Shifts in mass scaling of respiration, feeding, and growth rates across life-form transitions in marine pelagic organisms.

The metabolic rate of organisms may be viewed as a basic property from which other vital rates and many ecological patterns emerge and that follows a universal allometric mass scaling law, or it may be considered a property of the organism that emerges as a result of the adaptation to the environment, with consequently fewer universal mass scaling properties. Here, we examine the mass scaling of respiration and maximum feeding (clearance and ingestion rates) and growth rates of heterotrophic pelagic organisms over an ∼10(15) range in body mass. We show that clearance and respiration rates have life-form-dependent allometries that have similar scaling but different intercepts, such that the mass-specific rates converge on a rather narrow size-independent range. In contrast, ingestion and growth rates follow a near-universal taxa-independent ∼3/4 mass scaling power law. We argue that the declining mass-specific clearance rates with size within taxa is related to the inherent decrease in feeding efficiency of any particular feeding mode. The transitions between feeding mode and simultaneous transitions in clearance and respiration rates may then represent adaptations to the food environment and be the result of the optimization of trade-offs that allow sufficient feeding and growth rates to balance mortality.