What is not an impact that an invasive non-native species has on an ecosystem?
a) change food webs
b) decrease biodiversity
c) prey on native species
d) improves forest productivity and overall health

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.