Optimal body size and an animal's diet.

Area of Science:

• Ecology
• Evolutionary Biology
• Bioenergetics

Background:

• A common trend in animal taxa is that larger species consume lower-caloric food sources.
• Existing explanations based on energetics provide limits but not optima for body size.
• Large extant lizards, for example, are predominantly herbivorous, suggesting a link between size and diet quality.

Purpose of the Study:

• To develop a mathematical optimization model for determining optimum consumer body size.
• To investigate the influence of food search, capture, eating rates, and metabolic costs on body size.
• To reconcile model predictions with the observed trend of larger animals consuming lower-caloric foods.

Main Methods:

• Development of a simple optimization model incorporating energetic costs and rates of food acquisition.
• The model optimizes net daily calorie gain for consumers of varying body sizes.
• Analysis of the model's predictions regarding the effects of food quality, abundance, metabolic rate, and prey speed on optimum body size.

Main Results:

• The model predicts an optimum intermediate body size that increases with food quality.
• Body size is predicted to be more sensitive to increases in food abundance than food quality.
• Optimum consumer body size decreases with increased metabolic rate and prey speed.

Conclusions:

• The model explains the observed trend by linking large body size to the consumption of abundant, albeit low-quality, foods.
• Food abundance, in conjunction with food quality, is a critical factor in determining optimal body size.
• Energetic efficiency and resource availability are key drivers shaping body size evolution in animals.