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Chapter One: General Introduction
(Connor et al. 2000a). Despite these similarities, long-term studies revealed that the
fish-eating “resident” killer whales along the western coast of North America present
a particularly interesting system of social structure that has not been yet described in
any terrestrial mammal. Indeed, within these killer whale communities, neither males
nor females disperse from their natal group (while bonobo and chimpanzee females
do disperse). This pattern could be extended to other species of delphinids such as
the long-finned pilot whales (as suggested from molecular studies, Amos et al. 1993).
Although these comparisons appear as a promising framework to study the forces
behind the evolution of mammalian societies, it is obvious that such investigation is
still limited by the lack of knowledge on cetaceans in comparison to that available on
terrestrial mammals. Futhermore, the examples above illustrate the fact that it is not
simple to determine the evolutionary drivers behind the social patterns observed at
sea and on land.
1.3. Investigation of population structure
1.3.1. A challenging task in delphinid species
Populations constitute interbreeding units with more or less autonomous dynamics
and recruitment (but note that there are many different definitions of 'populations',
(Waples & Gaggiotti 2006)). Whilst the boundaries of some populations are rather
obvious, others are not. Yet, a crucial pre-requisite for management and effective
conservation of any population is a clear understanding of its structure within
demographic and evolutionary time scales (Lande & Barrowclough 1987, Taylor &
Dizon 1999). Note that in dolphin studies, and in analogy to primate studies, the
terms “community” or “society” (Struhsaker 1969) have often been employed as a
complement to, or instead of, the term “population” (e.g., Bigg 1982, Wells 1986).
Here, I will employ the definition proposed by Wells (1986, p19) for a dolphin
community: i.e., “an assemblage of dolphins that inhabited similar ranges and that
interacted socially more with each other than with adjacent assemblages”.
Investigating dolphin populations or communities poses a particular challenge
because of the lack of obvious geographical boundaries and because of the mobility
of individuals. It is hard to determine the population subdivisions of species that have
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