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

Abstract

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.

Testosterone has opposite effects on male growth in lizards(Sceloporusspp.) with opposite patterns of sexual size dimorphism

“…4 months winter dormancy in S. virgatus), roughly coincident with the onset of their respective mating seasons. On our study plot, most males and some females of each species attain sexual maturity as yearlings (Ballinger, 1973(Ballinger, , 1979Ballinger and Ketels, 1983;Smith et al, 1995). However, while yearling males of S. virgatus grow only half as fast as females during their spring mating season, yearling males of S. jarrovii grow more quickly than females during their fall mating season (Cox, 2005; R. M. Cox and H. B. John-Alder, manuscript submitted).…”

“…Both species are primarily saxicolous, employ sit-and-wait foraging tactics, share common prey and predators, attain sexual maturity as yearlings (i.e. within 12 months of birth), reproduce only once annually, and exhibit polygynous mating systems characterized by aggressive intrasexual male competition for breeding females (Ballinger, 1973(Ballinger, , 1979Ballinger and Ketels, 1983;Rose, 1981;Ruby, 1978;Ruby and Dunham, 1984;Smith, 1985;Smith et al, 1995;Vinegar, 1975b). However, while adult females of S. virgatus average 10% larger than adult males (longer in snout-vent length, SVL), adult males of S. jarrovii average 10% larger than adult females (Cox et al, 2003;Cox, 2005; R. M. Cox and H. B. John-Alder, manuscript submitted).…”

Demography of the lizard Sceloporus grammicus: exploring temporal variation in population dynamics

“…For instance, Texas spiny lizards (Sceloporus olivaceus Smith, 1934), mountain spiny lizards (Sceloporus jarrovi Cope in Yarrow, 1875), canyon lizards (Sceloporus merriami Stejneger, 1904), rose-bellied lizards (Sceloporus variabilis Wiegmann, 1834), and bunch grass lizards (Sceloporus scalaris Wiegmann, 1828) exhibit mean annual survival rates of 0.16, 0.36, 0.32, 0.12, and 0.15, respectively (Blair 1960;Ballinger 1973;Dunham 1981;Benabib 1991;Ortega-Rubio et al 2000). When compared with another population of S. grammicus located at a lower altitude (mean survival rate of 0.23 at 2480 m of elevation; Ortega-Rubio et al 1999a), the high survival rates that we found at PNZ are even more noticeable.…”

The life history strategy of the saxicolous desert lizard, Sauromalus obesus

“…These studies and others have shown that 3 major types of testicular cycles can be dis- .., .., ... occurs throughout the year. Some investigators (Ballinger and Shrank, 1973;Newlin, 1976) Though spermatogenesis represents only a portion of the total amount of energy involved in male reproductive effort (Ballinger andShrank, 1973 andNewlin, 1976) Comparison of some aspects of the breeding cycle can be made with populations of ~. obesus at some Mojave Desert localities.…”

“…Lizards are either early maturing (in one year), have short adult life expectancies, are almost always multiple-brooded, and produce relatively small clutches, or they are late-maturing (longer than one year), have long adult life expectancies, are usually single-brooded, and produce relatively large clutches. Numerous investigators have since described how various lizard species conform to this general theory (Pianka, 1970b: Turneret al, 1970Tinkle, 1972;Ballinger and Shrank, 1972;Ballinger et al, 1972;Tinkle and Ballinger, 1972;Ballinger, 1973;Gennaro, 1974;Vinegar, 1975;Ballinger, 1976;Parker and Pianka, 1976;Ballinger, 1977;Martin, 1977;Smith, 1977;Vitt, 1977;Vitt and Ohmart, 1977 a & b;Schall, 1978;Vitt et al, 1978;Ferguson et al, 1980;Dunham, 1982).…”