Overview

Population Dynamics
- A general study of population changes
Population
- Group of individuals of the same species living in the same area
Species
- All individuals that are capable of interbreeding
- A species is made up of a population
Demography
- Statistical Study of human populations
Five Key properties of any population
- Abundance
- Birth rates
- Death rates
- Growth rates
- Age structure
Human population data often reported as crude rates (per 1000) people
- 2 births per 1000 people

Exponential growth
- A population increasing by a constant percentage per unit time
Human population growth peaked at 2.1%
- 1965-1970 with rapid improvement of healthcare and food production
Now growth is at 1.2%
- Slowing in wealthy industrialized nations but still increasing in many less-developed nations

Stage 1
- Few million
- Hunter Gatherers
Stage 2
- Rise in Agriculture
- Allowed for an increase in population density
- Total population 5 million in 10,000 B.C. to about 100 million in A.D
- From A.D.1 to A.D. 1,000 the population increased to 200-300 million
Stage 3
- Industrial Revolution
- Improvements in health and food security
- Total population about 900 million (1800) doubling to 3 billion by 1960
Stage 4
- Currently
- Now over 8 billion
Saltaire (U.K.)
- Built in 1851 by Sir Titus Salt
- Largest industrial building in World
- Built houses vs slums in Bradford
- Wash-houses, bath-houses
- Hospital
- Library, concert hall, etc
Exponential growth and doubling time
- Time required for a population to double in size
- $\frac{growthRate}{70}$ (Rule of 70)
- Changes quickly as growth rate changes

Growth cannot continue forever (exponential growth)
Logistic growth
- S-shaped curve
- Growth increases exponentially to inflection point
- Reaches an upper population limit at logistic carrying capacity
Little evidence animal population follow these rules
Involves assumptions of
- Constant Environment
- Constant Carrying Capacity
- Homogeneous population
Unlikely if death rate continues to decrease
The most important statistic is total fertility rate
What controls the Total Fertility Rate
- Social Factors: cultural expectations, economic issues
- Technical factors: access to birth control, economic resources
First child decisions:
- Lengthen time between generations: slow growth
UN Projections of Human Growth
- Based on potential fertility rates

Exponential and logistic growth curves ignore characteristics of the environment that affect different age groups
- Food, water, shelter, disease
Age structure
- Express how populations is divided among age groups
- Implications for current and future social and economic conditions
- Impact on the environment
Type 1
- Pyramid: Population with many young and high death rate (short average lifetime)
- Social impacts of a high dependency ratio (young): infrastructure costs (education), impacts on economy
Type 2
- Inverted Pyramid: population with large elderly population and small youth (declining growth)
- Medical costs: current working population -> current retirees
Type 3
- Column: birth rate and death rate are low, little change in population size
Type 4
- Column with bulge: event in the past caused a high birth rate for some age group

Three stage pattern of change in birth rates and death rates
- A multistage pattern of change in birth rates and death rates
- Occurred during the process of industrial and economic development of Western nations
- Leads to decline in population growth rate
The demographic transition is not the same all around the world

Maximum lifetime
- Maximum possible age to which an individual in a species can live (125 yrs?)
Life expectancy
- Average number of years an individual in a species can expect to live
- Higher in developed, prosperous nations
- Japan: Highest (84.6 yrs)
- Central African Republic: Lowest at 45.9
Population growth occurred in human history with little change in maximum lifetime
Modern Medicine has reduced death rates
Acute diseases
- Appears rapidly in the population and then disappears
- Currently 60% of mortality in Ecuador, <20% in the United States
Chronic Diseases
- Always present in population (cancer, heart, etc)
- These figures have changed throughout history

Impact that all humans pose on the environment is a result of two factors
- Number of people
- Impact of each person on the environment
T = P x I
- T: total impact of the human population on environment
- P: population size
- I: average environment impact per person
Modern technology increases the use of resources and enables us to impact the environment in new ways
T = P x I equation is ironic
- Improving standard of living declines P
- But at the same time I increases so counters the benefit
How many people can live on Earth at the same time?
- Depends on the quality of life people desire and are willing to accept
Estimation methods
- Extrapolation from past growth
- Packing problem approach
- Deep ecology
Limiting Factors
- Short term: affect population immediately
- Intermediate term: affect population 1-10 years
- Long term: effects not apparent until after 10 years (soil erosion, decline in ground water)

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