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Bell Ringer: 3 Factors that affect population size: – Number of Births – Number of Deaths – Number of individuals entering or leaving a population (immigration vs. emigration) • Increase: births and immigration • Decrease: deaths and emigration Limits to Growth Section 5-2 Flora Limits to Growth Limiting Factor – factor that causes population growth to decrease Ex: – Competition – Predation – Parasitism – Human disturbances – Climate Extremes Types of Factors Density-dependent Density-independent Density-Dependent Factors DDLF – limiting factor that depends on population size These factors become limiting only when the population density reaches a certain level Usually occurs when population is large and dense Ex: competition, predation, parasitism, disease Competition Can occur within species or between different species More individuals leads to depleted resources Less individuals leads to less competition Predation Populations are often controlled by predation Predator prey relationships – mechanism of population control in which a population is regulated by predation Ex: page 126; figure 5-7 Parasitism and Disease Organisms are similar to predators Take nourishment at the expense of their hosts Density-Independent Factors Affect all populations in similar ways regardless of population size Ex: – – – – Weather Natural disaster Season cycles Human activities ** Populations often show rapid declines in these situations