Populations are dynamic groups of organisms that change in size and composition over time. This lesson introduces ways to describe a population and estimate how many individuals it contains.
These measurements provide different information. A forest might contain many trees overall, but they could be spread across a large area and therefore have low density. Population size and density can affect reproduction, competition, and survival. For example, individuals in a low-density population may have difficulty finding mates, while individuals in a crowded population may face more competition or disease transmission.
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What is an ecological population?
All individuals of the same species living in a particular area with the potential to interact.
How does mark-and-recapture estimate population size?
Researchers mark and release an initial sample, then capture a second sample. The estimate is N≈RM×C, where M is initially marked, C is captured later, and R is marked animals recaptured.
What conditions help make mark-and-recapture estimates reliable?
Marks remain identifiable, marked animals mix evenly with the population, and marking does not substantially affect survival or recapture probability.
What is a population dispersion pattern?
The way individuals in a population are spaced within a habitat at a particular time.
What information does a life table organize?
Survival and death information by age interval, sometimes separately by sex.
Quiz questions
Assuming other influences do not alter population size, what happens when births exceed deaths?Answer: The population grows.
A life-table interval begins with 500 individuals, and 10 die during that interval. What is the mortality rate per 1,000 individuals alive at the start?Answer: 20 deaths per 1,000 individuals.
Which description best fits a Type I survivorship curve?Answer: Most individuals survive early and middle life, with mortality rising in old age.
Which description best fits a Type III survivorship curve?Answer: Mortality is high early in life, but early survivors may live much longer.
Which condition can contribute to uniform spacing among individuals in a population?Answer: Territorial behavior that keeps individuals apart.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.