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Spatial Distribution of Desert
Tortoises (Gopherus agassi'ii)
at Twentvnine Palms.
californib: ~rn~~icatidns
for
Relocations1
Ronald J. Baxter2
The desert tortoise (Gopherus agassizii) is a species whose future is uncertain. Increased use of the deserts
by man (Luckenbach 1982) has led to
the point where the tortoise was officially listed as "threatened" in the
state of Utah (Dodd 1980).The U.S.
Fish and Wildlife Service stated in
1985 that "...listing [of the desert tortoise as a threatened or endangered
species] is warranted but precluded
by other pending proposals of higher
priority" (Federal Register. 50(234):
49868-49870,1985).
In California, the desert tortoise is
the official state reptile, and is fully
protected under law. The tortoise is
also protected in Arizona and Nevada.
As part of a larger population
study (Stewart and Baxter 1987) at
the Twentynine Palms Marine Corps
Air Ground Combat Center
(MCAGCC), the spatial distributions
of tortoise captures and burrows
were analyzed and compared against
randomly generated distributions.
Questions asked were: (1)Are tortoise captures and burrows randomly located across the landscape
Paper presented at symposium, Management of Amphibians, Repti!es, and
Small Mammals in North America. (Flagstaff, AZ,July 19-21 , 1988).
2RonaldJ. Baxter received his master's
degree in biology for working on the desert
tortoise while at California State Polyfechnic University,Pomona. He is currently completing his doctorate a t the Department of
Bi~logicalSciences, Northern Arizona University, Flagstaff, AZ, 860 1 1-5640.
Abstract.-The spatial distribution of desert
tortoises in relation to plant communities was
compared against randomness. Tortoise captures (n
= 120) and tortoise burrows (n = 160) exhibited nonrandom distributions across a 1.29 square kilometer
study plot at Twentynine Palms, ~alifornia.
Results
imply high diversity plant ecotones and
communities, and possibly soil characteristics are
important in determining tortoise densities. Nonrandomness in tortoise populations dictates that
relocation sites must include specific vegetafioml,
topographic and edaphic habitats used by the
parental populations.
and/or are they associated with certain habitat types or site characteristics, and if so, (2) what implications
do these distributions have for future
management decisions?
Methods
Twentynine Palms MCAGCC is Ioca ted approximately 5 kilometers
north of Twentynine Palms, San Bernardino County, California, in the
southwestern extreme of the Mojave
Desert. All fieldwork was performed
in the Sand Hill Training Area which
is in the southwest corner of the
MCAGCC. Elevations ranged from
865 meters atop Sand Hill to about
730 meters in the bottom of Surprise
Springs wash. Data were collected
Monday through Friday, 14 April
through 18 July, 1986.
Systematic searching methods for
tortoises and tortoise burrows were a
derivation of procedures described
by Berry (1984). A 1.29 square kilometer permanent study plot was established, with its approximate center being the NE 1/4, SW 1/4, NE 1/
4, of S7, T2N, R7E (San Bernardino
Base Meridian) This site offered a
wide variety of habitats including
washes, sandy basins, rolling hills
and alluvial bajadas. The plot was divided into 64 equal sized "grids" of
142 meters on a side, with grid corners marked by posts. Grids were
searched in parallel belts until the
entire plot had been searched twice;
once with the belts running northsouth, and once with the belts running east-west. The plot was also
randomly searched.
\'?hen an active tortoise was encountered, it was marked, weighed,
sexed, measured and photographed.
Each tortoise was assigned a unique
number, and rmaa~ginalscu tes were
notched with a small triangular file
for relatively permanent identification. The precise location of the capture was noted by its distance (meas-.
wed by rangefinder) and compass
aspect to the nearest grid past. Data
collected at each capture site included plant community, temperatures at the ground, 1 centimeter,
and 1 meter, cloud cover, wind
speed and direction, closest burrow,
closest plant, and any unusual behavior.
Precise location of tortoise burrows were similarly detern:ine$ by
rangefinder and compass. Data collected at each bumow included planl.
community, distance and identification of nearest ecotone, distance to
nearest wash, distance to nearest HiIaria rigda, slope aspect and steepness, opening compass aspect and
position, length, depth, and tunnel
characteristics. In this study area, it
was difficult to determine if a burrow high on a slope above a wash
was part of the wash "system."
Therefore, it was arbitrarily decided
to include burrows in the wash plant
community only if they were actually
found the wash bed.
Six visually identified plant communities (Latr/ Amdu, Hiri/ Amdu,
Mixed, Wash, Sparse Wash and
Meadow) were mapped within the
study plot, and seven 15-meter line
transects (total of 105 meters) were
measured which included bare
ground as a species. Transects were
1:LATWAMDU
2:MIXED
5 :MEADOW
:BURROW
3:SPARSE WASH #:WASH
4:HIRI/AMDU
u
I
NORTH
100
METERS
Figure 1 .-Approximate distribution of plant
communities and tortoise burrows across
the study plot. See text for explanation of
plant community names.
randomly located in each of these six
communities. Standard transect statistics (density, coverage, frequency,
relative density, relative coverage,
relative frequency and importance
values; Brower and Zar 1984) were
computed for each community.
Simpson's diversity indices (Simpson
1949) were computed and compared
with Student's t-tests (Keefe and
Bergerson 1977).Available annuals
as well as perennials were used to
give the best estimate possible for
diversity. In addition, seven soil
samples were taken in each community, and analyzed for soil separates
(Brower and Zar 1984) and soil calcium (Hach 1983).Finally, nine
"sand scats" were collected during
the field work and tested for calcium.
A random model for capture and
burrow locations was formed by
combining a number of statistical
tests. First a master map of the plot
was constructed from actual field
data at a scale of 1:2000. All capture
positions, burrows and plant community boundaries were plotted on
this map and checked against aerial
photographs. The area covered by
each plant community was then determined by the use of a planimeter.
An X-Y scale ranging from 0 to 8 was
plotted on the sides of the map, and
a list of 328 random numbers was
generated by computer. These numbers were paired, and the pairs be-
came the X-Y coordinates of random
positions against which observed
capture and burrow locations were
compared. Distances to the nearest
wash and ecotone were determined
for these random locations by measuring them on the map, and csmpared against observed by Student's
t-tests (Zar 1974). Observed capture
distances were sometimes combined
with previous data recorded in this
area (Baxter and Stewart 1986).
A lack of habitat preference may
be suggested if burrows and captures
were found in the same relative
abundance as the plant communities.
In addition, if the expected plant
abundance distribution differed significantly from random an extrapolation of observed distributional characteristics could be accomplished. An
assumption of this test was that a
distribution of randomly generated
locations (with randomness confirmed) produced a random frequency distribution. Expected frequencies for burrows and captures
were generated by multiplying the
total number of actual burrows or
captures by the percent of the plot
encompassed by each plant community. These values were compared by
a goodness-of-fit chi-square test (Zar
1974).In addition, the number of
burrows or captures per grid were
compared against expected values as
derived from the Poisson distribution by a goodness-of-fit test.
Results
Plant Communities and Soils
Vegetation analyses revealed six distinct plant assemblages (table 1; fig.
1). Plant community distributions
generally reflected the relief of the
plot. The higher, more well-drained
hills were dominated by an association of Larrea tridentata and Ambrosia
dumosa, which encompassed plot
area the most ("Eatr / Amdu"; table
1) and exhibited relatively high plant
diversity.
Found on 37.2%of the plot area
was the "mixed" community that
generally occupied intermediate areas between the Latr/Amdu and either washes or areas of high Hilaria
rigida density. It was characterized
by the association of L, iridenfata, A.
dumosa and H. rigida, and was found
most often on the slopes above, and
narrow linings next to washes. The
edge, or ecotone, of this community
with the Latr/Amdu community is
extensively discussed bebw.
A highly diverse plant community
was found in the washes (table 1; appendix 1).Such areas not only contained these perennial species, but
also a significant number of other
species found only in this cornmunity, giving it the highest species
richness of any community.
Small uplifts within wash channels
seemed to support a more open type
of wash vegetation, "sparse wash."
Such areas had many species common to the washes (appendix 1), yet
much of this community was essentially pure stands of the opportunistic grass, Schismus barbatus.
A community ("Hiri/Arndu")
consisting primarily of H. rigida and
A. dumosa was located in upland basins where L. tridentafa was not
found. Such areas were low in habit
and diversity, and very sandy.
Finally, near the south boundary
of the plot, a small "meadow" of
mostly Baileya multiradiata was
found. Since no tortoises or tortoise
burrows were found there, it was
eliminated from further analyses.
Bare ground, when treated as a
species in transect analyses, had
overriding importance values and
dominance in all communities (appendix 1). This is often the case in
desert environments. Likewise importance values of S. barbatus were
extremely high in all communities,
pointing to the generally disturbed
nature of the site. Comparisons of
Simpson indices for the communities
revealed significant differences (p <
0.05) in diversity for all communities
except two. The htr/Arndu and
wash communities were not significantly different (p > 0.50) in their diversity.
Soils were found to be somewhat
similar in constituency (table 21, each
being composed to a large degree of
sand. Soil calcium levels (table 3)
were shown to differ significantly.
No detectable calcium was found in
any of the sand scats tested.
Tortoise Burrows
A total of 164 tortoise burrows was
found on the study plot (fig. 1).Seventy-five percent were found under
bushes, 14%with the opening under
a bush but the tunnel proceeding into
an open area, 8% with entrances in
the open but the tunnels proceeding
under a bush, and 3%entirely in an
open area. Thus, almost all of burrows (97%)were associated with
shrubs. Of these, '71% were associated with L. tridentata, 13%each with
H. rigida and A. durnosa, and another
3%with other species.
Neither the distribution of observed or random burrows differed
significantly from the Poisson expected frequencies (table 4). Likewise, when the distribution of observed burrows was compared
against the distribution of random
burrows, no significant difference
was found (chi-square.= 2.224; DF =
5; p > 0.50). Thus, when the entire
plot area is considered, tortoise burrows exhibited a random pattern
across the landscape. However, this
was a relatively large scale test of
burrows per arbitrary unit area, and
says nothing about the pattern of tortoise burrows in relation to plant
communities.
The abundances of tortoise burrows (both observed and random) in
each plant community were compared against expected frequencies
generated by the abundances of the
plant communities (table 5). Burrows
were sparse in the.Hiri/Amdu and
wash communities. Observed burrow frequency distribution did not
differ significantly (p > 0.25) from the
expected frequency distribution. The
observed frequency distribution differed significantly from the random
distribution (chi-square = 11.74; DF =
5; p < 0.051, as did the expected distribution (chi square = 158.9; DF = 5;
p < 0.001).
Mean observed burrow distance
to the closest wash was compared to
the mean distance from the randomly located burrows (table 6).
Comparisons for the sparse wash
and Hiri/Amdu communities were
not done because they would be biologically meaningless or had too low
a sample size, respectively. For all
burrows, and for burrows found in
either the Latr/Amdu or mixed communities, no significant differences
between random and observed wash
distances were detected. Thus, observed tortoise burrows were not located closer to washes than a set of
random points predicted. However,
examination of the spatial pattern
(fig. 1) reveals a lack of burrows deep
within Latr/Amdu and Hiri/Amdu
areas which were furthest away from
any possible wash influence.
Fast observations seemed to indicate a correlation between burrow
location and the presence of the edge
of the H. rigida distribution (Baxter
and Stewart 1986).The approximate
distribution of observed burrows to
this edge may be seen in figure 1.
Mean edge (ecotone) distance of observed burrows was compared to
that of random sites (table 7). Highly
significant differences in ecotone distances were found in both communities, and also when combined. Thus,
burrows were found closer to tkie
ecotone than a set of random points.
Tortoise Captures
Similar analyses were performed for
tortoise capture sites. There were a
total of 120 tortoise captures and recaptures of 41 individual tortoises.
The observed captures per grid,
along with the randomly located capture frequencies (same points used
for random burrow sites) were compared against expected values derived from the Poisson distribution
(table 8). Observed capture sites
showed a statistically significant departure from Poisson expected frequencies by the goodness-of-fit test
(p < 0.05).
Frequencies of capture sites in
each plant community were compared against expected values gener-
ated by community abundance (table
9). Observed distributions for both
all captures, and for captures of active tortoises (those found outside of
burrows) differed significantly from
expected. These two observed distributions did not differ from each
other (chi-square = 0.5385; DF = 5; p
> 0.99), yet differed significantly
from the randomly generated distribution (chi-square = 18.957 and
19.556, respectively; DF = 5; p <
0.005). Thus, tortoise captures were
not found across the plot in a random fashion as would be predicted
by a set of randomly generated
points. Habitat preference for washes
was seemingly indicated, as was a
lack of preference for Hiri/Amdu
areas. These results also gave further
support to the non-randomness exhibited in the Poisson analyses.
To further examine this apparent
non-random distribution of capture
locations, the mean observed cavture
distance to washes was compared to
that of the randonlly located sites
(table 10).When all capture sites, or
captures within the mixed community were considered, a significant
A
difference between random and observed locations was demonstrated.
However, mean distance to washes
within Latr/Amdu sites was not significantly different from the random
set of points, possibly because the
Latr/ Amdu communities were generally located further away from
washes, as well as the high variation
in observed Latr/Amdu distances.
These results, along with the results
of the community analysis above,
seemed to indicate a high degree of
tortoise activity near the washes.
Distances to the edge of the H.
rigida were compared between randomly generated and observed capture locations (table 11).Highly significant differences in mean distances
were demonstrated for both the
Latr/Amdu community, and for captures found in the mixed and La&/
Amdu communities combined. Cap-
tures within the mixed community
alone were not significantly different
from randomly generated locations.
It seems then that captures, like burrows, were generally not found far
within Latr/ Amdu areas, but tended
to be near its edge with the H. rigida
distribution (i.e. the mixed comrnunity). Because there was no difference within the mixed community
alone, differences from random for
captures within the mixed and Latr/
Amdu communities combined were
probably significant due to the
higher number of observations
within the La&/ Amdu community
biasing the sample. Thus, it seems
that tortoises tended to stay either
near the washes, the mixed community, or its ecotone with the Latr/
Amdu community, and generally
were not going far within the Lab/
Amdu community.
Discussion
Since the establishment in 1975 of the
Desert Tortoise Council, the amount
of literature published on the desert
tortoise has been considerable.
Oddly enough, only a few papers
may be found that attempt to say
what exactly makes good tortoise
habitat.
A paper by Schwartzmann and
Ohmart (1978) quantified the frequency of use by tortoises in a number of "habitat types." Their study
took place in the Picacho Mountains
of Arizona's Sonoran Desert, where
tortoises are known to frequent
rocky hillsides and are absent from
valley bottoms (Fritts 1985). Habitat
preferences are just the opposite in
the Mojave Desert, and thus their results may not be applicable. Likewise, Walchuck and Devos (1982)
studied tortoise habitat, but this was
also in the Sonoran Desert of Arizona.
In a draft report, Weinstein et al.
(1986) performed several multivariate analyses on the large Bureau of
Land Management tortoise database.
Several attempts were made to correlate abundance with habitat characteristics. Not only were many of
these characteristics derived from the
extrapolation of large scale map data,
but the best fit analysis was found by
designating "corrected sign" of the
transects (the dependent variable;
not actual population numbers) into
arbitrary categories. Indeed, one of
the authors (Berry and Nicholson
1984) has shown that roughly onethird of population estimates (7 out
of 20 and 4 out of 6) based on sign
transects did not agree with intensive
plot censuses. Also, Turner et al.
(1982) stated that sign transects
"...cannot provide the accuracy and
precision needed. .." In addition,
Fritts (1985) stated that such
transects are "...subject to error."
Thus the accuracy of sign transects
are open to serious debate, and although the discriminant analysis
showed some promise as a method
for accessing regional abundances,
the nature of the analysis and the
underlying assumptions of both the
data acquisition and techniques leave
much to be desired.
When viewed from the larger
scale of regional or even plot area,
these data seem to indicate that burrows were found in a random fashion when predicted by burrows per
unit area. However, different results
may have been obtained by changing
the size and shape of the grids. For
example, 32 larger rectangular grids
may very well have produced different results than the 64 smaller square
grids used in this study. In addition,
such an analysis said nothing about
distributions in relation to habitat
characteristics. Therefore, such a test
should be used as a starting point
and/or support for other tests, and
locally is of limited use by itself for
describing ecologically meaningful
patterns which may exist.
With closer examination, these
data also indicate that burrow locations were assembled in a pattern
similar to the non-random distribution of plant communities. Withincornmunity examinations revealed
patterns of burrow site utilization,
and such patterns were strongly nonrandom. At Sand Hill then, while a
majority of burrows were not found
in washes, they were often found
within easy walking distance to a
wash. Very often, burrows were on
slopes high above washes, and possibly within its area of influence. They
were not found far within either the
Latr/ Amdu or Hiri/Amdu communities, but were tied strongly to the
edge of these communities with the
mixed community.
Washes are sometimes cited as
being of great importance to tortoise
populations (Burge 1978, Hohman
1977, Lowe 1964).However, results
of this study indicated that tortoise
burrows were not significantly closer
to washes than a set of randomly selected sites. Burge (1978) found 207
(26%) of 783 burrows and pallets
were associated with washes. Of
these, 56 (27%)were actually within
a wash bed. However, Burge apparently eliminated some burrows from
the analysis due to their physical
characteristics. The discrepancy may
be due to the definition used. In this
study, wash burrows were defined
as such, only if they were actually
within the sandy wash bottoms. In
this way, burrows which were on
wash banks, were counted as being
in the plant community of the bank.
Burrows located on wash banks, and
even further away, may have been
associated with the wash, and a reclassification of these burrows may
show washes to have a more important influence in burrow analyses.
Examinations of the actual burrow
distribution (fig. 1) seemed to indicate that they were mostly absent
from areas highly isolated from wash
influence.
The significance of capture locations in relation to the washes also
seemed to refute the burrow/wash
results. Washes clearly supported a
disproportionate amount of activity
in relation to their abundance on the
plot. Preliminary investigations of
tortoise communities near Kramer
Junction, San Bernardino County,
have also shown tortoises are probably localizing their activities in the
vicinity of washes (Baxter, unpub.
data).
Several things may explain the
disproportionate amount of captures
in the washes. Greater visibility of
tortoises in the washes may be a factor. Utilization of highly diverse
plant resources there may also contribute to the localization of activity.
Finally, washes may simply serve a
natural highways for tortoise movements. For instance, several relocated
tortoises at Kramer Junction abruptly
turned and followed trails and
washes upon their release (Baxter,
unpub. data). Regardless, these data
seem to support washes as an important habitat characteristic for tortoises at Sand Hill. If this population
is representative of other Mojave
populations, the importance of
washes in potential relocation sites
will be highly significant in assuring
the best chance of survival for the
relocates. Further, impacts to
washes may have highly significant
impacts on a population if it is localizing its activities there.
These data support the importance of large woody shrubs (i.e., L.
tridentata) for successful burrow construction at this site. Similar results
have been reported by Burge (1978)
who found 72% of "cover sites" associated with shrubs. Berry and
Turner (1984) found 75% of juvenile
burrows associated with bushes.
Support for the burrow roofs and
added protection from predators are
likely reasons for this association.
Regardless, the absence of L. tridentata from the Hiri/ Amdu community
is probably a major reason for the
tortoises not utilizing those areas.
Unsuccessful burrow construction by
virtue of the sandier soils is another
possibility. This latter assumption is
supported by the Weinstein et al.
(1986) analysis which showed "soil
diggibility" as a highly significant
regression variable.
However, the lack of burrows
deep within Latr/ Amdu communities is not explained by the spatial
abundance of L. tridentata. The high
frequency of burrows and captures
point out that something is being
sought there by the tortoises. Yet,
deep ventures within these areas apparently d o not provide resources
that are unavailable at their edges.
Perhaps the higher levels of soil calcium found there are being utilized.
Tortoises must support a massive,
ossified shell, as well as lay eggs, and
calcium may be a very important nutrient. Tortoises have been observed
eating dirt (geophagy) and then producing "sand scats," and calcium
levels have been hypothesized as an
explanation for this behavior (Sokol
1971).The lack of calcium in the sand
scats tested seems to support this
hypothesis.
In contrast, such deep ventures
would take the tortoises away from
the distribution of H. rigzda, and the
frequented and diverse washes. Although detailed scat analyses were
not performed, field examination of
hundreds of scats seemed to suggest
that H. rigida is a significant dietary
component. Turner and Berry (1986)
found H. rigida as a part of the diet of
tortoises near Goffs, California.
It would seem then that tortoises
in this area are exhibiting some characteristics similar to "edge" species.
That is, tortoise activity is centered
on the two communities with the
highest vegetational diversity that
border extensive areas of H. rigida.
Since burrows are closely associated
with L. tridentata, they in turn are
found primarily along the only
highly diverse ecotone of the H.
rigida distribution where L. tridentata
importance is the highest. This importance of H. rigida and L. tridentata
is further shown in appendix 1. The
two communities where tortoises
were not found (i.e., deep Latr/
Amdu and Hiri/Amdu) each lack
one of these species. The assumption
that they are focusing on high diversity areas is further supported by
Weinstein et al. (1968) which shows
"food availability" as the single most
significant regression variable. Finally, Spealce (1986) reports that for
the gopher tortoise (G. polyphemus),
"Edge habitats or ecotonal areas appear important to tortoises. In each
habitat type except oldfields tortoises
tended to cluster near the edges. In
general, the more edge availability in
a given hahitat, the higher the tortoise density."
In summary, tortoises utilized the
environment at Sand Hill in a mostly
non-random fashion. Tortoise captures were spread out between two
communities of highly diverse resources, with clustering occurring at
either edge. Tortoises frequented
washes and the ecotonal edge of the
Latr/ Amdu community, with many
found in the intermediate mixed
community. Tortoises were not
found deep within Latr/Amdu or
Hiri/Amdu areas. Burrows were
found close to the ecotone of the
mixed and Latr/Amdu communities.
Burrows were not found closer to
washes than randomly located burrows, although this point is far from
clear. Burrows were located close to
the one highly diverse edge of tortoise activity area where the importance of L. tridentata and soil calcium
were the greatest, and were not
found in Hiri/Amdu areas where L.
fridentata was absent; and soils were
the most unconsolidated.
Non-randomness in tortoi.~poplalations is especially important for the
management considerations of relocation. Clearly, despite the best efforts of concerned managers, the use
of the deserts will continue to increase and the frequency of tortoise
relocations will also undoubtedly increase. If tortoise distributions are
random, relocation management essentially becomes a search for safe
relocation sites roughly similar to the
"parental" area. No special consid erations of unique habitat types are
required. If on the other hand they
are not, then the relocation sit&)
must include such high-use habitats
as those found in the parental site. In
addition, severe disturbance of such
favored habitats will in turn have severe impacts on the populations, particularly if small.
This study indicates that the nonrandomness exhibited by the Sand
Hill tortoises is probably a function
of the non-randomness of highly diverse plant assemblages and edaphic
characteristics. Thus, the presence of
diverse land forms and their asswiated plant communities and diverse
edges within future relocation sites
should be of significant importance
to the manager. Areas which "look
good" to the relocation manager may
not supply the needed resources for
the relocates. These data are in need
of further support however. If such
patterns are exhibited in other populations, biologists and managers may
use such techniques to successfully
determine possible habitat requirements, and help insure the survival
of one of the Mojave's most enigmatic species.
The author wishes to express sincere
thanks to Dr. Glenn R. Stewart of Cal
Poly, Pomona for physical help and
moral support during the fieldwork,
and for his abiding friendship. Many
thanks also to the entire staff at the
MCAGGC for logistical support. Finally, t h a n k to K. Berry, D. Speake
and R. Szaro for their constructive
reviews of this manuscript.
This work was supported by
United State Navy contract
N6247484RPOOV48, which was administered by the Cal Poly Kellogg
Unit Foundation. Additional equipment support was supplied by
graduate research funds of Cal Poly,
and monies received from the Chuck
Bayless and Tim Brown memorial
scholarship funds. 'Travel funds were
supplied by Sigma Xi, The Scientific
Research Society.
Literature Cited
Baxter, Ronald J ., and Glenn R. Stewart. 1986. Report of the continuing fieldwork on the desert
tortoise (Gopherus agassizii) at the
Twentynine Palms marine corps
base. Proceedings of the symposium, [Palmdale, Calif., March,
19861. The Desert Tortoise Council, Long Beach, Calif [in press].
Berry, Kristin H. 1%4. A description
and comparison of field methods
used in studying and censusing
desert tortoises. Appendix 11. In
The status of the desert tortoise
(Gopherus agassizii) in the United
States. Kristin Berry, editor. Report to the U.S. Fish and Wildlife
Service, Sacramento, Calif. Order
NO. 11310-0083-81.
Berry, Kristin H., and Lori L.
Nicholson. 1984. The distribution
and density of desert tortoise
populations in California in the
1970's. In Kristin Berry, editor.
The status of the desert tortoise
(Gopherus agassizii) in the United
States. Report to the U.S. Fish and
Wildlife Service, Sacramento, CA.
Order No. 11310-0083-81.
Berry, Kristin H., and Frederick B.
Turner. 1984. Notes on the behavior and habitat preferences of juvenile desert tortoises (Gopherus
agassizii) in California. Proceedings of the symposium, [Lake Havasu City, Ariz., March, 19841. The
Desert Tortoise Council, Long
Beach, CA.
Brower, James E. and Jerrold Zar.
1984. Field and laboratory methods for general ecology. William
E. Brown, publishers. Dubuque,
Iowa.
Burge, Betty. 1978. Physical characteristics and patterns of utilization
of cover sites used by Gopherus
agassizii in southern Nevada. Proceedings of the symposium, [Las
Vegas, Nevada, 19781.The Desert
Tortoise Council, Long Beach, CA.
Dodd, C. Kenneth. 1980. Endangered
and threatened wildlife and
plants: listing as threatened with
critical habitat for the Beaver Dam
slope population of desert tortoise
in Utah. Federal Register 45(163):
55654-55666.
Fritts, Thomas H. 1985. Ecology and
conservation of North American
Tortoises (genus Gopherus). 11.
Evaluation of tortoise abundance
based on tortoise sign detected in
field surveys. Prepared for: U.S.
Fish and Wildlife Service, Denver
Wildlife Research Center, University of New Mexico, Albuquerque.
NM.
Hach Company. 1983. Soil calcium
and magnesium test kit (model
14855)instruction manual. Hach
Company, Inc., Loveland, CO.
Hohrnan, Judy P. 1977. Preliminary
investigations of the desert tortoise on the Beaver Dam slope in
Arizona. Proceedings of the symposium, [Las Vegas, Nev., March
19771. The Desert Tortoise Council, Long Beach, CA.
Keefe, T. J. and E. Bergerson. 1977. A
simple diversity index based on
the theory of runs. Water Resources 11:689-691.
Lowe, Charles. 1964. The vertebrates
of Arizona. The University of Arizona press, Tucson, Ariz.
Luckenbach, Roger A. 1982. Ecology
and management of the desert
tortoise (Gopherus agassizii) in
California. In R. Bruce Bury, editor. North American tortoises:
conservation and ecology. U.S.
Fish and Wildlife Service, Wildlife
research report No. 12, Washington, D.C.
Schwartzmann, James L., and Robert
D. Ohmart. 1976. Quantitative
vegetational data of desert tortoise
(Gopherus agassizii) habitat in the
lower Sonoran Desert. Proceedings of the symposium, [Las Vegas, Nev. March, 19781 The Desert
Tortoise Council, Long Beach, CA.
Appendix 1
Summary of Importance Values1From Plant Transect Data.
Plant Community2
Species
Bare Ground
128.2
Schismus barbatus
Larrea tridentata
Ambrosia dumosa
Hila ria rigida
Erodium texanurn
Malacothrix spp.
Eriogonum spp.
Wyrnenoclea salsola
Amsinckia spp.
Oenothera del toides
Baileya mu1tiradiata
Abronia villosa
Bromus rubens
Langloisia Mat thewsii
Langloisira Palmeri
0yzopsis hymenoides
Eriophyllum Wallacei
Menodora spinescens
Lesquerella Palrneri
Salazaria rnexicana
Dalea Fremontii
Cucurbita foetidissima
Euphorbia polycarpa
Isomeris arborea
Prunus fasiculata
Spheralcea am bigua
Salvia columbariae
Phacelia spp.
Petalonyx Thurberi
Unknown composite #1
Unknown composite #2
iImpotfance value = relative density + re/,domin. + re/. ireq.
2Plantcommunity: See texf for description of community names; Meadow and bare
areas not listed; I = Sparse Wash; 2 = Hiri/Amdu; 3 = Mixed; 4 = Latr/Amdu; 5 = Wash.
Simpson, E. H. 1949. Measurement of
diversity. Nature 163:466-467.
Sokol, 0.M. 1971. Lithophagy and
geophagy in reptiles. Journal of
Herpetology 5:69-71.
Speake, Daniel W. 1986. Gopher tortoise density in various south Alabama habitats. Alabama Cooperative Fish and Wildlife Research
Unit, Research Information Bulletin 86-105,l p. Auburn, Alabama.
Stewart, Glenn R., and Ronald J.
Baxter. 1987. Final report and
habitat management plan for the
desert tortoise (Gopherus agmsizii)
in the West and Sand Hill training
areas of the Twentynine Palms
MCAGCC. Report prepared for
the U.S. Department of the Navy,
San Bruno, Calif. Contract number
N6247484RPOOV48.
Turner, Frederick B., and Kristin H.
Berry. 1986. Population ecology of
the desert tortoise at Goffs, California, in 1985. University of California, Los Angeles publication
number 12-1544.
Turner, Frederick B., and Carl
Thelander, Daniel Pearson, and
Betty Burge. 1982. An evaluation
of the transect technique for estimating desert tortoise density at a
prospective power plant site in
Ivanpah Valley, California. Proceedings of the symposium, [Las
Vegas, Nev., March, 19821. The
Desert Tortoise Council, Long
Beach, CA.
Walchuck, Sandra L., and James C.
devos, Jr. 1982. An inventory of
desert tortoise populations near
Tucson, Arizona. Proceedings of
the symposium, [Las Vegas, Nev.,
March, 19821. The Desert Tortoise
Council, Long Beach, CA.
Weinstein, Michael and Frederick B.
Turner and Kristin H. Berry. 1986.
An analysis of habitat relationships of the desert tortoise in California. Draft report prepared for
Southern California Edison Company, Los Angeles, Calif.
Zar, Jerrold H. Biostatistical analysis.
1974. Prentice-Hall, Inc., Englewood Cliffs, NJ.