One example of parasitism that occurs in grassland biomes involves the cowbird. This brood parasite lays its eggs in the nests of other bird species in the grasslands, resulting in the other species oftentimes hatching the eggs and even raising the young. The cowbird gets the benefit of passing its genes on to the next generation without having to go through the effort of raising it.
In a parasitic relationship, one species receives an important element of sustenance from another. In some cases, the parasitic relationship leads to the death of the host, but in others, it simply leads to a degree of harm. Because the parasite relies on its host, its best interest lies in the continued thriving of the host. As a result, the parasite and host often evolve together, going through adaptations to improve their own chances of survival. Some hosts even form symbiotic relationships with a third organism to fight off the parasite.
Not all parasitic relationships involve animals, though. The herb genus Rhinanthus is considered parasitic because of the way it gains sustenance. Rhinanthus attaches itself to the roots of other plants and diverts a great deal of the water and nutrients to itself. When Rhinanthus is present, the grasses receive fewer nutrients and are less dominant in the biome, permitting the Rhinanthus and other herbs to grow as well.