Which model suggests that both sensitization and habituation occur in response to every stimulus presentation, and that it is the summed combination of these two independent processes that determines the strength of responding?

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.

it should be briana that has it to me

your spelling is a little off : ]