Permanently Flooded. Water covers the land surface throughout the
year in all years. Vegetation is composed of obligate hydrophytes.

Intermittently Exposed. Surface water is present throughout the
year except in years of extreme drought.

Semipermanently Flooded. Surface water persists throughout the
growing season in most years. When surface water is absent, the
water table is usually at or very near the land surface.

Seasonally Flooded. Surface water is present for extended periods
especially early in the growing season, but is absent by the end of
the season in most years. When surface water is absent, the water
table is often near the land surface.

Saturated. The substrate is saturated to the surface for extended
periods during the growing season, but surface water is seldom
present.

Temporarily Flooded. Surface water is present for brief periods
during the growing season, but the water table usually lies well
below the soil surface for most of the season. Plants that grow
both in uplands and wetlands are characteristic of the temporarily
flooded regime.

Intermittently Flooded. The substrate is usually exposed, but
surface water is present for variable periods without detectable
seasonal periodicity.

Model assumptions. This model assumes that the quantification of the
habitat variables presented here can be directly related to the suitability of
wetland and aquatic habitats for the slider turtle. Many of the model's
assumptions are based on subjective interpretation of the literature and
direct experience of the authors. The values presented for the Suitability
Index curves were not based on specific experimentation, but were the by-
products of quantitative empirical data accumulated during long-term studies
of the slider.

Although the model is intended for broad applicability, the following
assumptions could restrict its use: (1) available basking and nesting sites
are not limiting factors, and (2) any aquatic habitat within the geographic
range of this species is accessible (i.e., immigration and colonization are
expected). Other than in exceptional circumstances, most natural and environ-
mentally-altered habitats that the species might encounter should meet these
assumptions.

SOURCES OF OTHER MODELS

No other habitat models were found during literature searches on the
habitat needs of the slider turtle.

12

on


Water component. Hydrologic conditions are important to any aquatic
animal. Although the slider turtle is capable of overland movements, certain
limitations within the aquatic environment must be analyzed in any habitat
suitability assessment. Three key variables are used in this modal to quantify
the suitability of the water component: velocity, water depth, and water
regime. The relationship between velocity and habitat suitability is con-
founded by the numerous variables that are introduced in comparing habitats
and channel structure. The slider prefers quiet waters, such as those existing
in lacustrine environments, therefore, optimal conditions are considered to
exist when velocity is 0 cm/sec (Figure 3a). Sliders have also been observed
in the Savannah River in areas where average peak velocity approximates 80 cm/
sec in the middle of the river. Sliders observed in rivers at such high
velocity utilize microhabitats along the river margins or are simply
transients. For purposes of habitat analysis, rivers with average peak
velocity 280 cm/sec are assumed to have zero suitability for sliders. Rivers
with average peak velocity <80cm/sec are assumed to contain areas of lower
flow (e.g., eddies, oxbows) suitable for sliders; the sections of the river
with high velocity will be avoided in favor of the low velocity areas. This
assumption is appropriate for a typical river in the southeastern United
States, but will be inappropriate for high gradient, narrow streams. A high
gradient stream with an average peak velocity approaching 80 cm/sec will
likely not provide areas of low velocity suitable for sliders.

The slider occurs most often and at the highest densities in bodies of
water with a depth of 1 to 2m. Although this species will utilize deeper
waters, this appears to be limited to overwintering on the bottom and to
predator avoidance. Since aquatic vegetation provides cover and foraging area
for sliders, shallower littoral zones must be contiguous with deeper habitats
to support this species. The slider, however, does not occur frequently in
bodies of water with a maximum depth <0.5 m. Shallower waters usually do not
provide proper cover and, at some times of the year, are frequently depauperate
of other fauna. Although turtles will temporarily utilize shallow bodies of
water during overland travel or as juveniles, shallow water habitats usually
do not support this species year round. It is difficult to distinguish the
proximal effects of water depth, since it is directly related to the other
components in this model (Food/Cover and Temperature). For this model, it is
assumed that depths of 1 to 2 m are optimal for this species, depths of 0.5m
and 3 m represent marginal habitat, and depths <0.5 m approach the limits of
habitability (Figure 3b). Depths >3 m are assumed to provide a low level of
suitability, with the shallower areas being most suitable.

Wetlands containing permanent water will have the highest likelihood of
supporting slider turtles throughout the year. Wetlands where water is not
always present are of less suitability to sliders, since sliders must emigrate
from such wetlands when water is absent. Suitability indices can be assigned
to wetlands based on water regime. The relationship between water regime
modifiers (Cowardin et al. 1979) and habitat suitability is shown in Figure 3c
(see Application of the Model for definitions of water regime modifers).
Saturated wetlands rarely have surface water present and, therefore, have zero
suitability. Intermittently flooded wetlands are also assigned a zero suit-
ability due to the unpredictability of having surface water in such wetlands.

]


Take Pride in America

Preserve Our Wetlands

DEPARTMENT OF THE INTERIOR
U.S. FISH AND WILDLIFE SERVICE

As the Nation’s principal conservation agency, the Department of the interior has respon-
sibility for most of our.nationally owned public lands and natural resources. This includes
fostering the wisest use of our land and water resources, protecting our fish and wildlife,
preserving the environmental and cultural values of our national parks and historical places,
and providing for the enjoyment of life through outdoor recreation. The Department as-
sesses our energy and mineral resources and works to assure that their development is in
the best interests of all our people. The Department also has a major responsibility for
American Indian reservation commul $ and for people who live in island territories under
U.S. administration.

Cc)


This report should be cited as:

Morreale, S. J., and J. W. Gibbons. 1986. Habitat suitability index models:
Slider turtle. U.S. Fish Wild]. Serv. Biol. Rep. 82(10.125). 14 pp.


(>

REFERENCES.

Brattstrom, B. H. 1965. Body temperatures of reptiles. Am. Mid]. Nat.
73:376-472.

Cagle, F. 8. 1944. Home range, homing behavior, and migration in turtles.
Misc. Publ. Univ. Michigan Mus. Zool. 61:1-34.

___. 1950. The life history of the slider turtle, Pseudemys scripta
i (Holbrook). Ecol. Monogr. 20:32-54.

Carr, A. F. 1952. Handbook of turtles. Comstock Publ. Assoc., Ithaca, NY.
542 pp.

Clark, D. B., and J. W. Gibbons. 1969. Dietary shift in the turtle Pseudemys
scripta (Schoepff) from youth to maturity. Copeia 1969(4):704-706.

Conant, R. 1975. A field guide to reptiles and amphibians of eastern and
central North America. Houghton Mifflin Co., Boston. 429 pp.

Congdon, J. D., D. W. Tinkie, G. L. Brietenbach, and R. van Loben Sels. 1983.
Nesting ecology and hatching success in the turtle, Emydoidea blandingi. J.
Herpetol. 39:417-429.

Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Classifica-
tion of wetlands and deepwater habitats of the United States. U.S. Fish
Wild]. Serv. FWS/08S-79/31. 103 pp.

Ernst, C. H., and R. W. Barbour. 1972. Turtles of the United States. Univ.
Kentucky Press, Lexington. 347 pp.

Gibbons, J. W., and R. D. Semlitsch. 1982. Survivorship and longevity of a
long-lived vertebrate: How long do turtles live? J. Anim. Ecol. 51:523-527.

Gibbons, J. W., Jd. L. Greene, and J. D. Congdon. 1983. Drought-related
responses of aquatic turtle populations. J. Herpetol. 17:242-246.

Gibbons, J. W., J. L. Greene, and K. K. Patterson. 1982. Variation in repro-
ductive characteristics of aquatic turtles. Copeia 1982(4):776-784.

Hutchison, V. H. 1979. Thermoregulation. Pages 207-288 in M. Harless and
H. Morlock, eds. Turtles: perspectives and research. John Wiley and Sons,
New York.

Hutchison, V. H., A. Vinegar, and R. J. Kosh. 1966. Critical thermal maxima
in turtles. Herptologica 22:32-41.

Moll, €. 0., and J. M. Legler. 1971. The life history of a neotropical
slider turtle, Pseudemys scripta (Schoepff), in Panama. Bull. Los Angeles

County Mus. Nat. Hist. Sci. 11:1-102.

13


50272-101

REPORT DOCUMENTATION |} REPORT NO. 2 TS. Recipient's Accession No
PAGE Biologics! Severs 22101283
4 Title end Subtitle

TS. Report Date

a

Habitat Suitability Index Models: Slider Turtle September 1986
z
7. Author(s) 8. Performing Organization Rept. No.
S.J. Morreale and J.W. Gibbons
3 adorning Grganusiion Nome and Addreve

~ 10. Project/Task/Work Unit No.
Savannah River Ecology Laboratory

Drawer £
r 11. Cor MC) or Grant(G) No.
Aiken, SC 29801 mteacnic) oF GrankiGi No
«)
(G)
12. Sponsoring Organization Name and Address Division of Wildlife and Contaminant| 13. Type of Report & Period Covered |
Research
Fish and Wildlife Service
Department of the Interior 16.

Washington, DC 20240

15. Supplementary Notes

16. Abstract (Limit: 200 words) °

A review and synthesis of existing information were used to develop a Habitat
Suitability Index (HSI) model for the slider turtle (Pseudemys scripta). The model
consolidates habitat use information into a framework appropriate for field
application, and is scaled to produce an index between 0.0 (unsuitable habitat)
and 1.0 (optimum habitat). HSI models are designed to be used with Habitat
Evaluation Procedures previously developed by the U.S. Fish and Wildlife Service.

C

17. Document Analysis». Descriptors ~ ~
Turtles

Wildlife

Habitability

Mathematical models

b. Identifiers/Open-Ended Terms

Slider turtle

Pseudemys scripta
Habitat suitability

¢. COSATI Fleld/Group

18 Availability Statement — 19. Security Cless (This Report) 21, No. of Pages
Release unlimited Unclassifiec 14
20. Security Class (This 22, Price
Unclassified
(See ANS!-239.18)

j

See Instructions on Reverse

(Formerly NTIS~35)
Ye U.S. GOVERNMENT PRINTING OFFICE: 986-673-154 / 45327

Department of Commerce

OPTIONAL FORM 272 (4-77)


OT

Habitat variables

Percent cover of emergent and

Life requisites Cover type

Food/Cover

submerged vegetation

Velocity Deciduous forested
wetiand
Deciduous scrub/shrub
wetland i
Water depth~ — water Herbaceous wetland
Riverine
Lacustrine

Water regine

Water temperature So

Temperature

Figure 5. The relationship of habitat variables, life requisites, and cover type to an HSI value for

the slider turtle.


Cover

Highest densities of sliders occur where algae blooms and aquatic macro-
phytes are abundant and are of the tyre 3t form dense mats at the surface,
such as spiked watermilfoil (Myriophyllum soicatum) and lily pads
(Nymphaeaceae) (Schubauer 1981). Dense surface vegetation provides cover from
predators and supports high densities of aquatic invertebrates and small
vertebrates, which offers better foraging than open water. Similar species of
aquatic turtles, such as the midland painted turtle (Chrysemys picta
marginata), also prefer habitats with floating aquatic vegetation (Sexton
1959).

Reproduction

Mating occurs in the water, but some suitable terrestrial area is required
for egg-laying by nesting females. The nesting season extends from April
through July in the southeastern United States, and females may nest once or
twice during this period (Gibbons et al. 1982). Some females nest in open
sites close to water, and nests are usually placed in loose soil that remains
above the water table. Nest sites adjacent to water are not always necessary,
however, since females may travel 0.4 (Moll and Legler 1971) to 1.6 km (Cagle
1950) from the nearest water to nest. Nests are located on sandy ridges, open
areas in woods, meadows, old fields, levees, canal banks, and dirt roads (Carr
1952; Ernst and Barbour 1972).

Interspersion and Movements

Sliders move between habitats by both overland and aquatic routes
(Morreale et al. 1984; Parker 1984). Movements can be induced by a necessity
to find food (Cagle 1944) or to escape desiccating aquatic habitats (Gibbons
et al. 1983), and can result in the emigration of an entire population from a
site. Other movements result from sexual or genetic variations among
individuals. Adult females make excursions on land considerable distances
from water (Cagle 1950; Moll and Legler 1971), presumably to search for
appropriate nesting areas, as has been reported for other species of turtles
(Obbard and Brooks 1980; Congdon et al, 1983). Nesting excursions usually end
when the female returns to its original location prior to the movement. Adult
males will sometimes move from one aquatic site to another and can move over-
Yand for distances >3.5 km and aquatically up to 5 km (Morreale et al. 1984).
The frequency of movement between aquatic habitats is greater in males than
females and has been attributed to searching for mates. The likelihood that a
male will move between aquatic habitats increases with the age of the
individual (Parker 1984).

Individual variation in movements between habitats can be construed as
alternative strategies that maximize individual fitness. Except for nesting
females, movement from an aquatic habitet is not necessary for maintaining a
population, since many sliders remain in their natal habitats for years
(Gibbons and Semlitsch 1982). Thus, if a habitat provides suitable resources,
it can sustain a healthy population of these turtles.


CONTENTS

PREFACE ........
ACKNOWLEDGMENTS

HABITAT USE INFORMATION 2.0.0... 0.0 e cece eee eee eee eee eee eee eee
General 2.2.0... cece cece eee eee eee .
Food ....
Water .
Cover ... wee
Reproduction
Interspersion and Movements .....
HABITAT SUITABILITY INDEX (HSI) MOD
Model Applicability
Model Description
Application of the Model . see
SOURCES OF OTHER MODELS ....... co ieee ect tnt

REFERENCES 00... cece eect ttt e terete eee

a


PREFACE

This document is part of the Habitat Suitability Index (HSI) Model Series
[Biological Report 82(10)] which provides habitat information useful for impact
assessment and habitat management. Several types of habitat information are
provided. The Habitat Use Information Section is largely constrained to those
data that can be used to derive quantitative relationships between key environ-
mental variables and habitat suitability. This information provides the
foundation for the HSI model and may be useful in the development of other
models more appropriate to specific assessment or evaluation needs.

The HSI Model Section documents the habitat model and includes information
pertinent to its application. The model synthesizes the habitat use informa-
tion into a framework appropriate for field application and is scaled to
produce an index value between 0.0 (unsuitable habitat) and 1.0 (optimum
habitat). The HSI Model Section includes information about the geographic
range and seasonal application of the model, its current verification status,
and a list of the model variables with recommended measurement techniques for
each variable.

The model is a formalized synthesis of biological and habitat information
published in the scientific literature and may include unpublished information
reflecting the opinions of identified experts. Habitat information about
wildlife species frequently is represented by scattered data sets collected
during different seasons and years and from different sites throughout the
range of a species. The model presents this broad data base in a formal,
logical, and simplified manner. The assumptions necessary for organizing and
synthesizing the species-habitat information into the model are discussed.
The model should be regarded as a hypothesis of species-habitat relationships
and not as a statement of proven cause and effect relationships. The model
may have merit in planning wildlife habitat research studies about a species,
as well as in providing an estimate of the relative suitability of habitat for
that species. User feedback concerning model improvements and other sugges-
tions that may increase the utility and effectiveness of this habitat-based
approach to fish and wildlife planning are encouraged. Please send suggestions
to:

Habitat Evaluation Procedures Group
National Ecology Center

U.S. Fish and Wildlife Service

2627 Redwing Road

Ft. Collins, CO 80526-2899

Vii


Variable (definition)

Percent cover of emergent and
submerged vegetation (percent
of midsummer aquatic substrate
which, when viewed from above,
is covered by leaf or stem
tissue of emergent or
submerged aquatic plants).

Velocity (the average peak
rate at which water is
flowing at the surface,
j.e., the highest rate in
the cross section of the
river or wetland being
evaluated; to be measured
during periods of non-
flooding).

Water depth (the average
vertical distance from the
substrate to the water

surface in a river or

wetland; measured as the
average depth within 10 m

of the shore available

during the April through
September period, except during
flooding periods).

Water regime (the permanence
of surface water in a wetland,
defined by Cowardin et al.
1979. See text for
definitions).

Water temperature (mean surface
water temperature during peak
activity and growing season,
April through September).

Cover types
DFW, OSW,HW,R,L

OFW,DSW,HW,R,L

DFW, OSW,HW,R,L

DFW, DSW,HW,R,L

DFW, OSW,HW,R,L

Suggested technique

Quadrat, ocular
estimate

Flow meter,
floating body

Standard depth
meters, graduated
rod

National Wetlands
Inventory maps;
on-site inspection

Thermometers

Figure 6. Definition of variables and suggested measurement techniques.

il


gD

HABITAT USE INFORMATION

General

The slider turtle (Pseudemys scripta) is a predominantly aquatic turtle
that inhabits southern waters from Virginia to New Mexico and as far south as
Brazil, South America (Pritchard 1979). This species appears in virtually all
types of water bodies (e.g., rivers, ditches, sloughs, lakes, and ponds);
however, it prefers quiet water, approximately 1 to 2m in depth (Cagle 1950),
with a soft bottom, abundant vegetation, and suitable basking sites (Ernst and
Barbour 1972). The habitat requirements of the slider turtle are broad. It
exists sympatrically with other freshwater turtles within its range (Conant
1975). The slider is considered a diurnal turtle; it feeds mainly in the
morning and frequently basks on shore, on logs, or while floating, during the
rest of the day. At night, it sleeps lying on the bottom or resting on the
surface near brush piles and hummocks (Ernst and Barbour 1972).

Food

Sliders are omnivores. Juvenile sliders are primarily carnivorous,
whereas adults tend to be herbivorous (Clark and Gibbons 1969). Animal foods
include crustaceans, mollusks, adult and larval insects, fish, tadpoles, and
frogs. Plants in the diet include filamentous algae, duckweed (Lemna spp.),
and a wide variety of emergent and submerged aquatic plants.

The facultative feeding strategy of slider turtles contributes greatly to
their widespread distribution (Ernst and Barbour 1972). They frequently are
observed eating carrion found in the water. When a habitat provides abundant
sources of both vegetation and animal protein, the slider's dietary preference
tends toward increased animal protein (Parmenter 1980). A generalist diet, in
conjunction with an ability to migrate both aquatically and terrestrially
(Morreale et al. 1984; Parker 1984), enables sliders to thrive where resources
have a patchy distribution.

Water
Water is an essential requirement in the ecology of this semiaquatic

species. Water considerations are discussed under Cover, Reproduction, and
Interspersion.


BIOLOGICAL REPORT 82(10.125)
SEPTEMBER 1986

HABITAT SUITABILITY INDEX MODELS:
SLIDER TURTLE

Fish and Wildlife Service
U.S. Department of the Interior



Season. The model was designed to provide an index of habitat suitability
as a function of habitat requirements for the slider turtle throughout the
year.

Cover types. This model was developed for application in the following
cover types (terminology follows that of U.S. Fish and Wildlife Service 1981):
Deciduous Forested Wetland (DFW), Deciduous Scrub-Shrub Wetland (DSW),
Herbaceous Wetland (HW), Riverine (R), and Lacustrine (L).

Minimum habitat area. There is no statement in the literature of a
minimum habitat size for the slider turtle. This species occupies aquatic
habitats of almost any size, ranging from drainage ditches and small farm
ponds to major rivers and lakes.

Verification level. This model was developed at a workshop in October
1984 at the Savannah River Ecology Laboratory. The interpretations are based
on the expertise of the authors and review comments by Dr. Justin D. Congdon
and Dr. Carl H. Ernst.

Model Description

Overview. The model is intended to be applicable to most bodies of water
within the range of the slider turtle in the United States. A positive,
linear relationship between HSI and the carrying capacity of the habitat is
assumed. The model is based on a set of habitat variables that can be empiric-
ally related to abundance of slider turtles. The variables fall into three
general categories: (1) food/cover component, (2) water component, and
(3) temperature component. These categories represent possible limiting
factors for the slider turtle.

Two key life history requirements, nesting sites and basking areas, were
omitted from this model. In our opinion, nesting areas will not be a limiting
factor anywhere within the range of this species. As long as there is access
to land, individual slider turtles have the capability for long-range movement
to nesting areas (Cagle 1950; Moll and Legler 1971). The availability of
basking sites could be considered a potential limiting factor for this species,
although basking sites are abundant in most natural habitats. When no aquatic
basking sites are available, sliders will readily bask along the shore or at
the surface of the water. Therefore, we did not include basking sites as a
component of the model.

Food/cover component. The abundance of sliders in a habitat is assumed
to be directly related to the vegetative characteristics of the wetland. The
presence of emergent and submerged aquatic plants can directly affect the
amount of concealment from predators and exposure to direct sunlight. Vegeta~
tion is also a direct indicator of food availability, since it is a substantial
portion of the adult diet. There are also some important life requisites of
turtles that can be indirectly correlated to the amount and type of aquatic
vegetation in a habitat. In many cases, areas with abundant vegetation support
large quantities of aquatic larvae, insects, tadpoles and adult frogs, and



HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

Geographic area. This HSI model was developed for application throughout
the range of the slider turtle in the United States (Figure 1). The model
contains a temperature component that was designed specifically for use in the
L-reactor cooling lake at the U.S. Department of Energy Savannah River Plant
(SRP) near Aiken, South Carolina. The temperature component may be useful
elsewhere where water temperature is a critical component of the habitat.

Figure 1. Geographic applicability of the slider turtle HSI model within
the United States [see Ernst and Barbour (1972:152) for additional disjunct
populations].


ACKNOWLEDGMENTS

Justin D. Congdon and Carl H. Ernst offered constructive criticism
original manuscript. Manuscript preparation was aided by Contr .
DE-ACO9-76SRO0-819 between the U.S. Department of Energy and the University of
Georgia's Institute of Ecology.

Word processing was provided by Dora Ibarra, Elizabeth Barstow, and
Patricia Gillis. The cover of this document was illustrated by Susan Strawn.

vi


Morreale, S. J., J. W. Gibbons, and J. D. Congdon. 1984. Significance of
activity and movement in the yellow-bellied slider turtie /
scripta). Can. J. Zool. 62:1038-1042.

Obbard, M. E., and R. J. Brooks. 1980. Nesting mgr
turtle (Chelydra serpentina). J. Herpetol. 36:158-162.

ns of the snanving

Parker, W. S. 1984. Immigration and dispersal of slider turtles (Pseucemys
scripta) in Mississippi farm ponds. Am. Mid]. Nat. 112:280-293.

Parmenter, R. R. 1980. Effects of food availability and water temperature on
the feeding ecology of pond sliders (Chrysemys s. scripta). Copeia 1980(3):
503-514.

Pritchard, P. C. H. 1979. Taxonomy, evolution, and zoogeography. Pages 1-42
in M. Harless and H. Moslock, eds. Turtles: perspectives and research.
John Wiley and Sons, New York.

Schubauer, J. P. 1981. The ecology and behavior of an aquatic turtle,
Pseudemys scripta, inhabiting a thermally altered reservoir, Par Pond, South

Carolina. M.S. Thesis. State University of New York, Buffalo. 95 pp.

Sexton, 0. J. 1959. Spatial and temporal movements of a population of the
painted turtle, Chrysemys picta marginata (Agassiz). Ecol. Monogr.
29:113-140.

Standora, E. A. 1982. A telemetric study of the thermoregulatory behavior
and climate-space of free-ranging yellow-bellied turtles, Pseudemys scripta.
Ph.D. Dissertation. University of Georgia, Athens. 153 pp.

U.S. Fish and Wildlife Service. 1981. Standards for the development of

Habitat Suitability Index models. 103 ESM. U.S. Fish Wildl. Serv., Div.
Ecol. Serv. n.p.

14


Biclogical Report 82(16.1
September 1986

HABITAT SUITABILITY INDEX MODELS: SLIDER TURELE

by

Stephen J. Morreale
and
J. Whitfield Gibbons
Savannah River Ecology Laboratory
Drawer E
Aiken, SC 29801

Performed for
National Ecology Center
Division of Wildlife and Contaminant Research
Fish and Wildlife Service
U.S. Department of the Interior
Washington, DC 20240


Suitability Index (S1V2)

a
1.0% 1 1 1
0.8 L
0.6 L
0.4 L
0.2 L
0.04 ‘ T T
0 25 50 75 100+ (cm/sec)
0 0.8 1.6 2.5 3.34 (ft/sec)
Velocity
&

= 1.0 po

=

2 0.84

x

ov

Z 0.64

? 0.44

2 0.2 4

3

° 0.0

A BC DE
Water regime

F

G

Suitability Index (SIV3)

QmMTOVD

onhonu nnn

b

+

1.0 yo rae \
0.84 t
0.6 4 F
0.44 r
0.24 r
0.0 : nn ae en

0 0.51.0 1.5 2.0 2.5 3.0

0 1.6 3.3 4.9 6.6 8.2 9.9+

Water depth

Permanently flooded
Intermittently exposed
Semipermanently flooded
Seasonally flooded
Temporarily flooded
Saturated
Intermittently flooded

Figure 3. Relationships between habitat suitability and the variables
used to evaluate the water component in the slider turtle HSI model.

m.

(m)
(ft)


10 4et aa
ray

5 oe L

x A

s 0.64 - B 15 - 20C
= c 25 C
> oad L i) 30 C
B04 E 35 C
= F 40 C
20.24 F G = 40 C

s

A 0.0

A BC DE F G
Water temperature

Figure 4. Relationship between mean surface water temperature and habitat
suitability for the slider.

Application of the Model

Summary of model variables. The relationships between habitat variables,
life requisites (components), cover types, and an HSI for the slider turtle
are summarized in Figure 5. Definitions of the variables and suggested
measurement techniques are presented in Figure 6.

This model provides selected techniques for assessing the habitat suit-
ability of wetlands or aquatic habitats within the geographic range of the
slider, The characteristics chosen to describe habitat suitability, although
general, are appropriate because of the ubiquity of the species and its ability
to use most available aquatic habitats. In addition, the behavior and physio-
logy of the slider turtle allow for rapid dispersal into new habitats and the
capability to withstand a broad range of environmental conditions.

The water regime modifiers that are used in this model (Figure 3c) are
described below (Cowardin et al. 1979:24). The modifiers are intended to
apply primarily to wetlands and lacustrine cover types. Riverine cover types
are assumed to always have water flowing and should be classified as
permanently flooded.


Were the variables and curves clearly defined and useful? Yes No

If not, how were or could they be improved?

Were the techniques sugg
Appropriate? a
Clearly defined? Yes _ No

Easily applied? Yes No

If not, what other data collection techniques are needed?

Were the mode] equations logiral? Yes No

Appropriate? Yes = No

How were or could they be improved?

Other suggestions for modification or improvement (attach curves,
equations, graphs, or other appropriate information) _

Additional references or information that should be included in the model:

Model Evaluator or Reviewer _ Date

Agency

Address

Telephone Number Comm: _ FITS



MODEL EVALUATION FORM

Habitat models are designed for a wide variety of planning applica-
tions where habitat information is an important consideration in the
decision process. However, it is impossible to develop a model that
performs equally well in all situations. Assistance from users and
researchers is an important part of the model improvement process. Each
model is published individually to facilitate updating and reprinting as
new information becomes available. User feedback on model performance
will assist in improving habitat models for future applications. Please
complete this form following application or review of the model. Feel
free to include additional information that may be of use to either a
model developer or model user. We also would appreciate information on
model testing, modification, and application, as well as copies of modified
models or test results. Please return this form to:

Habitat Evaluation Procedures Group
U.S. Fish and Wildlife Service

2627 Redwing Road, Creekside One
Fort Collins, CO 80526-2899

Thank you for your assistance.

Geographic
Species _ Location
Habitat or Cover Type(s)
Type of Application: Impact Analysis Management Action Analysis

Baseline Other

Variables Measured or Evaluated

Was the species information useful and accurate? Yes _ No

If not, what corrections or improvements are needed?



small fish, which form the animal portion of the slider's diet. The presence
of submerged aquatic vegetation is generally inversely correlated with canopy
cover of overhead woody vegetation. More open area and, therefore, more
basking sites, would be available in habitats with minimal canopy cover.

Vegetation can be measured as the percent cover of emergent and submerged
vegetation in a defined area. The relationship between emergent and submerged
vegetation cover and habitat suitability (SIV1) is shown in Figure 2. Optimum
conditions are assumed to occur at 290% cover of emergent and submerged
vegetation, since peak densities of sliders occur at and above this level.
Sliders also occur in small numbers where the vegetative cover is 0%. The
suitability of the food/cover component (SIFC) is assumed to be equal to the
suitability level determined for the percent cover of emergent and submerged
vegetation (Equation 1).

SIFC = SIV1 (1)

1.0 n m 1

0.84 t

0.64 r

0.44 r

0.2 4 L

Suitability Index (SIV1)

0.0 T T
0 25 50 75 100
Percent cover of emergent
and submerged vegetation

Figure 2. Relationship between the percent cover of emergent and submerged
vegetation and habitat suitability for the slider turtle.


The remaining modifiers (permanently flooded, intermittently exposed, semi-
permanently flooded, seasonally flooded, and temporarily flooded) have been
assigned suitability indices based on their relative degree of water
permanence, with permanently flooded wetlands representing optimum conditions.
Riverine habitats occupied by sliders are all assumed to be in the lower
perennial category of Cowardin et al. (1979), where flowing water is present
throughout the year. Riverine habitats will, therefore, be assigned a

suitability for water regime corresponding to the permanently flooded category
(i.e., SIV4=1.0).

The suitability of the water component (SIW) is assumed to be the lowest
suitability index of the three water component variables (Equation 2).

SIW = minimum (SIV2, SIV3, SIV4) (2)

Temperature component. The thermal characteristics of a wetland are more
important in the L-reactor lake on the Savannah River Plant than in most
habitats throughout the range of the slider turtle. The slider inhabits warm
climates and is presumably limited by extreme winter cold in the more northern
latitudes. For the L-reactor cooling waters, the crucial factor for habitat
suitability is the high water temperature generated by reactor operations.

To quantify water temperature suitability in this model, upper avoidance
temperature (37 °C, Hutchison 1979}, critical thermal maxima (41 to 42 °C,
Hutchison et al. 1966), and thermal preferenda reported for the species were
used. The optimal range calculated from mean preferred temperatures was
reported as 25.5 °C (Brattstrom 1965) and 28 °C (Standora 1982) based on
behavioral observations, and from 26 to 29 °C based on digestive turnover
times and feeding efficiency in the populations (Parmenter 1980). Mean surface
water temperatures within the activity range of the slider are presented in
divisions of five degrees Celsius in Figure 4; the mean surface water tempera-
ture is based on the average of daily maximum and minimum temperatures during
the period of interest. Two assumptions are made in this portion of the
model: (1) temperatures above 40 °C at any time of the year are considered to
have a suitability index of 0.0, and (2) the critical period is during the
slider's growing period and when ambient water temperature is at its highest
level. This period corresponds to April through September in South Carolina.

The suitability of the temperature component (SIT) is assumed to be equal
to the suitability index determined for the mean surface water temperature
during the critical period (Equation 3).

SIT = SIV5 (3)

HSI_ determination. The HSI for the slider turtle is based on the concept

of limiting factors and is assumed to be the lowest of the suitability levels
determined for the three model components (Equation 4).

HST = minimum (SIFC, SIW, SIT) (4)