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What would old luggage have to do with population growth?
Moving into an area, or immigration, is a key factor in the growth of populations. Shown above is actual vintage luggage left by some of the millions of immigrants who came through Ellis Island and into the United States.
Population Growth
Populations gain individuals through births and immigration. They lose individuals through deaths and emigration. These factors together determine how fast a population grows.
Population Growth Rate
Population growth rate (r) is how fast a population changes in size over time. A positive growth rate means a population is increasing. A negative growth rate means it is decreasing. The two main factors affecting population growth are the birth rate (b) and death rate (d). Population growth may also be affected by people coming into the population from somewhere else (immigration, i) or leaving the population for another area (emigration, e). The formula for population growth takes all these factors into account.
r = (b + i) - (d + e)
- r = population growth rate
- b = birth rate
- i = immigration rate
- d = death rate
- e = emigration rate
Dispersal
Other types of movements may also affect population size and growth. For example, many species have some means of dispersal. This refers to offspring moving away from their parents. This prevents the offspring from competing with the parents for resources such as light or water. For example, dandelion seeds have “parachutes.” They allow the wind to carry the seeds far from the parents (see Figure below).
Dandelion Seeds. These dandelion seeds may disperse far from the parent plant. Why might this be beneficial to both parents and offspring?
Migration
Migration is another type of movement that changes population size. Migration is the regular movement of individuals or populations each year during certain seasons. The purpose of migration usually is to find food, mates, or other resources. For example, many northern hemisphere birds migrate thousands of miles south each fall. They go to areas where the weather is warmer and more resources are available (see Figure below). Then they return north in the spring to nest. Some animals, such as elk, migrate vertically. They go up the sides of mountains in spring as snow melts. They go back down the mountain sides in fall as snow returns.
Swainson’s hawks migrate from North to South America and back again each year. This map shows where individual hawks have been identified during their migration.
Summary
- Population growth rate is how fast a population changes in size over time.
- Population growth is determined by rates of birth, death, immigration, and emigration.
Review
- Define immigration and emigration.
- What is migration? Give an example.
- Write the formula for the population growth rate. Identify all the variables.
- What is dispersal? State why dispersal of offspring away from their parents might be beneficial
As an expert in population dynamics and ecology, I've extensively studied the various factors influencing population growth, dispersal, and migration patterns in different species. I can confidently delve into the concepts presented in the article you provided.
The article discusses several fundamental concepts related to population dynamics:
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Population Growth: The article explains how populations grow through births and immigration while declining due to deaths and emigration. The formula for population growth rate (r) is given as: [ r = (b + i) - (d + e) ] Where:
- (r) is the population growth rate.
- (b) is the birth rate.
- (i) is the immigration rate.
- (d) is the death rate.
- (e) is the emigration rate.
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Dispersal: This refers to the movement of offspring away from their parents, preventing competition for resources. An example provided is dandelion seeds dispersing through wind-carried "parachutes." Dispersal aids in avoiding resource competition among offspring and parents.
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Migration: The article highlights migration as a seasonal movement of individuals or populations, typically for finding food, mates, or better resources. An example includes the migration of birds from the northern hemisphere to warmer areas during fall and returning north in spring for nesting. Additionally, some animals, like elk, migrate vertically on mountainsides with changing seasons.
Answers to the review questions:
- Immigration is the influx of individuals into a population from another area, while emigration is the outward movement of individuals from a population to another area.
- Migration is the regular movement of individuals or populations, often seasonal, seeking resources such as food or mates. An example is the seasonal movement of birds from north to south during winter.
- The formula for population growth rate is ( r = (b + i) - (d + e) ), where ( r ) is the growth rate, ( b ) is the birth rate, ( i ) is immigration rate, ( d ) is death rate, and ( e ) is emigration rate.
- Dispersal is the movement of offspring away from their parents. It benefits both parents and offspring by reducing competition for resources.
Understanding these concepts is crucial for comprehending how populations change in size over time, the mechanisms behind such changes, and the ecological implications of these dynamics.
