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Herpetofaunal Use of Four Habitats
of the Middle Gila River Drainage, Arizona 1
Martin D. Jakle and Thomas A. Gatz
2
Abstract.--Data on reptiles and amphibians were gathered using
pit-fall traps and by observation along the Gila River northeast of F!orence,
Pinal County, Arizona. Four habitat types were sampled: desert wasn,
desert upland, mature salt cedar, and mesquite bosque. A total of 104
individuals of 12 species were trapped and an additional seven species
were observed. Based on trap data, species diversity was greatest in
the desert wash, and lowest in the salt cedar habitat. Reptiles and
amphibians showed little use of the salt cedar habitat which may reflect the
lack of structural diversity in the herbaceous and shrub layers and reduced
light penetration due to a dense canopy.
INTRODUCTION
Increasing attention is being focused on
riparian habitat because of its recognized high
values for wildlife and its rapidly dwindling
supply. Stream diversions, reservoir
construction, ground water overdraft, grazing,
phreatophyte clearing, recreational demands, and
other uses are taking their toll on a habitat type
that naturally occupies a small percentage of the
total landmass. Several workers have documented
the importance of riparian habitats to birds in
the Southwest (Carothers et al., 1974; Stevens et
al., 1977; Szaro and Jakle, in press); however,
few researchers have studied the Southwestern
riparian herpetofauna. This paper discusses the
herpetofauna of two riparian and two desert
habitats in Arizona.
STUDY AREA AND HABITAT DESCRIPTION
The study area is located in southcentral
Arizona 21 km east of Florence, Pinal County,
at an elevation of 500 m. The dominant plant
community in this area is the Sonoran desert scrub
formation and, more specifically, the palo
verde-cacti-mixed shrub series (Brown 1982). The
Gila River flows through this area and forms a
riparian corridor.
1
The salt cedar habitat was a strip of mature
trees bordering the Gila River. The strip was
approximately 350 m by 45 m, composed of an
even-aged stand of mature trees. The stand had
little species diversity, being composed of almost
100 percent salt cedar trees (Tamarix pentandra)
which were quite dense, and formed a thicket. The
density of the stand reduced light penetration and
precluded establishment of a herbaceous layer.
The mesquite bosque habitat also bordered the
Gila River, adjacent to the salt cedar habitat and
was approximately 1 km by 75 m. Mature mesquite
trees (Prosopis velutina) were the dominant
species present, but the stand was a heterogeneous
mix which included Goodding willow (Salix
gooddingii) and cottonwood (Populus fremontii).
This habitat type had greater structural diversity
which included a shrub and herbaceous layer.
The surrounding area consisted of two
habitats: desert upland and desert wash. In the
desert upland habitat the dominant tree species
were foothill palo verde (Cercidium microphyllum)
and saguaro (Carnegiea gigantea). The dominant
shrubs consisted of triangle leaf bursage
(Ambrosia deltoidea), which was by far the most
abundant, and ratany (Krameria parvifolia). The
herbaceous layer consisted primarily of an annual
grass, red brome (Bromus rubens), which grew
mainly under nurse plants.
The desert wash was located in a large sandy,
ephemeral drainage course, Donnelly Wash, which
emptied into the Gila River. This habitat was
patchy, consis~ing of large sandy areas devoid of
any vegetation interspersed with vegetated areas.
The dominant tree species were blue palo verde
(Cercidium floridum), ironwood (Olneya tesota),
and mesquite. Canyon ragweed (Ambrosia
ambrosioides), wolfberry (Lycium andersonii), and
gray thorn (Zizyphus obtusifolia) were the
dominant shrubs; red brome dominated the
herbaceous layer.
Paper presented at the North American
Riparian Conference, April 16-18, 1985, Tucson,
Arizo2-a.
Respectively, General Biologist and Supervisory Biologist, U.S. Bureau of Reclamation,
Phoenix, Arizona 85068.
355
METHODS
DISCUSSION
The herpetological array pit-fall trapping
technique developed by Campbell and Christman
(1982) and modified by Jones (1980) was used to
determine species composition and relative
abundance of reptiles and amphibians in the four
habitat types. This method uses four 18.4 1
pit-fall traps. One trap is located in the center
and connected to three peripheral traps by 7.2 m
aluminum flashing which extends from the center
trap at equal angles. Two arrays each were placed
in the desert wash, desert upland, and mesquite
bosque habitats, and one in the salt cedar
habitat. Trapping commenced on March 23, 1983, in
the desert habitats and 6 to 15 days later in the
riparian habitats. Trapping ended May 5, 1983.
Based on pit-fall trapping data, the desert
wash habitat had the highest species diversity and
equaled the desert upland as having the highest
abundance of the four habitats studied. The high
value of this habitat, i.e. palo verde-cacti-mixed
shrub, is supported by deVos et al. (1983). In a
study west of Tucson, Arizona, this habitat had
the greatest reptile and amphibian diversity of
the five habitats studied: palo verde-mixed
cacti, creosote-bursage, desert grassland,
mesquite bosque, mixed ripari~n woodland.
Traps were checked at least weekly. All captured
lizards were toe-clipped, weighed, measured,
sexed, and released at the capture site.
Recaptured individuals were not used to determine
diversity or abundance. Species diversity was
calculated based on the formula of Shannon and
Weaver (1948).
RESULTS
A total of 104 reptiles and amphibians ~ere
trapped during 406 trap days between March 23 and
May 5, 1985, an average of 0.26 individuals per
trap day for all habitats combined. The desert
upland and desert wash habitats had the highest
trap success, 0.31 individuals per trap day. The
mesquite habitat had the next highest trap
success, 0.22 individuals per trap day and the
salt cedar habitat had the lowest value with 0.06
individuals per trap day. There was a significant
difference between the number of individuals
captured in these two adjacent riparian habitats
(Chi Square Test= p<.01). A total of twelve
species were trapped (table 1). The greatest
species diversity (1.81) was found in the desert
wash and the lowest (0.63) was found in the salt
cedar (table 1).
A total of 21 species of reptiles and
amphibians were trapped or observed in the study
area (tables 1 and 2). Species which were only
observed, and not trapped, were primarily large
snakes.
Seven species of reptiles and amphibians were
collected in only one habitat; five species were
only trapped in the desert wash and two only in
the desert upland. The western whiptail lizard
(Cnemidophorus tigris) was the most abundant
species in all habitats except salt cedar, where
it did not occur. Two additional species, the
tree lizard (Urosaurus ornatus) and desert spiny
lizard (Sceloporus magister), were found in three
of the four habitats.
356
Although the salt cedar habitat had the
lowest density and diversity of all habitats
studied, the occurrence of 3 individual li~ards of
two species is noteworthy. K. Bruce Jones , in
several studies of salt cedar, has never collected
any re~tiles in this habitat type. Jakle and
Baucom conducted a bird census in a mixed salt
cedar and Goodding willow habitat at Picacho
Reservoir in central Arizona. During the census
only two individuals--a desert spiny lizard
(Sceloporus magister) and a coachwhip (Masticophis
flagellum)--were recorded in 17 km of bird
transects. Reptile populations were studied at
Whitlow Dam in central Arizona by Szaro and Belfit
(in press). They reported low numbers of reptiles
and amphibians in a riparian habitat consisting of
78 percent Goodding willow and 22 percent salt
cedar.
These studies all report a depauperate
herpetofauna in riparian habitats which were
composed of either salt cedar or a mixture of
Goodding willow and salt cedar. Szaro and Belfit
(in press) hypothesize that the recent development
of the riparian habitat behind Whitlow Dam (the
dam was constructed in 1959) and its isolation
from other such habitats may explain the relative
lack of reptiles. This area has no naturally
occurring relict riparian species nor has there
been any recent colonization. Jones et al (in
press) found that even naturally occurring
riparian habitats rapidly lose "riparian or
upland" species as they become more isolated.
However, another factor that all these habitats
have in common is a dense canopy. The dense
canopy reduces light penetration and inhibits the
developmeent of shrubs and a herbaceous layer of
ground cover. Indeed, Pianka (1966) studied
lizard populations in the western United States
and reported a strong positive correlation between
structural diversity and the total number of
lizard species.
3
Jones, K.B. 1983. Personal conversation,
U.S. Bureau of Land Management, Phoenix Training
Cente4, Phoenix, Arizona.
Jakle, M.D. and F.M. Baucom. 1983. An
inventory of birds and fish of Picacho Reservoir.
Unpublished report, Bureau of Reclamation,
Phoenix, Arizona.
Table 1.--Summary of amphibian and reptile abundance based on pit-fall trap data from the four habitat
types of the Florence study area, Pinal County, Arizona
Habitat Type
Desert
Upland
Species
Bufo punctatus
caTiisaurus draconoides
Cnemidophorus tigris
Gambelia wisli~
Holbrookia texana
Phrynosoma solare
Sceloporus ~er
Urosaurus ornatus
Uta stansburiana
Chflomeniscus cinctus
Leptotyphlops humilis
Tantilla planiceps
Total Individuals
Total Species
Total Trap Days
Species Diversity
1-~:/
Desert
Wash
Salt Cedar
Riparian
Mesquite
Riparian
( . 008 )!/
2 (.02)
6 (0.5)
10 (.08)
19 (.15)
1 (.008)
1
1
4
10
5
1
1
17 (.13)
3
6
43
1
1
1
14 (.13)
(.008)
(.008)
(.03)
(.03)
(.04)
(.008)
(.008)
5 (.05)
2 ( • 2)
2 (.05)
1 ( .01)
23 (.22)
4
106
1.05
3 (.06)
2
48
.63
1 (.008)
39 (.31)
5
126
.98
39 (.31)
9
126
1.81
Total
Individuals
11
13
22
1
1
1
(.007)
(.05)
(.10)
(.008)
(.002)
(.002)
(.03)
(.03)
(.05)
(.002)
(.002)
(.002)
104 (.26)
12
406
l/Indicates number caught
!/Indicates number caught per trap day
Table 2.--Summary of amphibian and reptiles observed but not trapped in the four habitat types of the
Florence study area, Pinal County, Arizona
Habitat Type
Species
Bufo woodhousei
COleonyx variegatus
Heloderma suspectum
Masticophis flagellum
Masticophis bilineatus
Salvadora hexalepis
Pituophis melanoleucus
Rhinocheilus lecontei
Crotalus atrox
Desert
Upland
Desert
Wash
Mesquite
Riparian
X
X
X
X
X
X
X.
X
X
X
X
357
X
Salt Cedar
Riparian
In the present study there was a significant
difference between the number of reptiles captured
in the two adjacent riparian habitats. A major
difference between these two habitats besides
plant species composition was habitat structure.
The mesquite bosque habitat had a well-developed
herbaceous dnd shrub layer, the salt cedar did not
because of its dense canopy. The reason salt
cedar habitat lacked these layers was due to its
dense canopy which reduced light penetration. In
addition to reducing structural diversity, reduced
light penetration also limited the number of
basking sites which are important to heliothermic
species. It is likely that the lack of structural
diversity and reduced light in a habitat limits
reptile and amphibian use.
LITERATURE CITED
Brown, D.E. 1982. Biotic communities of the
American Southwest--United States and
Mexico. Desert 'Plants 4:200-202.
Campbell, H.W. and S.P. Christman. 1982.
Field techniques for herpetofuana community
analysis. Herpetological Communities. USDI
Fish and Wildlife Service, Wildlife Research
Report 13, 239 pp.
s.w., R.R. Johnson, and
Aitchison. 1974. Population structure and social organizaDion of Southwestern
riparian birds. Amer. Zool. 14:97-108.
Carothers,
s.w.
The three individual lizards captured in the
salt cedar habitat were most likely strays from
nearby habitats. As previously stated, the salt
cedar habitat was a narrow band; the trapping
array was approximately 15 m from the edge of this
habitat type.
deVos, J.C., C.R. Miller, S.L. Walchuk, N.D. Ough,
and D.E. Taylor. 1983. Final report for the
biological resource inventory: Tucson
Division--Phase B, Central Arizona Project
Aqueduct. Contract No. 32-V0151, U.S. Bureau
of Reclamation, Phoenix, Arizona.
The pit-trapping technique we used worked
well for the smaller species of reptiles and
amphibians but did not adequately sample larger
species. Pit traps left in place for prolonged
periods of time may also attract predators that
eventually key in to the traps as a ready source
of easily captured prey. On one occasion we
recorded a large leopard lizard (Gambelia
wislizenii) escaping from a pit trap. This
species is known to prey on smaller lizards
(Stebbins 1966). By not trapping into the summer
rainy season, we also precluded getting an
adequate indication of the toad population in the
study area.
Jones, K.B. 1980. Distribution, ecology and
habitat management of the reptiles and
amphibians of the Hualapai-Aquarius Planning
Area, Mohave and Yavapai Counties, Arizona.
u.s. Bureau of Land Management Technical Note
No. 353, 134 pp.
Jones, K.B., L.P. Kepner and T.E. Martin. In
press. Species of reptiles occupying habitat
islands in western Arizona: a deterministic
assemblage. Oecologia.
Pianka, E.R. 1966. Convexity, desert lizards,
and spatial heterogeneity. Ecology 48:
1055-1059.
SUMMARY AND CONCLUSIONS
A total of 21 species of reptiles and
amphibians were either trapped or observed in the
study area. The desert habitats, desert wash and
upland, had higher species diversity and total
number of individuals than the riparian areas.
The desert wash had the highest number of habitat
specific species, five in comparison to the desert
upland which had two. The difference between the
two adjacent riparian habitats was pronounced.
Only three individuals of two species were
collected in the salt cedar habitat which was
significantly lower than any of the other habitats
sampled. The reason for this paucity of
herpetofauna suggested by the authors is its lack
of structural diversity and basking sites
resulting from a closed canopy which reduced light
penetration.
ACKNOWLEDGEMENTS
Our thanks go to Bruce Jones for his help in
the design of this study, data collection and
review of this manuscript. Our thanks also go to
Frank Baucom, Tice Supplee and the Bureau of Land
Management Wildlife Training Class for their field
assistance, and Scott Belfit, John Morgart, and
Robert Szaro for their review of this manuscript.
358
Shannon, C.E., and W. Weaver. 1948. The mathematical theory of communication, University
Illinois Press, Urbana, IL.
Stebbins, R.C. 1966. A field guide to western
reptiles and amphibians. Houghton Mifflin
Co., Boston, MA. 279 PP•
Stevens, L.E., B.T. Brown, J.M. Simpson, and
R.R. Johnson. 1977. The importance of
riparian habitat to migrating birds. In
importance, preservation, and management of
riparian habitat: A symposium. R.R. Johnson
and D.A. Jones, Tech. Coord., U.S.D.A. Forest
Service General Technical Report, RM-A3, pp.
156-164.
Szaro, R.C. and M.D. Jakle. In press. Avian use
of desert riparian and scrub habitats.
Condor.
Szaro, R.C. and s. C. Belfit. In press. The influence of a flood control dam on a central
Arizona herpetofauna. J. of Appl. Ecology.