Los parámetros poblaciones permiten conocer la viabilidad de las poblaciones, lo cual es sumamente importante para especies que se pretendan conservar. La ardilla endémica de Perote (Xerospermophilus perotensis), se encuentra clasificada a nivel nacional e internacional como una especie vulnerable a la extinción y que enfrenta serios problemas de conservación, ya que su hábitat se ha transformado y reducido drásticamente. Con el fin de obtener conocimiento acerca de las poblaciones de esta especie, entre los años 2010 y 2011 se evaluaron y compararon las densidades y estructuras poblacionales (edades, proporción de sexos y estado reproductivo) en tres sitios con diferente grado de perturbación dentro del Valle de Perote, Veracruz, México. La estructura poblacional y densidad se estudiaron mediante el método de captura-marcaje-recaptura en dos cuadros de una hectárea (por sitio), con un esfuerzo de muestreo total de 3,240 días/trampa. Los parámetros poblacionales evaluados, presentaron valores similares en los tres sitios de estudio. Las densidades fueron mayores en abril-junio (periodo reproductivo) con 24 ind/ha y menor en octubre (inicio de la hibernación) con 2 ind/ha. Respecto a las clases de edades, los adultos predominaron en los tres sitios. Los juveniles fueron más abundantes en agosto. En junio se presentó la mayor cantidad de individuos con características reproductivas (testículos escrotados, estado de preñez o lactancia). Los resultados encontrados aportan conocimiento básico sobre la ecología de esta especie que puede ser utilizado en futuros planes de conservación ya que la especie enfrenta densidades poblacionales bajas.
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INTRODUCTION:The density and structure of populations are basic demographic parameters to calculate for species with a conservation concern. The endemic Perote ground squirrel (Xerospermophilus perotensis) is distributed in the Oriental Basin, in the states of Puebla, Veracruz and Tlaxcala (Mexico). At present, this squirrel is facing serious conservation problems because their habitat has been drastically reduced and transformed, mainly by the conversion to agricultural lands, causing that it only persist in small and isolated populations. The International Union for Conservation of Nature and the Mexican government has classified this species as endangered and threatened respectively. Inasmuch as the species has a restricted distribution, small population and reduced habitat, our aim was to obtain the basic population parameters such as density and population structure.
METHODS:From years 2010 to 2011 we captured, marked, and recaptured individuals of X. perotensis to determine the age (juveniles and adults), weight, sex ratio and reproductive status (scrotal testes in males or pregnancy and lactation signs in females) in three sites in the Perote Valley, Veracruz, Mexico. The plant associations were the main difference among these sites. All samplings were carried out every two months just including the activity period of the squirrel (April-October).
RESULTS:The population parameters evaluated showed similar values at the three study sites (Figure 1). The densities were higher in April-June (breeding season) with 24 ind/ha and lowest in October (beginning hibernation) with 2 ind/ha. Adults predominated in all sites (Figure 2). Juveniles were more abundant in August. The highest number of individuals with reproductive characters (scrotal testes, pregnancy or lactation signs) was found in June (Figure 3). Densities were higher in April-June (breeding season) with 24 ind/ha and lowest in October (beginning hibernation) with 5 ind/ha. The number of juveniles and adults showed significant differences (P = 0.002).
DISCUSSION AND CONCLUSIONS:The results indicate that the population of the Perote ground squirrel is declining and shows low population recruitment. Also their habitat is being transformed rapidly and offers few opportunities for the development of the species. We suggest that the species should be categorized as an endangered species instead of threatened in Mexico. Also, farmers could allow the establishment of animals when they do not use the land, this action can stimulate the population growth.
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