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Ecology (1976) 57: pp. 445-458

ECOLOGICAL AND PHYSIOLOGICAL ASPECTS OF REPRODUCTIVE STRATEGIES IN TWO '

W. KENNETH DERICKSON2 Division of , Kansas State University, Manhattan, Kansas 66506 USA

Abstract. Two , the northern prairie lizard (Sceloporus undulatus garmani) from Reno County, Kansas and the northern (Sceloporus graciosus graciosus) from Washington County, Utah, were used to test four hypotheses and one assumption related to the theory of r- and K-selection. The northern prairie lizard is short-lived, matures early, and has a high reproductive effort (r-strategist) while the northern sagebrush lizard is long- lived, has delayed maturity, and a low reproductive effort (K-strategist). One of the assump- tions of the r- and K-selection theory is that for is more intense for K- strategists than for r-strategists. Given this assumption, greater food availability for the prairie lizard was hypothesized to result in (1) a higher level of body , (2) a higher rate of utilization, (3) a lower percentage of ingested available for , and (4) an expenditure of less energy per offspring than in the sagebrush lizard. Total lipid levels in the two species collected before and after hibernation indicated that prairie lizards had significantly higher lipid levels than sagebrush lizards during both collection periods. A comparison of the amount of body lipids lost and the amount of egg lipids gained during vitellogenesis of the first clutch suggested that more lipids are being utilized for egg production in prairie lizards than in sagebrush lizards. Sagebrush lizards apparently are better adapted physiologically to lower food levels since they had lower rates of lipid utilization during starvation studies and they extracted more energy usable for metabolism from ingested food than prairie lizards. Although both species expended about the same amount of energy on a given clutch of eggs, prairie lizards produced more offspring per clutch and therefore expended less energy per offspring. Prairie lizards produced as many as three clutches per as compared to two clutches per season for sagebrush lizards, and changes in length-lean weight relationships for the two species over a given season suggested that the additional clutch of eggs produced by prairie lizards may be contributing to the higher mortality observed in this species. Indirect evidence, based on precipitation levels and at the two study sites and mouthgapes of the two species, supported the assumption that more food was available to the prairie lizards than the sagebrush lizard. Higher precipitation levels (indicating greater insect biomass) occurred at the prairie lizard collection site and this species had a smaller mouthgape index, indicating greater specialization in utilization of sites.

Key words: Energy, available for metabolism, expended per offspring; Kansas; lipids; prairie swift; sagebrusli lizard; strategy, reproductive; Utah.

INTRODUCTION species, lipid storage is probably not important since food is always presumed to be limiting but never Although a number of studies have been done on critically short (e.g., still occurs at the importance of lipids in the histories of low levels). various , no one has attempted to correlate Nikolskii (1969) has shown that a correlation differences in lipid storage and utilization with life exists between lipid levels and in a num- history differences. In most seasonal spe- ber of commercial fishes. Odum (1960), Helms cies, lipids should be important since lipid storage (1968) and King (1970) demonstrated marked in- is a biochemically efficient way to package energy creases in lipid storage prior to migration in several for later usage. A gram of stored lipids represents passerine species. Jameson and Mead (1964) 38 kJ (9 kcal) of energy, while a gram of carbo- and Davis (1967) indicated that lipids are used hydrate or , with the higher H,O content, during hibernation in several small species. represents only 17-21 kJ (4-5 kcal) of energy. Sawicka-Kapusta (1968) found lipid depletion asso- Therefore, more energy can be stored in a smaller ciated with reproduction in mice. A vast body of literature on lizards indicates that some species use package with lipids. In nonseasonal (acyclic) animal lipids during hibernation (Dessauer 1955; Mueller

'Manuscript received 10 June 1974; revised 19 De- 1969, Derickson 1974), while others use lipids during cember 1975; accepted 19 January 1976. reproduction (Hahn and Tinkle 1965, Licht and Gor- 2 Present address: Division of Environmental Impact man 1970, Telford 1970). Church (1962) could find Studies, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 USA. no evidence of lipid deposition and utilization in 446 W. KENNETH DERICKSON , Vol. 57, No. 3 three species of Jamaican House Geckos which live in strategies, it is likely that this same factor may also a nonseasonal environment. explain observed differences in lipid storage and The literature on life history is also utilization. bountiful. Several authors (Cole 1954; MacArthur Differences in food availability per individual and Wilson 1967; Gadgil and Bossert 1970; Hairston should also lead to differences in (1) rates at which et al. 1970; Pianka 1970, 1972) have put forth lipids are utilized during periods of food shortage, arguments to explain variations in life history phe- (2) the percentage of ingested energy available for nomenon. As a result of work done by these authors metabolism, and (3) the amount of energy expended it is known that a gradient of life history strategies on each offspring. An individual of a species that (strategy being used in a teleological sense) exists, has historically been exposed to low food availabilities with the two extreme strategies being with should maximize its usage of available food. This may short , high reproductive efforts, and early ma- be done by maximizing net energy yield per unit of turity and those with long lives, low reproductive feeding , as suggested by Emlen (1966), Mac- effort, and delayed maturity. Tinkle (1969), Tinkle Arthur and Pianka (1966), MacArthur and Wilson et al. (1970), and Gadgil and Solbrig (1972) have (1967) and Schoener (1971), through utilization of presented empirical evidence on lizards and dande- prey with high caloric values or by utilizing prey that , respectively, that supports this dichotomy of life can be captured with a minimum of pursuit and cap- history strategies. This dichotomy has been more ture time. Given no difference in quality or captur- popularly referred to as r- and K-selection (Mac- ability of prey, a species that has been exposed to lower Arthur and Wilson 1967; Gadgil and Bossert 1970; food levels may maximize energy obtained from Pianka 1970, 1972; Gadgil and Solbrig 1972), al- ingested energy by (1) reducing losses of ingested though Hairston et al. (1970) choose to call it b and energy via respiration, , and excretions, and d selection. Basically, the theory of r- and K-selec- (2) by conserving stored energy during periods of tion states that is determined by r (intrinsic food shortage. On the other hand, individuals of rate of increase) in species living in an environment a species that has historically been exposed to where mortality is unpredictable, while in species abundant food supplies need to be less stringent in living in environments where mortality is more pre- their conservation of stored energy during periods of dictable, fitness is determined by K (environmental food shortage and in their utilization of ingested ). In other words, fitness is deter- energy. mined primarily by density independent factors in r- Food availability to the offspring may dictate how selected species and by density-dependent factors in a parent apportions the ingested and stored energy K-selected species. For lack of better terminology, r- available for reproduction. If the offspring and and K-selection will be used; however, the inde- adults of a given species have both been exposed pendent variable identified as the causative agent is to low levels of food, a parent may increase its fit- food availability per individual. This includes not ness by expending more energy per offspring in the only the potential available but also form of or by producing larger off- an 's access to that productivity. This (Smith and Fretwell 1974). This assumes avoids the issue of whether r-selected species are regu- that though fewer offspring are produced, their lated by density-independent factors and K-selected survivorship is enhanced by an increased competitive species by density-dependent factors. Also, to avoid ability. If, on the other hand, food is abundant to another problem with the theory it is assumed that both adults and offspring, the parent may increase the adult and juveniles of the species studied are both its fitness by expending less energy per offspring. utilizing similar . Other assumptions are This would result in the production of more offspring (1) that an optimum size for reproduction exists and it is assumed that survivorship is enhanced by and that greater food availability will result in reach- sheer numbers. Harper et al. (1970) indicated that ing this size at an earlier age; (2) that there is a under intense competition put more energy positive correlation between food availability and reproductive effort; and (3) that an inverse rela- into each offspring and produce fewer of them. Dr. tionship between reproductive effort per season and Eric R. Pianka (personal communication) compiled life span exists. a list of various lizard species and indicated that there Since differences in life history strategies and in tends to be a negative relationship between the patterns of lipid storage and utilization are known to amount of energy expended per offspring and the exist in lizards, it seems logical to conclude that number of eggs produced. the two may be interrelated. In other words, given By using a r- and K-selected lizard species, an at- the assumption that differences in food availability tempt will be made to verify the following hy- per individual can result in a variety of life history potheses: Late Spring 1976 ASPECTS OF REPRODUCTIVE STRATEGIES IN LIZARDS 447

1) Given greater food availability for the r-se- LaJ lected lizard species, this species should have m SCELOPORUS GRACIOSUS GRAC/OSUS higher lipid levels before and after hibernation z2 than the K-selected lizard species. I H S

2) Given greater food availability for the r-se- C H s lected lizard species, this species should have '1-I m a higher rate of lipid utilization during periods SCEZOPORUS UNDULATUS GARMANI of food shortage than the K-selected lizard species. co H S D 3) Given greater food availability for the r-selected lizard species, this species should obtain less ti H S D energy for metabolism per unit of ingested J A SON D J F M A MJJ A NDJFMAMJJASONDJ food than the K-selected lizard species. MONTH

4) Given greater food availability for the r-se- FIG. 1. Time required to reach sexual maturity and lected lizard species, this species should pro- the number of clutches produced seasonally by adults duce more offspring with less energy expended originating from the initial and final clutches of a season per offspring, while the K-selected lizard spe- of Kansas northern prairie lizards, Sceloporus undulatus garmani and Utah northern sagebrush lizards, S. gracio- cies should produce fewer offspring with more sus graciosus. Clear areas represent periods of either energy expended per offspring. maintenance, growth, or vitellogenesis. Stippled and cross-hatched areas represent periods of hibernation and SPECIES STUDIED reproduction, respectively. Hatching, sexual maturity, and are indicated by the letters H, S, and D, re- Females of the lizards Sceloporus undulatus gar- spectively. Only 2 yr out of potentially 6 are shown inani and Sceloporus graciosus graciosus were chosen graphically for S. g. graciosus. These graphs are partly based on data from studies done by Ferguson and Bohlen for this study. Some of the reasons for choosing (1973) and Tinkle (1973). lizards and these particular species were (1) they are easy to study either in the field or laboratory; (2) information related to the theory of the wait until prey come within striking distance and of life history strategies in lizards is available from then give pursuit. The average lifespan is 1 yr, age work done by Tinkle (1969) and Tinkle et al. at maturity 8-9 mo, and reproductive effort is about (1970); (3) a number of studies have looked at the three clutches/season (Ferguson and Bohlen 1973). role of lipids in lizards; (4) reproductive effort can An early age at maturity and production of three be better approximated (since lizards exhibit no pa- clutches results in considerable variation in egg-laying rental care, kilojoules per clutch and number of (Fig. 1). Offspring from the first clutch hatch clutches per season should provide a reasonably ac- in mid-July, the second in mid-August, and the third curate measure of reproductive effort); (5) these in early September. Lizards from the first clutch species are similarly sized; thus, effects of body size will be ready to reproduce the following spring, differences on metabolism are minimized; and (6) while those from succeeding clutches will not mature in terms of lifespan, age at maturity, and reproductive until late spring or early summer. First clutch off- effort, these two subspecies are known (Ferguson and spring have the potential for laying clutches in May, Bohlen 1973, on S. u. garmani and Tinkle 1973, on June, and July of their first breeding season. S. g. graciosus) to fit the r- and K-selection corre- Probably, because of this high reproductive effort lates of Pianka (1970). at such a young age, the first clutch offspring rarely Sceloporus undulatus garmani is a small iguanid reproduce a second season. Conversely, offspring lizard found predominantly in eastern Colorado, from the second and third clutches may produce 1-2 Kansas, Nebraska, and Oklahoma. This subspecies, clutches in their first breeding season. These off- hereafter referred to as the northern prairie lizard, spring from later clutches are more likely to survive is found in a variety of , including sandy a second winter (but most do not) and produce addi- areas, sandstone cliffs, sparse grass, woodpiles, and tional clutches of eggs. Therefore, an early age at old trash piles (Smith 1946). At the collection site, maturity and the production of three clutches by located in Reno County, Kansas, they were found some lizards results in considerable variation of lay- in grazed sand prairie around old fallen cottonwood ing times and size of lizards laying eggs. (Populus sp.) and refuse piles. Sceloporus graciosus graciosus is found predomi- Prairie lizards feed on , Coleoptera, Hy- nantly in Idaho, Nevada, Utah, and Wyoming at menoptera, Diptera, Orthoptera, and altitudes > l,500 m. As the common name, northern (Smith 1946). Their feeding strategy is to sit and sagebrush lizard, suggests, this species is common 448 W. KENNETH DERICKSON Ecology, Vol. 57, No. 3 in sagebrush , but also may be found in liminary studies indicated that complex lipids, those open flat lands, bouldered , and forested generally not available as storage lipids, represented slopes (Smith 1946). Tinkle (1973) studied this < 10% of the total lipids. A similar figure for com- subspecies in the Kolob of Zion National plex lipids was found in Sceloporus jarrovi by Hadley Park in southwestern Utah. The Kolob includes and Christie (1974). Since complex lipids represent sandy sagebrush (Artemisia sp.) flats and sandy areas such a small percentage of the total lipids, no at- between extensive areas of eroded sandstone. My tempt was made to exclude these lipids. Accordingly, collection site was a few kilometers east of Zion Na- all figures are slight overestimates of storage lipids tional Park East Gate. The altitude is comparable to in both species. that of Tinkle's study area, 2,000 m, and is char- Rates of lipid utilization were calculated for both acterized by sandy sagebrush flats. species from field samples by comparing lipid levels Sagebrush lizards have the same general diet and in lizards that had come out of hibernation with patterns as prairie lizards. They are known those ready to lay their first clutch (gravid-initial to be long-lived, > 6 yr, and mature in 2 yr (Stebbins clutch). Individual lipid levels (mg/g LDBW) of and Robinson 1946, Tinkle 1973). The number of the initial gravid sample was subtracted from the clutches produced probably varies with altitude and mean lipid level of the posthibernation lizards and latitude, however, in southwest Utah this species lays this figure was divided by the number of days be- two clutches of about four eggs each season (Tinkle tween these two samples. The same method was used 1973). This reproductive schedule will allow an to calculate rates of lipid deposition; only the mean average adult to produce about eight clutches in a lipid level of the final gravid sample was subtracted lifetime. Unlike prairie lizards, sagebrush lizard from individual lipid levels in the postreproductive hatchlings from first and second clutches reach re- sample. productive maturity at the same time, the beginning of the third season. This results from an extra sum- Experimental studies mer of growth prior to reproduction, which allows An additional 15 females of each species were all hatchlings to reach reproductive size before their collected in 1973 just after the lizards had finished third season (Fig. 1) . laying their last clutch of eggs (mid-July for both species). Three lizards from each species were MATERIAL AND METHODS analyzed for total lipids to determine initial lipid Prairie lizards and sagebrush lizard females were levels. The remaining lizards of both species were collected over a 2-yr period (1972-1973) from placed in animal cages under similar moisture Reno County, Kansas and Washington County, Utah, (watered every other day) and photoperiod regimes respectively. When possible 10 individuals of each (14L: lOD) and were studied simultaneously to de- species were collected after hibernation, during the termine rates of lipid deposition when fed and vitellogenic and gravid periods of each clutch of utilization when starved. An infrared lamp was eggs, and about 1 mo after reproduction had placed in one corner of the cage to allow the lizards ceased. These collection periods were based on to thermoregulate. Each female was fed a surplus observed lipid cycling patterns in other lizard species,weight of crickets every other day. Feces, urates, such as Anolis carolinensis (Dessauer 1955). and remaining crickets were removed and weighed before the next feeding. Feces and urates were Field samples frozen to prevent bacterial until they Seventy-eight prairie lizards and 88 sagebrush liz- could be analyzed for energy content. When the ards were collected in the field and kept cool until lizards had gained 10% of their body weight, six transferred to the laboratory, where they were quick- were sacrificed and analyzed for total lipids as de- frozen immediately and analyzed at a later date for scribed above, to determine rates of lipid deposition total lipids (simple and complex). The carcass for each species. Remaining lizards were starved (minus viscera) and eggs of each lizard were weighed until they had lost 10% of their body weight, then and dried to a minimal and constant weight in a analyzed to determine rates of lipid utilization. By thermal vacuum oven at 40?C and 30 psi (Horwitz knowing the initial lipid levels (mg/g LDBW) and et al. 1970). Each part was then homogenized in 2: 1 the number of days required to gain or lose 10% vol/vol chloroform-methanol solution in a of the body weight, rates of lipid deposition and homogenizer and the homogenates treated according utilization could be calculated. The initial lipid to the Folch method (Folch et al. 1957). Weight of level for the fattening study was determined from the total lipids for each depot were recorded as a per- initial sample of lizards mentioned above, while centage of the lean (no lipids) dry body weight the initial level for the starvation study was the (LDBW) to correct for variations in body size. Pre- lipid level of the lizards that had gained 10% of their Late Spring 1976 ASPECTS OF REPRODUCTIVE STRATEGIES IN LIZARDS 449 body weight. In both cases initial values were com- both within and between species to determine sta- puted as means and the difference between these tistically significant differences. Chow's (1960) tech- mean values and each starved or fattened lizard was nique was used to compare residual sums of squares determined. This calculation yielded the number of of the individual regressions with that of the data milligrams of lipid per gram LDBW gained or lost, combined into a single regression line. If weight was which was then divided by the appropriate number of correlated with a given parameter in both species, days to yield rates of deposition and utilization for this parameter was expressed on a per gram basis the two species. from the regression equations. If no relationship existed between LDBW and a given parameter in Calorimetry either species, the raw data were compared. The Both feces and urates collected during the fattening rationale for seeking a relationship between LDBW study and crickets and oviducal eggs from the differ- and each of the above parameters was based on ent clutches, were placed in a drying oven at 60?C observed relationship of clutch size and body weight and dried to a minimal and constant weight. Some in a number of lizard species. fecal and urate pellets, crickets, and oviducal eggs Evidence for the assumption that were then placed in a muffle furnace at 500?C for food level differences exist between 4 h to measure ash content. Remaining dried feces, prairie lizards and sagebrush lizards urates, crickets, and oviducal eggs were analyzed for caloric value using a Parr Semi-micro Bomb In order to provide some support for this as- Calorimeter (Model 1411) ' according to techniques sumption the following comparisons were made: (1) described in Paine (1971). All caloric values were precipitation levels in the two study areas over corrected for ash. From these data it was possible to the past 30 years using U.S. Bureau data; calculate calories per clutch of eggs, calories per egg, and (2) mouthgape (head length X mouth width) ingested and egested energy. Calories per clutch vs. snout-vent length for the two species. Insect was considered the major proportion of energy ex- biomass is correlated with precipitation (Janzen and pended on reproduction since lizards exhibit no pa- Schoener 1968) and mouthgape with prey sizes rental care. The percentages of ingested energy utilized (Schoener 1968). At low food levels a spe- available for metabolism (ME) and assimilation ef- cies should use a wider array of prey sizes. ficiency (AE) were calculated using the formulae, RESULTS ME IE- (FE + NE) /IE X 100 and Hypothesis 1 AE IE- FE/IE X 100, This hypothesis stated that r-selected lizard species where IE is ingested calories, FE is fecal calories, (prairie lizards) should have higher lipid levels prior and NE is nitrogenous waste calories. It was also to and after hibernation than K-selected lizard spe- possible to calculate what percentage of the ME cies (sagebrush lizards). My results support this was being stored as lipids since the ME and fattening hypothesis (Fig 2A). Total body lipids per gram studies were run concurrently. This was done by LDBW, pooled over the two collection years, were converting the lipid increases in the fattening study higher prior to and after hibernation in prairie to caloric values (a gram of lipid is 38 kJ, or 9 lizards than in sagebrush lizards. kcal), dividing this figure by the amount of ingested In prairie lizards, minimal lipid levels reached dur- energy available for metabolism, and multiplying by ing production of the middle clutch were lower than 100. in sagebrush lizards. In sagebrush lizards, lipid levels were minimal during production of the final clutch. Statistical analyses Neither species apparently depleted their storage Least squares analysis of variance was used to lipids since minimal levels (6%-7% of LDBW) compare lipid levels, calories per clutch, calories per were higher than polar lipid levels (2% of LDBW). egg, eggs per clutch, ME, AE, and the proportion However, prairie lizards utilized more of their stored of the energy available for metabolism that was con- lipids during reproduction than sagebrush lizards. verted to lipids. Rates of lipid deposition and utili- Lipid levels changed more in prairie lizards than zation represented deviations from the mean value in sagebrush lizards during egg production. The loss of the initial samples and these deviations were also of lipids from posthibernation to the initial gravid compared using least squares analysis of variance. sample was approximately 200 mg/g LDBW in Regression analyses were used to assess relationships prairie lizards versus about 60 mg/g LDBW in sage- between any of the above parameters and LDBW. If brush lizards. Simultaneously, there was an increase relationships existed regression lines were compared of about 210 and 220 mg of lipids in the eggs of 450 W. KENNETH DERICKSON Ecology, Vol. 57, No. 3

400 BODY LIPIDS LOST (mg/g LDBW) EGG LIPIDS GAINED(mg/g LDBW) 200 100 0 100 200

3003

FIG. 3. Histogram comparing mean body lipid loss -J'200 $ t1 4 with mean egg lipid gain (mg/g lean dry body weight, LDBW) in field samples of Kansas prairie lizards (clear

LLJ bar) and Utah sagebrush lizards (solid bar).

100- lipid gain in prairie lizards, while egg lipid gain far surpassed body lipid loss in sagebrush lizards. Presumably, sagebrush lizards had to rely more on other sources of energy (i.e., ingested) to produce B egg lipids than did prairie lizards. In fact, some prairie lizards had 30,125 J (7,200 cal) in stored lipids which seems more than enough to produce an 400 initial clutch of eggs with a mean energy value of 22,175 J (5,300 cal). In sagebrush lizards maximum lipid levels were equivalent to 15,062 J (3,600 cal),

9 less than a 21,338 J (5,100 cal) clutch of eggs. Table 1 further emphasizes that sagebrush lizards 300 100- 10 8 had to rely more heavily on external sources of -.4 ~~~20 13

U,

0-. TABLE 1. Mean rates of body lipid loss (negative value) or gain and mean rate of egg lipid deposition in field -~200 and laboratory samples of Kansas prairie lizards (PL) 0~~~2 and Utah sagebrush lizards (SL). LDBW - Lean Dry Body Weight; * = 0.05 level of significance; ** - 0.01 level of significance; NS - not significant m 20~~2 Body Eggs (mg/g LDBW day) (mg/g LDBW- day) 0 5+ 10 Period of lipid loss in field Posthibernation to gravid- A initial clutch PL -4.5 4.0 0 ** ** PH V 01 02 03 PR SL -0.6 6.7 SAMPLE FIG. 2. Seasonal variation of mean lipid levels (per Period of lipid gain in the field gram lean dry body weight, LDBW) in Kansas northern Gravid-second clutch to prairie lizards (open bars) and Utah northern sagebrush postreproduction lizards (solid bars). Samples are posthibernation (PH), PL 2.3 None NS vitellogenesis (V), gravid-initial clutch (01), gravid- middle or initial clutch (02), gravid-final clutch (03). SL 2.3 None Horizontal bars represent the means; vertical lines the Laboratory samples ranges; and vertical bars one standard error. Numbers Starvation above bars indicate sample sizes. (A) total body lipids; and (B) egg lipids. PL -17.0 None * SL -6.5 None prairie lizards and sagebrush lizards, respectively Fattening experiment (Fig. 2B). The relationship between body lipids PL 3.2 None lost and egg lipids gained in both species is expanded NS upon in Fig. 3. Body lipid loss was equivalent to egg SL 3.6 None Late Spring 1976 ASPECTS OF REPRODUCTIVE STRATEGIES IN LIZARDS 451

TABLE 2. Mean assimilation efficiency (AE), percent TABLE 3. Mean calories/dry g of egg, eggs/clutch, of ingested energy available for metabolism (ME), calories/clutch, and calories/egg in Kansas prairie and percent of ingested energy available for metabolism lizards (PL) and Utah sagebrush lizards (SL). Values stored as lipids (SF) in Kansas prairie lizards and for eggs/clutch and calories/clutch are functions of Utah sagebrush lizards during fattening . weight and were computed from linear regression * - 0.05 level of significance equations. Caloric values were corrected for ash to eliminate eggshell thickness differences. NC = no clutch produced at this time; NS - not significant at Prairie lizards Sagebrush lizards the 0.05 level; * = significant at the 0.05 level; ** = significant at the 0.01 level. To convert calories to AE n 12 86.16% n = 12 89.55% joules, multiply by 4.184 * *

ME n 12 76.17% n = 12 81.70% * * Clutch

SF n 4 12.51% n= 4 23.46% May June July * *

Calories/dry g of egg PL 6,088 6,453 6,657 energy than prairie lizards for egg production. The SL NC 6,453 6,688 rate of body loss (in milligrams per gram LDBW) Eggs/clutch exceeded the rate of egg lipid deposition in prairie PL 6.0 * 7.0 * 6.0 ** ** lizards. In sagebrush lizards the rate of body lipid SL NC 4.4 * 3.1 loss was < 10% of the rate of egg lipid deposition. Calories/clutch PL 4,450 * 5,000 * 4,450 Hypothesis 2 NS NS SL NC 4,450 NS 4,450 Based on this hypothesis, r-selected lizard species (prairie lizards) should have higher rates of lipid Calories/egg PL 677 * 734 * 854 utilization than K-selected lizard species (sagebrush ** ** lizards) during starvation. Data from the starvation SL NC 1,059 * 1,394 study supported this hypothesis (Table 1). The rate Hatchling size (mm) of lipid utilization was almost three times greater in PL 22.8 ** 24.1

prairie lizards than in sagebrush lizards. This dif- SL NC ference suggests that sagebrush lizards were better adapted to conserve lipids at lower food levels than prairie lizards. Prairie lizards not only were less efficient at utiliz- There was no significant difference between the ing energy, but a higher percentage of the energy two species in the rate of lipid deposition in either available for metabolism was devoted to metabolic field or experimental samples, although rates of depo- activities other than lipid storage. In sagebrush liz- sition were higher in the laboratory than in the ards, a higher percentage of energy available for field. This suggests that food is not unlimited for metabolism was converted into lipids. either species in the field. Since both species have Since house crickets were utilized as an energy roughly the same amount of time to store lipids source in this study, it is not known how accurately prior to hibernation there is no reason to suspect these efficiencies compare to actual efficiencies. differences in rates of lipid deposition between the However, the difference between the two species two species. should still be valid.

Hypothesis 3 Hypothesis 4

According to the third hypothesis, prairie lizards This hypothesis stated that sagebrush lizards should should have a lower percentage of ingested energy expend more energy per offspring than prairie lizards. available for metabolism than sagebrush lizards. Both Regression equations of calories per clutch versus assimilation efficiency and percentage of ingested LDBW were significant for both species (Fig. 4). energy available for metabolism were higher in sage- However, regression lines did not differ significantly brush lizards (Table 2). Not only were sagebrush (Table 3). Therefore, lizards of both species put lizards absorbing more of the ingested energy across about the same number of calories into eggs per the intestine, but a higher percentage of this assimi- clutch. The regression of number of eggs per clutch lated energy was retained and not lost as nitrogenous versus LDBW also was significant for both species waste (urates) . This higher assimilation efficiency (Fig. 5). Regression lines did differ significantly and percentage of ingested energy available for between species. A prairie lizard produced signifi- metabolism suggests that sagebrush lizards are better cantly more eggs per clutch than an equivalent-sized adapted for lower food levels than prairie lizards. sagebrush lizard (Table 3). Since the number 452 W. KENNETH DERICKSON Ecology, Vol. 57, No. 3

R:.992 . iR=.877 =R.972 11000 / ! 1 2 / /R,'.989 ,/-.8 ,j'R=.918

8~~~~~~~~~ 9000 / / / .' I- /* / I-. /~~~~~~~~A 7000 ~ ~ ~ ~ ~

m g<27 @ _@~~ ~ R =.839 3 7000 0~~~~~~~~

and /t hU-

0.0 1.0 2.0 3.0 5000- LEAN DRY BODY WEIGHT (g) FIG. 5. Eggs/clutch versus lean dry body weight in 0.0 1.0 .o2.0 3.0 Kansas prairie lizards (second clutch, * ~*; first LEAN DRY BODY WEIGHT (g) and third clutch, (D--(D) and Utah sagebrush lizards (first and second clutch, * - *). All regressions FIG. 4. Calories/clutch versus lean dry body weight were significant at the 0.01 level. The regression line for in Kansas prairie lizards (second clutch, s *; first sagebrush lizards differed significantly, 0.01 level, from and third clutch, ?--?) and Utah sagebrush lizards those for prairie lizards. (first and second clutch, (--O)r . All three regres- sions were significant at the 0.01 level. The regression line for sagebrush lizards did not differ significantly, at the elevations of these lines should change through- the 0.05 level, from those for prairie lizards. out the season, since lean dry body weights were used. Therefore, any decrease in slope or elevation repre-

of calories per clutch was the same for both species sents nonlipid tissue loss. The greater nonlipid tis- and the number of eggs per clutch was different for sue loss in prairie lizards may render this species the two species, calories per egg should and did more vulnerable to or harsh climatic con- differ (Table 3). ditions, which would in part explain the shorter In both species the calories per egg increased with

successive clutches. Thus more energy was expended TABLE 4. Estimated eggs/season, egg calories/season, on offspring in later clutches. Egg quality (calories eggs/lifetime, egg calories/lifetime, body calories, and egg calories /season-body calories in Kansas prairie per gram of eggs) also increased seasonally in both lizards (PL) and Utah sagebrush lizards (SL). Eggs/ species, but did not differ between species. season and egg calories/season were calculated by The number of calories per clutch per gram LDBW summing the average eggs/clutch and calories/clutch, respectively, for all clutches. Eggs/lifetime and egg and egg calories per body calories provide estimates calories/lifetime were computed by multiplying eggs/ of the cost per clutch of reproduction to the parent season and egg calories/season by the average number of breeding that members of each species ex- (Table 3). While the cost per clutch was about the perience. The values of 5,390 cal/gram and 5,300 same for both species, prairie lizards produced three cal/gram ash free dry body weight were used to cal- clutches versus two for sagebrush lizards. Thus, culate body calories for PL and SL, respectively. Figures in parentheses are on a per gram lean dry prairie lizards put considerably more energy into body weight basis. To convert calories to joules, eggs than sagebrush lizards each season (Table 4). multiply by 4.184 This additional expenditure of energy on egg produc- tion by prairie lizards resulted in nonlipid tissue Parameters PL SL loss (Fig. 6A). Comparing the regressions of LDBW Eggs/season 20.9 ( 19.0) 10.4 (7.5) versus snout-vent length for posthibernation and Egg calories/season 15,457 (13,900) 12,945 (8,900) Eggs/lifetime 20.9 ( 19.0) 41.6 (30.0) gravid-final clutch samples in both species revealed Egg calories/lifetime 15,457 (13,900) 51,780 (35,600) the prairie lizards lost more nonlipid tissue during re- Body calories 6,127 8,902 production than sagebrush lizards (Fig. 6B). If there Egg calories/season- is no net nonlipid catabolism, neither the slopes nor body calories 2.53 1.45 Late Spring 1976 ASPECTS OF REPRODUCTIVE STRATEGIES IN LIZARDS 453

72 /R=.992 KANSAS 3.0 /R. 48 _/ R=.995 24 I /

32.0 1" 72

UTAH 48 C:1~~~~~~~~~~1

mU // 24 1.0-A ,

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0+ /// INCHES OF PRECIPITATION

FIG. 7. Precipitation levels from 1944-1973 for Reno B County, Kansas and Washington County, Utah. The graphs represent the number of months out of the 30-yr period that had a given level of precipitation.

3.0 was available to the r-selected lizard species (prairie lizard) than the K-selected lizard species (sagebrush I- lizard). Sagebrush lizards also had a larger mouth- gape than equivalent-sized prairie lizards suggesting that they were able to utilize a wider array of prey 2.0 sizes than prairie lizards (Fig. 8). > <= .9~~~~~~~86 m / DISCUSSION

The results of this study suggest general models to 1.0- R _ =.985 explain observed differences in patterns of lipid storage and utilization of various lizard species. Specifically, the r-selected lizard (prairie lizards) stored more lipids than the K-selected lizard (sage- brush lizards). Greater lipid stores resulted in more lipids being available after hibernation in the r-se- 40 5b 70 lected species, and these were apparently used in the SNOUT-VENT production of theLENGTH first clutch of eggs. Because of(mm) the FIG. 6. Lean dry body weight versus snout-vent lack of total dependence on ingested food to produce length for posthibernation (0 0 ) and final clutch the first clutch of eggs, the r-selected species is able (*--*) in Kansas prairie lizards and Utah sage- to start reproducing earlier in the season which re- brush lizards. (A) prairie lizards; (B) sagebrush lizards. sulted in a higher reproductive effort. This higher All regressions were significant at the 0.01 level. Com- parisons between regression lines for both species were reproductive effort appeared to have a negative feed- significant at the 0.01 level. back on lifespan. Lower lipid levels in the K-selected lizard species resulted in this species being more de- pendent on ingested energy for egg production. Egg lifespan of females of this species. Since sagebrush laying occurred later in the season and fewer clutches lizards are not expending as much energy on egg were laid. This lower reproductive effort had less production each season, this may reflect positively on of a negative on life span than in the r-se- lifespan and enable sagebrush lizards to expend more energy on egg production in a lifetime than prairie lected species. The r-selected species also had a lizards (Table 4). higher rate of lipid utilization when starved, a lower percentage of ingested energy available for metabo- Assumption lism, and expended less energy per offspring than the The higher precipitation levels in Kansas than in K-selected lizard species. To test the generality of Utah (Fig. 7) suggests that potentially more food these findings, lipid storage and usage, rates of lipid 454 W. KENNETH DERICKSON Ecology, Vol. 57, No. 3

stansburiana and Takydromus tachydromoides, re- spectively. According to Tinkle (1969) and Tinkle et al. (1970), these two species are short-lived, mature 140 2x2 early, and have a high reproductive effort (r-strate- gists). Based on seasonal cycling of carcass, fatbody, 2 K and liver lipids in female Cnemidophorus tigris, R R930 Gaffney and Fitzpatrick (1973) estimated that > 3,000 calories of lipid go into egg production, as 120- / * / compared to 1,500 calories for hibernation. These authors collected their C. tigris from western Texas, 2~~~~~~~~ 100~ ~ ~ ~~~~~x/ / R.980 where they mature in 1 yr and produce two clutches/ season (r-strategist; Tinkle 1969). Female Ameiva festiva and A. quadrilineata (Smith 1968) and Cnemidophorus sexlineatus (Hoddenbach 1966) also showed decreases in fatbody size during reproduction. These three species can be classified as r-strategists /20 02 (Tinkle 1969, Tinkle et al. 1970). Licht and Gor- man (1970), Ruibal et al. (1972), and Gorman and 80- / R 98 Licht (1975) found an inverse relationship between 60 reproductive activity and fatbody size in a number of tropical anoles. Those species that reproduced throughout the year either had no fatbodies or very small ones, while those that exhibited reproductive cycles had large fatbodies during the nonreproductive phase (dry season) and lacked fatbodies while repro- 40 50 60 ducing (wet season). Licht (1974) also found that SNOUT-VENT LENGTH (mm) fatbodies in would increase during FIG. 8. Mouthgape (head length x mouth width) reproduction via supplemental feeding in the field. versus snout-vent length in Kansas prairie lizards ( 0 * ) and Utah sagebrush lizards ( X- -X ). Apparently, egg production and deposition in many Both regressions were significant at the 0.01 level. Com- of these anoles creates too much of an energy de- parisons between regression lines were also significantly mand to allow lipid storage from available food. All different at the 0.01 level. of the anoles studied by these authors could be classi- fied as r-strategists. Anolis carolinensis (an r-strategist; Tinkle 1969, utilization, percentage of ingested energy available Tinkle et al. 1970) may be an exception to the for metabolism, and energy expended per offspring hypothesis that r-strategists use lipids primarily for in other lizards will be examined. reproduction. According to Dessauer (1955), this species is active most of the year in New Orleans, but Supporting evidence from studies only reproduces from April to August. During the on other lizard species months of November and December they are inactive

It is difficult to compare lipid usage data avail- and lipid levels decreased markedly during this able on other lizard species with data in the present period of time. Mean air (and pre- study. Most of the data available on lipid usage is sumably body temperature) in these 2 months is anecdotal, and does not look at all potentially avail- relatively high (15?C) which may account for utili- able lipids, or at seasonal cycling of lipids. However, zation of large amounts of lipids. A higher hiberna- some data support my hypothesis that lizards with r- tion temperature than that of the other lizards strategist characteristics may have more lipids avail- mentioned above would result in greater metabolic able for reproduction. Based on limited data, Parker demands and hence greater utilization of lipid. Des- and Pianka (1973) observed no correlation between sauer (1955) also stated that A. carolinensis feeds reproductive activity and fatbody length/snout-vent little if at all during November and December. Lack length in female Sceloporus magister. They indicated of feeding activity plus high winter body temperature that this species requires at least 2 yr to reach matu- may impose a heavy drain on lipid reserves so that rity, produces 1-2 clutches/season, and is probably lipid levels are too low to use for reproduction in the long-lived (K-strategist). Hahn and Tinkle (1965) spring. and Telford (1970) found a significant decrease in Little or no data from the literature support my fatbody lipids during reproduction in female Uta results on rates of lipid utilization, percentage of in- Late Spring 1976 ASPECTS OF REPRODUCTIVE STRATEGIES IN LIZARDS 455 gested energy available for metabolism (ME), and From Ballinger and Clark (1973) and Tinkle and energy expended per offspring. This is the only Ballinger (1972) one can conclude that Colorado S. study of rates of lipid utilization in lizards, so more undulatus are putting more energy into each egg empirical data on a number of species are needed to than Texas lizards. In fact, if one uses the caloric determine whether a low rate of lipid utilization is and percent water content values estimated by Bal- common to K-strategists. Some comparative data linger and Clark for S. undulatus eggs (6,195 cal- are available on assimilation efficiencies and ME, but ories/g of egg and 54%), calories per egg can be it is difficult to draw conclusions from these. Mueller estimated for each of the S. undulatus (1970) found a ME of 83% for the sagebrush lizard studied by Tinkle and Ballinger. Such calculations which is consistent with my results (82%). He also yield an estimate of 1,168 calories/egg for Colorado found a ME of 83% for Sceloporus occidentalis. lizards and 612 calories/egg for Texas lizards. These This lizard requires 2 yr to reach maturity; how- figures are surprisingly close to those found for ever, it is intermediate to sagebrush lizards and sagebrush lizards and, prairie lizards respectively, in prairie lizards regarding lifespan and clutch number the present study. (Tinkle 1969, Tinkle et al. 1970, Goldberg 1973). Data from Tinkle and Hadley (1975) support my It is difficult to predict whether S. occidentalis conclusion that the higher reproductive effort by should have a high or low ME. Mueller (1970) felt prairie lizards results in a shorter lifespan. These a ME of 83% was an overestimate, because S. occi- authors examined a number of demographic variables dentalis was studied much of the time at body tem- and measures of reproductive effort in 11 lizard spe- perature below the optimum for this species. Sage- cies and found that the only significant correlation brush lizards, however, were studied at their optimum was an inverse relationship between clutch calories/ . If there is an inverse relationship body calories and annual adult survivorship. (Inter- between temperature and ME, S. occidentalis should estingly no correlation was noted for clutch weight/ have a lower ME than sagebrush lizards. However, body weight, frequently used as an index of it is still difficult to categorize S. occidentalis as a reproductive effort, and annual adult survivorship). r- or K-strategist. As seen in Table 4 the clutch calories/body calories Avery (1971) found that the lizard Lacerta vivip- index was 2.53 and 1.45 for prairie lizards and sage- ara, a viviparous K-strategist with delayed maturity brush lizards, respectively. Based on Tinkle and and low reproductive effort (Tinkle et al. 1970), had Hadley (1975), prairie lizards would be expected to an assimilation efficiency (AE) of 89%. In the have the lower annual adult survivorship that it does. present study, the sagebrush lizard had an AE of A comparison of this index with reproductive energy 90%. Finally, Johnson (1966) assumed an AE of total in these authors' study indicates 67% for S. undulatus, S. magister, and C. tigris when that clutch calories/body calories may not be a good he measured the number of calories of energy as- index of reproductive effort. For example, while similated per gram per day. However, these effi- U. stansburiana had a clutch calories/body calories ciencies are probably not accurate since my study index of 2.54 the calculated reproductive energy/total shows variation in ME between species, and both energy budget was 19%. In S. graciosus, on the other my data and Pough's (1973) indicate that an AE hand, these values were 1.45 and 24%, respectively. of 67% is low for insectivorous lizards. Most in- This discrepancy is readily resolved when looking at sectivorous lizards have high efficiency percentages differences in age-at-maturity. Uta stansburiana is (from the low 70s to > 80), which may be due to theessentially an annual species and does everything relatively high energy value of , 5,400 calories/ (matures, reproduces, and dies) in 1 yr, while S. g (Golley 1961). graciosus requires 2 yr to reach maturity. Therefore, Although data on calories per egg are generally for the comparisons to be meaningful, total energy lacking, egg weight data for S. undulatus support my budgets of U. stansburiana and S. graciosus would findings on energy expenditure per offspring. Tinkle have to be weighted to account for this difference. and Ballinger (1972) calculated egg weights for four This weighting should indicate that clutch calories/ populations of S. undulatus and found that, generally, body calories is a reasonable index of reproductive longer-lived populations produced heavier eggs than effort. shorter-lived populations. In Texas S. undulatus ma- In summary, evidence in the literature parallels tured in < 1 yr, produced about 27 eggs/season, and the findings of this study. There are correlations of each egg weighed 0.22 g. Conversely, Colorado S. reproductive strategies with lipid levels, percentage of undulatus matured in 2 yr, produced about 16 ingested energy available for metabolism, and energy eggs/season, and each egg weighed 0.45 g. Ballinger expended per offspring. Higher posthibernation lipid and Clark (1973) showed that relative clutch weight levels are correlated with higher reproductive effort, is a good estimator of relative calories per clutch. while percentage of ingested energy available for 456 W. KENNETH DERICKSON Ecology, Vol. 57, No. 3 metabolism and energy expended per offspring are hatchlings from both clutches are competing for food inversely related to reproductive effort. in sagebrush lizards, then survivorship should be higher for the larger hatchlings in both clutches. More energy per egg and fitness

Based on demographic data on prairie lizards (Fer- Evidence for food competition guson and Bohlen 1976) and sagebrush lizards A basic assumption underlying the hypotheses (Tinkle 1973) and my data on egg energy values, I tested in this study was that differences in the degree conclude that higher energy content per egg results of competition for food existed between the two in large hatchlings with higher survivorship. Tinkle species. Additionally, it was assumed that the off- and Ballinger (1972) indicated that survivorship of spring of each species were exposed to the same de- offspring from larger eggs (greater energy) was gree of competition for food as the adults. Although higher. Fourteen percent of Colorado S. undulatus no attempt was made to look at food levels in the hatchlings survive to the next spring compared to field, data on precipitation levels in the two study 5% for Texas hatchlings. In sagebrush lizards first areas and mouthgapes for both species suggest that clutch (4,431 J, or 1,059 cal/egg) hatchlings were these may be valid assumptions. larger (x snout-vent length = 26 mm) than first Analysis of weather data over the past 30 yr for clutch (2,833 J, or 677 cal/egg) hatchling prairie the two study areas, indicates that precipitation levels lizards (x snout-vent length - 23 mm). As men- are predictably lower in Utah than in Kansas (Fig. tioned earlier, this larger size in sagebrush lizards is 7). Janzen and Schoener (1968) showed that insect adaptive for using a wider array of food items at productivity increases with precipitation levels. lower food levels. Higher precipitation levels, typically, resulted in That selection is favoring larger size for lower greater insect diversity and . Therefore, food levels is further supported by comparing suc- a lower precipitation level suggests that there should cessive clutches of prairie lizards. The mean number be lower food levels in Utah. Interestingly, there is of joules (or calories)/egg was 2,833 (677), 3,071 a greater density, 208/ha, of sagebrush lizards (734), and 3,573 (854) for the first, second, and (Tinkle 1973) than prairie lizards, 42/ha (Ferguson third clutches, respectively. This suggests that the and Bohlen 1973). Less potential food and a greater hatchlings from these clutches should differ in size. density of lizards strongly suggest that there was less Indeed, hatchlings from the first clutch were signifi- food per individual for sagebrush lizards than for cantly smaller than those from the third clutch, 22.8 prairie lizards with their low density and more po- and 24.1 mm (Table 3). If food is critical at all for tential food. Mid-July until late October should be a prairie lizard hatchlings it should be when the last critical time for both the parents and offspring of the clutch is hatching, late August to early September. two species, since during this time they grow and During this period hatchling density is highest and store lipids for hibernation. Mean precipitation levels insect productivity should be declining which should at this time are 8.71 cm and 2.79 cm for Kansas and result in less food per individual. Utah, respectively. Lower precipitation levels should Even within a given clutch larger-sized prairie lizard result in less food being available for sagebrush lizard hatchlings can be shown to have a survival advantage adults and offspring. In sagebrush lizards, low adult to the next spring. Ferguson and Bohlen (1976) mortality during the breeding season results in large found that third clutch hatchlings with a snout-vent numbers of adults surviving (65/ha) during, at length > 24 mm had a significantly higher survivor- least, the early part of the mid-July to October ship than those < 24 mm (43% and 21 %, respec- period to compete with offspring for food. High tively). He found no significant difference in sur- adult mortality in prairie lizards during the breeding vivorship for different-sized hatchlings of the first season results in fewer adults (22/ha) to compete clutch. These data suggest that larger hatchling size with offspring. Data from Sexton et al. (1972) and is less important in the first clutch than in the third Parker and Pianka (1973) suggested that there is a clutch. Besides the advantage to larger hatchlings great deal of overlap in food resources of adult and of using a wider array of food, larger size confers a offspring lizards. Competition among the adults and advantage during social contests which offspring may further reduce the amount of food could be related to food territories (Rand 1967). available to sagebrush lizard offspring, although this Comparable data are not available on sagebrush may be mitigated by the juveniles utilizing smaller lizards. However, since joules (calories) per egg are prey due to their smaller mouths. Differences in pre- significantly higher in the second clutch than in the cipitation levels and adult mortality during the first, 5,832 (1,394) and 4,431 (1,059), respectively, breeding season, therefore, may result in differences the above data would suggest that second clutch in food availability for the two species after repro- hatchlings are larger than first clutch hatchlings. If duction has ceased. Late Spring 1976 ASPECTS OF REPRODUCTIVE STRATEGIES IN LIZARDS 457

Additional data suggesting food competition was LITERATURE CITED greater for sagebrush lizards were mouthgape and Avery, R. A. 1971. Estimates of food consumption by snout-vent length relationships for the two species the lizard, Lacerta vivipara Jacquin. J. Anim. Ecol. (Fig. 8). Regression lines showed that given a 40:351-365. prairie lizard and a sagebrush lizard of equal size, the Ballinger, R. A., and D. R. Clark, Jr. 1973. Energy content of lizard eggs and the measurement of repro- latter had a larger mouth. Schoener (1968) found ductive effort. J. Herpetol. 7:129-132. that average prey size and variance of prey size in- Chow, G. C. 1960. Tests of equality between sets of creased with head length in Bimini anoles. Presum- coefficients in two linear regressions. Econometrika ably, longer heads resulted in larger mouths in anoles. 28:591-605. Since sagebrush lizards had a larger mouthgape than Church, G. 1962. The reproductive cycles of the Jamaican House Geckos, Cosymbotus platyurus, Hemi- prairie lizards they should be able to utilize not only dactylus frenatus, and Peropus mutilatus. Copeia larger prey but also a wider range of prey sizes. 1962:262-269. Species that are food limited should be generalists Cole,in L. C. 1954. The consequences of life their food habits (Emlen 1973). The capacity to history phenomenon. Q. Rev. Biol. 29:103-137. handle a wider array of prey sizes suggests that Davis, D. E. 1967. The annual rhythm of fat deposi- tion in woodchucks (Marmota monax). Physiol. Zool. sagebrush lizards may be less specialized in their 67:391-402. food habits than prairie lizards. Derickson, W. K. 1974. Lipid deposition and utiliza- Finally, Licht (1974) suggested that differences in tion in the Sagebrush Lizard, Sceloporus graciosus: Its lipid levels are indicative of different food avail- significance for reproduction and maintenance. Comp. Biochem. Physiol. 49A:267-272. abilities. Licht was able to increase lipid levels in Dessauer, H. C. 1955. Seasonal changes in the gross Puerto Rican anoles by supplemental feeding in the composition of the lizard A nolis carolinensis. field. Lizards that were not given additional food J. Exp. Zool. 128:1-12. in the field had much lower lipid levels, suggesting Emlen, J. M. 1966. The role of time and energy in that a limited amount of food is available. My own food preference. Am. Nat. 100:611-617. . 1973. Ecology: An evolutionary approach. laboratory experiments (Table 2) demonstrated that Addison-Wesley Publishing Company, Reading, Massa- with ad libitum feeding, both species deposit lipids chusetts. 493 p. faster than field animals. Also, the discrepancy be- Ferguson, G. W., and C. H. Bohlen. 1973. The regula- tween lipid deposition rates in the field and laboratory tion of Prairie Swift (Lizard) populations. A progress report. Proc. Third Midwestern Prairie Conf. 3:69- were greater in sagebrush lizards (1.3 mg/g LDBW - 72. day) than in prairie lizards (0.9 mg/g LDBW - day). Ferguson, G. W., and C. H. Bohlen. 1976 (in press). Therefore, these data suggest that a positive correla- Demographic analysis: A for the study of natural tion exists between lipid levels and food availability selection of behavioral traits. In N. Greenberg and P. and that prairie lizards may have more food avail- McClean [ed.] Conference on brain behavior and evolution in lizards: A colloquium. Adana Press, able than sagebrush lizards. Washington, D.C. Folch, J., M. Lees, and G. H. Sloane Stanley. 1957. A ACKNOWLEDGMENTS simple method for isolation and purification of total I thank Donna, Kevin, and Todd for their support and lipids from animal tissues. J. Biol. Chem. 226:497- understanding. Their sacrifices made this study possible. 509. The patience, understanding, and considerable talents of Gadgil, M., and W. H. Bossert. 1970. Life historical my committee members, Drs. Stephen D. Fretwell, G. consequences of . Am. Nat. 104: 1- Richard Marzolf, Christopher C. Smith, and Roger Wein- 25. berg, were instrumental in the development and fulfill- Gadgil, M., and 0. T. Solbrig. 1972. The concept of ment of the project. Words cannot express my gratitude r- and K-selections: Evidence from wild and to my major professor, Dr. Gary W. Ferguson, for the some theoretical considerations. Am. Nat. 106:14-31. time and effort he devoted in helping me develop this Gaffney, F. C., and L. C. Fitzpatrick. 1973. Energetics research problem. Drs. Kenneth Kemp, George Milliken, and lipid cycles in the lizard, Cnemidophorus tigris. and Don Yamashita were interested and kind enough to Copeia 1973:446-452. aid with the statistical analyses. Dr. William Klopfen- Goldberg, S. R. 1973. Ovarian cycles of the Western stein provided the biochemical expertise. Gerard Hod- Fence Lizard, Sceloporus occidentalis. Herpetologica denbach and his three sons, Billy, Jimmy, and Johnny, 29:284-288. provided many of the lizards from Utah. Their interest and love of working with lizards was inspiring. Many Golley, F. B. 1961. Energy values of ecological ma- graduate and undergraduate students helped collect liz- terials. Ecology 50:517-519. ards and acted as sounding boards for my ideas. They Gorman, G. C., and P. Licht. 1975. Differences be- influenced my thinking and I am indebted to them. I tween the reproductive cycles of sympatric Anolis liz- am grateful to Dr. Donald Tinkle, Dr. Tom Poulson, and ards on Trinidad. Copeia 1975:332-336. two anonymous reviewers for their helpful comments Hadley, N. F., and W. W. Christie. 1974. The lipid and suggestions. This research was supported in part by a composition and triglyceride of eggs and fat NSF Doctoral Dissertation Improvement Grant (No. bodies of the lizard Sceloporus jarrovi. Comp. Bio- GB-35156) to me through Dr. Ferguson. The Division chem. Physiol. 48B:275-284. of Biology and its faculty supplied much of the materials Hahn, W. E., and D. W. Tinkle. 1965. Fatbody cycling and equipment needed for this research. and experimental evidence for its adaptive significance 458 W. KENNETH DERICKSON Ecology, Vol. 57, No. 3

to ovarian follicle development in the lizard Uta of the calorie to ecological problems. Annu. Rev. stansburiana. J. Exp. Zool. 158:79-86. Ecol. Syst. 2:145-164. Hairston, N. G., D. W. Tinkle, and H. M. Wilbur. 1970. Parker, W. S., and E. R. Pianka. 1973. Notes on the Natural selection and the parameters of of the iguanid lizard Sceloporus magister. growth. J. Wildl. Manage. 34:681-690. Herpetologica 29:143-151. Harper, J. L., P. H. Lovell, and K. G. Moore. 1970. Pianka, E. R. 1970. On r and K selection. Am. Nat. The shapes and sizes of seeds. Annu. Rev. Ecol. Syst. 104:592-597. 1: 327-356. 1972. r and K selection or b and d selection? Helms, C. W. 1968. Food, fat, and . Am. Am. Nat. 106:581-588. Zool. 8: 151-167. Pough, F. H. 1973. Lizard energetics and diet. Ecol- Hoddenbach, G. A. 1966. Reproduction in western ogy 54:837-844. Texas Cnemidophorus sexlineatus (Sauria: Teiidae). Rand, A. S. 1967. Ecological and social Copeia 1966:110-113. in the iguanid lizard Anolis lineatopus. Proc. U.S. Horwitz, W. P., P. Chichilo, and Helen Reynolds. 1970. Natl. Mus. 122:1-79. Methods of analysis. Association of Official Analyti- Ruibal, R., R. Philibosian, and J. L. Adkins. 1972. Re- cal Chemists, Washington, D.C. 1015 p. productive cycle and growth in the lizard Anolis Jameson, E. W., Jr., and R. A. Mead. 1964. Seasonal acutus. Copeia 1972:509-518. changes in fatbody fat, water, and basic weight in Sawicka-Kapusta, K. 1968. Annual fat cycle of field Citellus lateralis, Eutamias speciosus and E. amoenus. mice, Apodemnes flavicollis (Melchior, 1834). Acta J. of Mammal. 45:359-365. Theriol. 19:329-339. Janzen, D. H., and T. W. Schoener. 1968. Differences Schoener, T. W. 1968. The Anolis lizards of Bimini: in insect abundance and diversity between wetter and partitioning in a complex . Ecology drier sites during a tropical dry season. Ecology 49: 49:704-726. 96-110. 1971. Theory of feeding strategies. Annu. Johnson, D. R. 1966. Diet and estimated energy as- Rev. Ecol. Syst. 2:369-404. similation of three Colorado lizards. Am. Midl. Nat. Sexton, 0. J., Joan Bauman, and E. Ortleb. 1972. Sea- 76:504-509. sonal food habits of Anolis limifrons. Ecology 53: King, J. R. 1970. Photoregulation of food intake and 182-186. fat metabolism in relation to avian sexual cycles, p. Smith, C. C., and S. D. Fretwell. 1974. The optimal 365-385. In J. Benoit and I. Assenmacher [ed.] La balance between size and number of offspring. Am. Photoregulation de la reproduction chez les oiseaux Nat. 108:499-506. et les mammiferes. Editions du C. N. R. S. Paris. Smith, H. M. 1946. Handbook of lizards. Comstock Licht, P. 1974. Response of Anolis lizards to food Publishing Company, Ithaca, New York. 557 p. supplementation in . Copeia 1974:215-221. Smith, R. E. 1968. Studies on reproduction in Costa Licht, P., and G. C. Gorman. 1970. Reproductive and Rican Ameiva festiva and Ameiva quadrilineata fat cycles in Caribbean Anolis lizards. Univ. Calif. (Sauria: Teiidae). Copeia 1968:236-239. Publ. Zool. 95:1-52. Stebbins, R. C., and H. B. Robinson. 1946. Further MacArthur, R. H., and E. R. Pianka. 1966. On opti- analysis of a population of the lizard Sceloporus mal use of a patch environment. Am. Nat. 100:603- graciosus gracilis. Univ. Calif. Publ. Zool. 48:149- 609. 168. MacArthur, R. H., and E. 0. Wilson. 1967. The Telford, S. R., Jr. 1970. Seasonal fluctuations in liver theory of island . Monographs in Popu- and fatbody weights of the Japanese lacertid Takydro- lation Biology, Princeton, New Jersey. 203 p. mus tachydromoides. Copeia 1970:681-689. Mueller, C. F. 1969. Temperature and energy char- Tinkle, D. W. 1969. The concept of reproductive ef- acteristics of the Sagebrush Lizard (Sceloporus gracio- fort and its relation to the evolution of life histories sus) in Yellowstone National Park. Copeia 1969: of lizards. Am. Nat. 103:501-516. 153-160. . 1973. A population analysis of the Sagebrush 1970. Energy utilization in the lizards Lizard, Sceloporus graciosus in southern Utah. Copeia Sceloporus graciosus and S. occidentalis. J. Herpetol. 1973:284-296. 4:131-134. Tinkle, D. W., and R. A. Ballinger. 1972. Sceloporus Nikolskii, G. V. 1969. Theory of fish population undulatus: A study of the intraspecific comparative dynamics as the biological background for rational demography of a lizard. Ecology 53:570-584. exploration and management of resources. Tinkle, D. W., and N. F. Hadley. 1975. Lizard repro- Oliver and Boyd, Edinburgh. 323 p. ductive effort: Caloric estimates and comments on its Odum, E. P. 1960. Lipid deposition in nocturnal mi- evolution. Ecology 56:427-434. grant . Proc. 12th Inst. Omithol. Congr. p. 563- Tinkle, D. W., H. M. Wilbur, and S. G. Tilley. 1970. 576. Evolutionary strategies in lizard reproduction. Evolu- Paine, R. T. 1971. The measurement and application tion 24:55-74.