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 size 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 contribution 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.

Reduced food availability in 1974 significantly altered the reproductive characteristics of a popul.atwn of Ur?sa~r_us orn_atus near Animas, Hidalgo County, New Mexico compared to 1973. ~elatlve food avatlabiitty, .which was moni.tored using sticky traps, was attributed to reduced precipita-tiOn levels. Fat storage pnor 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.fem~es (90%~ m 1973 to only one clutch in 1974 (8.7% produced two). The reproductive s~rategy ~~ th1~ populatiOn o~ [J_rosaurus compared to that previously presented for a Texas population ?1ffers P?manly by a restn.cti.on of the reproductive season and reduced clutch frequency but an mcrease.m clutch s1ze. The ltm1ted reproducti<:m i~ a low resource year may represent an adaptation to redu~e nsk and effort when current reproductiOn IS less profitable than survivorship and future reproduction.

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 variation in replacement rate and population size at low than at high altitude.

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.

No abstract

We review the ecological consequences of habitat and microhabitat use in lizards. Different habitats have different biotic and abiotic properties and thus are likely to have different consequences for the lizards that occur in them. Individual performance and life histories are influenced by habitat use, particularly when habitats differ in thermal characteristics that may influence physiological processes or constrain activity. We know relatively little about how the effects of habitat use on individual performance translate into population dynamics. We do know that the ability of lizards to use particular habitats can influence the persistence of populations in the face of habitat changes. Community-level processes (e.g., competition) and community structure (e.g., diversity) can be influenced by habitat use in lizards, often by habitat use facilitating co-existence of two or more potentially competing species. We know relatively little about how other community processes, such as predation and parasitism, are influenced by habitat use.

No abstract

We studied the thermal ecology of Sceloporus grammicus occurring in very different thermal environments at 3700 and 4400 m elevation on the Iztaccihuatl Volcano, Mexico. Despite differences in the thermal environment between study sites, individual lizards maintained similar active body temperatures (around 31.5"C). Similar body temperatures at the two study sites probably result in differences in the cost of the thermoregulatory behavior. Lizards at the high-altitude site, an open area with few predators or competitors, presumably incur a lower thermoregulatory cost than those at the low-altitude site, which has a considerable number of shaded spots and more predators and competitors. Lizards at the low-elevation site showed a greater resistance to high temperatures than those at the high-elevation site. Physiological acclimatization to higher environmental temperatures at low elevation is likely to explain the greater heat tolerance. Freezing tolerance, thermoregulatory behavior, and low energy requirements permit S. grammicus to survive at high altitudes.RCsumC : Nous avons etudie l'kcologie thermique de Sceloporus grammicus dans des milieux h regimes thermiques trks differents, a 3700 et 4400 m d'altitude, sur le volcan Iztaccihuatl au Mexique. En depit de differences de regime thermique aux deux endroits, les lezards actifs avaient des tempkratures semblables (d'environ 3 1,5 "C) . Ces temperatures semblables aux deux endroits resultent probablement de differences dans les coQts relies aux comportements thermoregulateurs. Le site de haute altitude, une zone ouverte oh le nombre de predateurs et de competituers est moins important, correspond probablement a une thermoregulation moins coQteuse que le site de basse altitude qui comporte un nombre considerable de zones ombragees, plus de predateurs et plus de competiteurs. Les lezards du site de basse altitude ont manifeste une plus grande resistance aux temperatures elevees que les lezards de haute altitude. Un phenomkne d'acclimatation physiologique h des temperatures ambiantes plus elevees h basse altitude explique probablement la plus grande tolerance h la chaleur. La tolerance au gel, le comportement thermoregulateur et les besoins energetiques reduits permettent h S. grammicus de survivre h haute altitude. [Traduit par la Redaction]