Gamaliel Castañeda

NICHE SEGREGATION WITHIN A DUNE LIZARD COMMUNITY IN COAHUILA, MEXICO

Abstract We studied niche segregation among 3 syntopic lizards, Uta stejnegeri, Uma exsul, and Aspidoscelis marmorata, in the sand dunes of Viesca, Coahuila, Mexico. In 2004, we analyzed both microhabitat and substrate niches during a warm season and a cold season. Niche breadth and overlap were calculated, and a selection index was used. Each lizard species selected microhabitats that focused on a single perennial plant species and a specific range of sand compactness. Uta stejnegeri was highly associated with the perennial Suaeda nigrescens and highly compacted sand. Uma exsul was associated with sites with deep, loosely compacted sand and Larrea tridentata. Aspidoscelis marmorata was associated with the occurrence of Prosopis glandulosa and moderately compacted sand. Associations described here could help to develop a future conservation and management program for these sand dunes, where the endemic U. exsul and other species are protected.

Phylogenetic Constraints Do Not Block Food Chemical Discrimination in the Omnivorous Phrynosomatid Lizard Uma exsul

Abstract In lizards identification of food using chemical cues allows active foragers to locate hidden prey and omnivores and herbivores to identify palatable plant food, but ambush foragers identify food visually rather than chemically. Omnivores and herbivores derived from ambushing ancestors discriminate food chemicals from control substances. The only known exception is the omnivorous phrynosomatid lizard Sceloporus poinsettii, which lacks food chemical discrimination and which might have been constrained from evolving it by scarcity of chemoreceptors. We studied food chemical discrimination by the phrynosomatid Uma exsul, an omnivore whose diet is 25% plant by volume. In 60 s trials in which chemical cues from mealworms, romaine lettuce, cologne, and water were presented on cotton swabs, lizards responded more strongly to plant and animal chemicals than control stimuli. Food chemical discrimination by Uma exsul strengthens evidence that plant chemical discrimination evolves in tandem with plant diet and prey chemical discrimination also appears in omnivores or herbivores derived from ambush foragers. Confirmation of food chemical discrimination in U. exsul vitiates the evolutionary constraint hypothesis for S. poinsettii. That lizards tongue-flicked and bit infrequently, yet discriminated, is unusual, suggesting that lingually mediated plant chemical discrimination may have evolved recently, few tongue-flicks are needed to evaluate nutritive properties of plant foods, or plant chemical discrimination is an adaptively unimportant epiphenomenon of plant consumption. Because they do not search actively for prey or tongue-flick before attacking, phrynosomatids presumably evolve prey chemical discrimination by genetic correlation with plant chemical discrimination.

VARIATION IN HOME RANGE OF THE SIDE-BLOTCHED LIZARD, UTA STEJNEGERI, IN COAHUILA, MEXICO

Abstract We studied seasonal variation in size and fidelity of home range in a population of eastern side-blotched lizards, Uta stejnegeri, in southern Coahuila, Mexico. Field work was carried out during the active seasons of 2002–2004. Home ranges during breeding and non-breeding seasons were larger for males than females and were reduced in both sexes during non-breeding months (autumn). There was greater intersexual overlap of home range during summer and less in autumn. Intrasexually, males had more overlap in home range than females (particularly during summer), which could be related to their large home ranges during that season. Fidelity to home range from one season to the next in a given year was similar in males and females. Although males had greater length and mass than females, neither measure correlated with size of home range. Density of adult lizards was negatively correlated with size of home range during the reproductive period. During non-reproductive months, density of all age classes combined was negatively correlated with size of home range. Our results indicate that home range sizes of U. stejnegeri vary considerably over the year and diverse factors are involved.

Demography of the Side-Blotched Lizard, Uta stansburiana, in Sand Dunes of the Central Chihuahuan Desert

Abstract We studied demography of a population of side-blotched lizards, Uta stansburiana, in the sand dunes of Reserva de Biosfera de Mapimí, Durango, Mexico, during 1989–1994. Reproduction in females occurred during January–July, which coincided with late dry and early wet seasons. Reproductive activity was highest in the middle of the dry season (February–March). At an average age of 10 months, 32% of females had reached sexual maturity. A notable feature of summer and autumn was the greater number of hatchlings and juveniles, coinciding with the wet season. Overall sex ratio did not differ from 1:1. Density of adults was 1–59/ha. This population had early maturity, a relatively short life expectancy, and many offspring. Resumen Estudiamos la demografía de una población de la lagartija de manchas laterales, Uta stansburiana, en las dunas de arena de la Reserva de Biosfera de Mapimí, Durango, México, durante 1989–1994. La reproducción en las hembras ocurrió durante enero–julio, lo cual coincidió con el fin de la estación seca y principio de la estación húmeda. La actividad reproductora fue más alta a la mitad de la estación seca (febrero–marzo). A una edad promedio de 10 meses, el 32% de las hembras habían alcanzado la madurez sexual. Una característica notable en el verano y el otoño fue el mayor número de crías y jóvenes, coincidiendo con la estación húmeda. La proporción global de sexos no fue diferente de 1:1. La densidad de adultos fue de 1–59/ha. Esta población tenía una madurez temprana, una esperanza de vida relativamente corta, y muchas crías.

Spatial Segregation of Microhabitats Within a Community of Lizards in Médanos de Samalayuca, Chihuahua, Mexico

Abstract We described seasonal microhabitats of the lizards Uta stansburiana, Phrynosoma modestum, and Aspidoscelis tigris in the sand dunes of Medanos de Samalayuca, Chihuahua, Mexico. Uta stansburiana and A. tigris used many resources in common and frequently were observed under honey mesquites Prosopis glandulosa, the most common and largest shrub on our study site. In contrast, P. modestum was more common in bare areas. Uta stansburiana and A. tigris showed moderate to high overlap in vegetative cover and compaction of substrate. With respect to Uta stansburiana and A. tigris, P. modestum showed low-to-moderate overlap in microhabitats.