1. Population Review Notes Chapter 71
Population Review Notes Chapter 7

2. Populations
= Individuals of a species that live in the same place at the same time Are dynamic – constantly changing Evolution occurs at this level

3. Definition of population dynamics
Population dynamics refers to changes in a population over time
Population dynamics includes four variables:
density
dispersion
age distribution
size

4. social/population structure
Population Density
Population density (or ecological population density) is the amount of individuals in a population per unit habitat area
Some species exist in high densities
ex. mice
Some species exist in low densities
ex. Mountain lions
Density depends upon
social/population structure
mating relationships
time of year

5. Population Dispersion
Population dispersion is the spatial pattern of distribution
There are three main classifications
clumped: individuals are lumped into groups
ex. Flocking birds or herbivore herds
due to resources that are clumped or social interactions
most common

6. Population Dispersion (cont)
Uniform: Individuals are regularly spaced in the environment
ex. Creosote bush
due to antagonism between individuals, or do to regular spacing of resources
rare because resources are rarely evenly spaced
Random: Individuals are randomly dispersed in the environment
ex. Dandelions
due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals
rare because these conditions are rarely met

7. Population growth affects the environment
The IPAT model: I = P x A x T x (S)
Our total impact (I) on the environment results from the interaction of population (P), affluence (A) and technology (T), with an added sensitivity (S) factor
Population = individuals need space and resources
Affluence = greater per capita resource use
Technology = increased exploitation of resources
Sensitivity = how sensitive an area is to human pressure
Further model refinements include education, laws, ethics
Humanity uses 1/3 of all the Earth’s net primary production

8. Calculating The Growth Rate
Crude Growth Rate formula =
Crude Birth Rate – Crude Death Rate = Crude Growth Rate
Crude Rates are based on 1,000 individuals
Population Change Formula =
(birth rate + immigration rate) – (death rate + emigration rate) = Population Change
The CGR for the Earth is roughly 1.2% right now !

9. Total Fertility Rate (TFR)
The Total Fertility Rate or TFR is an estimate of the average number of children who will be born alive to a woman during her lifetime if she passes through all her childbearing years (ages ) conforming to age-specific fertility rates of a given year.
In simpler terms, it is an estimate of the average number of children a woman will have during her childbearing years.

10. Replacement Level Fertility (RLF)
The Replacement Level Fertility or RLF is the number of children a couple must have to replace them.
The average for a country or the world usually is slightly higher than 2 children per couple (2.1 in the United States and 2.5 in some developing countries) because some children die before reaching their reproductive years.

11. Population Growth Populations show two types of growth Exponential
J-shaped curve
Unlimited Growth
Growth is independent of population density
Logistic
S-shaped curve
Growth affected by environmental stress
Growth is not independent of population density

12. Exponential and Logistic Population Growth: J-Curves and S-Curves
Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.
Figure 8-4

13. History of Human Population Growth
1. Early period of hunter and gathers - the total population was < a few million (>10,000 yrs ago)
2. Rise of agriculture- allowed for increase in population density and increased human population
3. Industrial revolution - improvements in health and food supply led to rapid inc in population
4. Today - the rate of growth is slow in industrialized nations but high in less developed nations

14. Human Population Growth
What are the implications of these graphs?
Why are the “developing” countries contributing so much to the population growth on the planet?

15. Rule of 70
To determine the doubling time of a population, divide 70 by the percentage of growth.
Uses the exponential growth calculation
If the growth rate is 2%, then,
70 ÷ 2 = 35 years

16. What do “per capita” rates mean?
If 1000 individuals produce 10,000 young in one year, than the per capita birth rate is:
b = 10/yr
although some individuals may have bred and others may not have
If there are 500 individuals this year, but only 250 of these same individuals survive to the next year, then the per capita death rate is :
d = .5/yr
athough some individuals died completely, and others are still alive

17. What do “per capita” rates mean?
r can also be thought of as the change in population size over time
ex. If a population is growing at a rate of 2% per year, that means that 2 new individuals are added to the population for every 100 already present per year. In this case, the r is the decimal form of the growth rate, or r = .02

18. Carrying Capacity (K)
Exponential curve is not realistic due to carrying capacity of area
Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

19. K-selected vs. r-selected species

20. Survivorship curves
Type I: late loss, K-strategists that produce few young and care for them until they reach reproductive age thus reducing juvenile mortality
Type II: constant loss, typically intermediate reproductive strategies with fairly constant mortality throughout all age classes
Type III: r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age

21. Age Structure
The age structure of a population is usually shown graphically (also known as population pyramids)
The population is usually divided up into prereproductives, reproductives and postreproductives
Implication for current and future social and economic conditions - What if no one is having babies? What if 70% of the population is under age 30? (true in several countries)
Impact on the environment - do older people have as large an impact as young people?
The age structure of a population dictates whether is will grow, shrink, or stay the same size

22. Population pyramids are used to show information about the age and gender of people in a specific country.
Male
Female
There is also a high Death Rate.
In this country there is a high Birth Rate
Population in millions
This population pyramid is typical of countries in poorer parts of the world (LEDCs.)

23. Age Structure Four general types
Pyramid- population w/ many young and high death rate (short average lifetime)
Inverted pyramid- top heavy (Japan?)
Column- birth rate and death rate are low and a high % of pop is elderly
Column w/ a bulge- event in the past caused a high birth or death rate for some age group

24. Population characteristics

25. Age Structure: Young Populations Can Grow Fast
How fast a population grows or declines depends on its age structure.
Prereproductive age: not mature enough to reproduce.
Reproductive age: those capable of reproduction.
Postreproductive age: those too old to reproduce.

26. The demographic transition
Demographic transition = a model of economic and cultural change to explain the declining death and birth rates in industrializing nations
Stable preindustrial state of high birth and death rates change to a stable post-industrial state of low birth and death rates
As mortality decreases, there is less need for large families
Parents invest in quality of life

27. The demographic transition’s four stages
Early transitional
Late transitional
Population growth is seen as a temporary phenomenon

28. The International Conference on Population and Development
In 1994 Cairo, Egypt, 179 nations called on all governments to offer universal access to reproductive health care within 20 years
Offer better education and health care and alleviate poverty, disease, and sexism
Despite the success of family planning, recent administrations in the U.S. have declined to fund family-planning efforts
For example, Bush cancelled funding as one of his first acts on becoming U.S. president in 2001

29. Conclusion
The human population is larger than at any time in the past and getting older
Populations are still rising, even with decreasing growth rates
Most developed nations have passed through the demographic transition
Expanding rights for women slows population growth
Will the population stop rising through the demographic transition, restrictive governmental intervention, or disease and social conflict caused by overcrowding and competition?
Sustainability requires a stabilized population in time to avoid destroying natural systems