features of populations
what is a population
A population is a group of organisms of the same species, all living in the same area and interacting with each other. Since they live together in one area, members of the same species reproduce together. Ecologists who study populations determine how healthy or stable the populations are. They also study how the individuals of a species interact with each other and how populations interact with the environment. If a group of similar organisms in the same area cannot reproduce with members of the other group, then they are members of two distinct species and form two populations. Ecologists look at many factors that help to describe a population. First, ecologists can measure the number of individuals that make up the population, known as population size. They can then determine the population density, which is the number of individuals of the same species in an area. Population density can be expressed as number per area, such as 20 mice/acre, or 50 rabbits/square mile. Ecologists also study how individuals in a population are spread across an environment. This spacing of individuals within a population is called dispersion. Some species may be clumped or clustered ( Figure 1.1) in an area. Others may be evenly spaced ( Figure 1.2). Still others may be spaced randomly within an area. The population density and dispersion have an effect on reproduction and population size. What do you think the relationship is between population density, dispersion and size? Clumped species are closer together. This may allow for easier reproduction. A population of cacti in the Sonoran Desert generally shows even dispersion due to competition for water. Ecologists also study the birth and death rates of the population. Together these give the growth rate (the birth rate minus the death rate), which tells how fast (or slow) the population size is changing. The birth rate is the number of births within a population during a specific time period. The death rate is the number of deaths within a population during a specific time period. Knowing the birth and death rates of populations gives you information about a populations health. For example, when a population is made up of mostly young organisms and the birth rate is high, the population is growing. A population with equal birth and death rates will remain the same size. Populations that are decreasing in size have a higher death rate than birth rate.
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members of a species that are clumped together may have a better chance of reproducing.
--> a. true b. false
birth rate + death rate = growth rate
a. true --> b. false
10 spiders/square meter is an example of
a) population size. b) population dispersion. --> c) population density. d) all of the above
a population with equal birth and death rates
a) will grow in size. --> b) will remain the same size. c) will decrease in size. d) will fluctuate in size.
a population of mostly young organisms and a high birth rate will
--> a) grow in size. b) decrease in size. c) will stay the same size. d) will grow than drop in size.
individuals of zebra may showed clustered dispersion because
a) this makes hunting easier. --> b) this offers protection from predators. c) this allows them to save water. d) all of the above
which of the following statements is correct?
a) members of the same species that live in the same area can form two different populations. b) members of two species that live in the same area can form one population. --> c) members of two species that live in the same area form two different d) individuals of the same species that live in the same area but cannot reproduce form two different populations.
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