ENERGY TRANSFER

Populations

What is a Population?

A group of the same species of organism living in the same place

Characteristics of Populations

4 Major Characteristics of Populations:– Geographic Distribution– Density– Growth Rate– Age Structure

#1 - Geographic Distribution

Describes the area in which a certain population lives

Varies greatly in size depending on the type of organism and population size

#2 - Population Density

The Number of Organisms Per Unit Area/Volume

Measures the “crowdedness” of a population

Some population densities

for human populations

#3 - Population Growth Rate

The Amount by which a Population Size Changes in an Given Time Period

Depends on: – A) # of Births (birthrate)– B) # of Deaths (death rate)– C) # of Organisms entering or leaving population

Immigration Emigration

#3 - Population Growth Rate

Exponential Growth Model– Indefinite Growth of a population due to unlimited resources

(food, shelter,etc) and a lack of limiting factors (predators, disease, competition, and other factors that decrease population growth).

– Forms a J-Shaped Curve!– This does not happen except

in rare conditions for short

periods of time (like Bacteria in

a culture).

More on Exponential Growth…

When a population has unlimited resources, and it continues to grow to its FULL LIVING POTENTIAL, it is called Biotic Potential.

A population that has reached biotic potential has reached its maximum reproductive capacity (i.e. it has reproduced as much as it possibly can)

#3 - Population Growth Rate

Logistic Growth Model– More realistic; accounts for Limiting Factors– Begins with exponential growth but slows down or stops as

limiting factors influence the population– Populations reach a Carrying Capacity (K), the # of

individuals the environment can support over a long period of time.

– Forms an S-Shaped Curve!

Region A= very close to exponential growthRegion B= declining birthrate; inc. death rateRegion C= pop. reaches K; usually fluctuates

around Carrying Capacity

Limiting Factors

2 Types: (1) Density-Dependent Factors (2) Density-Independent Factors

DENSITY-DEPENDENT FACTORS are those factors that affect a population depending on its size- these include food, predation, parasitism, and disease- Competition can be Interspecific or Intraspecific.- As the population increases, it is more affected by density-dependent factors

The Effect of Predation

Populations in nature are often controlled by predation

The regulation of a population by predation takes place within the predator-prey relationship (one of the best known mechanisms of population control)

Limiting Factors

DENSITY-INDEPENDENT FACTORS affect all populations similarly regardless of population size.

The majority of these factors are abiotic. Examples include: natural disasters, rapid

climate changes (drought or floods), and human activity and disturbances

#4 – Age Structure

Describes how many individuals of different ages make up a population

Populations with large numbers of young offspring have greater potential for rapid growth

Population Pyramids, or Age-Structure, Diagrams, show age structure in a population.

Human Population Growth

It took from the beginning of mankind to around 1800 for the human population to reach 1 Billion.

In the last 200 years, the Human Population has reached just over 6 Billion.

The U.N. estimates the world’s population to be 12.5 Billion by 2050.

What effects will these numbers have on the Earth? Other forms of

life?

Patterns of Population Growth

The scientific study of human populations is called demography– Examines the characteristics of human

populations and attempts to explain how those populations will change over time

Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly

The Demographic Transition

Over the past century, population growth in the US, Japan, and much of Europe has slowed dramatically.

One hypothesis as to why these countries have slowed in their growth is the demographic transition (a dramatic change in birth and death rates).

As countries modernize, there are advances in nutrition, medicine, and sanitation.

– These result in more children surviving into adulthood and more adults living to old age.

– These changes lower the death rate and begin the demographic transition.

The Demographic Transition