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Biology LibreTexts

45.4B: Overcoming Density-Dependent Regulation

  • Page ID
    14197
  • Humans have exceeded density-dependent limits on population by enacting various environmental changes to accommodate our needs for hygiene, shelter, and food.

    Learning Objectives

    • Describe ways in which humans overcome density-dependent regulation of population size

    Key Points

    • Humans’ ability to alter their environment is an underlying reason for human population growth, enabling people to overcome density-dependent limits on growth, in contrast with all other organisms.
    • Abilities, such as construction of shelter, food cultivation, and the sharing of technology, have helped humans overcome factors that would have otherwise limited their population growth.
    • Originating from Africa, human migration to nearly every inhabitable area of the globe has enabled colonization of areas where people were previously absent.
    • Advances in medicine, notably vaccines and antibiotics, as well as improvements in nutrition and vector control, have significantly curbed mortality from disease.

    Key Terms

    • density-dependent: Processes that occur when population growth rates are regulated by the size of a population in a given amount of resources such as food or habitat area.
    • vaccine: A substance given to stimulate the body’s production of antibodies and provide immunity against a disease, prepared from the agent that causes the disease, or a synthetic substitute.
    • infectious disease: Illness caused by introduction of a pathogen or parasite into the body via contact with a transmitting agent such as vector organism or an infected person.

    Humans are uniquely able to consciously alter their environment to increase its carrying capacity. This capability is an underlying reason for human population growth as humans are able to overcome density-dependent limits on population growth, in contrast with all other organisms.

    Human intelligence, society, and communication have enabled this capacity. For instance, people can construct shelters to protect them from the elements; food supply has increased because of agriculture and domestication of animals; and humans use language to pass on technology to new generations, allowing continual improvement upon previous accomplishments. Migration has also contributed to human population growth. Originating from Africa, humans have migrated to nearly every inhabitable area on the planet.

    Public health, sanitation, and the use of antibiotics and vaccines have lessened the impact of infectious disease on human populations. In the fourteenth century, the bubonic plague killed as many as 100 million people: between 30 to 60 percent of Europe’s population. Today, however, the plague and other infectious diseases have much less of an impact. Through vaccination programs, better nutrition, and vector control (carriers of disease), international agencies have significantly reduced the global infectious disease burden. For example, reported cases of measles in the United States dropped from around 700,000 a year in the 1950s to practically zero by the late 1990s. Globally, measles fell 60 percent from an estimated 873,000 deaths in 1999 to 164,000 in 2008. This advance is attributed entirely to a comprehensive vaccination program.

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    Measles cases reported in the United States, 1944-2007: Measles cases reported in the United States, represented as thousands of cases per year, declined sharply after the measles vaccine was introduced, in 1964.

    Developing countries have also made advances in curbing mortality from infectious disease. For example, deaths from infectious and parasitic diseases in Brazil fell from second place as the most important causes of death in 1977 to fifth place in 1984. The improvement is attributed in part to increased access to essential goods and services, reflecting the country’s rising prosperity. Through changes in economic status, as in Brazil, as well as global disease control efforts, human population growth today is less limited by infectious disease than has been the case historically.

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    Countries by Fertility Rate Comparison: The advent of modern medicine is very closely tied to childhood mortality, as well as the number of children per mother (Fertility Rate). As modern medicine decrease child mortality, the birth rate decreases.