Potential costs and benefits of tail autotomy in lizards have been inferred almost exclusively from experimental study in semi-natural enclosures and from indirect comparative evidence from natural populations. We present complementary evidence of the costs of tail autotomy to the lizard Uta stansburiana from detailed demographic study of a natural population. On initial capture, we broke the tails of a large sample of free-ranging hatchlings (560) and left the tails of another large sample (455) intact, and then followed subsequent hatchling growth and survival over a 3-year period. Surprisingly, in 1 out of the 3 years of study, survival of female hatchlings with broken tails exceeded that of female hatchlings with intact tails. Furthermore, no effects of tail loss on survivorship were detected for male hatchlings. However, in 2 years when recaptures were very frequent (1961, 1962), growth rates of hatchlings with broken tails were significantly slower than those of their counterparts with intact tails. We discuss our results in the broader context of estimating the relative costs and benefits of tail autotomy in natural populations. and suggest that long-term demographic studies will provide the best opportunity to assess realized fitness costs and benefits with minimum bias. We also describe how experimentally induced tail autotomy can be used as a technique to complement experimental manipulation of reproductive investment in the study of life-history trade-offs.

An 11—yr study of life history and demographic variation in the sagebrush lizard Sceloporus graciosus was carried out on two study areas (Rattlesnake Ridge and Ponderosa Flat) in the Kolob Mesa Section of Zion National Park, Utah. Two primary objectives of this mark—recapture study were to: (1) quantify variation in age structure, age and size at maturity, age—specific survivorship and fecundity, and individual growth rates, and (2) conduct a series of density reduction experiments designed to elucidate the effects of density on growth rates and survival of posthatchling lizards. In addition, we examined the relationships of variation in population density and deviation from long—term average precipitation and temperature to variation in individual growth, reproduction, and demography. At both sites the active season was °160 d, extending from early April to mid—September. Reproduction occurred during a 50—d period between mid—May and early July. Mean clutch size was 3.7 eggs and most females produced their first clutch in the 2nd yr of life (their third active season) at an age of °22—24 mo and a minimum snout—vent length of °50 mm. Most mature females produced two clutches of eggs per year, and there was no statistically significant variation in either mean clutch size or body—size—adjusted clutch size among the 11 yr of study. Clutch size was significantly correlated with body size. Relative clutch mass averaged 0.247 and was not significantly correlated with body size. Since hatchlings first appeared in early to mid—August, their first growing season was °2 mo long. There was no significant sexual dimorphism in growth rate or body size in either population. There was great variation in estimates of egg—yearling survival among years. Egg—yearling survival probability varied from 0.12 to 0.59 with a mean of 0.28. At Ponderosa Flat, the survival of yearling males (0.38) was significantly lower than that of yearling females (0.47). Survival of yearling males (0.45) and females (0.43) at Rattlesnake Ridge was not significantly different. There were no other significant differences in the survival of males and females (X = 0.56 for both sexes) within any age class in any year of the study. However, the survival of yearlings was significantly lower than that of older lizards in both populations. Mean posthatchling survival over all years was 0.45, and there was significant heterogeneity in posthatchling survival among years. Average annual survival of immigrants (0.32) was significantly lower than that of residents (0.44). There was a significant negative linear relationship between yearling body size in late June and total density of posthatchling lizards. A stepwise linear regression model revealed significant effects of both rainfall (and presumably resource availability) and population density on the growth of yearlings. This model explained 78% of the annual variation in yearling growth. Rank correlation analysis revealed that survivorship of hatchlings was negatively correlated with density of conspecific lizards. The negative correlation implies direct density dependence of hatchling mortality rates and is a potentially important mechanism of population regulation. Removals of almost all yearling and older age lizards from the study sites resulted in significant increases in growth rates of hatchlings in the year of the removal and yearlings during the following year. Four results from this study combine to suggest substantial resource limitation of S. graciosus on the Kolob Mesa. (1) Snout—vent lengths attained by yearling lizards were positively correlated with deviations from long—term mean rainfall values. (2) Body sizes attained by yearlings were greatest in the years following density reductions. (3) Body size attained by yearlings was negatively correlated with density of conspecifics. And (4), in a year in which a density reduction followed a warm, wet spring, more yearling females reached maturity than in all other years of the study combined.

Reproduction of snapping turtles was studied from 1978-1983 and nesting ecology and demography of hatchling snapping turtles were studied from 1976 through 1982 in south- eastern Michigan. The plastron lengths of reproductive females varied from 159-235 mm. Mean clutch size over 6 yr was 27.9 eggs (range = 12-41) and showed a significant positive linear rela- tionship with body size of females. Females produced only one clutch per year. The youngest known-age, reproductive female was 12 yr of age. Duration of the nesting season varied from 13- 31 days, and the initiation date varied by 22 days (22 May-12 June). The beginning of nesting activity each year was significantly correlated with the amount of heat available during March, April and May. Daily nesting activity was essentially bimodal with a major peak occurring between 0600 and 1100 h and a lesser peak of activity between 2000 and 2300 h. Nest construction averaged 111 min. Body temperatures of females at the time of nest completion ranged from 20.4-28.0 C (x = 22.9 C). Nests averaged 183 m straight-line distance from the nearest relatively permanent water, and no significant difference was found between the distances from water of those nests destroyed by predators and those escaping predation. Females nested in open areas that were adjacent to their marsh of residence or adjacent to other bodies of water. Observed females moved as far as 1625 m (straight-line distance) in preparation for nesting. Some females that were observed nesting in more than 1 yr constructed nests within 5 m of a previous nest, whereas other females changed nesting areas and constructed nests up to 1000 m apart. Predation rates on nests averaged 70% and ranged from a high of 100% in 2 yr to a low of 30% in 1 yr. The majority of nest predation occurred within 24 h of nest construction. The major predators were raccoons and foxes. Nests preyed upon by foxes were significantly older and further from water than nests destroyed by raccoons. An average of 4.14 eggs or developing embryos died in nests that escaped predation. Weekly mean tempertures in exposed and shaded nests ranged from 17.2-23.3 C during the entire incu- bation period. Nest temperatures were significantly lower in the shaded nest for all weeks except the first week following egg laying. These data indicate that shaded nests do not provide enough heat to allow complete development. Dates of hatchling emergence ranged from late August to early October, with the majority of emergence occurring in September. The average number of days from egg laying to hatchling emergence was 93.2. All sources of mortality resulted in a probability of 0.22 of surviving from age zero to age 1 (an approximately 90-day period from egg laying to hatchling emergence from the nest).

Le cycle evolutif et les variations demographiques de populations de Sceloporus undulatus et S. clarki sont etudies dans l'Arizona

Metabolic rates of free-ranging Sceloporus graciosus (Sauria: Iguanidae) were measured during the summer using doubly labeled H2O. Adults of either sex and juveniles did not differ in field metabolic rates (0.26 mL CO2∙g−1∙h−1or 160 J∙g−1∙day−1). Field metabolic rates were 2.4 times the resting metabolic rate, and activity respiration was 3.1 times the resting metabolic rate at lizard activity temperatures. Activity accounted for 59% of the energy consumption due to respiration. Calculated rates of feeding indicated a 415 J∙day−1 deficit in metabolizable energy intake, and this was reflected in rate of loss of body mass throughout the study. Daily energy harvested by 200 lizards (31 kJ∙day−1), which approximates densities (per hectare) on the study area, would supply only 40% of the daily energy requirements of one insectivorous bird with similar body mass and activity level of a Phainopepla (79 kJ∙day−1).

A study of three species of sceloporine lizards (Sceloporus clarki, S. undulatus, and Urosaurus ornatus) was begun in 1971 and continued into 1977 in a very diverse (at least 11 species) lizard community in central Arizona, USA. The present paper reports the results of a density manipulation experiment carried out with these three lizards to ascertain whether direct evidence for interspecific competition could be found in a community of lizards in which circumstantial evidence suggested its importance. In May 1975 the study area was divided along a natural constriction into an experimental area and a control area and an attempt was made to remove all U. ornatus and S. clarki from the experimental areas. This experimental treatment was maintained until the termination of the experiment in 1977. Patterns of habitat utilization, population density, survivorship, and individual body size of S. undulatus on experimental and control areas both before and after the removals were analyzed for evidence of competitive interactions. There were no detectable effect of the removal of S. clarki and U. ornatus on habitat selection, perch height, survivorship, population density, or individual body size of S. undulatus inhabiting the removal area. Implications of these results for studies of lizard community structure are discussed.

Nesting ecology and reproduction of painted turtles (Chrysemys picta) in southeast Michigan were intensively studied from 1975 to 1978. The average clutch size of Michigan painted turtles was 7.55, with body size accounting for only 9—13% of the variance. Data on nesting frequency indicate that from 30 to 50% of the females possibly do not reproduce every year and that °6% reproduce twice in a given year. Predation within 48 h of egg—laying is responsible for the failure of 20% of the nests. An additional 12% nest failure is due to various other causes. These data substantially alter the life table previously reported for this population of painted turtles.

Samples of lizards of the genus Uta were collected from many of the islands in the Gulf of California. Other species of lizards coexisting with Uta were collected simultaneously. These samples provided data for a detailed analysis of body size and degree of sexual dimorphism in each island uta population and the correlation of body size with numerous independent variables such as the number and abundance of potentially competing species. This study tested the null hypothesis that competiting species had no significant influence on the body size or sexual dimorphism of the utas on particular islands. Various corollaries of the general hypothesis were also tested. The results not only supported the null hypothesis of no competitive effect, but demonstrated that independent variables not obviously associated with competition explained at least much of the variance in Uta body size as did variables directly related to competition. Previous studies on the evolution of body size in insular lizards have become paradigms of a presumed causal relationship between both size and intensity of interspecific competition. Our study invites caution to the indirect type of approach to the study of competition used in these previous studies. The weaknesses of past approaches are discussed at better approaches to the study of competition are suggested. Selective pressures that might have at least as great an effect on body size of organisms as does competition from other species are identified.

Reproductive effort is defined as that proportion of the total energy budget of an organism that is devoted to reproductive processes. Reproductive effort at a given age within a species will be selected to maximize reproductive value at that age. Reproductive effort is not directly affected by changes in juvenile survivorship, nor necessarily reduced by an increase in adult survivorship. Selection for high levels of reproductive effort should occur when extrinsic adult mortality is high, in environments with constant juvenile survivorship, and in good years for juvenile survivorship in a variable environment, provided that the quality of the year is predictable by adults. Data necessary to measure reproductive effort and to understand how selection results in different levels of effort between individuals and species are discussed. We make several predictions about the effect of increased resource availability on reproductive effort. The empirical bases for testing these predictions are presently inadequate, and we consider data on energy budgets of organisms in nature to be essential for such test. We also conclude that variance in life table parameters must be known in detail to understand the selective bases of levels of reproductive effort.

The energy content of eggs of 10 lizard species was determined and used as a measure of reproductive effort (ratio of clutch calories to body calories). Values for eggs ranged from 5.87 to 7.20 cal/mg ash—free dry weight (°=6.37). Species differences in calories going into reproduction during a breeding season, however, were primarily due to differences in clutch size and clutch frequency between species. Correlation analysis between three measures of reproductive effort, including the preceding, and a suite of demographic variables revealed only one significant correlation (negative) between clutch calories to body calories ratio and mean annual adult survivorship. The energy allocated to eggs in comparison to total annual energy expenditure was estimated for three of the species investigated. Sceloporus graciosus had the highest reproductive effort, with proportional values for first and older breeders about the same. The proportion of total energy expended on reproduction was slightly lower for UTA stansburiana, with first and older breeders exhibiting the same effort. Sceloporus jarrovi had the lowest reproductive effort, but showed an increasing effort with increasing age. These data suggest that the demographic environment may not be the primary selective pressure determining reproductive effort, and that reproductive effort may not be positively correlated with age in all species.

Evolutionary theory has not yet determined the necessary and sufficient environmental factors that can be used to explain the observed diversity of life history patterns in plants and animals. Although recent theoretical treatments of the evolution of life history rely heavily on the concepts of r- and K-selection, we find this framework inadequate to explain life histories of many well-known organisms. Instead, using well-studied examples from the literature, we attempt to identify causal mechanisms in the evolution of their life histories. The density of the population in relation to resources, the trophic and successional position of the population, and predictability of mortality patterns all appear to be important determinants of adaptive strategies. Therefore, consideration of many environmental dimensions seems essential to provide complete understanding of the evolution of life histories.

GORMAN, G. C. 1968. The relationships of Anolis of the roquet species group (Sauria; IS, D. E. 1958. The role f density in agessive behavior of house mice. Anim. Behav. Iguanidae)-III. Comparative study of display behavior. Brevoria, Mus. Comp. Zool. No. 284:1-31. GREENBERG, B., AND G. K. NOBLE. 1944. Social behavior of the American chameleon, (Anolis carolinensis). Physiol. Zool. 17:392-439. JENSSEN, T. A. 1970. The ethoecology of Anolis nebulosus (Sauria, Iguanidae). J. Herpetol. 4: 1-38. MILSTEAD, W. W. 1970. Late summer behavior of the lizards Sceloporus merriami and Urosaurus ornatus in the field. Herpetologica 26: 341-357. RAND, A. S. 1967. The ecology and social organization in the iguanid lizard Anolis lineotopus. Proc. U. S. Nat. Mus. 122:1-79. SCHOENER, T. W., AND G. C. GORMAN. 1968. Some niche differences in three Lesser Antillean lizards of the genus Anolis. Ecology 49: 819-830. STAMPS, J. A., AND G. W. BARLOW. In Press. Variation and stereotypy in the displays of Anolis aeneus (Sauria, Iguanidae). Behaviour.

MARTOF, B. S. 1953. Territoriality in the green frog Rana clamitans. Ecology 34:165-174. , AND THOMPSON, E. F., JR. 1964. A behavioral analysis of the mating call of the chorus frog, Pseudacris triseriata. Amer. Midland Nat. 71:198-209. SAVAGE, J. M. 1968. The Dendrobatid frogs of Central America. Copeia 1968:745-776. SEXTON, O. J. 1960. Some aspects of the behavior and of the territoriality of a Dendrobatid frog, Prostherapsis trinitatis. Ecology 41:107-115. SIEGEL, S. 1956. Nonparametric statistics for the behavioral sciences. New York: McGrawHill.