After the third hour, there should be 8000 bacteria in the flask. In another hour, each of the 2000 bacteria will divide, producing 4000 bacteria. If 1000 bacteria are placed in a large flask with an abundant supply of nutrients (so the nutrients will not become quickly depleted), the number of bacteria will have doubled from 1000 to 2000 after just an hour. This division takes about an hour for many bacterial species. Bacteria are prokaryotes that reproduce largely by binary fission. The best example of exponential growth in organisms is seen in bacteria. Malthus published a book in 1798 stating that populations with unlimited natural resources grow very rapidly, which represents an exponential growth, and then population growth decreases as resources become depleted, indicating a logistic growth. Exponential GrowthĬharles Darwin, in his theory of natural selection, was greatly influenced by the English clergyman Thomas Malthus. Neither model adequately describes natural populations, but they provide points of comparison. The second model, logistic growth, introduces limits to reproductive growth that become more intense as the population size increases. The first of these models, exponential growth, describes theoretical populations that increase in numbers without any limits to their growth. The two simplest models of population growth use deterministic equations (equations that do not account for random events) to describe the rate of change in the size of a population over time. An accurate model should be able to describe the changes occurring in a population and predict future changes. Population ecologists make use of a variety of methods to model population dynamics. Compare and contrast density-dependent growth regulation and density-independent growth regulation giving examples.Give examples of how the carrying capacity of a habitat may change.Give examples of exponential and logistic growth in natural populations.Explain the characteristics of and differences between exponential and logistic growth patterns.Learning Objectives By the end of this section, you will be able to:
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