There are also strong selective pressures that can act against aggregation in space or time. In some species a group of individuals may actually concentrate a predator's attention (the opposite effect to the 'selfish herd'). However, the foremost diluting forces are certain to be the more intense competition suffered by crowded individuals (see Chapter 5) and the direct interference between such individuals even in the absence of a shortage of resources. One likely consequence is that the highest rates of dispersal will be away from the most crowded patches: density-dependent emigration dispersal (Figure 6.6) (Sutherland et al., 2002), though as we shall see below, density-dependent dispersal is by no means a general rule.
Overall, though, the types of distribution over available patches found in nature are bound to be compromises between forces attracting individuals to disperse towards one another and forces provoking individuals to disperse away from one another. As we shall see in a later chapter, such compromises are conventionally crystallized in the 'ideal free' and other theoretical distributions (see Section 9.6.3).
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