Aparticular species of seabird has a mutation in the gene pool that gives it a bigger beak. individuals with this mutation can more easily break open clams and other mollusks for food. they can also defend themselves better against predators. over time, most of the organisms in the population have big beaks. what’s this an example of

Natural Selection in the process of Darwin's Evolution theory. 

The rate that would change would be the  searching efficiency/attack rate. there are only two other rates in this model: the  growth rate of prey, and the  predator or consumer mortality rate.the  searching efficiency/attack rate is what indicates how effectively can a predator capture its prey whether in the searching process or actual capturing/attacking process.