Chapter 7. Population Principles
Outline
Population Characteristics
A population Growth Curve
Human Population Growth
Conclusion
References
1. Population Characteristics
A population can be defined as a group of individuals of the same species inhabiting an area.
Natality refers to the number of individuals added to the population through reproduction over a particular time period. It is usually described in terms of the birthrate, the number of individuals born per 1000 individuals per year.
The growth of a population is not determined by the birthrate (natality) alone.
Mortality, the number of deaths in a population over a particular time period is also important.
The population growth rate is the birthrate minus the death rate.
The population growth rate is usually expressed as a percentage of the total population.
In human population studies, the population growth rate is usually expressed as a percentage of the total population.
The population growth rate is greatly influenced by sex ratio and age distribution of the population.
The sex ratio refers to the relative numbers of male and female. It is typical in most species that the sex ratio 1:1. However, there are populations in which this is not true. In many social insect population(bees, ants, and wasps), the number of females greatly exceed the number of male at all times.
In humans, about 106 males are born for every 100 females. However, in the United States, by the time people reach their mid-twenties, a higher death rate for males has equalized the sex ratio.
The higher male death rate continues into old age, when women out number men.
The Democratic Republic of Congo’s population has a large prereproductive and reproductive component. This means that it will continue to increase rapidly for some time.
The United States has a very large reproductive component with declining number of prereproductive individuals. Eventually, if there were no immigration, the U.S. population would begin to decline if current trends in birthrates and death rates continued.
Germany has an age distribution with high postreproductive and low prereproductive portions of the population. With low numbers of prereproductive individuals entering their reproductive years, the population of Germany has begun to decline.
Population density is the number of organisms per unit area.
Populations have an inherent tendency to increase in size. At the simplest level, the rate of increase is determined by subtracting the number of individuals leaving the population from the number entering.
2. A Population Growth Curve
Population growth often follows a particular pattern:
Lag phase,
An exponential growth phase, and
A stable equilibrium phase.
During the first portion of the curve, known as the lag phase.
Since more organisms are reproducing, the population begins to increase at an accelerating rate. This stage is known as the exponential growth phase.
The death rate and the birthrate will come to equal one another, the population will stop growing and reach a relatively stable population size. This stage is known as the stable equilibrium phase.
3. Human Population Growth
The human population is increasing at a rapid rate.
The Earth’s ultimate carrying capacity for humans is not known.
The causes for human population growth are biological, social, political, philosophical, and theological.
4. Conclusions
A population can be defined as a group of individuals of the same species inhabiting an area.
At the simplest level, the rate of increase is determined by subtracting the number of individuals leaving the population from the number entering.
5. References
Enger, E. D, & Smith, B. F, (10th Edition): Environmental Science: A Study of Interrelationship. Published by McGraw Hill Higher education (2006).
Question
1. How is biotic potential related to the rate at which a population will grow?
2. List three characteristics populations might have.
3. Why do some populations grow? What factors help to determine the rate of this growth?
4. Under what conditions might a death phase occur?
5. List four factors that could determine the carrying capacity of an animal species.
6. How do the concepts of birthrate and population growth differ?
7. How does the population growth cure of humans compare with that of bacteria on a petri dish?
8. How do r-strategists and K-strategists differ?
9. As the human population continues to increase, what might happen to other species?
10. All successful organisms overproduce. What advantage does this provide for the species? What disadvantages may occur?
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