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, 7 (11), e50096

Cost of Living Dictates What Whales, Dolphins and Porpoises Eat: The Importance of Prey Quality on Predator Foraging Strategies

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Cost of Living Dictates What Whales, Dolphins and Porpoises Eat: The Importance of Prey Quality on Predator Foraging Strategies

Jérôme Spitz et al. PLoS One.

Abstract

Understanding the mechanisms that drive prey selection is a major challenge in foraging ecology. Most studies of foraging strategies have focused on behavioural costs, and have generally failed to recognize that differences in the quality of prey may be as important to predators as the costs of acquisition. Here, we tested whether there is a relationship between the quality of diets (kJ · g(-1)) consumed by cetaceans in the North Atlantic and their metabolic costs of living as estimated by indicators of muscle performance (mitochondrial density, n = 60, and lipid content, n = 37). We found that the cost of living of 11 cetacean species is tightly coupled with the quality of prey they consume. This relationship between diet quality and cost of living appears to be independent of phylogeny and body size, and runs counter to predictions that stem from the well-known scaling relationships between mass and metabolic rates. Our finding suggests that the quality of prey rather than the sheer quantity of food is a major determinant of foraging strategies employed by predators to meet their specific energy requirements. This predator-specific dependence on food quality appears to reflect the evolution of ecological strategies at a species level, and has implications for risk assessment associated with the consequences of changing the quality and quantities of prey available to top predators in marine ecosystems.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Differences between the quality of diets and the metabolic costs of living in cetaceans.
Means ± s.d. with different letters (a, b, c) show significantly different groups of cetaceans. A: Mean energy density of the diets (kJ⋅g−1 wet mass). B: Cost of living as measured by the mitochondrial density of the muscle. C: Cost of living as measured by the lipid content of the muscle (% dry mass). Colours reflect the group of similarity identified for the mean energy density of diets: Group a in red, Group b in green and Group c in blue.
Figure 2
Figure 2. Relationships between body mass, the quality of diet and the metabolic cost of living in cetaceans.
Cost of living is represented only by mitochondrial density of the muscle (lipid content of the muscle showed the same patterns but was measured for fewer species). Each data point represents a single individual. A: Mitochondrial density of the muscle as a function of log body mass (kg). B: Mean energy density of diets (kJ⋅g−1 wet mass) as a function of log body mass (kg). C: Mean energy density of diets as a function of mitochondrial density of the muscle.
Figure 3
Figure 3. Branching diagrams showing the ecological and evolutionary relationships among cetaceans.
Sizes of the cetaceans are shown to scale, and colours reflect whether the species have high (red), moderate (green) or low (blue) costs of living. A: The ecological strategy tree was produced using a cluster analysis of the three combined indicators (mitochondrial density of the muscle, lipid content of the muscle and diet quality). Species are arranged from highest (top) to lowest (bottom) costs of living. B: The actual cetacean phylogenetic tree . Species are grouped by family from top to bottom into Phocoenidae (harbour porpoise); Delphinidae (bottlenose, striped and common dolphins, and long-finned pilot whale), Ziphiidae (Cuvier's beaked whale and Mesoplodon whales), Kogiidae (pygmy sperm whale), Physeteridae (sperm whale) and Balaenopteridae (minke and fin whales).

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Grant support

The data collection and analysis was funded by the French Ministry in charge of the Environment and the University of La Rochelle. JS was supported by the Agence Nationale de la Recherche Technique with a CIFRE grant. AWT was supported in part by the North Pacific Marine Science Foundation through the North Pacific Universities Marine Mammal Research Consortium. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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