. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 286 C. K. HEMELRIJK animals when unfamiliar individuals are put in a group to- gether, but the decline of aggression has so far never been attributed to a widening of the group.) A consequence of the decline of aggression is that the hierarchy becomes more stable ((3) in Fig. 3). Further, because low-ranking individuals flee from everyone else, they end up at the periphery of the group; this automatically leaves the dominants in the center ((5) in Fig. 3). This spatial structure develops in spite of a total lack of any prefe
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 286 C. K. HEMELRIJK animals when unfamiliar individuals are put in a group to- gether, but the decline of aggression has so far never been attributed to a widening of the group.) A consequence of the decline of aggression is that the hierarchy becomes more stable ((3) in Fig. 3). Further, because low-ranking individuals flee from everyone else, they end up at the periphery of the group; this automatically leaves the dominants in the center ((5) in Fig. 3). This spatial structure develops in spite of a total lack of any preference of the individuals to be in the center. Yet such a preference (a so-called centripetal instinct) is assumed in the "selfish herd" theory by Hamilton (1471). It is supposed to have been evolved because individuals are better protected in the center, where they are shielded on all sides from possible predators. However, the model shows that even without such a centripetal instinct, whenever the hierarchy is steep, we must expect a spatial structure with dominants in the center. Spatial centrality, in turn, stahili/.es the hierarchy and supports its differentiation ((5) and (6) in Fig. 3). This arises because the spatial structure causes individuals to be close to partners of similar dominance rank: therefore, if inciden- tally a dominance-reversal occurs, it is usually between individuals that are similar in dominance, and thus the extent to which dominance values are changed is only a minor one. In this way, the spatial structure strengthens the hierarchy ((?) and (6) in Fig. 3). This becomes evident when we eliminate spatial centrality. We can do this by decreasing the SearchAngle. If the SearchAngle for returning to the group is made smaller, so that individuals return more slowly and the group therefore spreads out more and more, no spatial structure develops. In this case (for the same number of dominance interactions), the hierarchy becomes weaker (, dom
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
