population dynamics. principles of population ecology objectives: 1.define population ecology...

Population Dynamics

Principles of Population EcologyObjectives:

1.Define Population Ecology

2.Define growth rate and explain the factors that produce changes in population size

3.Explain how human population change is calculated

4.Understand how the following terms are related to population growth: intrinsic rate of increase, exponential population growth, environmental resistance, and carrying capacity.

5.State how the J-curve and S-curve relate to exponential population growth

Principles of Population Ecology

Population Ecology – the branch of biology that deals with the numbers of a particular species found in an area and how and why those numbers change over time.

Population ecologists ask:

1) How many are in the population?

2) Are its numbers increasing / decreasing?

3) What is its pattern of reproduction?

4) What is its pattern of mortality?


Population Density:

• Not enough to know just how many.

• Need to know per unit area.

20 / 100 m220 / 25 m2


How Do Populations Change in Size?

On a global scale (closed system):



Global scale:

r = b – d

Growth rate

Birth rate

Death rate



On a local scale (open system):



Local scale:

r = (b – d) + (i – e)

Growth rate

Birth rate

Death rate

Immigration rate

Emigration rate


Maximum Population Growth-

under ideal conditions = intrinsic rate of increase

J-shaped curve (exponential growth)


Intrinsic rates of increase for a species depend on:•Age that reproduction begins•Fraction of life span during which a species can reproduce•Number of reproductive periods per lifetime•Number of offspring produced during reproduction


Environmental Resistance

Exponential growth cannot occur forever.

What factors prevent it from doing so?

S-shaped curve (logistic growth)


Population growth depends on the interplay between biotic potential and environmental resistance

Biotic Potential Environmental Resistance

•Reproductive rate •Lack of food or nutrients

•Ability to migrate or disperse

•Lack of water•Lack of suitable habitat

•ability to invade new habitats

•Adverse weather conditions•Predators

•Defense mechanisms •disease

•Ability to cope with adverse conditions

•Parasites•competitors


Overshooting the carrying capacity can lead to a population crash.

Reproductive Strategies

Objectives:

1.Compare r-selected species to K-selected species with respect to survivorship curves


Each species has its own unique life history strategy that represents a tradeoff between energy required for survival and energy required for reproduction. This strategy includes:

• Reproductive characteristics

• Body size

• Habitat requirements

• Migration patterns

• behaviors


Life History Strategies

r-selected K-selectedvs.

high growth rate slow growth rate

small body size large body size

early maturity late maturity

short life span long life span

large broods small broods

little / no parental care high parental care


Survivorship- the proportion of newborn individuals that are alive at a given age

Factors that Affect Population Size

Objectives:

1.Distinguish between density-dependent and density-independent factors that affect population size and give examples of each.


Density-Dependent Factors-

• Factors with effects on population growth that change as population density changes

Examples:

• Predation, competition, disease.


Density-Dependence and Boom-or-Bust Population Cycles


Case-in-Point: Predatory Prey Dynamics on Isle Royale


Density-Independent Factors-

• Factors that affect the size of a population regardless of population density.

Examples:

• Extreme weather (frost, blizzard, hurricane, etc.; fire.

The Human Population

Objectives:

1.Define demography and summarize the history of human population growth

2.Identify Thomas Malthus, relate his ideas on human population growth.

3.Explain why it is impossible to determine the earth’s carrying capacity for humans.


Demography – the science of population structure and growth

Demographics – the application of population statistics


Current Population Numbers

Today = ~7.1 billion

Check out:

http://www.census.gov/main/www/popclock.html

• The world’s birth rate has declined over the last 200 years

• The large increases in population are a result of decreased death rates.

http://www.census.gov/main/www/popclock.html


Decreases in the death rate can be attributed to:

• Greater food production

• Better medical care

• Improvements in water quality

• Sanitation practices


Current Population Numbers

Rapid growth primarily due to drop in death rate

Mexico

(1900-2000)

The Human PopulationProjecting Future Population Numbers

When will zero population growth occur?

Demographics of Countries

Objectives:

1. Explain how highly developed and developing countries differ in population characteristics such as infant mortality rate, total fertility rate, and age structure.

2. Interpret age structure diagrams


Most Populous Countries Insert Table 8.1


Developed vs. Developing Countries Demographics Insert Table 8.2 (note

reconstruction)


Demographic Stages


Age Structure of Countries

Generalized Age Structure


Examples:


Effects of an Aging Population

• Reduction in productive workforce

• Increasing tax burden

• Strain on social security, health, and pension systems

• Lower crime rates????

Demographics of the US

Case-in-Point: US Immigration

population dynamics. principles of population ecology objectives: 1.define population ecology...

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