Overpopulation is a phenomenon in which a species population becomes larger than the carrying capacity of its environment. Specifically, human overpopulation refers to the state whereby the human population rises to an extent exceeding the carrying capacity of the ecological setting. This can occur due to increased birth rates, lowered death rates, immigration, and medical breakthroughs. Overpopulation can lead to environmental deterioration, worsening quality of life, or even the disintegration of the population. In ecology, overpopulation causes the entire population of the species in question to become weaker, as no single individual is able to find enough food or shelter. Overpopulation is characterized by an increase in the diseases and parasite-load which live upon the species in question, as the entire population is weaker. Judgments regarding overpopulation involve both facts and values, and societies may be judged overpopulated when their human numbers cause impacts that degrade ecosystem services, decrease human health and well-being, or crowd other species out of existence.