An example of parasitism in the desert is a flea living on a coyote. The flea drinks the blood from the coyote, deriving nutritional benefit. However, the coyote does not benefit; instead, it loses vital blood and experiences pain from the process. Also, the coyote could develop diseases.
A parasitic relationship involves two organisms, but only one benefits. By taking needed nutrients from the organism, the parasite benefits itself over time, but the host organism suffers a result, often losing needed nutrients and other substances to the parasite.
Desert mistletoe is a plant that grows on desert willow trees. The mistletoe attaches to the willow tree and takes the nutrients that it needs from the willow. This does not harm the willow tree, as long as the willow is taking in enough water and nutrients for itself and the desert mistletoe. However, if the environmental conditions change and the willow tree no longer receives the nutrients that both organisms need to survive, the mistletoe takes the nutrients before the willow tree can process them for itself. As a result, the willow tree eventually dies if the environment does not change, while the mistletoe thrives until the willow has died and can no longer sustain the mistletoe.