In a food web the arrows indicate energy being transferred to the animal it's pointing to from the animal it's pointing away from. In other words the arrow points at the animal that ate the one it is pointing away from. Since the Mountain Lion has the most arrows pointing to it, it's the highest predator in this food web. Since it is at the top it is a tertiary consumer.
A tertiary consumer is an animal that eat primary consumers and secondary consumers. From this knowledge we can conclude that the tertiary consumer is the mountain lion since nothing consumes the animal and it is on the top of the food web for consuming the most energy.
