What factors drive the movements of global air masses

The 4 types of air masses are polar, tropical, continental and maritime. Their classification depends on their location where they are formed.

Explanation:

One major influence of air mass movement is the upper level winds such as the upper level winds associated with the jet stream. The jet stream wind is often referred to as a steering wind. The troughs and ridges of the jet stream will help transport cold air toward lower latitudes and warm air toward high latitudes.

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sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.