CHAPTER 4 POPULATION ECOLOGY Section 4 1 Population

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CHAPTER 4: POPULATION ECOLOGY Section 4. 1: Population Dynamics Section 4. 2: Human Population

CHAPTER 4: POPULATION ECOLOGY Section 4. 1: Population Dynamics Section 4. 2: Human Population

 • Graphing population growth isn’t like graphing the amount you get paid at

• Graphing population growth isn’t like graphing the amount you get paid at a job or how many averages pages you can read in a book per hour Linear Line

 • Graphing population will display a J-shaped curve. WHY? • This illustrates Exponential

• Graphing population will display a J-shaped curve. WHY? • This illustrates Exponential Population Growth

Exponential Growth Model § Exponential growth means that as a population gets larger, it

Exponential Growth Model § Exponential growth means that as a population gets larger, it also grows faster. § All populations grow exponentially until some Limiting Factor slows the population’s growth.

Logistic Growth Model § The population’s growth slows or stops following exponential growth, at

Logistic Growth Model § The population’s growth slows or stops following exponential growth, at the population’s Carrying Capacity.

 • Until the Industrial Revolution in the 1800 s, human population growth was

• Until the Industrial Revolution in the 1800 s, human population growth was relatively slow. • During the Industrial Revolution, a sharp increase in human population growth began. • Today the Earth has reached a population of over 7 billion people • This is double the population of 1965

Carrying Capacity § The maximum number of individuals in a species that an environment

Carrying Capacity § The maximum number of individuals in a species that an environment can support for an indefinite period of time § Carrying capacity is limited by the energy, water, oxygen, and nutrients available (limiting factors)

Population-Limiting Factors § There are two categories of limiting factors §Density-independent factors §Density-dependent factors.

Population-Limiting Factors § There are two categories of limiting factors §Density-independent factors §Density-dependent factors.

Density-Independent Factors § Any factor in the environment that does not depend on the

Density-Independent Factors § Any factor in the environment that does not depend on the number of members in a population per unit area § Weather events § Fire § Human alterations of the landscape § Air, land, and water pollution

Density-Dependent Factors § Any factor in the environment that depends on the number of

Density-Dependent Factors § Any factor in the environment that depends on the number of members in a population per unit area § Biotic factors § Disease § Competition § Parasites

Population Ranges • A species might not be able to expand its population range

Population Ranges • A species might not be able to expand its population range because it cannot survive the abiotic conditions found in the expanded region. Common dolphin Pupfish

Human Population Growth § Demography = the study of human population size, density, distribution,

Human Population Growth § Demography = the study of human population size, density, distribution, movement, and birth and death rates is.

§ A population stops increasing when the number of births is less than the

§ A population stops increasing when the number of births is less than the number of deaths or when emigration exceeds immigration. §Births < deaths §Emigration > immigration To calculate a country’s population growth rate: Birthrate – Death rate = Population Growth Rate (PGR)

Zero Population Growth § Zero population growth (ZPG) occurs when the birthrate equals the

Zero Population Growth § Zero population growth (ZPG) occurs when the birthrate equals the death rate. § The age structure eventually should be more balanced with numbers at prereproductive, and postreproductive ages being approximately equal.

Age Structure §A population’s age structure is the number of males and females in

Age Structure §A population’s age structure is the number of males and females in each of three age groups: Pre-reproductive Stage, Reproductive Stage, and Post-reproductive Stage.

Comparing Age Structures • Replacement occurs when a couple has only two children. •

Comparing Age Structures • Replacement occurs when a couple has only two children. • If there is an average of more than two children born to each couple, the population will grow. • A graph of the number of individuals of each age can show if the population is stable, growing or declining. • A growing population will have a pyramid shaped age structure graph

Increasing Population Decreasing Population

Increasing Population Decreasing Population

Stable Population

Stable Population

Human Population Growth Rate • Although the human population is still growing, the rate

Human Population Growth Rate • Although the human population is still growing, the rate of its growth has slowed • Because of the rapid increase in the human population, there are concerns that the human population may someday reach its carrying capacity

Trends in Human Population Growth § Population trends can be altered by events such

Trends in Human Population Growth § Population trends can be altered by events such as disease, war, & zombies. § Human population growth is not the same in all countries.

 • The more-developed countries have modest population growth rates due largely to decreased

• The more-developed countries have modest population growth rates due largely to decreased birthrates. WHY? • The less-developed countries have higher population growth rates because birthrates remain high. WHY?