Answer
Frequency of stimulus can change the force of muscle twitch.
Explanation
Twitch is tension produced by the contraction of a small muscle or it is muscle fasciculation. Its strength depends on the stimulation frequency. If the frequency is higher then temporal summation takes place and produce higher tension in the muscle. If the frequency is weak then less tension is produced in the muscle. This force also depends on the cross-sectional area of muscle.

Last option: Preserve an ecosystem

• The establishment of a bird reservation is a way to preserve an ecosystem because reservation provides suitable environment to organism. A healthy ecosystem means large number of biodiversity.
Answer:
Other species that rely on those fish would die off. The extinction of one species can lead to the extinction of another and so on.