Optimal Body Size in Lesser Antillean Anolis Lizards‐‐A Mechanistic Approach

Abstract

For the past twenty years, it has been recognized that body size is convergent among solitary species of Anolis lizards endemic to different island banks of the Lesser Antilles. Community ecologists have assumed that this "solitary size" is an optimal size, yet the basis behind such optimality has not been shown. Our goal in this study was to explore the existence of an energetic basis of an optimal body size in these lizards. A computer model is presented that incorporates quantitative descriptions of lizard metabolism, locomotion, digestion, and visual acuity, and simulates foraging in a sit—and—wait predator. Quantitative estimates of daily foraging energetics are presented, which are then used together with estimates of resting metabolism to simulate growth. An optimal growth strategy is incorporated to determine adult body sizes that maximize lifetime reproductive output. Such optimal body sizes were determined for different prey densities and activity levels, predator life expectancies, and field metabolic rates. Predicted optimal body sizes are close to the observed body sizes of Lesser Antillean anoles, and are relatively insensitive to both levels of prey activity and up to fourfold differences in prey density, while life expectancy and rates of field metabolism may influence predictions. The insensitivity of predicted optimal body size to prey density lends support to the assumption that the solitary size observed among anoles throughout the Lesser Antilles is an optimal body size. Additional findings were made regarding home—range sizes, growth patterns, and visual constraints to foraging performance.