Mathematical models allow researchers to make different predictions by varying assumptions. Which of the following parameters was an assumption varied by Lima, Valone, & Caraco (1985) in their model of squirrel food carrying?

A) Fitness increases with energy intake rate
B) Individuals vary in their mating behavior
C) Movement speed varies with the type of predator
D) Fitness increases as more time is spent away from trees
E) Female and male behavior differ