Spatial positioning in the selfish herd
Authored by Graeme D Ruxton, Lesley J Morrell, Richard James
Date Published: 2011
DOI: 10.1093/beheco/arq157
Sponsors:
United Kingdom Natural Environment Research Council (NERC)
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Model Documentation:
Other Narrative
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Abstract
The antipredator benefits of grouping are relatively well understood;
however, predation risk often differs for individuals that occupy
different positions within a group. The selfish herd hypothesis
describes how individuals can reduce risk of predation by moving to
specific positions within the group. In existing theory, this movement
occurs through the adoption of possible ``movement rules{''} that differ
in their cognitive complexity. Here, we investigate the effectiveness of
different previously suggested rules in reducing risk for central and
peripheral individuals within a group. We demonstrate that initial
spatial position is important in determining the success of different
risk-reducing movement rules, as initially centrally positioned
individuals are likely to be more successful than peripheral ones at
reducing their risk relative to other group members, regardless of the
movement rules used. Simpler strategies are effective in low-density
populations; but at high density, more complex rules are more effective.
We also find that complex rules that consider the position of multiple
neighbors are the only rules that successfully allow individuals to move
from peripheral to central positions or maintain central positions, thus
avoiding predators that attack from outside the group. Our results
suggest that the attack strategy of a predator should be critically
important in determining prey escape strategies in a selfish herd
context and that prey should modify their behavioral responses to
impending attack in response to their position within a group.
Tags
Segregation
Predation risk
Model
Animal groups
Attack
Avoidance
Aggregation behavior
Size choice
Fish
shoals
Danger