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Populations • A population - a group of organisms of the same species in the same area. Population Topics A. What affects population size B. Population growth patterns C. Limits to population growth • “Analyzing Data” • Make a graph showing fruit fly population growth • Make a graph showing rabbit population growth Page 123 A. Population Size • Factors that increase population size: • Natality (births) • Immigration • Factors that reduce population size: • Mortality • Emigration • Calculate the Population Size of Akron, CO: • • • • • In 2010, there were 1400 residents. 92 babies born 47 new people moved there 88 people died 41 people moved away • IN 2011: 1410 residents! B. Population Growth Exponential Growth • Under ideal conditions with unlimited resources, a population will grow exponentially. • Exponential growth occurs when the individuals in a population reproduce at a constant rate. • The population becomes larger and larger until it approaches an infinitely large size. Logistic Growth • As resources become less available, the growth of a population slows or stops. • Logistic growth occurs when a population's growth slows or stops following a period of exponential growth Logistic Growth – 3 phases Logistic Growth – 3 phases 1. Exponential Growth Phase – there is unlimited growth of the population due to absence of limiting factors. • Examples: • germinating annual plants in a new season. • a bacterial population during the initial phases of an infection. • The population of any species occupying a previously unoccupied habitat Logistic Growth – 3 phases 2. Transitional Phase – limiting factors start influencing the rate of increase of the population. Population is still increasing, but not as rapidly. Examples: • Organisms start competing with each other for available resources • Survival of the fittest • predators move in Logistic Growth – 3 phases 3. Plateau Phase – Population stops increasing, due to limiting factors. The population has reached its carrying capacity. Natality + Immigration = Mortality + Emigration Carrying Capacity – the maximum number of individuals of a species that can be supported by the environment. • What are some things that would limit: • Plant population growth? • Animal population growth? Think with a partner C. Limiting Factors 1. Animals • • • • Amount of food available Presence of diseases or parasites Amount of predation Available nesting sites 2. Plants • • • • Amount of light available Temperature Amount of water available Space