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Microhabitats of Lizards in a Southwestern Riparian Community 1
2
K. Bruce Jones and Patricia Conley Glinski
3
Abstract.--Relationships between lizard abundance and
distribution, and certain selected microhabitats were determined for a southwestern riparian community. Distribution
of lizards in riparian habitat appear to reflect availability
of preferred habitats; certain lizards and microhabitats were
widespread while others were limited to small portions of the
study area. Patterns of lizard distribution in microhabitats
are discussed.
INTRODUCTION
cottonwood-willow community approximately 10 km
southeast of Wickenburg on the west side of the
river (elevation ca. 585 m). The study site was
on private land which is primarily managed as a
resort and bird sanctuary. Other than a small
number of cows grazed during winter months, there
was little disturbance on the site.
Concern over large-scale loss of riparian
habitat throughout the West has lead to numerous
recent studies on relationships between wildlife
and these vegetation communities. Although many
studies have documented relationships between
riparian habitat structure and birds (Stevens et
al. 1977, to name one), little data are available
on similar relationships in lizards. Literature
available on lizard microhabitats in riparian
communities are generally limited to a few
selected species. For example, Vitt et al. (1981)
determined differences in microhabitat among 3
arboreal lizards (Sceloporus magister, Urosaurus
ornatus, and Urosaurus gracios~in a mesquite
woodland. Although these studies provide
information on selected lizard species, they do
not assess habitat partitioning among an entire
riparian lizard community.
Overstory on the study area consisted of
cottonwood (Populus.fremontii), willow (Salix
gooddingii), mesquite (Prosopis velutina~nd
salt cedar (Tamarix sp.). Seep willow (Baccharis
salicifolia) made up the entire shrub understory,
and bermuda grass (Cynodon dactylon) was the only
perennial grass. Tree species were unevenly
dispersed throughout the study area; cottonwoods
and willows were near water or in areas where the
stream bed was formerly located, and mesquite was
on elevated sections dominated by sand (fig. 1).
The study area was approximately 1 m above
the stream bottom, with three small drainages
transecting approximately 1/2 the width of the
grid (fig. 1). Periodic flooding in these
drainages (observed 4 times during the study)
caused accumulation of debris (logs, limbs,
leaves, and occasionally tires) at the base of
trees, especially multibranched willows and
cottonwoods (hereafter referred to as debris
heaps, fig 2). Debris heap size varied, with some
piles as large as 1.8 m high and 6 m wide.
Although debris heaps are formed by flooding, the
top of these structures do not represent the high
water line during flooding; debris heap height is
achieved by addition of flood debris at the base
which forces formerly deposited material up along
the tree.
We studied a lizard community along the
Hassayampa River near Wickenburg, Arizona
primarily to determine associations between
lizards and riparian microhabitats.
THE STUDY AREA
The Hassayampa River south of Wickenburg,
Arizona provided an outstanding opportunity to
study a lizard community along a relatively
unaltered desert stream (no major water impoundments upstream). The study site consisted of a
1.9 hectare plot (60 x 315 m) in a mature
1
Paper presented at the North American
Riparian Conference, April 16-18, 1985, Tucson,
Arizona.
Substrate on the study area was mostly sand,
although there were areas with limited amounts of
rock (10-30 em dia). Rocky areas were mostly
limited to the three small drainages previously
described (fig. 1), and the river bed. Downed
logs, limbs, and leaf litter were abundant
throughout most of the study area, except in areas
2
Wildlife Biologist, U.S. Bureau of Land
Management, Phoenix, Arizona ·85068
3
Wildlife Manager, Arizona Game and Fish
Department, Wickenburg, Arizona 85358
342
M
(/)
~LLI
o•
o::<t
cw
l
._----TRAPS
1-22----------------------~
Figure !.--Distribution of habitats
cottonwood-willow stand, OS =
strate, OR = open canopy/rock
stand, DS = desert shrub, and
areas are the river and small
dominated by mesquite (fig. 1). Some leaf litter
patches under trees and shrubs were as deep as
10 em.
in the study area. CW =
open canopy/sand subsubstrate, M = mesquite
d = debris heap. Dark
drainages.
open between 3 March and 30 October 1984, and
checked every three days. Lizards captured in
traps were measured (snout-vent), weighed, sexed,
toe-clipped for individual identification, and
released into potential cover approximately 2 m
from the capture site. Pit-fall trapping was used
because it effectively traps most lizards,
including skinks which are inadequately sampled by
line transects.
METHODS
Lizard occurrence and abundance was
determined by a pit-fall trapping system
consisting of 110, double-deep 3 lb coffee cans
placed 15 m apart in a 22 x 5 grid trapping
configuration (1.9 ha, fig. 1). Covers were
placed approximately 15 em over the top of each
trap to reduce loss of animals due to
desiccation. Each cover was given a letter
representing a row (A-E) and a number (1-22) for
identification (fig. 1). Traps were continuously
While traveling between pit-fall traps, we
recorded observations of lizards on certain microhabitats (listed in table 1). These observations
included lizard age class, time of day and date,
the type of microhabitat, location on the grid
(nearest trap), and weather.
Microhabitat data were collected at each trap
by a point-center quarter method (Muller-Dombois
and Ellenberg 1974); each trap was used as the
center point for the procedure. This procedure
determines spatial arrangement of microhabitats
around each trap as a function of distance (total
110 points, 440 quarters or samples). In
addition, physical sizes of each microhabitat were
determined. Table 1 provides a list of microhabitats and measurements taken around each trap.
Table 1.--List of habitat components (microhabitats) measured around each trap.
Frequency = number of quarters with a certain component
1
Soil Type (at trap)
1
Vertical Cover (over trap)
1
Distance to leaf litter patch
Leaf Litter Depth
Leaf Litter Frequency
Distance to Log 1
Log Diameter
Log Frequency
1
Distance to Debris Heap
Debris Heap Width
Debris Heap Depth
Debris Heap Frequency
Distance to Rock I
I Microhabitats also recorded for lizard observations
Figure 2.--Example of a debris heap (2 m deep
x 3m wide).
343
Rock Width
~~~~a!~:q~:n~~ee 1
Tree Height
Tree Width (Crown)
Tree Frequency by species
Distance to Shrub 1
Shrub Height
Shrub Width (Crown)
Shrub Frequency
Distance to Grass Patch 1
Grass Height
Grass Frequency
Individual lizard species abundance (total
number of different individuals of each species)
was compared to microhabitat data at each trap and
submitted to a Step-wise Multiple Regression
analysis to determine significant relationships
between lizards and microhabitat. In addition,
habitat data were submitted to a Principle
Components Analysis, and mean factor scores for
each lizard were computed to graphically compare
species associations with microhabitat.
Chi-squared goodness of fit tests on lizard
abundance reveal that only tree (Urosaurus
ornatus) and desert spiny lizards were randomly
distributed over the entire grid (p >.05), whereas
all other lizards were found in clustered,
nonrandom patterns (p <.05). Earless and sideblotched (Uta stansburiana) lizards were trapped
only in areas dominated by cobble and gravel,
whereas zebra-tailed lizards (Callisaurus
draconoides) were trapped in areas with little
canopy and sand substrate. Earless and
zebra-tailed lizards were not trapped together
anywhere on the grid. Direct observations of
these lizards reveal similar relationships; earless and side-blotched lizards were observed
almost entirely on rocks, and zebra-tailed lizards
were always observed on open sand or leaf litter
(table 2). Western whiptail lizards
(Cnemidophorus tigris) were trapped or observed
mostly in areas-of low shrubs, leaf litter, and
open canopy (table 2), while Arizona skinks were
most abundant in areas with large debris heaps and
leaf litter.
Niche breadths were determined from a
Shannon-Wiener diversity index (see Vitt et al.
1981).
Species abundances at each trap were
submitted to a chi-squared goodness of fit test to
determine if species were randomly distributed
over the sample area. In addition, daily and
monthly activity patterns were determined for
lizards using trapping and observation data.
RESULTS
Based on microhabitat use (from observation
data only), tree and spiny lizards had the
greatest niche breadths, and earless and sideblothed lizards had the lowest (table 2).
Although Arizona skinks had a niche breadth of 0,
there was only one sighting of this lizard during
the entire sampling period.
Seven species of lizards were trapped on the
study site. The desert spiny lizard (Sceloporus
magister) was by far the most abundant species and
the greater earless lizard (Cophosaurus texana)
the lease common (table 2). Only Arizona skinks
(Eumeces gilbert! arizonensis) and greater earless
lizards were limited exclusively to the riparian
community; all other lizards occur in adjacent
Sonoran Desert habitats (Jones unpubl. data). In
addition to lizards, five species of snakes, one
aquatic turtle, and three species of amphibians
were trapped during the study (table 2).
Table 2.--Abundance, microhabitat use and niche breadth for 7 lizards on the
study area based on observation data. Niche breadth was computed
from a Shannon-Wiener diversity index from observation data. Numbers
in parentheses indicate the number of individuals pit-fall trapped.
Number of other reptiles and amphibians trapped are also listed.
Litter
(open)
(canopy)
Litter
(under)
(shrubs)
Open
Sand
Large
Logs
Rocks
Tree
Debris
Heaps
Shrub
Niche
Breadth
Western whiptail lizards (104)
40
.32
72
Multiple step-wise regression of lizard
abundance with 29 habitat variables listed in
table 1 revealed only a few significant relationships. Forty percent of the variation in
abundance of Arizona skinks was explained by the
depth, nearness and frequency of debris heaps and
leaf litter (Multiple corr. coef. = .67, p < .05).
Side-blotched and greater earless lizards were the
only other lizards with variation in abundance
explained by a habitat variable; 37% of abundance
in the former and 53% in the later was explained
by rock frequency and nearness of rock to traps
(Multiple corr. coef. = .67, p <.05) •
Arizona skinks (77)
.00
Zebra-tailed lizards (52)
39
.19
Greater earless lizards (11)
33
.14
13
.11
Side-blotched lizards (17)
Tree lizards (120)
Desert
~
Additional
snake (6),
mud turtle
toad (17),
Daily activity patterns of lizards were very
similar; peaks were generally between 1030 and
1200 h. Activity of Arizona skinks are probably
earlier, but we observed only one lizard. Monthly
activity patterns were relatively similar in the
spring; most lizard peak activity occurred in May
or June. Spiny, earless and zebra-tailed lizards
had another activity peak in September and
October, when primarily hatchlings and juveniles
were active. Although zebra-tailed lizards are
active a month earlier than earless lizards, their
monthly activity patterns are almost identical.
Similarly, activity patterns of skinks and whiptail lizards in the spring are nearly identical,
but small late summer and fall peaks do not
overlap, i.e. August in skinks and September in
whiptails.
24
47
31
30
17
19
• 60
lizards (182)
When mean factor scores are plotted for
lizards based on reduction of 29 variables listed
in table 1 into three axes via a Principle
.43
captures: Black-headed snake (6), Ground snake (1), Western blind
California kingsnake (1), Black-necked garter snake (1), Sonoran
(2), Woodhouse's and Southwestern toad hybrid (89), Colorado River
and W~stern spadefoot toad (7).
344
:·.·.·.,_,
Components Analysis, relative association of
lizards with microhabitats are illustrated (fig.
3). Generally, these data support trapping and
lizard observation data previously discussed.
breadth of tree lizards in our study vs. that of
Vitt et al. (1981) probably reflect greater
microhabitat diversity and abundance on our study
area, especially leaf litter, vegetation debris,
and rocks.
Body size and foraging style may play major
roles in determining association between lizards
and microhabitats. Because they are relatively
large, desert spiny lizards are less susceptible
to rapid ambient temperature changes, whereas the
smaller tree lizard's internal temperature will
change more rapidly with fluctuations in environmental temperatures. Vitt et al. (1981) suggest
that by remaining in the canopy of trees (and in
our study shrubs), lizards are less susceptible to
rapid ambient temperature change; tree and shrub
canopy modify the climate immediately surrounding
the lizard.
DISCUSSION
Our data show that lizards are partitioned in
two dimensions: spatially (microhabitat use) and
temporally (activity periods). A third dimension,
food, probably represents a third partitioning
dimension since lizards vary in size and
morphology, and use different microhabitats and
foraging styles (see Vitt et al. 1981). Daily and
monthly activity patterns of lizards on the study
area do not seem to play a major role in the
partitioning of habitat space; most lizards showed
little difference in activity patterns. Similar
to findings of Vitt et al. (1981) and Ortega et
al. (1982), microhabitat partitioning appears to
be of primary importance.
In addition to body size, other morphological
adaptations may also account for microhabitat uses
in riparian lizards. Zebra-tailed and earless
lizards are ecologically similar; both use a "sit
and wait" foraging strategy (Pianka 1966). The
major difference in foraging behavior between
these lizards is that zebra-tailed lizards wait
for prey on sand substrate, occasionally burrowed
(Belfit personal comm.), while earless lizards
perch on rocks or gravel (observed in this
study). Zebra-tailed lizards are morphologically
adapted for movement on open sand substrates (long
forelegs and hindlegs, Pianka and Parker 1972).
Presumably this adaptation would also enhance
burrowing, but makes use of other microhabitats,
such as rock, less adaptive (see Vitt 1981 for
discussion of morphological adaptations and
microhabitat use). This may in part explain
current allopatry of these two lizards on the
grid, although competitive exclusion can not be
ruled out.
The distribution of lizards on the study area
appear to reflect availability of certain microhabitats, although most lizard abundance was not
specifically correlated to microhabitat. Capture
of lizards in transit between preferred microhabitat may account for lack of correlation
between lizard abundance and certain microhabitats.
Desert spiny and tree lizards are common
throughout the study site, which reflect the
area's consistently abundant tree and surface log
microhabitats. Widespread distribution also
reflect these lizards ability to use different
microhabitats as evidenced by their relatively
high niche breadths. Vitt et al. (1981) showed
similar relationships between these lizards and
tree and surface log microhabitats. Greater niche
1.5
o
0
a:
Association of side-blotched and greater
earless lizards with rock may reflect these
lizards' foraging style. Both lizards use a "sit
and wait" foraging strategy (Pianka 1966).
Presumably, this type of foraging style would be
enhanced by use of rock (better visibility). This
advantage would be partially offset by increased
predation due to exposure. The western whiptail
lizard uses a "widely foraging strategy", moving
along the ground and feeding in litter patches
(similar to a bird) in areas near trees and shrubs
where sunlight penetrates (Pianka 1970). This
strategy appears to explain this lizard's
association with similar microhabitats on our
study area.
1- Whiptail Lizard
6- Tree Lizard
2- Arizona Skink
7- Spiny Lizard
3- Zebra-tolled Lizard
4- Ear less Lizard
5- Side- blotched Lizard
2
-.5
-.25
0
.25
.5
Although we understand how many of the
behavioral and morphological adaptations make
certain lizards more adaptive in specific
microhabitats, it is impossible to infer
contributions made by each adaptation in
organizing current lizard distributions on the
study area (see Vitt et al. 1981; Ortega et al.
1982). Competition may have played a major role
in determining initial segregation of lizards into
microhabitats during colonization of the area, but
.75
COMPONENT II
Figure 3.--Arrangement of riparian lizards along
three habitat vectors (principle components).
345
this mechanism probably plays a minor role in
maintaining current distribution of lizards in the
riparian community; competition has been reduced
by behavioral and morphological adaptations as
previously discussed (see Vitt 1981; Vitt et al.
1981; Ortega et al. 1982; Tinkle 1982; Price et
al. 1985).
LITERATURE CITED
Belfit, S. C.
Personal communication.
Fitch, H. S. 1955. Habits and adaptations of the
Great Plains skink. Ecol. Monog. 25:59-83.
Gates, G. 0. 1958. A study of the herpetofauna in
the vicinity of Wickenburg, Maricopa County,
Arizona. Trans. Kansas Acad. Sci. 60:403-418.
The association of Arizona skinks with debris
heaps and litter, and secretive behavior (only one
lizard observed at large during the entire study),
are consistent with data from other studies of
skinks (Fitch 1955; Jones 1981; Jones et al.
1985). Although we observed only one lizard in a
debris heap, skinks are known to deposit eggs and
seek cover in these microhabitats (Fitch 1955,
Jones unpubl. data).
Jones, K. B. 1981. Effects of grazing on lizard
abundance and diversity in western Arizona.
Southwest. Nat. 26(2):107-115.
Jones, K. B. 1985.
Amph. and Rept.
The Arizona skink is known only from the
Hassayampa River (Jones 1985), and this site is
nearly 350 m lower than any other location for the
species in Arizona (Jones et aL 1985). Most
skinks occur within the Upper Sonoran Life-zone.
Therefore, it appears that the Arizona skink has
survived on the Hassayampa River due to moderating
effects of deciduous trees, perennial water, and
large debris heaps and leaf litter. The loss of
these microhabitats due to alteration of the
riparian community would probably extirpate this
subspecies. For example, water impoundment
upstream could reduce flood conditions and prevent
the formation of large debris heaps. Likewise,
excessive livestock grazing could dramatically
reduce willows and cottonwoods which assist in
formation of debris heaps. Significant losses in
riparian habitat may also extirpate the earless
lizard, black-headed snake (Tantilla
hobartsmithii), Sonoran whipsnake (Masticophis
bilineatus), ring-necked snake (Diadophis
punctatus) and Sonoran mudturtle (Kinosternon
sonoriense) from the area since these reptiles do
not occur in adjacent Sonoran Desert habitat
(Gates 1958; Jones unpubl. data).
Eumeces gilbert!.
In Press. •
Cat. Amer.
Jones, K. B., L. P. Kepner, and T. E. Martin.
1985. Species of reptiles occupying habitat
islands in western Arizona: a deterministic
assemblage. Oecologia In Pres~.
Mueller-Dombois, D., and H. Ellenberg. 1974.
and methods of vegetation ecology.
p. 110-118. John Wiley and Sons, NY.
Aims
Ortega, A., E. Maury, and R. Barbault. 1982.
Spatial organization and habitat partitioning
in a mountain lizard community of Mexico.
Oecologia 3(3):323-330.
Pianka, E. R. 1966. Convexity, desert lizards,
and spatial heterogeneity. Ecology
47:1055-1059.
Pianka, E. R. 1970. Comparative autecology of the
lizard Cnemidophorus tigris in different parts
of its geographic range. Ecology 51:703-720.
Pianka, E. R., and W. S. Parker. 1972. Ecology of
the iguanid lizard Callisaurus draconoides.
Copeia 1972:493-508.
It is interesting to note that some lizards
known to inhabit adjacent Sonoran Desert do not
occur in the riparian community. Most of these
species, including banded geckos (Coleonyx
variegatus), Gila monsters (Heloderma suspectum),
and leopard lizards (Gambelia wislizeni) use
rodent burrows as cover sites. In our study area,
there were few rodent burrows. In fact, only pack
rats (Neotoma sp.) and desert shrews (Notiosorex
crawford!) were trapped on the grid; both species
use debris heaps for cover. Lack of burrowing
rodents may reflect inadequate burrowing substrate
(mostly sand and large rock) and a high water
table, which makes our study area unsuitable to
lizards that rely on rodent burrows for cover.
Price, A. H., J. L. LaPointe and J. W. Atmar.
1985. The ecology and evolutionary implications of competition and parthenogenesis in
Cnemidophorus. Biology of the Cnemidophorus.
In Press.
----
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. USDA Forest Service Gen.
Tech. Rp., RM-A3, p. 156-164.
Tinkle, D. W. 1982. Results of experimental
density manipulation in an Arizona lizard
community. Ecology 63:57-65.
Vitt, L. J. 1981. Lizard reproduction; habitat
specificity and constraints on relative clutch
mass. Amer. Nat. 117(4):506-514.
ACKNOWLEDGEMENTS
We thank Scott C. Belfit, Richard Glinski,
Lauren P. Kepner, and William G. Kepner for review
of this manuscript. We also thank Richard
Glinski, Chuck Hunter, and John McConnaughey for
helping with data collection.
Vitt, L. J., R. c. van Loben Sels, and R. D.
Ohmart. 1981. Ecological relationships among
arboreal lizards. Ecology 62(2): 398-410.
346
,·;·:.·: