I am pleased to announce the publication of a new paper entitled: "The
social structure and strategies of delphinds: Predictions based on an
ecological framework" by Shannon Gowans, Bernd Würsig and Leszek
Karczmarski in Advances in Marine Biology (2008) volume 53 pages 195-294.
Please contact me if you would like a pdf copy.
Thank you.
Shannon Gowans
[EMAIL PROTECTED]
Abstract
Dolphins live in complex social groupings with a wide variety of social
strategies.
In this chapter we investigate the role that differing habitats and
ecological
conditions have played in the evolution of delphinid social strategies. We
propose a conceptual framework for understanding natural patterns of
delphinid
social structure in which the spatial and temporal predictability of
resources
influences the ranging patterns of individuals and communities.
The framework predicts that when resources are spatially and temporally
predictable, dolphins should remain resident in relatively small areas.
Predictable
resources are often found in complex inshore environments where dolphins
may hide from predators or avoid areas with high predator density.
Additionally,
available food resources may limit group size. Thus, we predict that
there are few
benefits to forming large groups and potentially many benefits to being
solitary
or in small groups. Males may be able to sequester solitary females,
controlling
mating opportunities. Observations of inshore populations of bottlenose
dolphins
(Tursiops sp.) and island-associated spinner dolphins (Stenella
longirostris) seem
to fit this pattern well, along with forest-dwelling African antelope
and primates
such as vervets (Cercopithicus aethiops), baboons (Papio sp.),macaques
(Macaca
sp.) and chimpanzees (Pan troglodytes).
In contrast, the framework predicts that when resources such as food are
unpredictable, individuals must range further to find the necessary
resources.
Forming groups may be the only strategy available to avoid predation,
especially
in the open ocean. Larger home ranges are likely to support a greater
number of individuals; however, prey is often sparsely distributed,
which may
act to reduce foraging competition. Cooperative foraging and herding of prey
schools may be advantageous, potentially facilitating the formation of
longterm
bonds. Alternately, individuals may display many short-term affiliations.
These large groups make it difficult for a male or a small group of males to
sequester a female, and polygynandry is the most likely mating strategy.
While
it is difficult to study wide-ranging delphinids to examine these
predictions, this
ranging and behavioural pattern has been suggested for dusky dolphins
(Lagenorhynchus obscurus), coastal bottlenose dolphins (Tursiops sp.) and
mixed species of dolphins in the Eastern Tropical Pacific. These
patterns also
resemble the ranging and social strategies of open savannah African
antelopes
and desert-dwelling macropods.
Resource availability exists in a range of complex distributions and we
predict
that delphinid ranging patterns will also vary. At intermediate-ranging
patterns,
the framework predicts that individuals should form mid-sized groups
balancing
intra-group competition with predation protection. Humpback dolphins
(Sousa sp.) appear to fit this pattern, with some site fidelity over
relatively
large ranges. They display fluid associations with other individuals.
Predation
pressure is not sufficiently high to cause large groups to form, and
individuals
probably reduce predation pressure more by hiding whenever possible. This
pattern is likely to prevent the formation of long-term complex bonds. In
contrast, killer whales (Orcinus orca) also display intermediate-ranging
patterns,
but have extremely strong social bonds within familial groups. Cooperative
and altruistic behaviour in killer whales facilitate the formation of
life-long
bonds, similar to those observations in sperm whales (Physeter
macrocephalus)
and elephants (Loxodonta africana).
This conceptual framework remains largely untested, and for many species it
is not currently possible to describe ranging behaviours, anti-predator
tactics or
social behaviour in sufficient detail for appropriate examination of
these ideas.
Few studies on dolphins have been conducted to explicitly test this type of
framework; however, existing observations of delphinid social strategies and
communities are used throughout this chapter to examine this framework.
Additionally, we anticipate that the present framework may provide a
starting
point to test hypotheses regarding the evolution of social strategies of
delphinids.
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title:Assistant Professor
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