What would be a likely effect of increased body mass on metabolic rate?

Increased body mass generally leads to an increased metabolic rate because larger bodies have a higher demand for energy to maintain physiological functions such as cellular respiration, tissue growth, and the maintenance of body temperature. As an organism grows or gains mass, it typically requires more energy to support its greater muscle mass, organ function, and other metabolic activities.

This relationship is often described in metabolic scaling laws, where metabolic rate does not just increase linearly with mass but follows a power function, typically increasing at a rate that is less than proportional to mass but still overall resulting in greater energy demands for larger animals.

Thus, the increased metabolic activity associated with a larger body mass reflects the enhanced energy requirements necessary for sustaining life processes and physical activity.