Final answer:
The California Ground Squirrel is less vigilant in larger groups due to the dilution effect, which lowers the risk of predation for individual squirrels. This communal advantage reduces the need for constant individual vigilance.
Step-by-step explanation:
The California Ground Squirrel spends less of their time being vigilant with increased group size because of the dilution effect (a). In the context of predation, the dilution effect refers to the decreased probability of an individual animal being preyed upon when it is part of a larger group. This effect essentially 'dilutes' the risk of predation for any single member of the group, as with more individuals present, the chance of being the one attacked by a predator is lower.
With a decreased individual risk, each ground squirrel does not have to be as vigilant in watching for predators because there are more eyes to detect threats, leading to an overall reduction in the amount of time and energy each squirrel must allocate to vigilance. This concept is well documented in prey species and highlights how social living can be an evolutionary advantage in terms of predator avoidance.