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 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 Population Growth

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 the population’s Carrying Capacity.

Until the Industrial Revolution in the 1800s, 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 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.

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 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 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, movement, and birth and death rates is.

Birthrate – Death rate = Population Growth Rate (PGR) 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 death rate. The age structure eventually should be more balanced with numbers at pre-reproductive, reproductive, and post-reproductive ages being approximately equal.

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. 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

Stable Population

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 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 birthrates. WHY? The less-developed countries have higher population growth rates because birthrates remain high. WHY?