In many hierarchical animal societies, dominant individuals control
group membership owing to their power to evict subordinates. In such
groups, the presence of subordinates, and therefore group stability, is
continually dependent on subordinates being tolerated by dominants.
The dominant decision to tolerate or evict is, in turn, dependent on the
costs and benefits to dominants of subordinate presence. We investigated
the effect of subordinate presence on dominants in the female
dominance hierarchy of the dwarf angelfish Centropyge bicolor, using both
observations of natural groups and experimental removals of subordinates.
We found that the presence of subordinates had no effect on
dominant access to resources, as measured by dominant foraging rates
and home range areas, nor on dominant fitness, as measured by growth
rates and spawning frequencies. Our results suggest that the presence of
subordinates has a neutral effect on the current fitness of dominants, so
that dominants have no great incentive to evict subordinates. We discuss
the possibility that tolerance of subordinates might be further
explained by considering future fitness, as dominant females in these
haremic protogynous angelfish stand to inherit the male position,
whereupon subordinate females change from potential competition to
useful mates.
Ethology
Ethology 117