Two European men and two Polynesian women settled on a previously uninhabited tropical island. All four of the settlers have brown eyes, a dominant trait, but one of the Europeans is heterozygous and carries the recessive gene for blue eyes.
After several generations, 35 percent of the island population is found to have AB+ blood. This is much higher than the percentage of AB+ people in the populations from which the original settlers came. The high percentage of AB+ blood is probably due to:

founder effect

Explanation:

When a few individuals from a population migrate to some new habitat and start a new population, the gene pool of the new population may not have the same allele frequencies as that of the original population. This change in the allele frequency of the new population is called the founder effect. In the given population, the increased frequency of the AB+ phenotype might have resulted from the founder effect. This is a chance event that occurs when a few individuals with a small fraction of genetic variations found a new population.

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 would be heredity