, surface-oating
plant. The samples from Red-eared Sliders contained not only duckweed (in canal
samples), but also structures from other plant species.
Common Map Turtles consumed 92% of the total taxonomic groups (not in-
cluding unidentiable and styrofoam categories) identied in this study, giving a
species richness value of 11 (Table 1). The species richness of Red-eared Sliders
across both the IMA Lake and Central Canal was 6 (50% of the total taxonomic
groups identied). More specically, prey taxon richness values for Red-eared Slid-
ers at IMA Lake and Central Canal were 4 and 5, respectively. It should be noted
that species richness can be inuenced by sample size, and therefore the difference
in taxon richness may be explained in part by the higher capture-frequency of
Common Map Turtles. The Shannon index value was accordingly higher for Com-
mon Map Turtles (H' = 0.721) than for Red-eared Sliders (H' = 0.088) in the same
habitat. However, H' = 1.83 for Red-eared Sliders found in IMA Lake, indicating
a much higher dietary diversity than in the Central Canal. The results were similar
using the Simpson index values of 0.331, 0.029, 0.511 for Common Map Turtles,
Central Canal Red-eared Sliders, and IMA Lake Red-eared Sliders, respectively.
Most of stomach-content volume consisted of plant material (99%) for Red-
eared Sliders in the Central Canal (Fig. 2). Plant material made up < 1% of the total
stomach contents in Common Map Turtles within the same habitat. Additionally,
Figure 2. Percent abundance of total stomach contents of the most abundant taxa listed in
the diet of Common Map Turtles (Gg) and Red-eared Sliders (Ts) from the Central Canal
and IMA Lake, Indianapolis, IN, USA. “Other” includes all taxa, other than those listed
here, from Table 1.
Urban Naturalist
7
J.D. Stephens and T. J. Ryan
2019 No. 21
the Common Map Turtle diet was primarily composed of snails (Gastropoda; 81%),
with Red-eared Sliders showing no consumption of this prey in either habitat. The
Horn–Morisita index value was 0.989 between Common Map Turtles and Red-
eared Sliders in the Central Canal. This nding indicates very little dietary overlap
between the 2 species. Comparisons of Red-eared Sliders between the 2 habitat
types show similar preferences, as the Horn–Morisita index value was 0.085.
Discussion
We were unable to capture Common Map Turtles at IMA Lake that were of suf-
cient size (carapace length >15 cm) to conduct stomach ushing (see also Conner
et al. 2005), therefore we could not make diet comparisons between the 2 habitats
for this species. However, the stomach contents of Common Map Turtles from
Central Canal indicate a predominately molluscivore diet, which is consistent with
other diet studies for this species (Gordon and MacColluch 1980; Lindeman 2006,
2013; Richards-Dimitrie et al. 2013; Vogt 1981; White and Moll 1992). The lack
of adult Common Map Turtles at IMA Lake may be attributed to the relatively low
abundance of snails in this habitat (T.J. Ryan, pers. observ.). The Central Canal
supports a robust population of several aquatic snail species; IMA Lake lacks these
populations (Conner et al. 2005; T.J. Ryan, pers. observ.). The absence of snails
may be a result of the characteristics of this type of human-made aquatic habitat.
Freshwater snails typically prefer lake bottoms covered with leaf litter and other
plant detritus (Dillon 2000, Spyra 2010). IMA Lake, however, is a converted gravel
pit with a deep, rock basin and steep-banked slopes. Our results, together with the
lack of adult Common Map Turtles at IMA Lake (Conner et al. 2005), indicate that
the difference in abundance of Common Map Turtles between the 2 habitats may
be attributed to preferred food availability.
Common Map Turtles in the Central Canal preyed on a high diversity of prey
items besides mollusks, especially compared to Red-eared Sliders in that habitat.
Specically, ~30% of Common Map Turtles captured consumed decapods (i.e.,
craysh), though they made up only 5.5% of total prey volume. This nding is not
unusual, as Common Map Turtles, while mollusk specialists, have also been known
to feed on craysh (Ernst and Lovich 2009, Lagler 1943, Penn 1950). Excluding
unidentiable material, all other items combined made up the remaining 2% of total
prey contents, most of which may have been consumed incidentally. The continued
presence of Common Map Turtles within the urban landscape appears to be largely
dependent on the fact that the biota of the Central Canal, despite its anthropogenic
origins, approximates that of more natural habitats, like the nearby White River,
which is also inhabited by Common Map Turtles (T.J. Ryan, pers. observ.).
Despite the wide breadth of food items available in the Central Canal, it is
interesting to note that Red-eared Sliders were specializing on vegetation. Vegeta-
tion accounted for 98.8% volume and occurred in all individuals sampled. In more
natural settings, Red-eared Sliders tend to be opportunistic omnivores, consuming
vegetation and soft-bodied insects (Ernst and Lovich 2009, Minton 2001, Parmenter
and Avery 1980). However, changes in diet are well documented for this species,
Urban Naturalist
J.D. Stephens and T. J. Ryan
2019 No. 21
8
whereby juvenile Red-eared Sliders tend to have a more carnivorous diet with a
shift towards herbivory coming with maturation (Clark and Gibbons 1969, Hart
1983, Marchand and Litvaitis 2004b). To prevent possible harm to small turtles, we
did not conduct stomach-ushing procedures on juveniles, which may have biased
our analyses relative to Red-eared Sliders. Another possible interpretation for the
high abundance and volume of vegetation in the Central Canal Red-eared Sliders’
diet may be the overall plant abundance in the Central Canal. Previous research
in the Central Canal found that this turtle species non-randomly associates with
areas lined by woodlots (Ryan et al. 2008), where vegetation is more prevalent.
In addition, Parmenter and Avery (1990) hypothesized that Red-eared Sliders may
consume vegetation in areas with greater plant abundance due to the ease of forag-
ing compared to available animal matter; our ndings were consistent with their
hypothesis. In the lake habitat, Red-eared Sliders appeared to be generalists, with
vegetation only making up 67% of food content volume. While this result may be
due in part to there being less aquatic vegetation in IMA Lake compared with the
Central Canal (T.J. Ryan, pers. observ.), Red-eared Sliders at IMA Lake may be
experiencing a release from competition for food with the other species, which are
typically more abundant in the Central Canal.
The populations of Red-eared Sliders and Common Map Turtles located in the
Central Canal show a high degree of resource partitioning with almost no overlap in
prey. This difference in diet may help explain the differences in movement patterns
between these 2 species in the Central Canal. We found that Red-eared Slider and
Common Map Turtle females moved the same distance on a daily basis, but female
Common Map Turtles tended to have larger ranges than female Red-eared Sliders
(Ryan et al. 2008). While these 2 species move amongst basking sites throughout
the day (Peterman and Ryan 2009), the basking-related movements did not ad-
equately account for the movement difference between species. The difference in
range size may be attributed to a preference for snails by Common Map Turtle,
necessitating active foraging over a larger area as local prey availability becomes
scarce (Pluto and Bellis 1988, Vogt, 1981).
Studies of diet differences have aided in elucidating life history (Ford and
Moll 2004) and habitat selection (Hart 1983, Plummer and Farrar 1981) for many
populations of turtles in natural settings. This study is, to our knowledge, the rst
to describe the diets of Red-eared Sliders and Common Map Turtles in explicitly
urban habitats. Our results suggest that within an urban landscape, diet may help
shape turtle assemblages and it may account for differences in home ranges and
habitat selection for these species, although other factors are likely important as
well (e.g., water depth and buffer-zone width; see Elston et al. 2016). We found no
signicant deviation from patterns reported in previous diet studies conducted in
more natural habitats, which underscores the fact that urban planners should con-
sider all facets of species’ ecology—including the needs of both dietary specialists
and generalists—when creating or altering urban aquatic habitats to promote and
sustain diversity.
Urban Naturalist
9
J.D. Stephens and T. J. Ryan
2019 No. 21
Acknowledgments
We thank the Indianapolis Water Company and the Indianapolis Museum of Art for al-
lowing us to trap on their properties. We are also grateful to Sean Sterrett and 2 anonymous
reviewers for helpful comments and suggestions that greatly improved this manuscript.
We followed Butler University ACUC Protocol 132 and our study was conducted under
an Indiana DNR permit (scientic collector’s license number 2599). This manuscript is a
contribution of the Center for Urban Ecology at Butler University.
Literature Cited
Bowen, S.H. 1983. Quantitative description of the diet. Pp. 325–336, In L.A. Nielsen and
D.L. Johnson (Eds.). Fisheries Techniques. American Fisheries Society, Bethesda, MD,
USA. 468 pp.
Cagle, F.R. 1939. A system of marking turtles for future identification. Copeia
1939:170–172.
Clark, D.B., and J.W. Gibbons. 1969. Dietary shift in the turtle Pseudemys scripta
(Schoepff) from youth to maturity. Copeia 1969:704–706.
Conner, C.A., B.A. Douthitt, and T.J. Ryan. 2005. Descriptive ecology of a turtle assem-
blage in an urban landscape. American Midland Naturalist 153:426–435.
Demuth, J.P., and K.A. Buhlmann.1997. Diet of the turtle Deirochelys reticularia on the
Savannah River Site, South Carolina. Journal of Herpetology 31:450–453.
Dillon, R.T. 2000. The Ecology of Freshwater Molluscs. Cambridge University Press,
Cambridge, UK. 524 pp.
Dolan, R.W., J.D. Stephens, and M.E. Moore. 2011. Living just enough for the city:
Persistence of high-quality vegetation in natural areas in an urban setting. Diversity
3:611–627.
Elston, J., V. Rolland, and S.E. Trauth. 2016. Urban-ditch characteristics associated with
turtle abundance and species richness. Herpetological Conservation and Biology
11:132–141.
Ernst, C.H., and J.E. Lovich. 2009. Turtles of the United States and Canada. Johns Hopkins
University Press, Baltimore, MD, USA. 840 pp.
Faulkner, S. 2004. Urbanization impacts on the structure and function of forested wetlands.
Urban Ecosystems 7:89–106.
Fields, J.R., T.R. Simpson, R.W. Manning, and F.L. Rose. 2003. Food habits and selective
foraging by the Texas River Cooter (Pseudemys texana) in Spring Lake, Hays County,
Texas. Journal of Herpetology 37:726–729.
Ford, D.K., and D. Moll. 2004. Sexual and seasonal variation in foraging patterns in the
Stinkpot, Sternotherus odoratus, in southwestern Missouri. Journal of Herpetology
38:296–301.
Gibbs, J.P., and D.A. Steen. 2005. Trends in sex ratios of turtles in the United States: Im-
plications for road mortality. Conservation Biology 19:552–556.
Gibson, C.J., K.L. Stadterman, S. States, and J. Sykora. 1998. Combined sewer overows:
A source of Cryptosporidium and Giardia? Water Science and Technology 38:67–72.
Gordon, D.M., and R.D. MacColluch. 1980. An investigation of the ecology of the Map
Turtle, Graptemys geographica (Le Sueur), in the northern part of its range. Canadian
Journal of Zoology 58:2210–2219.
Harden, L.A., S.J. Price, and M.E. Dorcas. 2009. Terrestrial activity and habitat selection
of Eastern Mud Turtles (Kinosternon subrubrum) in a fragmented landscape: Implica-
tions for habitat management of golf courses and other suburban environments. Copeia
2009:78–84.
Urban Naturalist
J.D. Stephens and T. J. Ryan
2019 No. 21
10
Hart, D.R. 1983. Dietary and habitat shift with size of Red-eared Turtles (Pseudemys
scripta) in a southern Louisiana population. Herpetologica 39: 285–290.
Lagler, K.F. 1943. Food habits and economic relations of the turtles of Michigan with spe-
cial reference to sh management. American Midland Naturalist 29:257–312.
Legler, J.M. 1977. Stomach ushing: A technique for chelonian dietary studies. Herpeto-
logica 33:281–284.
Legler, JM., and L.J. Sullivan. 1979. The application of stomach-ushing to lizards and
anurans. Herpetologica 35:107–110.
Lindeman, P.V. 2006. Zebra and Quagga Mussels (Dreissena spp.) and other prey of a Lake
Erie population of Common Map Turtles (Emydidae: Graptemys geographica). Copeia
2006:268–273.
Lindeman, P.V. 2013. The Map Turtle and Sawback Atlas: Ecology, Evolution, Distribution,
and Conservation. University of Oklahoma Press, Norman, OK, USA. 488 pp.
Marchand, M.N., and J.A. Litvaitis. 2004a. Effects of landscape composition, habitat
features, and nest distribution on predation rates of simulated turtle nests. Biological
Conservation 117:243–251.
Marchand, M.N., and J.A. Litvaitis. 2004b. Effects of habitat features and landscape com-
position on the population structure of a common aquatic turtle in a region undergoing
rapid development. Conservation Biology 18:758–767.
Minton, S.A. 2001. Amphibians and Reptiles of Indiana (revised), 2nd Edition. Indiana
Academy of Science, Indianapolis, IN, USA. 422 pp.
Mitchell, J.C., R.E.J. Brown, and B. Bartholomew (Eds.). 2008. Urban Herpetology. Soci-
ety for the Study of Amphibians and Reptiles, Salt Lake City, UT, USA. 608 pp.
Oksanen, J., F. Blanchet, R. Kindt, P. Legendre, R.B. O’Hare, et al. 2010. Vegan: Commu-
nity ecology package, version 2.0-7. Available online at http://vegan.r-forge.r-project.
org. Accessed 8 August 2011.
Parmenter, R.R., and H.W. Avery. 1980. The feeding ecology of the Slider Turtle. Pp. 257–
266, In J.W. Gibbons (Ed.). Life History and Ecology of the Slider Turtle. Smithsonian
Institution Press, Washington, DC, USA. 368 pp.
Patrick, R. 1973. Use of algae, especially diatoms, in the assessment of water quality. Pp.
76–95, In J. Cairns and K.L. Dickson (Eds.). Biological Methods for the Assessment of
Water Quality. American Society for Testing Materials. Philadelphia, PA, USA. 265 pp.
Paul, M.J., and J.L. Meyer. 2001. Streams in the urban landscape. Annual Review of Ecol-
ogy and Systematics 23:333–365.
Penn, G.H. 1950. Utilization of crawsh by cold-blooded vertebrates in the eastern United
States. American Midland Naturalist 44:643–658.
Peterman, W.E., and T.J. Ryan. 2009. Basking behavior of emydid turtles (Chysemys picta,
Graptemys geographica, and Trachemys scripta) in an urban landscape. Northeastern
Naturalist 16:629–636.
Plummer, M.V., and D.B. Farrar. 1981. Sexual dietary differences in a population of Trionyx
muticus. Journal of Herpetology 15:175–179.
Pluto, T.G., and E.D. Bellis. 1988. Seasonal and annual movements of riverine Map Turtles,
Graptemys geographica. Journal of Herpetology 22:152–58.
R Development Core Team. 2008. R: A language and environment for statistical comput-
ing. R Foundation for Statistical Computing, Vienna, Austria. Version 2.14.1, ISBN
3-90051-07-0. Available online at http://www.R-project.org. Accessed 8 August 2011.
Richards-Dimitrie, T.M., S.E. Gresens, S.A. Smith, and R.A. Seigel. 2013. Diet of Northern
Map Turtles (Graptemys geographica): Sexual differences and potential impacts of an
altered river system. Copeia 2013:477–484.
Urban Naturalist
11
J.D. Stephens and T. J. Ryan
2019 No. 21
Ryan, T.J., C.A. Conner, B.A. Douthitt, S.C. Sterrett, and C.M. Salsbury. 2008. Movement
and habitat use of 2 aquatic turtles (Graptemys geographica and Trachemys scripta) in
an urban landscape. Urban Ecosystems 11:213–225.
Ryan, T.J., W.E. Peterman, J.D. Stephens, and S.C. Sterrett. 2014. Movement and habitat
use of the Snapping Turtle in an urban landscape. Urban Ecosystems 17:613–623.
Spyra, A. 2010. Environmental factors inuencing the occurrence of freshwater snails in
woodland water bodies. Biologia 65:697–703.
Steen, D.A., and J.P. Gibbs. 2004. Effects of roads on the structure of freshwater turtle
populations. Conservation Biology 18:1143–1148.
Thorne, R.S.J., W.P. Williams, and C. Gordon. 2000. The macroinvertebrates of a polluted
stream in Ghana. Journal of Freshwater Ecology 15:209–217.
US Census. 2018. Quickfacts United States. Available online at https://www.census.gov/
quickfacts/fact/table/US/PST045217. 1 March 2018.
Vogt, R.C. 1981. Food partitioning in three sympatric species of map turtle, genus Grapte-
mys (Testudinata, Emydidae). American Midland Naturalist 105:102–111.
Walsh, C.J., A.H. Roy, J.W. Feminella, P.D. Cottingham, P.M. Groffman, and R.P. Morgan
II. 2005. The urban-stream syndrome: Current knowledge and the search for a cure.
Journal of the North American Benthological Society 24:706–723.
White, D., Jr., and D. Moll. 1992. Restricted diet of the Common Map Turtle, Graptemy
geographica, in a Missouri stream. Southwestern Naturalist 37:317–318.
Wolda, H. 1981. Similarity indices, sample size, and diversity. Oecologia 50:296–302.
Woodroffe, R., and J.R. Ginsberg. 1998. Edge effects and the extinction of populations
inside protected areas. Science 280:2126–2128.
Wright, I.A., B.C. Chessman, P.G. Fairweather, and L.J. Benson. 1995. Measuring the im-
pact of sewage efuent on the macroinvertebrate community of an upland stream. The
effect of different levels of taxonomic resolution and quantication. Australian Journal
of Ecology 20:142–149.
Zuma, B.M. 2010. Microbial ecology of the Buffalo River in response to water-quality
changes. M.Sc. Thesis. Rhodes University, Grahamstown, South Africa.
