Abstract:
Dilution of predation risk within groups allows individuals
to be less vigilant and forage more while still facing lower risk
than if they were alone. How group size influences vigilance when
individuals can also adjust their space use and whether this relationship
differs among individuals contributing differently to space use
decisions remain unknown.We present a model-based study of how dilution
affects the optimal antipredator behavior of group members in
groups where all individuals determine their vigilance level while group
leaders also determine space use.We showed that optimal vigilance did
not always decrease with group size, as it was sometimes favorable for
individuals in larger groups to use riskier patches while remaining vigilant.
Followers were also generally less vigilant than leaders. Indeed,
followers needed to acquire more resources than leaders, as only the latter
could decide when to go to richer patches. Followers still benefit
from dilution of predation risk compared with solitary individuals.
For leaders, keeping their leadership status can be more important than
incorporating new group members to increase dilution. We demonstrate
that risk dilution impacts both optimal vigilance and space use,
with fitness reward being tied to a member’s ability to influence group
space use.
