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Describing Populations

Describing Populations. From 1900 to 2000, the white-tailed deer population of New York state grew from about 20,000 to more than 1 million. Densities of more than 100 deer per sq mi occur in some metropolitan areas. Population Defined.

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Describing Populations

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  1. Describing Populations From 1900 to 2000, the white-tailed deer population of New York state grew from about 20,000 to more than 1 million. Densities of more than 100 deer per sq mi occur in some metropolitan areas.

  2. Population Defined • A population is all of the members of a species living together in the same place at the same time. • The word population can refer to the group in general and also to the size of the population or the number of individuals it contains. • An example of a population is all of the daisies found in a field in Latrobe, PA. They are NOT in the same population as all of the daisies found in a field in Buffalo, NY.

  3. Population Size • Population size describes the number of individual organisms present in a given population at a given time. • The overall health of a population can be indicated by monitoring how the population changes over time. Rapid decrease can be a red flag for extinction. • The story of the Passenger Pigeon. LINK Did You Know?The passenger pigeon was once North America’s most abundant bird. Hunting drove them to extinction in less than 100 years.

  4. Population Density • Population density describes the number of individuals within a population per unit area. • High population density can be good and bad. • The good: easy to group together, easy to find mates, protection from predators. • The bad: conflict, competition, disease transmission, vulnerability to predators, etc.

  5. Population Distribution • Populations can be distributed randomly, uniformly, or in clumps. • Random = individuals are arranged in a space in no particular pattern. • Uniform = individuals are evenly spaced throughout an area. • Clumped= organisms arrange themselves according to availability of resources needed to survive. This is the most common pattern.

  6. Age Structure and Sex Ratio • Different populations have different mixtures of ages and proportions of males and females. • Age structure describes the relative numbers of organisms of each age in a population. • Sex ratio is the proportion of males to females. Lack of balance can cause problems.

  7. Review Questions • How is a population’s size related to its well being? • Which population of flamingos is most dense: 15 flamingos in a 5-square meter area, or 40 flamingos in a 10 square meter area? • Paleontologists use fossils to study past life on Earth. Paleontologists have documented several times in Earth’s history when massive numbers of species have declined and then disappeared from the fossil record all at once. Why do you think population ecologists studying living organisms might be interested in these mass extinction events?

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