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Population control is the practice of artificially altering the size of any population. It typically refers to the act of limiting the size of an animal population so that it remains manageable, as opposed to the act of protecting a species from excessive rates of extinction, which is referred to as conservation biology. ==Factors influencing population control== Population control can be influenced by a variety of factors. Humans can greatly influence the size of animal populations they directly interact with. It is for example relatively common (and sometimes even a legal requirement) to spay or neuter dogs. Spaying - removing the ovaries and uterus of a female animal - medical term = ovariohysterectomy. Neutering - removing the testes of a male animal - medical term = orchiectomy. Various humans activities (e.g. hunting, farming, fishing, industrialization and urbanization) all impact various animal populations. Population control may involve culling, translocation, or manipulation of the reproductive capability. The growth of a population may be limited by environmental factors such as food supply or predation. The main biotic factors that affect population growth include: *Food- both the quantity and the quality of food are important. Snails, for example, cannot reproduce successfully in an environment low in calcium, no matter how much food there is, because they need this mineral for shell growth. *Predators- as a prey population becomes larger, it becomes easier for predators to find prey. If the number of predators suddenly falls, the prey species might increase in number extremely quickly. *Competitors- other organisms may require the same resources from the environment, and so reduce growth of a population.For example, all plants compete for light. Competition for territory and for mates can drastically reduce the growth of individual organisms. *Parasites- These may cause disease, and slow down the growth and reproductive rate of organisms within a population. Important Abiotic factors affecting population growth include: *Temperature- Higher temperatures speed up enzyme-catalyzed reactions and increase growth. *Oxygen availability- affects the rate of energy production by respiration. *Light availability- for photosynthesis. light may also control breeding cycles in animals and plants. *Toxins and pollutants- tissue growth can be reduced by the presence of, for example, sulphur dioxide, and reproductive success may be affected by pollutants such as estrogen like substances. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「population control」の詳細全文を読む スポンサード リンク
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