Chapter 5 Populations

Location of the ecosystem – Aleutian Islands, Alaska

Change in sea otter populations around the Aleutian Islands

WHY? With your group, discuss as many reasons that you can think of that might be causing the sea otter population decline

Change in sea otter populations around the Aleutian Islands

Killer whale prey in the Aleutians

If you were a killer whale… With your partners, rank the order of the three prey species that you would prefer to eat. Give a reasoning for your ranking.

So who cares if the otters go extinct? With your partners, make a prediction about what will happen to the kelp forests of the Aleutian Islands habitat if the sea otters become extinct

What’s next? With your partners, sum everything up. What will eventually happen to all the members of this ecosystem if the sea otters become extinct?

5 – 1 How Populations Grow What characteristics are used to describe a population? What factors affect population size? What are exponential growth and logistic growth?

Characteristics of Populations Three important characteristics of a population are: 1. geographic distribution – The area inhabited by a population 2. density - # of individuals per unit area 3. growth rate – how fast the population grows

Population Growth Three factors can affect population size: 1. The # of births 2. The # of deaths 3. How fast the population numbers grow

Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially When the individuals in a population reproduce at a constant rate

Exponential Growth

Logistic Growth Obviously, the conditions for exponential growth are rarely ever met As resources become less available, the growth of a population slows or stops

Logistic Growth Occurs when a population’s growth slows or stops following a period of exponential growth Q: Why does this happen? A: Lack of resources, lack of space

Carrying Capacity The largest number of individuals that a population can support Q: What is the growth rate when a population is at carrying A: Zero

5 – 2 Limits to Growth What factors limit population growth?

Limiting Factor A factor that causes population growth to decrease Ex.) Parasitism, disease, drought, extreme weather A resource base that is limited can also affect the long term survival of a species

Density – dependent Factors Limiting factors that depend on population size Density dependent factors become limiting only when the population density reaches a certain level These factors operate most strongly when a population is large and dense Density dependent factors include:

Competition

Predation

Parasitism

Disease

Density – Independent Factors Affect all populations in similar ways regardless of the population Ex.) unusual weather, natural disasters, seasonal cycles, human activities

Unusual Weather

Natural Disasters

Seasonal Cycles

Human Activities

Density – Independent Factors In response to such factors, many species show a characteristic crash in population size Environments are always changing, and most populations can adapt to a certain amount of change Populations often grow and shrink in response to such changes Major upsets in an ecosystem can lead to long term declines in certain populations

5 -3 Human Population Growth How has the size of the human population changed over time? Why do population growth rates differ in countries throughout the world?

Historical Overview Like the populations of many other living organisms, the size of the human population tends to increase with time In the U.S. and other developed countries, the current growth is low In some developing countries, the human population is growing at a rate of 3 people per. second The human population is well on its way to reaching 9 billion in your lifetime

Exponential Human Growth The following factors have caused a rapid increase in population growth:

Agriculture

Industry

Reliable food source

Shipping

Improved sanitation

Medicine

Technology

Patterns of Population Growth Q: Why can’t the human population keep growing exponentially forever? A: The resources on earth are limited

Demography The scientific study of human population Birthrates, death rates, and age structure of a population help to project why some countries have a high growth rate while others grow more slowly

The Demographic Transition

Age Structure Population growth depends, in part, on how many people of different ages make up a given population

Age-structure diagrams (population profile) – show the population of a country broken down by gender and age group

World Population: YearAverage Annual Growth Rate (%) Population ,555,360, ,039,669, ,136,556, ,206,072, ,708,067, ,454,607, ,275,407, ,078,684, ,812,009, ,515,218, ,127,227, ,646,671, ,078,850,714