Food Habits of the Western Whiptail Lizard (Cnemidophorus Tigris) in Southeastern New Mexico

Great Basin Naturalist

Volume 45 Number 3 Article 17

7-31-1985

Food habits of the western whiptail lizard (Cnemidophorus tigris) in southeastern New Mexico

Troy L. Best University of New Mexico, Albuquerque, New Mexico

A. L. Gennaro Eastern New Mexico University, Portales, New Mexico

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Recommended Citation Best, Troy L. and Gennaro, A. L. (1985) "Food habits of the western whiptail lizard (Cnemidophorus tigris) in southeastern New Mexico," Great Basin Naturalist: Vol. 45 : No. 3 , Article 17. Available at: https://scholarsarchive.byu.edu/gbn/vol45/iss3/17

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. FOOD HABITS OF THE WESTERN WHIPTAIL LIZARD {CNEMIDOPHORUS TIGRIS) IN SOUTHEASTERN NEW MEXICO

Troy L. Best' and A. L. Gennaro"

Abstract. — This study presents the first food habit assessment for the western whiptail hzard {Cnemklophoriis ti^ris) in the shinnery oak-mesquite habitat {Quercus havardii-Prosnpis glandulosa) of southeastern New Mexico. Short-horned grasshoppers, termites, anthons, beetles, and spiders formed the major portion of the diet during the four-year stud\'. Discriminant analyses were used to evaluate annual, seasonal (monthly), and sexual variation. Incidental food categories were responsible for most of the annual and seasonal variation. Dominant foods varied little between months and years. Sexual variation was more evident; it may act to reduce intraspecific competition for food resources and may be associated with secondary sexual size dimorphism.

Food habits of the western whiptail Hzard and because no extensive studies of C. tigris {Cnemidophorus tigris) have been studied in have been conducted in the shinnery several areas of the western United States oak-mesquite association of southeastern (e.g., Pack 1923, Milstead 1957a, 1958, 1961, New Mexico, the present study was initiated. 1965, Johnson 1966, Echternacht 1967, Our objectives were to assemble a listing of Medica 1967, Milstead and Tinkle 1969, Pi- food items consumed in that area and to exam- anka 1970, Bickham and MacMahon 1972, ine annual, seasonal (monthly), and sexual Scuddav and Dixon 1973, Vitt and Ohmart variation. 1977, Mitchell 1979, Best and Polechla 1983). Some of these investigators have examined Materials and Methods intraspecific variation: e.g., Johnson (1966) found that the diet of immature whiptails was From 1976 through 1979, 174 C. tigris were similar to that of adults, and Johnson (1966) collected approximately 40 km E of Carlsbad and Pianka (1970) found little difference in in Eddy and Lea counties, New Mexico diet between sexes. Conversely, there is con- (within an 8-km radius of drill hole ERDA 9, siderable geographic (Milstead and Tinkle SE corner. Sec. 20, T22S, R31E). Specimens 1969, Pianka 1970), seasonal (Johnson 1966, were fixed in 10% formalin and stored in 40% Milstead and Tinkle 1969, Pianka 1970, Vitt isopropyl alcohol. Stomach contents were and Ohmart 1977, Mitchell 1979), and annual later removed, placed into individual vials, variation (Milstead 1965, Medica 1967, Mil- and identified. Arthropod taxonomy follows stead and Tinkle 1969, Mitchell 1979). Borroretal. (1981). In southeastern New Mexico, Best and Two separate data sets were used in the Polechla (1983) reported diet data for C. tigris analyses. One contained the number of indi- in their study of C. gularis, but their sample of viduals in each arthropod order. The second C. tigris was small and the habitat where they included the number of individuals identified collected specimens was quite different from to family except where identification was im- where those examined herein were obtained. possible (e.g., unidentified Coleoptera were Subsequently, Best and Gennaro (1984) stud- entered as Coleoptera, Buprestidae was an- ied Uta stanshuriana from the shinnery other character, Cleridae another, etc.). Dis- oak-mesquite habitat of southeastern New criminant analyses (Nie et al. 1975) were used Mexico using specimens collected in sympa- to test for annual, seasonal (monthly), and try with the C. tigris reported herein. In view sexual variation in food habits. Best and Gen- of the previous studies of food habit variation naro (1984) presented a summary of this tech-

'Ceneral College. Department of Biology, and Museum of Southwestern Biology, University of New Mexico, Albuquerque, New Mexico 87131. -Llano Estacado Center for Advanced Professional Studies and Research, Natural History Museum, Eastern New Mexico University, Portales, New Mexico S8130.

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Table 1. Food items found in 174 western whiptail lizards {Cnemidophorus tigris). Sample sizes are given in parentheses and occurrence data are presented as: number of lizards containing a food category; total items observed.

Food category July 1985 Best, Gennaro: New Mexico Lizard 529

Table 2. Discriminant analyses between years and months for Cnemidophorus tigris. 530 Great Basin Naturalist Vol. 45, No. 3

Table 3. Discriminant analyses between sexes for Cnemidophorus tigri.s. July 1985 Best, Gennaro: New Mexico Lizard 531

Table 4. Food items in Cnemidophorus tigris collected during 1978 and 1979, See Table 1 for data presentation format.

Food category 532 Great Basin Naturalist Vol. 45, No. 3

all except Solifugae and Hemiptera were Of the three variables accounting for the dif- present in both sexes (Table 4). Using all ferences, only Hymenoptera was present in arthropod taxa, 96% of the specimens were both sexes (Table 4). Considering all classified correctly, with Myrmeleontidae, arthropod ta.xa, 85% of the specimens were Solifugae, Isoptera, Tenebrionidae, Scorpi- classified correctly, with Araneae, Elateridae, onida, Araneae, Hymenoptera, and Coleop- Arthropoda, Formicidae, and Lepidoptera ac- tera accounting for the most differences. counting for the differences between sexes. Solifugae, Hymenoptera, and Coleoptera oc- Elateridae, Formicidae, and Lepidoptera occurred in females only, and the others were curred in both sexes. Because of the small found in both sexes. For July 1978, 85% of the sample for August 1979, discriminant analyses specimens were classified correctly to sex were not performed.

(Table 3). Of the variables accounting for the differences, all but Neuroptera occurred in Discussion females only (Table 4). Using all arthropod taxa, 90% were classified correctly, with Ela- In his examination of geographic variation teridae, Solifugae, Termitidae, Tettigoniidae, in the diet of C. ti^ris. Pianka (1970) found the Myrmeleontidae, and Noctuidae accounting same major food items as in previous studies, for the differences. Except for Myrmeleonti- but there was a pronounced latitudinal shift in dae, all of these variables occurred in female diet. His southern lizards consumed large stomachs only. The August 1978 analysis cor- numbers of termites, but northern lizards re- rectly classified 100% of the lizards to sex lied on other foods. He indicated that this

(Table 3). Coleoptera and Homoptera were could possibly be because there were simply found in females only (Table 4). Considering fewer termites in his Great Basin flatland all arthropod taxa, 100% were classified cor- desert habitats. Additionally, Pianka (1970) rectly with Coccoidea, Termitidae, Gryllidae, observed that food species diversities re- Scarabaeidae, Myrmeleontidae, and Asilidae flected the latitudinal change in diet. Our re- accounting for the differences. Myrmeleonti- sults were similar to previous studies in that dae and Asilidae were in both sexes, and the Orthoptera, Coleoptera, Isoptera, and Lepi- others were in females only. doptera were among the most abundant food For May 1979, 100% of the specimens were categories. The diversity of food categories classified correctly to sex (Table 3). Of the found in our specimens is as great or greater three variables accounting for the differences, than any of the previous C. tigris food habit only Araneae was found in both sexes (Table studies. This may indicate a greater diversity

4). When all arthropod taxa were used in the of food organisms was available for consump- analysis, 100% of the specimens were classi- tion by our lizards, that a greater diversity was fied correctly. The variables accounting for taken by our lizards, that there were varying the differences were Pentatomidae, Ge- degrees of expertise in identifying the stom- ometridae, and Araneae. Pentatomidae oc- ach contents, or that different taxonomic lev- curred in males only, and the other two were els have been used in identifying the food in both sexes. For June 1979, 100% of the categories. specimens were classified correctly to sex Several previous in\ estigators ha\e noted

(Table 3). Of the variables accounting for the the presence of annual diet \'ariation in C most differences, only Hymenoptera, tigris (Milstead 1965, Medica 1967, Milstead Isoptera, Lepidoptera, and Coleoptera oc- and Tinkle 1969, Mitchell 1979). Our findings curred in both sexes (Table 4). Considering all also indicated some annual variation was arthropod taxa, 100% of the lizards were clas- present. However, the differences we found sified correctly. In decreasing order of impor- between years were primarily the result of tance, variables accounting for the differences incidentally occurring food categories. The were Isoptera, Sphingidae, Termitidae, Kho- consistency of the major food categories be- palidae, Myrmeleontidae, Formicidae, Scor- tween years indicated that C. tighs was not a pionida, and Blattidae. None of these oc- completely opportunistic feeder. The species curred in both sexes. For July 1979, 80% of takes certain arthropod taxa very regularly the lizards were classified correctly (Table 3). from \ear to year (i.e., Orthoptera, July 1985 Best, Gennaro: New Mexico Lizard 533

Coleoptera, Isoptera, and Lepidoptera) and is Gennaro 1984). B(\st and Gennaro (1984) pos- opportunistic only in the sense of" taking other tulated these differences may be related to taxa that may fall into, for example, the proper secondary sexual size dimorphism. Since C. size, taste, or behavioral category. Cnemi- tigris also shows secondary sexual size dimor- dophorus tigris takes foods within its normal phism (e.g., Medica 1967), we expect that the "requirements" in greater abundance when sexual diet differences reported herein may they are available in greater abundance. We also be related to size variation. Diet differ- believe a completely opportunistically feed- ences between sexes would act to reduce in- ing species is one that takes food as it more or tersexual competition for food resources—an less randomly encounters it, such as is done adaptation that is known for other vertebrates by coyotes (e.g., Best et al. 1981). The consis- (e.g., birds, Selander 1966). tency of various food categories in the diet of Our study of the feeding ecology of C. tigris C. tigris indicated that some selection must in southeastern New Mexico has shown the have been taking place. From Best and Gen- presence of a small amount of annual and sea- naro's (1984) study oiUta stanshuriana on the sonal variation, and a considerable amount of same study area, we know that large numbers sexual variation. The annual and seasonal vari- of ants (Formicidae) and true bugs ation was attributed to the temporary abun- (Hemiptera) were also available as food items. dance of a variety of arthropod taxa that were However, possibly because of different forag- taken as available. Sexual differences in diet ing habits (e.g., Milstead 1957b, Pianka 1970, were possibly related to differences in sec- Vitt and Ohmart 1977, Parker and Pianka ondary sexual size dimorphism and may be 1977) or selection of foods, ants and certain acting to reduce intraspecific competition for other arthropods were rarely found in C. food in the semidesert environment of south- tigris stomachs. During times of environmen- eastern New Mexico. tal adversity, we expect that C. tigris would take food species that may not be "preferred" Acknowledgments just to survive.

The presence of seasonal variation in the We thank J. C. Schaffner, Texas A&M Uni- diet of C. tigris has been addressed by some versity, and N. Jorgensen, Eastern New Mex- previous workers (Johnson 1966, Milstead ico University, for identifying the stomach and Tinkle 1969, Pianka 1970, Vitt and contents. B. Hoditschek, P. J. Polechla, and Ohmart 1977, Mitchell 1979). We found vary- numerous other graduate student assistants ing degrees of separation between months. aided in specimen collection and data prepa- This seasonal variation was probably caused ration. This project was funded as a portion of by the taking of a variety of temporarily abun- the Los Medaiios Waste Isolation Pilot Plant dant arthropods as the growing seasons pro- studies by Sandia National Laboratories (Con- gressed. In the Chihuahuan desert of south tract 13-2097) and Westinghouse Electric central New Mexico the seasonal rainfall pat- Corp. (Subcontract WFC-53431-SD). S. A. tern as well as total amount of rainfall affects Cole assisted in proofreading, and N.J. Scott, the primary productivity and hence the Jr., S. Neuhauser, and D. J. Hafner critically availability of arthropods as foods for lizards reviewed the manuscript. (Whitford and Creusere 1977). Sexual differences in diet of C. tigris have Literature Cited been examined by Johnson (1966) and Pianka (1970). They noted there were only slight dif- Best. T L and D VV Jackson. 1982. Statistical evalua- collected at the Los ferences between sexes. Our data from south- tion of plant density data Medanos site. New Mexico (1978-1980), xi-^374 eastern New Mexico indicated there was a pp. In Braswell, J., and J. S. Hart, eds., Ecosys- great deal of difference between sexes. Sexual tem studies at the Los Medaiios site, Eddy differences have also been shown for Anolis County, New Mexico. U.S. Dept. Energy, Albu- querque, New Mexico, TME 3141, 3 vols., 982 + (Schoener 1967, 1968); they differed dramati- pp. cally in size ate quite different foods. Sex- and of Best, T. L , and A. L. Gennaro. 1984. Feeding ecology ual differences have been found in U. stans- the lizard Uta stanshuriana in southeastern New 18:291-301. huriana (Parker and Pianka 1977, Best and Mexico. J. Herpetol. 534 Great Basin Naturalist Vol. 45, No. 3

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