Population Growth Chapter 5 Ecology Notes 5 Population Growth Chapter 5

Graph #1 – Bacterial Growth

Graph #2 – Field Mice Growth

Graph Questions Questions How are the two graphs you made similar? Just list 2 - 3 characteristics. How are the two graphs you made different? Just list 2 – 3 characteristics. Propose 2 hypotheses for the changes in the mouse population growth pattern.

Question Answers Similarities – specific time, monitoring population growth, both line graphs, Differences – time scale (minutes vs. years), organisms, 1st graph only increases & 2nd graph fluctuates 2 Hypotheses – Mouse has a predator regulating population size Mouse might not have regular access to resources like food, water, mates, & habitat space

1. Population Growth Population Growth - an increase in population size Population Growth Rate = change in the number of individuals / Time

1. Population Growth Population size is affected by 3 main factors: Number of Births Number of Deaths Number of Immigrants or Emigrants Immigration – entering a population Emigration – exiting a population

2. Population Growth Curves Exponential Growth – occurs when individuals of a population reproduce at a constant rate There are no factors affecting how quickly this population can increase in size This is often how populations grow when they first inhabit an environment. Populations generally cannot maintain exponential growth.

2. Population Growth Curves Exponential Model of Population Growth Notice that an Exponential Growth curve has a “J” shape It is often called a “J Curve” Exponential Growth # of I N D V U A L S TIME \

2. Population Growth Curves Logistic Growth – occurs after exponential growth when a population’s size might slow or stop Population growth slows when: Death rate equals or exceeds birth rate Emigration equals or exceeds immigration Carrying Capacity for an environment is met

2. Population Growth Curves Logistic Model of Population Growth Graph shows indicates carrying capacity Notice the graph’s “S” shape This type of graph is often called an “S Curve” Carrying Capacity Number of Yeast Cells Time (hours)

2. Population Growth Curves Limiting Factors: conditions which control a population’s ability to grow Carrying Capacity: the limited number of individuals in a population that a particular environment can support

3. Limiting Factors Limiting factors can be: Density Dependent - affect population members according to density (size in space) Examples: availability of food, mates, and habitat space; spread of disease Density Independent Factors - affect population members regardless of how big the population is Examples: environmental disasters (floods, earthquakes, tornados, human impact, etc)

Population Growth With Limiting Factors 60 2400 50 2000 40 1600 30 1200 20 800 10 400 1955 1960 1965 1970 1975 1980 1985 1990 1995 Moose Wolves This graph shows how predator/prey interactions affect population size of both predators (wolf) and prey (moose).

4. Human Population Growth How Fast Are We Growing? Until about 500 years ago, the world’s human population remained fairly stable. Then, as advances in medicine, agriculture, and technology occurred, the human population began growing very rapidly. Today, the world’s human population is greater than 7 billion people, and it continues to grow, but at a slower rate.

4. Human Population Growth Industrial Revolution begins Agriculture begins Bubonic plague Plowing and irrigation

4. Human Population Growth The human population is increasing by about 1.4 percent each year. Assume that the population is 6 billion (6,000,000,000). How large will the population be in one year? 6,000,000,000 X 0.014 = 84,000,000 people will be added in one year, so the population would be 6.08 billion in one year.