Diet of the Tepalcatepec Valley whiptail, Aspidoscelis calidipes (Squamata: Teiidae), in Michoacan, Mexico.
The teiid lizard Aspidoscelis calidipes is endemic to the Balsas-Tepalcatepec Basin in the states of Michoacan and Guerrero, Mexico (Duellman, 1961; Perez-Ramos et al., 2000). Although, the International Union for Conservation of Nature (2011) places A. calidipes in the category of "Least Concern," Mexican conservation laws (Diario Oficial de la Federacion, 2010) categorize it as requiring special protection due to its degree of endemism and the loss and degradation of its habitat, Alvarado-Diaz et al. (2013) consider A. calidipes to have a high vulnerability. Data available on A. calidipes are restricted to a species description (Duellman, 1955) and limited field observations on type of habitat (arid tropical dry forest, particularly the Cercidium-Prosopis-Apaplonesia associations) and activity (active throughout the day, including the hottest times of the day when ground temperatures frequently reach [greater than or equal to] 40[degrees]C) (Duellman, 1960). We assessed the food habits of this species, specifically the differences in diet composition between adults and juveniles.
Our study was conducted at Nuevo Centro in the municipality of La Huacana (18[degrees]44'N, 102[degrees]00'W) in the Balsas-Tepalcatepec Basin of Michoacan, Mexico. Vegetation type in the area is dry tropical forest (CONANP, 2006). Mean annual temperature is 28[degrees]C with an average annual rainfall of 500 mm, 80% of which falls June-September, after 7-8 months of dry season (Garcia, 1988; Villaseuor et al., 2008).
We caught 22 lizards in March 2010 and February 2011. For each individual we measured (using a vernier caliper, to the nearest 0.1 mm) the snout-vent length (SVL). Lizards were assigned to two size-age classes (adults, SVL > 69 mm; juveniles, SVL < 69 mm). We assigned individuals to either category following Duellman's (1960) description of A. calidipes (juveniles present a dark dorsum and bluish tail; adults present a cocoa brown dorsum with reddish tail). We extracted stomach contents by stomach flushing (Rivas et al., 1996) and preserved food items in 70% ethanol. After we obtained the stomach contents, we released the lizards at the capture site. We identified prey items to taxonomic level of order or family. We counted prey and measured prey items volumetrically. We calculated the relative abundance by number (% N), relative abundance by volume (% V), and relative number of stomachs that contained the respective food item as frequency of occurrence (% F). Using these values, we calculated the index of relative importance (IRI): IRI = (% N + % V) x (% F) (Pinkas et al., 1971). This index ranges from 0.0-20,000, with higher values representing food types of greater importance. We estimated dietary diversity and overlap using the index of relative importance. We calculated the Shannon-Wiener index (H') to estimate diet diversity (Krebs, 1999). The diversity index increases with an increment in the number of dietary items; therefore low values represent dietary specialists and high values represent dietary generalists. As a descriptive measure for the similarity of diet between adult and juvenile lizards, we used the index of Morisita-Horn (Wolda, 1981).
The mean SVL of adult lizards (n = 12) collected was 74 [+ or -] 5.0 mm (range: 72-77 mm) and mean weight was 11.75 [+ or -] 0.38 g (range: 9.2-13.8 g). The mean SVL of juveniles (n = 10) was 63 [+ or -] 1.5 mm (range: 53-69 mm) and mean weight was 6.48 [+ or -] 0.55 g (range: 4.0-9.8 g). Of the 22 lizards examined only two presented empty stomachs. Aspidoscelis calidipes consumed 27 different prey types. Termites (Termitidae: Gnathamitermes) were the dominant prey item, presenting the highest values of IRI, number, volume, and frequency of occurrence in the overall sample and in adults and juveniles (Table 1). The next most important dietary items were Hymenoptera, Formicidae, and Coleoptera (Table 1). Overall dietary diversity was H' = 0.45. Afidae, Carabidae, Psyllidae, and Tingidae were absent in the diet of adults and Apidae, Coreidae, and Myrmeleontidae were absent in the diet of juveniles. The diversity index was higher in juveniles (H0 = 1.15) than in adults (H' = 0.28). Dietary overlap between adults and juveniles was 49%.
The low dietary diversity (H' = 0.45) found in A. calidipes resulted from the markedly high contribution of one prey item (termites) to diet composition. Dominance of termites in diet composition is a common phenomenon in species of the Teiidae (e.g., Mitchell, 1979; Baltazar and Hernandez, 1985). Although we registered differences in diet composition in some secondary food items between adults and juveniles of A. calidipes, as has been reported for other Aspidoscelis species (e.g., Vitt and Ohmart, 1977; Gannon et al., 1990), termites were the dominant item in both size classes. Dietary studies of Aspidoscelis deppii varies in different populations, from Coleoptera and Hymenoptera (Altamirano and Soriano, 2006) to termites, as the primary items (Vitt et al., 1993), suggesting that diet of different populations could be due to differences in prey availability rather than differences in feeding preferences (Altamirano and Soriano 2006). As an active forager (Huey and Pianka, 1981; Pianka, 1986) A. calidipes forages mainly in patches that support large numbers of relatively sedentary prey such as termites, a prey type that feeds lizards that are active foragers worldwide (Pianka and Vitt, 2003). The termites found in the stomach samples of A. calidipes correspond to the genus Gnathamitermes, i.e., "desert termites," which are restricted to desert and arid lands (Baker and Marchosky, 2005). These termites construct extensive networks of tunnels and chambers underground (Light and Pickens, 1934).
We conclude that A. calidipes presents the general pattern of wide-foraging behavior typical of the family Teiidae (Pianka and Vitt 2003) with a diet composed mainly of relatively sedentary prey. The rank of termites as the main prey item in both adults and juveniles might be the result of isopterans being small-sized prey, with reduced variation in size. Additionally, the aseasonal occurrence of termites, as well as their clumped distribution, makes them advantageous prey for A. calidipes, independent of lizard size.
We thank L. Reyes-Solorio and his family for their logistical support in field activities. We thank A. L. Escalante-Jimenez for identifying food items. We thank O. Medina-Aguilar, J.T. Perez, J. Orozco, and J. Paz-Gutierrez for their collaboration in the field. Field work was conducted under Secretaria de Medio Ambiente y Recursos Naturales (SEMARNAT) permit FAUT-0113. We thank to the Coordinacion de Investigacion Cientifica de la Universidad Michoacana de San Nicolas de Hidalgo. The results of the present study are part of the professional thesis of the principal author, under the direction of Dr. Ireri Suazo-Ortuho.
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Submitted 21 October 2013.
Acceptance recommended by Associate Editor, Fausto Mendez de la Cruz, 18 January 2015.
ERNESTO RAYA-GARCIA, * IRERI SUAZO-ORTUNO, AND JAVIER ALVARADO-DIAZ
Instituto de Investigaciones sobre los Recursos Naturales, Universidad Michoacana de San Nicolas de Hidalgo.
Morelia, Michoacan 58000, Maxico
* Correspondent: firstname.lastname@example.org
Table 1--Stomach contents of Aspidoscelis calidipes in Michoacan, Mexico. The top line in each entry is presented as follows: percent in numbers/percent in volume ([mm.sup.3])/percent of frequency of occurrence. The number in the second line of each entry corresponds to the index of relative importance. Food item Adults Juveniles Pooled (n = 12) (n = 10) Acridae 0.10/4 0.38/1 0.16/3 24.03 9.74 36.84 Afidae 0 0.77/0 0.16/0 0 3.85 0.80 Apidae 0.20/0 0 0.16/0 11.43 0 7.47 Araneae 0.10/0 0 0.08/0 0.51 0 0.40 Blattodea 0.10/0 0 0.08/0 2.86 0 1.87 Carabidae 0 0.38/0 0.08/0 0 5.83 1.87 Coleoptera 0.71/4 4.62/3 1.52/4 81.21 38.70 112.66 Coreidae 0.10/0 0 0.08/0 5.21 0 3.34 Curculionidae 0.40/1 1.15/3 0.56/2 27.24 46.69 69.08 Diptera 0 0.77/0 0.16/0 0 15.50 4.54 Formicidae 2.53/2 3.08/1 2.64/2 127.90 69.59 193.79 Homoptera 0.10/0 6.15/2 1.36/1 0.51 133.32 47.78 Hymenoptera 0.51/4 11.92/31 2.88/14 26.06 431.73 263.50 Isoptera 0 2.31/0 0.48/0 0 15.44 3.87 Lepidoptera 0.10/0 0.77/4 0.24/2 5.21 27.28 25.90 Mantodea 0 0.38/7 0.08/2 0 40.99 15.08 Myrmeleontidae 0.20/1 0 0.16/0 8.07 0 5.21 Neuroptera 0 0.38/0 0.08/0 0 5.83 1.87 Opiliones 0.10/0 0 0.08/0 1.68 0 1.13 Orthoptera 0.10/0 1.15/3 0.32/2 5.21 75.90 47.52 Oxyopidae 0.10/0 0.38/0 0.16/0 2.86 5.83 7.47 Psyllidae 0 1.15/0 0.24/0 0 7.72 1.94 Salticidae 0.20/0 1.54/3 0.48/2 11.43 54.45 50.72 Solipugida 0.40/1 0.38/0 0.40/1 23.71 5.83 28.56 Termitidae 93.93/73 60.38/29 86.95/56 7,530.53 2,690.44 10,783.33 Thysanura 0 0.38/0 0.08/0 0 5.83 1.87 Tingidae 0 0.38/0 0.08/0 0 1.92 0.40
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|Author:||Raya-Garcia, Ernesto; Suazo-Ortuno, Ireri; Alvarado-Diaz, Javier|
|Date:||Mar 1, 2015|
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