Answer:
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. The population growth and decline of species depends on the amount of their food availability. The more available food, the more the population grows to meet it. The less nutritious food, the less fertile a species of reproductive age becomes. 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 the growth of a population. For instance, 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.
Direct human impacts are not the only ways humans can control animal populations. Often times, humans are indirectly controlling animal populations, in other words, the humans are not aware that their actions are controlling animal populations. For example, new infrastructure and roads can lead to animals being displaced from their natural habitat. Their new habitats that they are forced to move to may not provide the same necessities to them that they require for survival. This will result in a decreasing population as a result of human actions.