Rev. Biol. Trop., 46(1): 145-155, 1998

Growth effort of Sceloporus scalaris (Sauria: ) at La Michilía Biosphere Reserve, Mexico

Alfredo Ortega-Rubio' *, Robert Barbault2,Gonzalo Halffterl,AraditCastellanos%nd Federico Salinas" ' Instituto de Ecología, Apdo. Postal No. 63 Xalapa, Veracruz 91000 México. Ecole Normale Superieure, 46 Rue D'Ulm, Paris Cedex 05, France. * Present address: ' Centro de Investigaciones Biológicas del Noroeste, Apdo. Postal No. 128. La Paz, 23000, Baja California Sur, México.

Received 13-XI- 1996. Corrected 24-IX- 1997. Accepted 09-X- 1997

Abstract: Using Mark-Recapture methods the growth effort of Sceloporits sc«.luris was studied at La ~ichiljaBiosphere Reserve, Durango, Mexico. A total of 146 recaptures on 68 individuals wereobtained over four years on a50 000 m'transect. To calculate the growth rate of Sceloporus sculuris individuals, we analyzed the data from two sources. The first using the recapture records of the same individuals over different seasons and the second using the records of cohons during different periods. The growth effon of S. scuklris drastically diminishes as the organism grows. The growth rate of males and females is about equal for individuals from both clutches. In adults, where it is possible to compare among seasons, we measure quicker growth during the spring. The growth pattern of S. scalaris at La ~ichiljafollows the predictions proposed by the Benalanffy model. Maximum growth rates are in the younger age classes and these rates decrease as size increases. The growing period of S. sculuris is correlated with the seasons at La ~ichiliaBiosphere Reserve. Newborn S. scu1uri.r appear when the availability of nourishment is still the most propitious for growth at faster rates. Such adaptations to the environment determine many key population attributes of this in this zone. The sexual maturity age of S. sitrlaris is very early at La Michilia, only 4.5 to 6 months. Undoubtedly, the growth pattern of S. sculuris at La Michilb Biosphere Reserve can help explain the structure and dynamics of this population.

Key words: Durango; Growth Effon; La Michilía Biosphere Reserve; ; Mexico; Sceloporits sculuris.

The bunch grass , Sceloporus scalaris 1974,Newlin 1976). Thereare noprevious works Wiegmann is an small (62 mm SVL), very dealing with the growth patterns of this species. common and abundant Mexican lizard which distribution includes 22 states of the Mexican The growth pattern is a key aspect in the life Republic (Smith 1939).In spiteoftheirabundance history of any species (Andrews 1982). Growth and wide distribution, there exists relatively few rates determine, among other important attributes, studies concerning the ecological aspects of this the length reached at sexual maturity and the (Ballinger and Congdon 1981). Most of maximum size (Andrews 1976, Barbault 1975, the previous studies are devoted to taxonomical Kaufmann 1981, Van Devender 1978). Body (Srnith andpoglayen 1958, Smith and Hall 1974, size, in many . determines crucial Thomas and Dixon 1976, Stebbins 1966, reproductivecharacteristics such as reproductive Anderson 1972, Van Devender and Lowe 1977), effort arid clutch size (Barbault 1974, 1981). and reproductive aspects (Stebbins 1954, Thus, the study of growth patterns can help us to Anderson 1962, Greene 1970, Smith and Hall understand the structure, dynamics, and 146 REVISTA DE BIOLOGIA TROPICAL demography of any lizard population (Barbault To calculate the growth rate of Sceloporus 1975, 198 1, Van Devender 1978). scalaris individuals, data from two sources were analyzed. The first uses the recapture records of the same individualsduringdifferent seasons and the second uses the records of cohorts followed MATERIALS AND METHODS during different periods.

Study area: The study site, La ~ichilla The data of individual recapture records were BiosphereReserve, is in thesoutheastof theStatc pooled by age class and by season. Using the size of Durango, México, between 104"20 ' and 104 differences between capture and recapture of a "07 ' W and 23 " 20 ' and 23" 30 ' N. Field work particular individual, the Instantaneous Growth was done in the buffcr zone of the Reserve. Rate (IGR) was calculated using the Barbault (1 973) formula: The climatcof thc zone is temperate subhumid with a mean annual tcmpeiature range between 17.4 " C and 20.7 " C and a inean annual LI - LI IGR = precipitation of 567 mm, conccntrated in the summcr. The vegetation oí' the zone is typically T, -TI an oak-pine forest but highly diversilicd, including 207 plantspecies thatcontain 18diI'l'erent Quercus Where: species and I O differcnt Pin~ls\pccies (~art~nez L,=Individual size at time TI;at initial capture. and Saldivar 1978). L,= Individual size at time T,; at recapture. Methods: A transcct of 50 x 1 000 m marked with stakeseach I Om, wasestablishcd andcensus Based on the IGR, the Growing Effort index \vere takcn over 4 ycars during the following (GE) was calculated using the Barbault (1973) months: September and December 1979; March, formula: May, and Septcrnbei 1980 and 1982 and al1 the IGR months oi' 1981. Each one of thcse 20 stays GE = --- comprised 15 days. Duringeach day, the transect L was traversed by 3 pcrsons lor 4 to 7 hours in the search for liaard individuals. For each lizard obscrvcd, we rccoi-ded the datc, the hour, its sex, Where Lis the averageindividual lengthduring its location in relation b thc nearest stake and the time interval T, - TI,and it was calculated thcn we capturcd the liaard by hand. using the formula:

For cach li~ardcaptured, we rccorded the I lollowing data: body temperaturc with a cloaca1 L = -(L, + L?) thermomcter (Wescott): snout-vcnt length and 2 tail lcngth to the ncarcst 0. I mm with a metal calipcr (Scala 222); and body mass to the nearest 0. I g with a Pesolii (TM). Captured individuals Thedifferences in individual body data, among were marked both by toc clipping and by paint captures and recaptures, were adjusted to the code (Tinkle 1967). differential cquations of the curves and models rnost frequently used to describe animal growth. For this purpose, we calculated the size iricrease per day percentage, also called Relative Growth Ratc(RGR), using the methodof Kaufman (1 981): ORTEGA-RUBIO et ~11.:Growth effort of Scelol>orus sca1uri.v 147

graph paper, then the logistic or the Bertalanffy curves be can be used (Bertalanffy 1957, 1960, Kaufman 1981). It is possible to calculate the linear regression for the plotted data, and calculating the origin and the slope, to establish Where: the differential equation that defines the pattern observed. S,= Body size at the beginning of the time period. S,= Body size at the end of the period. t- Time period. RESULTS

A total of 146 recaptures on 68 individuals RGR value is thenplottedagainstthegeometric weremade during the4 years of study. Individual means (S) ofthe individual body size, S, which is averages were grouped by seasons on Table 1.At calculated in the following way: La ~ichilia,summer was humid and hot and winter was cold and dry (Martinez and Saldivar S= (S, 1978). The age classes considered were (Ortega 1986):juveniles, individuals < 3 months for both clutches; subadults, individuals between 3 and 7 If the plotted data yield a straight line using months for the first clutch individuals and í'rom 3 semilog paper, a Gompertz curve can be used to to 5.5 months for the second clutch individuals; describe the observed data pattern (Kaufman Adults 1, individuals reaching sexual maturity 1981). If a straight line is obtained using from7 to 12months forthefirst clutch individuals logarithmic paper, then a potency curve must be and from 5.5 to 12 months Por the second clutch used and, if a straight line is obtained with linear individuals; Adults 11, individuals older than one year.

TABLE I

Averclgr groici/r,q

Season 1 2 3' 4 Average Age class

Juvenile 0.050 0.050

Subadult iiiale

Subadult fcriialc

Adult iriale 0.0 13 I

Adult feiiiale 0.014 I

Adult inale 0.003 I I 148 IIEVISTA DE BlOLOGlA TROPICAL

As we can observe in Tables 1 and 2, GE Thereexists goodfit both with thesemilogand drastically diminishes as the organisms grow. linear plots, for both clutches individuals. Testing The maximurn GE is showed by the juveniles statistically the correlation coefficients found in during the autumn. Males and females exhibit each plot (with Student's t-test and f test), we practically equal GEin al1 ageclassesconsidered. found thebestfit is forthe plot number 1d) for the In the case of the adults, where il is possible to first clutch individuals, where y = 0.3205 X - compare among seasons, we see a slight quicker 0.0049; r = 0.81; and the plot number 2 d) for growth during spring. those of the second clutc h, where y = 0.2426 x - 0.0028; r = 0.65.

' TABLE 2

Aiiertige growirlg ~fj'ort(jn~rz.dr~y-'. 10). hy setison und rige clriss,for rhe se<:oitd clutclz <:trptured S. scrrlnris individuuls.

Season I 2 3 4 Average Age class

Juvenile 0.090

Subadult Male

Subadult Fernale

Adult rnale 0.014 I

Adult female 0.0 17 I

Adult male 0.004 II

Adult female 0.003 1 I

Figs. I and 2 show the calculated pair values for the RGR and the geometric mean of the individual body size for each individual recaptured, plotted in semilog, log, and linear paper. ORTEGA-RUBIO el al.: Growth effort of Sceloporus scalaris

A .O08 RGR = (-0.0026)(ln L) + (0.0118) in RGR = (-4.82)(1n L) + In 12.04 r = -0.56 r = -0.46 .O07

SVLmm

RGR = (-0.0002)(L) + (0.0114) 7 ,008- RGR = (0.2426)(1 B) - (0.0038) r = -0.37 r - 0.65

E 9 ,005- L m 0 ,004- a, . -> m -Ym ,003- a, E ,002-

.O01 -

.O00 .

SVLmm

Fig. l.Sceloporus ~ca1~1ri.~first ciutch growth data adjusted to: a). A Gompenz curve. b). A Power curve. c). A logistic curve. d). A Bertalanffy curve. REVISTA DE BlOLOGIA TROPICAL

.o10 - RGR = (-0.0065) (In L) + (0.0274) r = -0.64 .O09

,008 1 ln RGR = (-2.49) (In L) + In 3.34 m r = -0.57 0.007

SVLrnrn

d) 1 RGR = (0.325)(1 h) - 0.0049

SVLrnrn SVLrnrn

Fig. 2. S(.elo/~or~rs.rc.r~l~iris second clutch growth data adjusted to: a). A Gompertz curve. b). A Power curve. c). A Logistic curve. d). A Bcrtalanffy curve. ORTEGA-RUBIO et ul.: Growth effort of Scelol~orussctrlaris 1.51

The growth curve that fits the S. scalaris ThegrowthpatternofS. scalaris, at~a~ichilia growth data best is the Bertalanffy curve. The follows the predictions proposed by the integrated equation of this curve is: Bertalanffy model, i.e., maximum growth rates are reached in the younger age classe; and these rates decrease as the size increases. S = S,,[1-Exp "(t + T,,)] 'i'he second data source, independent of the Where: mark-recapture data analyzed, was the measure of the monthly size of individuals of the same cohort during one year. This could be only S = Size achieved because S. scalaris, newborn appear in 1 = Time two short well-defined period: 15 days during S,,= Asymptotic size September for the first clutch individuals and 15 b = Intrinsic growth rate days during October for the second clutch. t,,= Initial time The measured growth rates by day and by The Bertalanffy model is based on the month, for 1981, are showed in Table 3. Growth hypothesis that the growth rcpresents the rates are relatively high Srom October to March difference between synthetic (anabo1ic)processes for both clutch individuals. Themaximum growth and degradation (catabolic) processes and the forfirst clutch individualsoccurs from October to synthetic processes are directly proportional to December.During January to March exhibit lower the body mass (Bertalanffy 1957, Fabens 1965). growth values than second clutch individuals, Although it is more accurate to use the integrated which reach their highervalues during this period. equation, it iseasier touse thedifferential equation, From May to September the growth rates fa11 which establishes Lhe relationship between the drastically, for both clutch size individuals, and Relative Growth Rate and the si~e(Kaufmann show littlechange up to theageof 1 year (the next 1981): October).

Integrating the data by the mark-recapture methods and by the cohort-record method, it was possible to build the body evolution curves for both males and females (Fig. 3). Juvcnile males grow quickly Srom September to April and Where: a is the axis interccpt and b is the slope relatively slowly from May. Juvcnile females of the line (Figs. Id and 2d). show, Srom September to April, a lower growth rate Lhan juvenile males, but from May they do The BertalanSSy linear growth model is the not exhibit an abrupt decline in rate as do the most common found Por reptiles (Trivers 1976, males. Thus, at the age of 13 months and with a Turner and Gist 1970, Schoener and Schoener size of 51 mm (he females reaches the average 1978, Van Devender 1978). Previously, it had size of the males. From the second April (month been reported that for sinall andshort-lived lizards 17) females not only are bigger, but grow more Ii ke S. scalaris, (he best model fitted is the logistic quickly than males. one (Andrews 1982,Dunham 1978,Tinkle 1967). The growth patlerns of bigger reptiles of longer life lollow the Bertalanffy model (Chebreck and Joanen 1979, Webh et al. 1978, Wilbur 1975). REVISTA DE BIOLOGIA TROPICAL

TABLE 3

Crowinl: rcite (m~n/duy)j0r S.scufuris individuuls,f¿)rthe 1981 yeur,

Age (rnonths) Age (months) First clutch Males Females Second clutch Males Females

Periods: 1= Sep to Oct; 2= Oct to Nov; 3= Nov to Dec; 4= Dec to Jan: S= Jan to Feb; 6= Feb to Mar; 7= Mar to Apr; 8= Apr to May; 9= May to Jun; 10= Jun to Jul; 1 I= Jul to Aug, and 12= Aug to Sep.

The secondclutch individualsfollows basically between nourishrnent and growth rate could be the sarne pattern, but their growth rate is slightly rnasked by theeffect on the growth ratesproduced faster, for both males and fernales, which is even by water availability (Nagy 1973, Smith 1977) or more easily observed from the second January by the existence ofcircadian rhythrns of appetite . (month 16) to their second May (month 20). At and other endogenous factors (Jackson 1970, the age of 20 months and with a size of 55 mm the Licht 1972). second clutch individuals reaches in size to the first clutch individuals and it is not possible At the La ~ichiliaBiosphere Reserve, the posteriorly to differentiate arnong them only by rnaxirnum prey-availability period for S. scalaris their size. is frorn June tooctober. During thesemonths the abundance and biomass of their prey reaches their peak (Ortega and Herwndez 1983).Because DISCUSSION of this, wemust expect themaximum growthrate for S. scalaris individuals to be from June to There are rnany interdependent factors that October, which does not occur. determine the growthrateofany animal: available nourishment and water, phenological phase of From June to Septernber there are only adult theindividual, inter- andintraspecific cornpetition, individuals of this species in the zone (Ortega predation, social environment, and for lizards, 1986).Juvenile individuals reaches their highest even tail breakage. numbers from October to January, and the subadults from January toMarch. Forthis reason, Individual growth varies with the available in spite thatmaxirnum nourishment availability is energy, thus rnany lizard species exhibit quicker foundduring thesurnrnermonths,thefaster growth growth rates during the season of higher prey rates are found from October to March. The availability (Dunham 1978, Medica et al. 1975) younger age classes shows the quickest growth or when they have access to supplementary food rates in spite than they growthonly during the last (Licht 1974). However, the direct relationship optimurn rnonth of the year (October). ORTEGA-RUBIO er d.: Growth effort of Scelol?orusscciluris 153

ACKNOWLEDGMENTS

This work wassupportedjointlyby theconsejo Nacional de Ciencia y Tecnología (CONACyT), the Instituto de Ecología, and The Centro de Investigaciones Biológicas del Noroeste, of México; by the Ecole Normale Superieure, the Counceil National de la Recherche Scientifique -FlRST CLUTCH MALES (CNRS) of France and by the MAB UNESCO -3 FlRST CLUTCH FEMALES program. We thank J. Monge-Nájera and two -SECOND CLUTCH MALES a -0 SECONDCLUTCH FEMALES anonymous reviewers for their helpful suggestions on an earlier version of this manuscript, Ellis Glazier for editing of the English language text Age (rnonths) and Lolita Vázquez for typing the manuscript.

Fig. 3. Body evolution of S. s<.cilarisrriales and females

Tlie reproductive period of S. scalaris is RESUMEN correlated with theseasonality oftheenvironment at La ~ichiliaBiosphere Reserve. Adult S. Usando métodos de Marca-Recaptura estudiamos el esfuerzo de crecimiento de Scelo~~orussccikiris en la Reserva scalaris oviparous females exhibit two periods de la Biosferade La Michilía, Durango, México. Se analizaron carrying oviducal eggs, June and August (Ortega 146 registros de recaptura sobre 68 individuos en cuatro años 1986). Reproductive activities occurs just when de estudio en un transecto de 50 000 m'. El esfuerzo de the nourishment availability is themostpropitious crecimiento disminuye drasticamente conforme el individuo for use this energy for reproductive purposes crece, es casi igual para los machos y hembras de las dos puestas, y en el caso de los adultos se registró un crecimiento (Ortega 1983).Besides, S. scalariseggsare laying rnás rapido en primavera. El patrón de crecimiento sigue las duririg the rainy season, it is to say during the predicciones propuestas por el modelo de Bertalanffy. Los optimum humidity conditions to conclude the recién nacidos de S. scularis eclosionan cuando la embrionary development (Ortega 1986).The new disponibilidad de alimento es todavía la más propicia. La madurez sexual de los individuos es muy precoz en La S. born scalaris individuals appears during the Michilía: de 4.5 a 6 meses. El patrón de crecimiento de S. last month of the optimum period ofthe year and scciluris en La Michilía ayuda a explicar la estructura y growth at the fastest rates. dinámica de esta población.

Such adaptations to theenvironmentdetermine many key population attributes of this species in this zone (Ortega 1986). The sexual maturity age ofS. scalarisis very early at ~a~ichilia,only 4.5 to 6 months (Ortega 1986). Undoubtedly, the growth pattern oí' S. scalaris at La ~ichil~a Biosphere Reservc can help explain the structure and dynümics of this population. REVISTA DE BlOLOGlA TROPICAL

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