Impala share the african plains with other grazing animals and predators. which change would lead to a decrease in the impala population?

Since impala and other grazing animals use the same food resources of the African plains, this is an example of competition. Competition is an interaction between members of the same species or between different species. If resources, such as food, water, sunlight, territory, are limited and several species depend on these resources, then, they must compete with other species to gain the resources. The more successful species in this competition will have more food resources for themselves, leaving less successful species (in this case impala) with less food. Without enough food, the population of the impala will decrease.

i think its the first one

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.