Frederick B. Turner

Home Ranges and Body Size of Lizards

The relationship between home range, A (m2) and body weight, W (g) among adults of 13 species of terrestrial lizards was estimated as: A = 171.4W0.95. The slope of the logarithmic regression is steeper than that relating standard metabolic rate, M (cm3 O2/hr) at 30°C and body weight: M = 0.82W0.62. These functions are compared with similar regressions relating the home ranges and basal metabolic rates of birds and mammals to body size. Two major difficulties in the interpretation of such data are discussed. See full-text article at JSTOR

Reproduction and survival of the desert tortoise (Scaptochelys agassizii) in Ivanpah Valley, California

Eighty-seven adult desert tortoises (58 females, 29 males) in Ivanpah Valley, California, were fitted with radiotransmitters in 1980 and 1981. All were marked, weighed, and measured and released. Tortoises were then recaptured, weighed and released about every two weeks in 1980 and weekly in 1981. The experiment concluded in the spring of 1982, when 62 tortoises were recovered. Survival of males and females did not differ, but the observed death rate in 1981-82 (18.4%) was significantly greater than that in 1980-81 (4.4%). Females > 200 mm in plastron length exhibited two periods of distinct loss of mass in 1980 (15-28 May, 12-25 June) when masses of males were essentially unchanged. Losses of > 100 g were interpreted as evidence of egg-laying. Eleven of 15 females for which we had season-long records in 1980 laid two clutches, two laid one clutch and two did not lay eggs. The mean number of clutches laid was 1.60. Of 40 females considered in 1981, 20 laid one clutch, 12 laid two clutches and eight did not lay. The mean number of clutches was 1.10. The estimated dry standing crop of forbs in 1980 was about 100 times that in 1981. Estimated biomass of grasses in 1980 was about 25 times that measured in 1981. Analyses of tortoise feces showed that grasses were eaten with equal frequency until mid-May in both years, but that after this time grasses essentially disappeared from 1981 diets. Annuals and seeds were much better represented in early spring diets in 1980 than in 1981. Cacti were more frequent in scats collected in 1981, particularly after mid-May-when about 87% of material in feces was from such plants. Cacti may serve as a reserve supply of energy, but more importantly as a potential source of water. This may partially explain the egg production in 1981-one of the most unfavorable years on record in the Mojave Desert.

Frequencies of broken tails among Uta stansburiana in southern Nevada and a test of the predation hypothesis

Frequencies of broken tails among hatchling (1-4 months), yearling (7-12 months) and 2-year old Uta stansburiana (19-24 months) in southern Nevada were examined for the years 1966-1973. Frequencies among males and females in the two older age groups did not differ significantly. The frequency of broken tails in hatchlings (0.06) was lower than that in yearlings (0.30), which was, in turn, lower than that in 2-year old Uta (0.51). Break frequencies among yearlings varied from 0.26 to 0.37 in different years, while frequencies among 2-year olds varied from 0.33 to 0.64. These differences were not statistically significant. Among hatchling Uta, tail break frequencies ranged from as low as 0.029 (1971) to as high as 0.099 (1966), and differences between years were highly significant. Tail break frequencies in all age groups were analyzed in terms of spring densities of Uta and of an important predator (Crotaphytus wislizenii). Tail breaks in yearling and 2-year old Uta were not correlated with either density variable. Tail-break frequencies of hatchling Uta were significantly correlated with predator density (r = 0.88), and multiple regression analysis (with densities of both lizards as independent variables) yielded an R2 of 0.80. This is the first test of the tail break

A demographic analysis of fenced populations of the whiptail lizard, Cnemidophorus tigris, in southern Nevada

Between 1964 and 1967, spring densities of Cnemidophorus tigris in four study areas in southern Nevada ranged from 3-8 per acre. Estimated biomass ranged from around 43 to 114 g/acre. The sex ratio was 1:1. Minimal annual survival of adults was 54-60%, and life-spans of at least 7 years are postulated. An undetermined proportion of mature females laid two clutches of eggs in 1965, but the general pattern was one clutch of 2-4 eggs per year. Large females produced more eggs than small ones. Occasionally females 9-10 months of age laid eggs, but sexual maturity normally was attained at about 21 months. By assuming that all mature females laid two egg clutches in 1965 our fecundity estimates could be approximately reconciled with the observed size and age composition of populations in the spring of 1966. Possible compensatory errors in this analysis are discussed. One of the challenging problems of contemporary ecology is the analysis of ecosystems and the development of mathematical models capable of simulating the trophic transfers of energy and materials and the interactions between species which collectively constitute ecosystem function. This endeavor requires not only an understanding of the processes of primary production, but also the roles of primary and secondary consumers. The net production and material transfers of a consumer population can be estimated only if one understands the time changes in the structure and size of such populations, i.e., the rates of age-specific mortality and the schedule of recruitment by which the population is sustained. In another paper we have discussed the demography of Uta stansburiana and related annual changes in densities of this species to changes in schedules of female survival and fecundity (Turner et al., 1 Present address: PO Box 236, Zion National Park, Springdale, Utah 84767

HORMONAL INDUCTION OF COLOR CHANGE IN FEMALE LEOPARD LIZARDS (CROTAPHYTUS WISLIZENII).

Follicle stimulating hormone (FSH) will induce red-orange pigmentation in non-ovariectomized female leopard lizards (Crotaphytus wislizenii) in 7-21 days depending upon the season. Progesterone is judged to be an important hormone in the process of color change, and will bring about pigmentation in the absence of ovarian tissue. Estrogen alone has no apparent effect on color change, but when administered before progesterone it appears to have a priming effect.

The Distribution and Abundance of the Flat-tailed Horned Lizard (Phrynosoma mcallii)

The occurrence of the flat-tailed horned lizard (Phrynosoma mcallii) was investigated in 458 sections (each 2.59 km2) in Riverside, San Diego and Imperial counties, California, in 1979. In all sections, 40 P. mcallii (0.09/man-hour) and 2,191 horned lizard scats (4.8/man-hour) were counted. When sections were grouped in 12 general areas, mean numbers of horned lizards ranged from 0.40/ hr (north of Benson Dry Lake) to 0.00/hr (northern East Mesa, Coyote Wells area). The density of P. mcallii in a plot in the Yuha Basin (40 km west of El Centro) was 6-8/ha. The flat-tailed horned lizard is similar to P. platyrhinos in terms of sex ratio (1:1), age at maturity (20 months), and ability to la more than one clutch of eggs in favorable years. Mean home ranges for five male an m-ale P. mcallii (estimated as convex polygons) were 0.13 ha and 0.05 ha, respectively. P. mcallii feeds almost exclusively (>95% of items) on ants. The most commonly consumed species are harvester ants (Veromessor pergandei, Pogonomyrmex californicus and P. magnacanthus). In 1980 the relative abundance of P. mcallii (L), density (P), diversity (A,) of perennial plants and relative abundance of harvester ants (A) were estimated in ten plots in southeastern California. The abundance of the lizard was positively correlated (r = 0.93) with perennial density, and a clear positive association between lizard and ant densities was exhibited in nine of the ten plots. A regression model accounted for 91% of observed variation in lizard density, and predicted relative abundance of P. mcallii as:

Allozyme Variation in Mojave Populations of the Desert Tortoise, Gopherus agassizi

Whole blood samples were obtained from a total of 146 desert tortoises from western (Kramer Hills region) and eastern (Chemehuevi Valley) parts of the Mojave Desert in San Bernardino County, California. These samples were examined electrophoretically for allozyme expression at 23 loci, eight of which were polymorphic. Heterozygosity levels and other measures of genetic variability were comparable for the eastern and western Mojave samples. Intrapopulation chi-square tests did not falsify our null hypothesis of random mating at each location. Genetic distance measures and interpopulation FsT values suggested that genetic differentiation of eastern and western Mojave Desert tortoises was minimal. However, a contingency chi-square test and multivariate analyses demonstrated significant differences between these geographic samples, falsifying the hypothesis that these Mojave samples are part of a single randomly breeding population. From the perspective of allozyme characteristics, we have no reservations regarding relocation of tortoises between the Kramer and Chemehuevi sites. Allozyme characters of transplanted tortoises should be documented for historical record.

Effects of Radiation on a Fenced Population of Horned Lizards (Phrynosoma platyrhinos) in Southern Nevada

Between 1964 and 1966 minimum spring densities of horned lizards ranged from 1.0-2.5/hectare (ha) in 3 8 ha enclosures in Rock Valley, Nevada. Minimal survival of hatchling horned lizards to the age of 8 months was about 26-38 per cent. Annual minimal survival of older lizards was 50-60 per cent. Female horned lizards usually laid one clutch of eggs per year, but multiple clutches were observed in 1969. Conversely, no reproduction was observed in 1970. The maximum life span of horned lizards is at least 94 months. One of the enclosures was subjected to continuous gamma irradiation from a centrally located source of 137Cs. Between 1964 and 1966 numbers of horned lizards declined in all 3 plots. Between 1967 and 1970 numbers of horned lizards increased in the two control areas, but continued to decline in the irradiated plot. Female sterility owing to regression of ovaries is judged to be the cause of the population decline. Similar radiation effects have previously been observed among leopard lizards (Crotaphytus wislizenii), whiptail lizards (Cnemidophorus tigris), and side-blotched lizards (Uta stansburiana). * * *

Some Sampling Characteristics of Plants and Arthropods of the Arizona Desert

A major endeavor of contemporary ecology is the evaluation of the energy dynamics of communities. In the course of such work it is necessary to know something of the numbers (and fluctuations in numbers) of various producers and consumers. When an area of considerable extent is involved, direct enumeration of organisms is rarely feasible and various indirect methods of estimating numbers are used. Estimating numbers on the basis of incomplete counts introduces the problems associated with nonrandom dispersions (see Cole 1946, Morris 1960), so it is important to know something of the manner in which populations are distributed in space. Estimation of arthropod numbers has not, to my knowledge, been attempted by means of the removal method (Zippin 1958), but there is no theoretical reason why it could not. This method assumes a uniformity of susceptibility to capture during the sampling. Whether this assumption is realized in arthropod populations is not known. The following is an analysis of the dispersion of 6 arthropods and 2 plants near Phoenix, Arizona, in an attempt to assess the suitability of incomplete counts as bases for estimating total numbers. The distributions of captures of arthropods over a one-month period are examined in order to evaluate the reliability of the removal method of estimating numbers.

Reproduction by Uta stansburiana (Reptilia, Lacertilia, Iguanidae) in Southern Nevada

Monthly mean clutch sizes of Uta stansburiana in southern Nevada were measured over a 10-year period. Overall mean clutch sizes of female Uta >12 months of age were 4.40 (March-April), 3.80 (May), 3.04 (June), and 2.65 (July). Overall means of yearling females (<12 months of age) were about 82-90% of those of older females between April and June. Reproduction by Uta in 1973 surpassed that observed in any of nine previous years. The mean size of the first clutch laid by older females was 5.35, and some females deposited up to eight eggs. The minimum number of clutches laid was four and the maximum seven. The net reproductive rate (R/sub 0/) estimated for 1973 was 2.34, exceeding an earlier estimate for 1966 (1.65).