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BIOLOGY CHAPTER 5 POPULATIONS SECTION 1. HOW POPULATIONS GROW Edited for Keystone content emphasis The study of population increases and decreases is called population dynamics. Population Growth Three factors can affect population size: • the number of births • the number of deaths • the number of individuals that enter or leave the population A population can grow when its birthrate is greater than its death rate. Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall Exponential Growth Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall Logistic growth is characterized by an S-shaped curve. Copyright Pearson Prentice Hall SECTION 2. LIMITS TO GROWTH Limiting Factors • The primary productivity of an ecosystem can be reduced when there is an insufficient supply of a particular nutrient. • Ecologists call such substances limiting nutrients. Copyright Pearson Prentice Hall • A limiting nutrient is an example of a more general ecological concept: a limiting factor. • In the context of populations, a limiting factor is a factor that causes population growth to decrease. Copyright Pearson Prentice Hall Examples: • Growth of the population of a predator is limited by the amount of prey. • Availability of sunlight limits the growth of phytoplankton in the deep ocean. The largest size population that can be supported by the ecosystem is the carrying capacity. A population may temporarily grow past the carrying capacity, but this cannot be sustained; eventually a resource will run out and it must decrease back to the carrying capacity. The carrying capacity can change if conditions change. Example: elimination of predators such as wolves can increase the ecosystem’s carrying capacity for deer. Predation Populations in nature are often controlled by predation. The regulation of a population by predation takes place within a predator-prey relationship, one of the best-known mechanisms of population control. Copyright Pearson Prentice Hall Ex. - hare and lynx in Northern Canada • Prey population decreases, less food for predators. They decrease. • Prey population can then increase. • This gives more food for predators, so they increase, etc. www.math.duke.edu The wolves and moose of Isle Royale in Lake Superior have been studied since 1958 Wolf and Moose Populations on Isle Royale Copyright Pearson Prentice Hall