58
P.P. Molloy et al.
An understanding of the proximate and evolutionary causes and consequences of
spawning aggregations will provide new insight into the taxonomic and geographic
distribution of aggregation-spawning, as well as the potential impacts of heavy
exploitation on these species.
3.1 Introduction
Two types of questions can be asked about animal behaviour: how and why. The
former addresses real-time stimuli for behaviours such as hormonal or environmental
cues; the latter addresses the evolutionary benefi t afforded by a particular behaviour
and is the stuff of behavioural ecology. In this chapter, we provide a behavioural
ecological perspective of the phenomenon of aggregation-spawning.
One area of research that has captivated behavioural ecologists for a long time is
why organisms form groups (Krause and Ruxton 2002 ) . Of particular interest are
those species that are solitary most of their lives but form aggregations to breed.
Although fi sh species have been used as model systems for research into virtually
all types of reproduction, fi sh breeding aggregations (or spawning aggregations)
have received comparatively little attention. A spawning aggregation is a grouping
of a single fi sh species that has gathered at a specifi c location, at a density that is at
least four-times greater than normal, with the specifi c purpose of reproducing
(Chap. 1 ). To form aggregations, fi sh may travel very long distances. For example,
some Nassau groupers, Epinephelus striatus , travel hundreds of kilometres to
spawning sites (Bolden 2000 ) . The resulting aggregations may comprise dozens
to tens of thousands of individuals and can offer a breathtaking visual spectacle.
The scarcity of behavioural research on spawning aggregations may be largely
due to the logistical diffi culties associated with accessing aggregations and manipulating them experimentally (Claydon 2004 ) . However, fi sh spawning aggregations
need not remain an unsolved mystery. The theoretical frameworks developed
through studies of other group-breeding taxa allow us to cast some indirect light on
spawning aggregations in fi shes and derive some insight into their possible evolutionary advantages. Our objective in this chapter is to use a behavioural ecological
perspective to explore the costs and benefi ts of aggregating to breed, to examine the
mating systems and reproductive behaviours of a range of aggregation-spawning
species and to draw parallels with similar mating systems in a diversity of other
taxa. Finally, we formulate novel predictions tailored specifi cally to aggregating
fi shes and suggest ways in which they may be tested.
3.2 General Overview of the Adaptive Signifi cance
of Reproductive Aggregations
There are two general explanations for the evolution of reproductive aggregations in
animals, irrespective of the time and place of reproduction. First, limitation of suitable space or habitat can force animals to occupy higher densities than they would
P.P. Molloy et al.
An understanding of the proximate and evolutionary causes and consequences of
spawning aggregations will provide new insight into the taxonomic and geographic
distribution of aggregation-spawning, as well as the potential impacts of heavy
exploitation on these species.
3.1 Introduction
Two types of questions can be asked about animal behaviour: how and why. The
former addresses real-time stimuli for behaviours such as hormonal or environmental
cues; the latter addresses the evolutionary benefi t afforded by a particular behaviour
and is the stuff of behavioural ecology. In this chapter, we provide a behavioural
ecological perspective of the phenomenon of aggregation-spawning.
One area of research that has captivated behavioural ecologists for a long time is
why organisms form groups (Krause and Ruxton 2002 ) . Of particular interest are
those species that are solitary most of their lives but form aggregations to breed.
Although fi sh species have been used as model systems for research into virtually
all types of reproduction, fi sh breeding aggregations (or spawning aggregations)
have received comparatively little attention. A spawning aggregation is a grouping
of a single fi sh species that has gathered at a specifi c location, at a density that is at
least four-times greater than normal, with the specifi c purpose of reproducing
(Chap. 1 ). To form aggregations, fi sh may travel very long distances. For example,
some Nassau groupers, Epinephelus striatus , travel hundreds of kilometres to
spawning sites (Bolden 2000 ) . The resulting aggregations may comprise dozens
to tens of thousands of individuals and can offer a breathtaking visual spectacle.
The scarcity of behavioural research on spawning aggregations may be largely
due to the logistical diffi culties associated with accessing aggregations and manipulating them experimentally (Claydon 2004 ) . However, fi sh spawning aggregations
need not remain an unsolved mystery. The theoretical frameworks developed
through studies of other group-breeding taxa allow us to cast some indirect light on
spawning aggregations in fi shes and derive some insight into their possible evolutionary advantages. Our objective in this chapter is to use a behavioural ecological
perspective to explore the costs and benefi ts of aggregating to breed, to examine the
mating systems and reproductive behaviours of a range of aggregation-spawning
species and to draw parallels with similar mating systems in a diversity of other
taxa. Finally, we formulate novel predictions tailored specifi cally to aggregating
fi shes and suggest ways in which they may be tested.
3.2 General Overview of the Adaptive Signifi cance
of Reproductive Aggregations
There are two general explanations for the evolution of reproductive aggregations in
animals, irrespective of the time and place of reproduction. First, limitation of suitable space or habitat can force animals to occupy higher densities than they would