Biology Reference
In-Depth Information
CHAPTER 6
Living in Groups
Photo © iStockphoto.com/stevedeneef
Animal groups provide some of the most remarkable spectacles of the natural world. In
winter, as dusk falls, flocks of starlings,
Sturnus vulgaris
, fly from the fields where they
have been foraging all day towards their night-time roosts, such as buildings in city
centres or woods in the countryside. From all directions they come, congregating into a
vast flock, often with tens or hundreds of thousands of individuals wheeling in ever-
changing smoke-like formations before they go to roost. In the seas, vast shoals of fish
perform similar, spectacular coordinated movements, circling in a tight sphere, forming
a torus (a doughnut-like shape with a hollow centre), or suddenly scattering in all
directions with flashes of silver (Fig. 6.1).
In this chapter we shall first consider why individuals often form groups like these,
despite the potential costs of increased competition for resources and infection by
pathogens. There are many potential benefits of group living, including protection from
climatic extremes (e.g. huddling for warmth) and aerodynamic or hydrodynamic
advantages in locomotion, but we shall focus on two main benefits, namely reducing
predation and improving foraging success (Table 6.1). We shall also analyse the costs
and benefits of different group sizes. Is there an optimal group size to maximize
individual fitness? How can grouping be stable despite individual conflicts of interest?
Finally, we shall consider the mechanisms of group decision making. How do groups
make such wonderful, coordinated movements? How do groups decide when and where
to go next? Are there leaders and followers? Or do individuals reach a consensus
by voting?
Questions about
grouping
behaviour
