95
chapter five
Feeding mechanisms
Christopher D. Marshall and Jeremy A. Goldbogen
5.1 Introduction
Feeding is an essential behavior that is required not only to sustain the organism but
also to acquire the energy needed for reproduction. Therefore, feeding adaptations are
directly tied to fitness and these phenotypes experience strong selection pressures. The
physical forces experienced in an aquatic environment impart strong selection pressures upon all vertebrates and have influenced the evolution of foraging strategies. This
basic conceptual framework is fundamental in understanding marine mammal feeding
mechanisms of a diverse guild of predators and grazers that evolved from terrestrial
ancestors. With respect to evolutionary history, marine mammals collectively represent a
paraphyletic group because several independent mammal lineages made this transition
back to aquatic environments at different evolutionary time scales. Mapping traits associated with different feeding mechanisms onto a phylogeny demonstrates a diversity of
feeding methods and foraging strategies among marine mammals. The ancestors of the
orders Cetacea and Sirenia were among the first mammals to make the transition back
to the sea, followed by pinnipeds (walruses, otariids, and phocids), sea otters, and polar
bears more recently. The selection pressure for these multiple re-invasions was abundant
food. Therefore, evolutionary innovations for specific feeding mechanisms and strategies
are driving factors in marine mammal evolution. This assemblage of marine mammal
lineages and the timing of their transition to a fully aquatic or semi-aquatic life history
manifest itself into a diversity of foraging strategies that we are only now beginning to
explore and appreciate.
Contents
5.1 Introduction .......................................................................................................................... 95
5.2 Knowledge by order ............................................................................................................ 96
5.2.1 Order Cetacea: Whales and dolphins ................................................................... 96
5.2.1.1 Cetacea: Odontoceti .................................................................................. 96
5.2.1.2 Cetacea: Mysticeti...................................................................................... 99
5.2.2 Order Sirenia: Manatees and dugongs ............................................................... 100
5.2.3 Order Carnivora: Pinnipedia ............................................................................... 102
5.2.3.1 Suction and biting feeding modes ........................................................ 105
5.2.4 Order Carnivora: Sea otters .................................................................................. 108
5.2.5 Order Carnivora: Polar bears ............................................................................... 109
5.3 Tools and methods for studying feeding strategies in marine mammals ................ 110
5.4 Future directions ................................................................................................................ 110
References .................................................................................................................................... 111
chapter five
Feeding mechanisms
Christopher D. Marshall and Jeremy A. Goldbogen
5.1 Introduction
Feeding is an essential behavior that is required not only to sustain the organism but
also to acquire the energy needed for reproduction. Therefore, feeding adaptations are
directly tied to fitness and these phenotypes experience strong selection pressures. The
physical forces experienced in an aquatic environment impart strong selection pressures upon all vertebrates and have influenced the evolution of foraging strategies. This
basic conceptual framework is fundamental in understanding marine mammal feeding
mechanisms of a diverse guild of predators and grazers that evolved from terrestrial
ancestors. With respect to evolutionary history, marine mammals collectively represent a
paraphyletic group because several independent mammal lineages made this transition
back to aquatic environments at different evolutionary time scales. Mapping traits associated with different feeding mechanisms onto a phylogeny demonstrates a diversity of
feeding methods and foraging strategies among marine mammals. The ancestors of the
orders Cetacea and Sirenia were among the first mammals to make the transition back
to the sea, followed by pinnipeds (walruses, otariids, and phocids), sea otters, and polar
bears more recently. The selection pressure for these multiple re-invasions was abundant
food. Therefore, evolutionary innovations for specific feeding mechanisms and strategies
are driving factors in marine mammal evolution. This assemblage of marine mammal
lineages and the timing of their transition to a fully aquatic or semi-aquatic life history
manifest itself into a diversity of foraging strategies that we are only now beginning to
explore and appreciate.
Contents
5.1 Introduction .......................................................................................................................... 95
5.2 Knowledge by order ............................................................................................................ 96
5.2.1 Order Cetacea: Whales and dolphins ................................................................... 96
5.2.1.1 Cetacea: Odontoceti .................................................................................. 96
5.2.1.2 Cetacea: Mysticeti...................................................................................... 99
5.2.2 Order Sirenia: Manatees and dugongs ............................................................... 100
5.2.3 Order Carnivora: Pinnipedia ............................................................................... 102
5.2.3.1 Suction and biting feeding modes ........................................................ 105
5.2.4 Order Carnivora: Sea otters .................................................................................. 108
5.2.5 Order Carnivora: Polar bears ............................................................................... 109
5.3 Tools and methods for studying feeding strategies in marine mammals ................ 110
5.4 Future directions ................................................................................................................ 110
References .................................................................................................................................... 111