POPULATION DYNAMICS OF SCELOPORUS GRAMMICUS (SAURW ) AT ,

ALFREDOORTEGA-RUBIO, ROBERT BARBAULT, AND GONZALOHALFFTER

Instituto de Ecolog'a. Apdo. Postal No. 63, Xalapa, Veracruz 91000, México (AO-R, GH) Ecob Nmab Superieure, 46 Rue D'Ulm, Pan's Cedex 05, France (RB) Present Address of AO-R. Centro de Investigaciones Biológtcas del Noroeste, Apdo. Postal No. 128, La Paz, 23000, Baja California SU^ México, aortega@aInzozmx

kbs~n~c~-Populationdynamics of Scelopmus grammicus were studied at La Michilía Biosphere Reserve, Durango, Mexico, from 1979 to 1982 using mark-recapture methods. Estimated popula- tion density waq 166 individuals (adults and subadults) per hectare, with adults averaging 42 individuals per hectare. Sex ratio wai approximately 1:1, with females slightly dominating at older ages. Six differerit age classes were established: a) juveniles from O to 3 months of age, b) sub adults from 3 to 5 months of age, c) adults 1, individuals in their first reproductive season from 5 to 12 months of age, d) adults 11, individuals in their second reproductive season and older than 1 year, e) adults 111, individuals in their third reproductive season and older than 2 years, and f) adults IV, individuals in their fourth reproductive season and older than 3 years. Average litter size for females was 6.17 neonates I1.65 SE and varied widely (three to nine neonates) as a function of female body size. Estimated number of neonates in 10 hectares was 1,482 and embryo mortality was 7.2%. Mter hatching, he average mortality was higher than 55% from one age-class to the next. The mortality rate was lowest for the male adult 1 class (53.8%), and highest for the male adult 111 class (89.0%), below only the 100% mortality exhibited by adult IV individuals (the final age class). The population life table indicates a Slobodkiri Type IV survivorship curve, with high mortality occurring at younger ages and a population replacement rate (net reproductive rate) close to 1.00. Average generation time for this population was 1.09 years. This is the first study of the population dynamics of this .

RESUMEN-La dinámica poblaciorial de Scelopmus grammicus fue estudiada en la Reserva de la Biósfera de La Michilía, Durango, México, de 1979 a 1982 usando méi:odos de marca recaptura. La densidad poblacional estimada fue de 166 individuos (adultos más subadultos) por hectárea, promediando los adultos 42 individuos por hectárea. La proporción sexual fue de aproximada- mente 1:l dominando las hembras en las mayores clases de edad. Seis diferentes clases de edad fueron establecidas: a) juveniles, de O a 3 meses de edad, b) subadultos, de 3 a 5 meses de edad, c) adultos 1, individuos en su primera estación reproductiva de 5 a 12 meses de edad, d) adultos 11, individuos en su segunda estación reproductiva y mayores que 1 año, e) adultos 111, individuos en su tercera estaci6n reproductiva y mayores que 2 años, y f) adultos 1V. individuos en su cuarta estación reproductiva y mayores que 3 años. El tamaño promedio de camada para las hembras fue de 6.17 neonatos I1.65 DE, variando ampliamente (de 3 a 9 neonatos) en función del tamaño corporal de la hembra. El número estimado de neonatos en 10 hectáreas fue de 1482 y la mor- talidad de embriones fue de 7.2%. Después del nacimiento la mortalidad promedio fue superior al 55% de una clase de edad a la siguiente. La tasa de mortalidad fue menor para la clase de machos adultos 1 (53.8%) y la más alta para la clase de machos adultos 11 (89.0%), por debajo sólo del 100% de mortalidad que alcanzan los adultos IV (la clase final). La tabla de vida de la población indica una curva de sobrevivencia de tipo IV de Slobodkin,.con la más alta mortalidad en las clases de edad más jóvenes y con un crecimiento poblacional (tasa neta reproductiva) cercana a 1.OO. El tiempo promedio generacional para esta población fue de 1.O9 años. Este es el primer estudio sobre la dinámica poblacional de esta especie.

Knowledge of life history traits, such as age 1975; Vinegar, 1975; Barbault, 1981; Andrews at maturity, age-specific fecundity, and survi- and Wright, 1994; Smith, 1996). Furthermore, vorship, is basic to understanding how a spe- from studies of life history have grown at- cies is adapted to its environment (Barbault, tempts to uncover adaptative patterns of de- March 1999 Ortega-Rubio ei al.-Popiilation dynarnics of SceZ@ms grammicus 65 mographic attributes of species (Tinkle, 1969; 0.1 g using a spring scale (Pesola). During the last 3 Tinkle et al., 1970; Ballinger, 1973; Barbault, days of each 15-day period we coriducted eight 50- 1975; Parker and Pianka, 1975; Barbault, rnin censuses each day to count marked and un- 1981). To see these patterns, it is necessary to marked individiials found inside the plot. gather more data on population dynamics of captures were not rnade during these censuses, and we started each census froni a different locatioii in- more species. Because of their diurna1 habits side the plot to try to avoid btases caiised by chang- and their usual ease of capture, serve as ing lizard activity over the course of the day. admirable subjects for studies of population Population StructureLizards were classified by sex dynamics (Van Devender, 1982; Grant and and age group from morphological and chrornatic Dunham, 1990; Anderson, 1994; Smith, 1996). characters. Because most of the S. grammicus neo- Although Sceloporus grammicus is a wide- nates are born in a single period of only 15 days spread and abundant lizard whose distribution during May, age class can be easily determined ~ising includes 25 states of México (Smith, 1939), SVL cohort data. Secondary sexiial characteristics of there exist relatively few studies of this species. males and fernales, such as ventral color patches in males, were evident frorn a very early age and were Of those studies that exist, most are of a taxo- used to determine the sex of individuals. nomic nature (Hall, 1973; White, 1978; Sites, DensityDensity of adults and subadults was esti- 1980, 1983), or concern its reproduction (Ax- mated each rnonth fro~nrnark-recapture data usiiig te11 and Axtell, 1970; Guillette and Casas-An- the Petersen index (Bailey, 1952; Caughley, 1977). dreu, 1980, 1981; Reed and Sites, 1995), with Natali+Natality was computed by applying size- only a few dealing with ecological aspects (Le- specific fecundity estimates to resident fernales. We mos-Espina1 and Ballinger, 1992, 1995a, conducted 120 autopsies of different-sized gravid fe- 1995b), and none on its population dynamics. males frorn outside the study plot to obtain these The purpose of this work is to report the prin- size-specific fecundity estimates. cipal population attributes and dynamics of Mortality and SurvivorshipMortality rate was esti- mated by analyzing recapture data of marked indi- one population in northwest Mexico over a vidual~frorn each age class to the next. This esti- four-year period. mation was correci.ed by siibtracting the knowii nurnber of emigrants for each age class. We peri- METHODSAND MATERIALS-The study site, La odically searched for rnarked individuals in a 500-m Michilía Biosphere Reserve, is located in the solith- wide zone adjacent to the margins of our study plot. east portion of Durango, México, between 104"20' Marked individiials found in this zone were consid- and 104"07'W, and 23"201 and 23"301N.The climate ered emigrants and were not tallied as deaths. Pre- of the zone is ternperate with a mean annual tem- natal or embryoriic mortality was deterrnined by perature ranging between 17.4"C and 20.7"C. and a counting the number of non-viable embryos and mean annual precipitation of 567 mm. with most atrophic eggs in ovidiicts of autopsied fernales and rain occurring during summer. Vegetation of the by contrasting the niimber of corpora lutea in their zone is typically a highly diversified oak-pine forest ovaries with the total number of eggs found in ovi- including 207 plant species of which 18 are (2uercus ducts. species and 10 are Pinus species (Martinez and Sal- dívar, 1978). A stiidy plot measuring 500 by 1,000 m was RESUI.TS-Dmsity-Table 1 shows the aver- marked with stakes every 10 m and cerisused over 4 age estimated density for adults and subadults years duririg the following months: September and per hectare calculated for each field visit. The December of 1979; March, May, and September of estimates for adults, where it is possible to com- 1980 arid 1982, and every month of 1981. Each one pare among al1 months, were significantly dif- of these 20 intervals of field work lasted 15 days. ferent among months (ANOVA: F,,,,, = 9.1 1; 'Three people searched the plot for lizards frorn 4 to P < 0.001).There exist two well-differentiated 7 hours per day. For each observed lizard we record- groups of months according to their density ed its location in relation to the nearest stake. We values: October, March, February, and Decem- then captured the individual by hand. Captured in- ber were the months with statistically highest dividual~were marked both by toe clipping arid by paint code (Tinkle, 1967a), and the following data density, whereas June, July, August, and No- were recorded: sex, snout-vent length (SVL), tail vember were those with statistically lowest den- length, and body mass. Body lengths were measured sities (Tukey-Kramer post hoc test: F,,,,, = 1.0 the nearest 0.1 mm with metal calipers (Scala 7.28; P < 0.01). 222), and body rnass was measiired to the nearest Population StructureWe differentiated six 66 Thc South711estmNaturalist vol. 44, no. i

TABL.E1-Sceloporus pmmims average density per adult I,5 to 12 months old and reaching sexual hectare (1 SD in parentheses) calculated for the last maturity, with SVL froin 48.1 to 53 mm for three days of each field visit. males and from 42.1 to 50 mm for females; and 4) adult 11, individuals in their second repro- Number Number of ductive season, reaching a maximum size of 62 of adult sub-adult min SVL for both inales and females. It was not Month Year individuals individuals possible to determine from size alone whether January 1981 42.3 (8.1) 0.0 the individual was 2,3, or 4 years old. However, February 1981 54.2 (7.3) 0.0 from skeletochronology cohort data (Ortega et Marrh 1981 55.4 (3.2) 0.0 al., 1993) we differentiated 5) adult 111, indi- April 1981 47.6 (12.7) 0.0 vidual~in their third reproductive season; and April 1982 54.8 (12.9) 0.0 6) adult IV, individuals in their fourth repro- May 1981 44.4 (6.7) 3.2 (1.1) ductive season. May 1980 42.3 (12.1) 51.5 (21.9) June 1981 25.6 (3.3) 190.7 (37.8) Table 2 shows estimated numbers (derived Jilly 1981 26.8 (5.3) 184.9 (39.9) from density estimates) of each age and sex August 1981 24.5 (4.4) 72.8 (19.1) group for 10 ha throughout the year. Juveniles Septeniber 1981 46.1 (12.1) 51.3 (18.5) appear during May and their nuinbers increase Septeniber 1982 58.2 (8.3) 0.0 quickly, reaching a maximum in June. Juve- October 1981 58.3 (16.8) 0.0 niles are replaced in August by subadults, Octobei- 1979 41.1 (2.4) 0.0 which decline during September, being re- November 1981 31.4 (2.1) 0.0 placed by the adult 1 group. The adult 1 group, December 1981 52.3 (12.8) 0.0 particularly males, can show abrupt oscilla- tions. Nuinbers of adult 1 males reach their highest from October to December, declining age-groups for Sceloporus grammicus at La Mich- slowly from February to May. Female adult 1 ilía Biosphere Reserve: 1) juveniles, younger numbers also are high in October through De- than 3 months, with SVL <38 mm for males cember, but are lower than those of same-aged and <34 mm for females; 2) subadults, 3 to 5 males. Females of this age group reach their months, with SVL from 38.1 to 48 mm for highest numbers during February and March, males, and from 34.1 to 42 mm for females; 3) or at least more are seen then than earlier.

TABI.E2-Demographic striicture for the population of S. g-rammicus at La Michilía. Nuinber of individuals is calciilated for 10 hectares.

Class Fe- Fe- Male Female Male Female Male Female Male male Male male sub- silb- adult adult adiilt adult adult adult adult adult Month Iiivenile adult adult 1 1 11 11 111 111 IV IV Totals January February March April May June July August Septeniber October November December Totals March 1999 Ortega-Rubio et al.-Population dynarnics of Sceloporus gramrnicu.,~ 67

TABLE3-Percentage of females in different age groups of the studied population.

Class Month Juveniles Subadults Adults 1 Adults 11 Adults 111 Adults N Average January February M arc h April M~Y June .Ju~Y Augus~ Septernber October November Decernber Average

Male and female adult 11 classes reach their plying the number of females per age class by maximum density during September and their average litter size per age class, we calculated lowest during November and December. natality. The estimated number of S. grammicus Table 3 shows the percentage of females in born in 10 ha was 1,482 (Table 4). different age groups throughout the year. At Mortality and Survival-From the 120 autop- younger ages, the sex ratio is almost 1:1, but sies performed on females during the repro- changes in favor of females in older age classes. ductive season, only 25 atrophic eggs from a Additionally, for older ages there is a tendency total of 348 eggs were found, thus percent em- for females to be more abundant during the bryo failure was relatively low ('7.2%),suggest- first half of the year, but during the second half ing a low prenatal mortality rate (Table 5). Dis this proportion is reversed. This tendency is appearance of individuals estimated by mark- even greater in the adult 11 group. The overall recapture methods also is shown in Table 5. sex ratio is 56.2% females. The average disappearance from one age class NatalityFrom the autopsied females we es- to the next was higher than 58% for al1 age tablished that average litter size for S. pmmi- groups and both sexes. Minimum disappear- cus females was 6.17 (SE = 1.65) neonates per ance occurred for adult 1 males, and the max- female. Litter size varied widely from female to female, ranging from three to nine neonates TABLE5-Mortality, emigratiori, and survival of S. depending on female SVL. There exists a grammicus iridividuals. strong significant relationship between litter size and body size (litter size = 0.361 SVL - Average 12.891; r = 0.88; df = 43; P < 0.05). By multi- percent Percent disap- ernigra- Class pearance tion MortalitySurvival TABLEGEstirnated productivity of S. grammicus for the nionth of May Prenatal Juveniles Male adult I Fernales Average Average Newborn Female adult 1 in 10 size clutch pro- Male adult 11 Group hectares mrn size duced Female adult 11 Adult 1 180 47.03 4.08 734 Male adult 111 Adult 11 74 58.00 8.04 595 Fernale adult 111 Adult 111 15 58.00 8.04 121 Male adult iV Adult N 4 58.00 8.04 32 Fernale adult iV 68 The Southwestern Naturail~t vol. 44, no. 1

TABL.E6-Life tahle for the S. grarnrnicus populatioii at the Michilía biosphere reserve; X = age in years; Lx = proportion of original populatiori alive at the start of age iiiterval; dx = proportion of the origirial populatioii dying in the age interval; qx = age-specific mortality (dx/lx); mx = age-specific fecundity; Lxmx = age-specific contribution to the net reproductive rate (Ro); Vx = Reproductive Value; Vx* = Residual reproductive valur; and Ex = Life expectancy of those attaining age x.

Age group X Lx dx qx mx Lxmxl Xlxmx Vx Vx* Ex Embryo O 1.00 0.071 0.071 O O O 0.983 0.983 2.313 .Tuvenile 0.17 0.929 0.646 0.696 O O O 1.058 1.058 1.413 Adult 1 0.63 0.283 0.196 0.692 2.04 0.577 0.364 3.475 1.435 1.357 Adult 11 1.63 0.087 0.075 0.862 4.02 0.048 0.126 4.667 0.647 1.161 Adult 111 2.63 0.012 0.010 0.862 4.02 0.048 0.126 4.690 0.670 1.067 AdultIV 3.63 0.002 0.002 1.000 4.02 0.008 0.029 4.020 0.000 1.000

' 2 lxmx = Ro == 0.983. imum value occurred for adult 11 males. Dis ture is length of the hatching period. S. gram- appearance less emigration is mortality. Emi- micus has a discontinuous, short and wellde- gration is highest for juveniles, who also show fined reproductive season (Type 11-Barbault, high mortality (Table 5). As expected, mortal- 1975). This kind of reproduction is similar to ity is highest for the oldest age classes (Table 5). that of most lizards in temperate and desert The life table for Sceloporus gramminrs (Table habitats (Blair, 1960; Fitch, 1970; Ballinger, 6) indicates a Slobodkin (1962) Type IV sur- 1971; Marion and Sexton, 1971; Schrank and vivorship pattern as described by Deevey Ballinger, 1973; Burkholder and Tanner, 1975; (1947) in which heavy mortality occurs in the Goldberg, 1975), and several tropical lizard younger age groups. Net reproductive rate is species (Carpenter, 1966; Fitch, 1973). In the

0.98 and average generation period is 1.09 case of age-specific-. survival, the main factor in- years. fluencing age structure is average longevity. In this aspect, S. grammicus is relatively short-lived, DISGUSSION-BensityLizard density is ex- similar to many tropical and temperate lizard tremely variable between species, families, and species (Barbault, 1973, 1976~).The combi- regions of the world. Lizard density varies from nation of short birthing periods and reduced less than 1 individual/ha as in the case of Ure longevity determines the age structure ob- mastix acanthinurus in Algeria (0.01 individu- served in the S. grammicus population at La als/ha; Grenot, 1976) and the Komodo dragon Michilía. Age groups were clearly defined, in Indonesia (0.02 individuals/ha, Dareskivj showing the highest density in the juveniles and Terentev, 1967), up to densities higher and adult 1 groups. than 1,000 individuals/ha, as in the case of An- Our results show that the number of cen- olis limiji-ons in (1,171 individuals/ha; sused adults oscillates from month to month. Sexton, 1967). However, the most common This is probably an artifact related to the visual densities fluctuate from 10 to 100 adults/ha recapture method used. Our censuses depend (Barbault, 1975), and according to calculations on the number of active individuals observed of Tumer (1977), average density for lizards is during the last three days of each visit. The around 51 individuals/ha. The average adult activity of each individual depends on a wide density for S. grammicus at La Michilía (42 in- range of factors, physiological and behavioral, dividuals/ha) is close to the general averages. both intrinsic aspects of the individual, and ex- We were unable to find any previous study on trinsic factors of the physical and even social S. grammirus density at other locations. environment. For instante, male adult 1 num- Population StructureThe age structure of a bers reach their peak during December, even population depends on both age-specific fe- though that is a-relatively cold month. How- cundity and age-specific survivorship schedules ever, December is the month when copulation (Barbault, 1975). In the case of age-specific fe- takes place (Ortega and Barbault, 1984). So, cundity, the main factor influencing age struc- that is when male adult 1 individuals become March 1999 Ortega-Riibio et al.-Population dynamics of Srelopoms (~rammict~s 69 more active, patrolling and defending territo- ential activity could affect numbers of males ries and looking for females. Thus, a greater and females counted, and thus the observed proportion of the adult 1 males alive then are sex ratio. seen and counted by our method than at later Natality-Lizard species show a wide variety times. of clutch and litter sizes, varying from the sin- Likewise, numbers of adult 1 females gle egg of Anolis up to more than 50 eggs for reached their peak during February and large chameleons (Barbault, 1975). The aver- March, even though just as many had to be age number of lizard eggs per female varies alive in the months immediately preceding. from two to six (Fitch, 1970). Comparing the From October to December the rainy season average litter size of the S. grammicus popula- yields maximum availability of prey for S. gram- tion of La Michilía with other S. grammicus pop- micus (Ortega and Hernández, 1983). During ulations, we found that females of La Michilía these months adult 1 females do not need to were more prolific (6.2 young) than those move very far in search of food. Also, from Oc- studied at Zoquiapan (Guillette and Casas-An- tober to December, the activity leve1 of S. gram- dreu, 1980) and in (Werler, 1951), av- micus predators shows its maximum (Ortega, eraging 5.2 and 5.7 young, respectively. How- 1986). So, as a posible adaptation to preclude ever, S. grammicus females of La Michilía had predation, adiilt 1 females remain secretive. smaller litters than females of other Texas pop- Both these aspects may decrease the chance ulations (11.7 young) studied by Axtell and Ax- that an adult female is seen and counted, even te11 (1970). while males are active defending territones Clutch or litter size in lizards is closely relat- and seeking mates. On the contrary, during ed to female body size (Barbault, 1975). The February and March, the drought arrives and average body size of lizard females of La Mich- prey grow scarce (Ortega and Hernández, ilía (52.8 i 4.1 mm) was considerably larger 1983). During these months adult 1 females, than the body size of S. grammicus females at which are pregnant and with elevated nutrition Zoquiapan (48.5 2 0.8 mm; Guillette and Ca- requirements as compared to post-reproduc- sas-Andreu, 1980). This larger size could help tive males, must move more in search of food. to explain the larger litters of La Michilía fe- This increased activity likely translates to a males compared to those at Zoquiapan. There greater chance that these females are seen and were no data on female body sizes for Texas coun ted. populations (Werler, 1951; Axtell and Axtell, Sceloporus grammicus sex ratio at birth is very near 1:1, similar to most other lizard species 1970). (Barbault, 1975) with the exception of parthe- Clutch frequency per reproductive season nogenetic species or (Grassé, 1970). also varies widely in lizards, ranging from only With increasing age, it is common to observe one (Iverson, 1979) to more than nine (Porter, a change in sexual proportion, usually in favor 1972). Clutch size and frequency in lizards are of females (Hirth, 1963; Barbault, 1974a), but higher in tropical species (Wilhoft, 1963; Dun- in some cases favoring males (Alcala, 1966; ham, 1982) than in species inhabiting temper- Turner et al., 1969). In other cases, numeric ate climates (Ballinger, 1979). Also, clutch size equality between males and females remains and frequency are greater for smaller and ear- constant (Brooks, 1967; Telford, 1969). In the lier-maturing lizards (Barbault, 1976b) than case of S. grammicus at La Michilía, the sexual larger-sized lizards at maturity (Crisp, 1964). proportion is biased in favor of females in old- Viviparous lizard species, such as S. grammicus, er classes. have only one litter per year (Ballinger, 1973), The tendency for a greater female-bias dur- whereas oviparous species frequently have sev- ing the first part of the year within an age class eral clutches per year (Parker, 1972). c,ould be an artifact of differential activity of As a result of variation in clutch and litter the sexes. As we explained in the last section, size and frequency, total fecundity varies widely due to their reproductive behavior, S. grammi- among females of different species. However, cus males are much more active during the last the average varies between five and 20 eggs for part of the year, and females are more active oviparous species, being more fecund than the during the first part of the year. This differ- viviparous ones, with an average from three to 70 The Southwtlrtn7i Natu?ahst vol. 44, no 1

10 neonates per female (Barbault, 1975). S. high predation pressure on this population, grammicus total fecundity is within this average. determine the observed mortality patterns. In Mortality and Survival-Prenatal mortality turn, the species' fecundity schedule is adapt- varies widely among lizard populations, rang- ed to this imposed pattern of mortality. It will ing from less than 5% (Ballinger, 1971) to 90% be necessary to conduct more studies, partic- (Blair, 1960; Barbault, 1973), but the most ularly on the impact of predators, to confirm common values range from 40% to 60% this idea. (Brooks, 1967; Tinkle, 1969; Barbault, 1974b). Thus, S. grammicus prenatal values were low This work was supported jointly by the Consejo (7.2%) compared to these averages. Nacional de Ciencia y Technología (CONACyT), the Juvenile mortality also varies widely among Instituto de Ecología, and the Centro de Investiga- ciones Biológicas del Noroeste, of México; by the lizard populations, ranging from less than 10% Ecole Normale Superieure and the Council National (Blair, 1960) to nearly 50% (Zweifel and Lowe, de la Recherche Scientifique (CNRS) of France and 1966; Brooks, 1967), up to more than 90% by the MAB UNESCO program. We thank three (Ballinger, 1971). However, the most common arionymous reviewers for their kind and helpful sug- values vary around 50% to 80% (Barbault, gestions, which highly irnproved an early version of 1975). Juvenile mortality for S. grammicus the manuscript. We also thank R. Bowers for editing (69.7%) was close to average values for al1 liz- the English and L. Vazquez who typed the niaiiu- ards. script. Mortality rates also vary widely among adult lizards, ranging from less than 20% from year 1 to year 11 (McCoy, 1965; Zweifel and Lowe, ALTALA, A. C. 1966. Populations of three tropical liz- 1966; Burrage, 1973) to very high mortality ards on Negros islands, Philipines. Unpublished rates of more than 90% (Tinkle, 19676; Turner Ph.D. dissertation, University of Michigan, Ann et al., 1969), and up to 100% for the annual Arbor. species (Barbault, 1974b). Adult mortality for ANDEKCON,R. A. 1994. Functional and population S. grammicus from year 1 to year 11 (61.3%) was responses of the lizard Cnemidophorus tigris to en- virorirriental fluctuations. Anierican Zoologist 34: close to that of species with high mortality rates 409-421. during this adult period of life. ANDREWS,R. M., AND S. J. WRIGHT.1994. Long-terni Adult survival determines the longevity of population fliict~iationsof a tropical lizard: a test the species. For lizards, published data indicate of causality. 111: Vitt, L. J., ;ind E. R. Pianka, edi- a wide variation in longevity. In captivity, sev- tors. Lizard ecology: historical and experimental eral lizard species live from 20 to 50 years perspectives. Princeton University Press, Prince- (Mertens, 1959; Pfeffer, 1959; Moehn, 1962), ton, New Jersey. Pp. 267-285. but in nature, lizard longevity averages from 1 AXTELL,A. (J., AND R. W. AXTEL.L..1970. Hiberriacula to 9 years (Barbault, 1975). Frequently, the birth and young of Scelopmzis grammirus disparilis species that are similar in size to S. grammicus (). Southwestern Naturalist 14:363-366. BAILEY,N. T. 1952. Iniprovements in the interpreta- live from 1 to 3 years (Blair, 1960; Tinkle, 1969; tion of recapture data. Journal of Aninial Ecology Porter, 1972).AL La Michilía, the oldest recap- 21:120-127. tured S. grammicus individuals were 4 years old. BALUNGEK,R. E. 1971. Comparative deniography of According to general life-history theory two viviparous lizai-ds (Sceloporus ,jarrovi and Sce- (Tinkle, 1969; Tinkle et al., 1970; Barbault loporus poinsetti) with co~isiderationsof the evo- 1976c), S. grammicus as a viviparous and single- lutionary ecology of viviparity in lizards. Unpub- brooded lizard should show lower mortality lished Ph.D. dissertation, Texas A8rM University, and a longer life compared to oviparous, mul- College Station. tiple-brooded lizards. However, our data show BALLINGEK,R. E. 1973. Coniparative deniography of a clear contradiction to this expectation. Com- two viviparous iguanid lizards (Sceloporus jorrov¿ and Sceloporus poinsctti). Ecology 54:262-238. paring the demographic data of S. grammicus BALL.INGER,R. E. 1979. Intraspecific variation in de- with the general rules proposed by r-Kgeneral niograpliy and life history of the lizard. Scelopmzis theory (Tinkle et al. 1970; Barbault 1976c),we jarrovi along an altitudinal gradient in southeast- conclude that the marked seasonality of the ern Arizona. Ecology 60:901-909. environment, arid the rigorous conditions of BARBAULT,R. 1973. Structure et dinaiiiique d'un the physical environment and probably the peuplenient de lézards: les Scincides de la savane March 1999 Ortega-Rubio et al.-Popiilation dynamics of Scelopatus grammicus 7 1

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