Royce E. Ballinger

REPRODUCTIVE STRATEGIES: FOOD AVAILABILITY AS A SOURCE OF PROXIMAL VARIATION IN A LIZARD'

Reduced food availability in 1974 significantly altered the reproductive characteristics of a population of Urosaurus near Animas, Hidalgo County, New Mexico compared to 1973. Relative food availability, which was monitored using sticky traps, was attributed to reduced precipitation levels. Fat storage prior to reproduction was greatly reduced in 1974. As a result, size of the first clutch was reduced from 10.9 (1973) to 6.8 eggs, and clutch frequency was reduced from two clutches by most females (90%) in 1973 to only one clutch in 1974 (8.7% produced two). The reproductive strategy in this population of Urosaurus compared to that previously presented for a Texas population differs primarily by a restriction of the reproductive season and reduced clutch frequency but an increase in clutch size. The limited reproduction in a low resource year may represent an adaptation to reduce risk and effort when current reproduction is less profitable than survivorship and future reproduction See full-text article at ...

Sceloporus Undulatus: A Study of the Intraspecific Comparative Demography of a Lizard

Population studies were conducted on the eastern fence lizard in South Carolina, Texas, Ohio, and Colorado. Hatching occurs in early to middle summer and well into the fall in southern populations, but is restricted to late summer and early fall in Colorado and Ohio. The hatchlings in Texas reach a mature size in 3 months and these lizards, as well as those in South Carolina, reproduce before they are a year old. In Colorado and Ohio the lizards do not mature until almost 2 years of age, but at a larger size than those in Texas or South Carolina. Lizards in the four populations differ significantly in average clutch size (7.4—11.8) and in clutch frequency (1—3) and in egg size (.23—.42 g per egg). In all populations there is a significant positive correlation between clutch size and body and the regression lines for these variables differ in slope between populations. Survivorships of eggs, hatchlings, yearlings, and adults differ among the populations and these differences have been related indirectly to increased predation in the southern and western populations. The adult mortality rates are inversely related to population density. Life tables for the populations show large differences among the populations in the contributions made by each age class to the total population replacement rate. The life table characteristics of each population show that the measured parameters are consistent with maintenance of stable population numbers even though the life history strategies are clearly different. Evolutionary explanations are provided for these differences and the relevance of the data to the concept of r— and K—selection is discussed.

Comparative Demography of Two Viviparous Iguanid Lizards (Sceloporus Jarrovi and Sceloporus Poinsetti)

Population studies of Sceloporus jarrovi using mark—recapture procedures were conducted on two study plots near Portal, Chiricahua Mountains, Cochise Co., Arizona during the summer months of 1969 and 1970. Similar studies of Sceloporus poinsetti were conducted on a study plot near Mertzon, Irion Co., Texas during the summer months of 1968, 1969, and 1970. Series of these lizards were taken from areas near the study plots and autopsied to determine their reproductive condition. The reproductive cycle of both species involved mating in the fall, with parturition occurring the following June. A single litter was produced each year. S. poinsetti attained maturity during the second mating season after birth, at about 16—17 months, although approximately 60% of the S. jarrovi females matured in their first mating season at about 5 months. Female S. jarrovi which matured as yearlings produced an average of four young in their 1st year, whereas older females produced an average of 10.5 young (7—15). The increase in litter size with snout—vent length was one embryo per 3 mm of body length. S. poinsetti females produced an average of 10.4 young (6—23) with an increase of one embryo per 3 mm of body length. Body sizes of young at birth were 29—35 mm in S. poinsetti and 25—32 mm in S. jarrovi. Newborn of both species were larger than hatchlings of similar sized oviparous species of Sceloporus. Newborn of S. poinsetti from large litters were significantly smaller than newborn from small litters. Populations of both S. jarrovi and S. poinsetti had 50:50 sex ratios. In June, the ratio of yearlings to older animals was approximately 50:50 in S. poinsetti and 60:40 in S. jarrovi. Of the eggs ovulated, 4.5% died before parturition in both species. Percent annual mortalities of S. poinsetti and S. jarrovi were respectively 86% and 81% (newborn), 54% and 56% (yearlings), and 57% and 63% (adults). The life history strategy of S. poinsetti appears to be relatively K—selected. S. jarrovi is more r—selected than S. poinsetti but more K—selected than most oviparous species.

Intraspecific Variation in demography and Life History of the Lizard, Sceloporus Jarrovi, Along an Altitudinal Gradient in Southeastern Arizona

Mark—recapture studies were conducted on a low (1675 m) and high (2542 m) altitude population of Sceloporus jarrovi in southeastern Arizona, USA from 1973 through 1976. Average age—specific mortality rates differed between altitudes only in the 0—1 yr age class. The increased mortality of neonates are low altitude was correlated with an increased number of potential predators and a significantly greater frequency of natural tail—breaks. Tail—break frequency did not differ between sites for older age classes. Survivorship and age at maturity were greater at high altitude. Low—altitude females mature in their first reproductive season. Transfer of neonates between altitudes indicate that high—altitude females do not mature in their first season even if raised at low altitude. Age at maturity appears to be adaptively adjusted by the demographic environment. Fertility schedules indicate that °40% of the replacement of low—altitude populations results from reproduction by 1st yr animals. There was a greater va...

Reproductive Cycles of Three Species of Anoline Lizards from the Isthmus of Panama

A study of the reproductive cycle of three species of lizards, a forest form, Anolis limifrons, a forest edge species, A. tropidogaster, and a grassland species, A. auratus, was carried out in the Isthmus of Panama from November 1965 until September 1969. The collecting sites were: Pacific side for all three species, mid—Isthmus for A. limifrons and A. auratus and Caribbean side for A. limifrons. Females of all three species of all sites were reproductively active during the wet season (May through December). For A. tropidogaster and A. auratus egg production almost ceases during the dry season. In A. limifrons egg production essentially ceases at the drier Pacific site and is reduced at the other two wetter ones during the same January—to—April period. The testes of males of all three species have mature spermatozoa during the dry season but mean testis weight declines from wet season highs. The male changes occur before the corresponding ones in their females so that the cycles of the two sexes may be controlled by different factors. Lipid levels of adults from the mid—Isthmus site show high values in the late dry season and lower ones throughout much of the wet season. Precipitation, food level, temperature, photoperiod, soil and leaf litter, wind, and evaporation are considered as cues influencing the cycle. The most likely candidate for the female cycle is precipitation with certain limitations. The flexible reproductive system of A. limifrons enables it to reproduce at low rates in some areas where the other two species must cease reproduction during dry periods.

Energetics, Temperature and Water Relations in Winter Aggregated Sceloporus Jarrovi (Sauria: Iguanidae)

Metabolic rates and water fluxes in winter—aggregated Yarrows spiny lizards (Sceloporus jarrovi) were measured in the field using doubly—labeled water. Resting metabolic rates were estimated from measurements of microhabitat and lizard body temperatures. During the month (November) following aggregation at the hibernaculum and the month (April) before dispersal, lizards were relatively active and their metabolic rates averaged 0.071 ml CO2°g—1°h—1, °40% of their warm season rates. From December through March, lizards basked but were relatively inactive with metabolic rates averaging 0.031 ml CO2°g—1°h—1, °15% of warm season rates. Water influx rates averaged 10.3 ml°kg—1°day—1 during the 120—day inactive period. Water loss was slightly higher than gain and lizards lost weight slowly while hibernating, having ended the 6—mo aggregation period with a 22% decline in body mass. Total energy expenditures during the aggregation period averaged °7.53 kJ, 3 times as much energy during the aggregation period as would a lizard remaining inactive in a crevice at 10°C for the entire 6 mo. Possible benefits of winter basking are discussed.

Ontogenetic Stages of Reproductive Maturity in the Viviparous Tizard, Sceloporus jarrovi (Iguanidae)

Stages for ovarian and testicular histology are described for an ontogenetic series of Sce- loporus jarrovi from birth to reproductive maturity. Testicular development to reproductive maturity mimics development during seasonal reproductive episodes. Testes enlarge as spermatogenesis begins and reach maximum sizes during spermiogenesis. Ovarian development proceeds through a series of nine developmental stages, the longest of which is the luteal phase which persists throughout the winter gestation period and culminates coincident with parturition in late spring. After parturition the ovary recycles to stage three (immature ovary) before the next annual reproductive period. The general stages of reproduction described for this species should permit comparisons of the reproductive cycle among species, and thus provide a common base upon which the evolution of reproductive types can be understood.

Reproductive Ecology of a West Texas Population of the Greater Earless Lizard, Cophosaurus texanus

The reproductive cycle of Cophosaurus texanus, in the vicinity of San Angelo, Texas, was determined from examination of 220 females and 105 males. Reproduction begins in early April and ceases by mid-August. Females mature in a single year at approximately 50 mm snout-to-vent length. Older females begin reproduction earlier and lay a larger first clutch and produce larger eggs than females just maturing. The smaller eggs of the first clutch of younger females are attributed to the lack of adequate fat storage. Approximately three clutches of six eggs each are laid by each female during 1 rep,roductive season.

Male Reproductive Cycle of the Lizard Sceloporus virgatus

of egg-retention, egg-guarding and viviparity in single-brooded species. The discovery of varying degrees of egg-retention in a number of typhlopids bears on this problem. Both temperate (T. bibronii) and tropical (T. diardi) species display prolonged egg-retention, indicating that in typhlopids temperature may not be the main selective pressure in the evolution of viviparity. However, nothing is known concerning thermal requirements of these species. In addition other climatic factors, such as seasonal drought, may be involved. Acknowledgments.-We thank Wulf Haacke (Transvaal Museum) for permitting us to study specimens in his care.

Survivorship of the lizard, Urosaurus ornatus linearis, in New Mexico

Dunham (1982) reviewed demographic and life history data from four populations of Urosaurus ornatus and commented on the implications these data have for testing life history theory. Dunhams review included data from the Animas, New Mexico population which my research group studied (Ballinger, 1976, 1977; Michel, 1976). Here I present additional data on adult survivorship and other population characteristics of Urosaurus at Animas which were not available for Dun-