Final answer:
The population will be oscillating when the prey isocline turns in a counterclockwise motion indicating a cyclical interaction between predator and prey populations based on the Lotka-Volterra model.
Step-by-step explanation:
When the prey isocline turns up in a counterclockwise motion where they cross on the predator isocline, the population will be oscillating. This indicates an ongoing cycle where prey populations increase, leading to an increase in predator populations. Subsequently, the predator population's increase causes a decrease in prey numbers, which then leads to a decrease in predator numbers, and the cycle repeats. This is reflective of Lotka-Volterra predator-prey model which shows the interdependent fluctuations of predator and prey populations over time.