Diet selectivity in relation to food quality and availability by the endemic Perote squirrel (Xerospermophilus perotensis)

THERYA, 2018, Vol. 9 (2): 121-127 DOI: 10.12933/therya-18-553 ISSN 2007-3364 Diet selectivity in relation to food quality and availability by the endemic Perote squirrel (Xerospermophilus perotensis) Julio C. Hernández-Hernández1, Jorge E. Morales-Mávil1, Matthias Laska2 and Laura T. Hernández-Salazar1* Laboratorio Biología de la Conducta, Instituto de Neuroetología, Universidad Veracruzana. Av. Dr. Luis Castelazo Ayala s/n, Colonia Industrial Ánimas, CP. 91190, Xalapa. Veracruz, México. Email: (JCHH), (JEMV), (LTHS). 2 IFM Biology, Section of Zoology. Linköping University, SE-581 83, Linköping, Sweden. Email: (ML). *Corresponding author 1 Climatic fluctuations have a biogeochemical effect on food availability and quality, resulting in adjustments of the foraging and food selection behavior of animals. Our study aimed to evaluate the influence of seasonal variation on abundance of food resources and its effect on food selection of Xerospermophilus perotensis, an endemic species of ground squirrel in the Oriental Basin. Food selection behavior was recorded using focal animal and continuous behavior sampling on a squirrel population inhabiting the grassland of a semi-arid area. The results show that their diet consisted of 6 plant species with significant differences in the time spent feeding on each plant species (X2 = 128.96; P = 0.01). The species with the highest feeding times included Scleropogon brevifolius (63.6 %), Verbena bipinnatifida (10.6 %) and Erigeron pubescens (10.5 %). These plant species had the highest percentage of vegetation cover and availability among seasons, but they were of low nutritional quality with regard to their protein/fiber ratio. However, during specific periods, associated either with gestation and lactation or prior to hibernation, the squirrels increased their protein consumption. This suggests that squirrels are opportunistic feeders, and under certain conditions tend to select plant species that provide them with better quality diets. Las fluctuaciones climáticas tienen un efecto biogeoquímico sobre la calidad y la disponibilidad de los alimentos, lo que resulta en ajustes en la conducta y la selección de los alimentos de los animales. Nuestro objetivo fue evaluar la influencia de la variación estacional en la abundancia de los recursos alimenticios y su efecto sobre la selección de alimentos por Xerospermophilus perotensis, una especie de ardilla endémica de la Cuenca Oriental. La conducta de alimentación se registró utilizando un muestreo animal-focal con registro continuo en una población de ardillas que habita en los pastizales de una zona semiárida. Los resultados mostraron que su dieta consistió en 6 especies de plantas con diferencias significativas en el tiempo de alimentación de cada especie (X2 = 128.96; P = 0.01). Las especies con los mayores tiempos de alimentación fueron Scleropogon brevifolius (63.6 %), Verbena bipinnatifida (10.6 %) y Erigeron pubescens (10.5 %). Estas especies de plantas tuvieron el mayor porcentaje de cobertura vegetal y disponibilidad entre estaciones, pero fueron de baja calidad nutricional con respecto a su relación proteína / fibra. Sin embargo, durante períodos específicos, asociados con la gestación y la lactancia o antes de la hibernación, las ardillas aumentaron su consumo de proteínas. Esto sugiere que las ardillas son consumidores oportunistas, y bajo ciertas condiciones tienden a seleccionar especies de plantas que les proporcionen dietas de mejor calidad. Key words: Diet; endemism; ground squirrel; nutritional quality; seasonal variation. © 2018 Asociación Mexicana de Mastozoología, www.mastozoologiamexicana.org Introduction Seasonality refers to recurrent climatic variations that tend to occur over an annual period. These variations define the type of vegetation that exists in a place and directly affect the abundance and quality of food resources (Schaik and Brockman 2005). Such seasonal variations in food abundance and quality have been reported to cause concurrent alterations in the abundance and/or dietary habits of herbivorous species (Gutiérrez 1998; Hirsch 2009; GarcíaGarcía and Santos-Moreno 2014; Penezić and Ćirović 2015; Tsindi et al. 2016). Although herbivory is largely determined by external factors that regulate food abundance and availability, dietary flexibility plays an important role as it depends on individual digestive processes that regulate the acquisition of metabolizable energy and nutrients (Karasov et al. 1986). In this way, the chemical characteristics of the food directly affect the selection of the diet of the animals, and a preference for certain types of food can be the consequence of its chemical composition (Ulappa et al. 2014). In this context, each animal faces the dilemma of having to obtain an adequate food in terms of quantity and quality to meet its nutritional needs, and protein and fiber are considered the chemical constituents that determine this preference (Stephens and Krebs 1986; Grier and Burk 1992; Rezsutek and Cameron 2011). Within nutritional ecology there are four hypotheses with regard to the aims of diet selection, each of which proposes that dietary selection has a different nutritional primary objective: 1) maximization of energy uptake (Schoener 1971). 2) The maximization of nitrogen uptake (Mattson 1980; White 1993). 3) Toxin evasion (Freeland and Janzen 1974; Dearing et al. 2005). 4) The acquisition of a nutritionally balanced diet (Raubenheimer and Simpson 2004, Robbins et al. 2007). The quantification of these different nutritional goals is a challenge, especially in studies of wild animals, where research requires detailed data on feeding behavior RUNNING HEAD: SQUIRREL DIET QUALITY of animals over continuous periods, adequate analysis of all food consumed, and an analytical framework to address the complex nature of nutritional data (Felton et al. 2009). In fact, the diet of herbivorous mammals is considered one of the most complex in comparison with that of other dietary specialists (Belovsky 1978; Owen-Smith and Novellie 1982). This notion is supported by the fact that herbivores can consume foods in high abundance but of low quality, which often lack essential nutrients, so that they require supplementary intake of different food items to maintain nutritional balance (Westoby 1978). In semi-arid environments, herbivores must develop even more efficient strategies for harnessing food resources, as the supply of quality vegetation is usually low. These strategies are both behavioral (ability to select proper feeding sites and selection of dietary components) and physiological (development of a digestive system that optimizes food processing; Benítez et al. 2006). Ground squirrels that live in semi-arid environments are therefore a good model to study because of the selectivity of their diet in relation to its quality and availability, which varies seasonally (Valdés 2003). The ground squirrel of Perote (Xer (...truncated)