Testing Models of Optimal Diet Assembly by the Generalist Herbivorous Lizard Cnemidophorus Murinus

Abstract

The diet of the predominantly herbivorous Bonaire Island whiptail lizard (Teiidae: Cnemidophorus murinus) was examined to assess three models of diet selection by generalist herbivores. These models were: single—nutrient maximizing, toxin avoiding, and nutritional wisdom. At three sites were gathered data on the diet of the lizard over a full year (both wet and dry seasons) on the relative abundance of all plant food types available to the lizards during that period, and on the nutritional composition of each plant type. Thirteen nutritional variables were measured, including content of energy, protein, minerals, water, and potentially toxic plant secondary compounds, and digestibility of protein. The lizards were generalist feeders, consuming a wide variety of flowers, fruits, leaves, nectar, and some animal material. Most stomachs contained more than one food type, suggesting C. murinus typically samples several kinds of plant materials each day. The lizards were selective with regard to foods eaten; most foods were not taken in proportion to their availability in the environment. Potential plant foods varied in nutritional quality, but no one nutrient was correlated with dietary preferences. Multivariate analysis revealed that preference or avoidance of a potential food type could be predicted by a combination of nutritional properties, but these differed among sites. Despite differing plant assemblages at each site, annual intake of nutrients by the lizards was similar among sites. The results best support the nutritional wisdom hypothesis; the Bonaire whiptail lizard may assemble its diet to obtain the proper balance of required nutrients, while avoiding dangerous levels of plant secondary compounds.