What affects population size? A population is a group of organisms belonging to a single species that lives in a given area.

How Populations Grow A. Characteristics of Populations -Populations are organisms of the same species that live in the same ecosystem and who can potentially interbreed. -Members of populations compete with one another for resources. -populations are the unit that evolution acts on as it selects for favorable characteristics within the gene pool that confer survival on some members at the expense of others. B.2 kinds of Population Growth 1. Exponential Growth rapid, unchecked growth J shaped graph 2. Logistic growth limited by some factor shaped graph

Factors that affect population growth A situation that causes the growth of a population to decrease is called a limiting factor. Some limiting factors depend on the size of the population. Other limiting factors affect all populations in similar ways, regardless of the population size. 2 Kinds of limiting factors: 1. Density Dependent 2. Density Independent

Think about it! 1. Imagine a small island that has a population of five rabbits. How might each of the following factors affect the rabbit population? a. climateb. food supply c.predation How would the same factors affect this population? 3. Which of the factors depend on population size? (food supply and predation ) 4. Which factors do not depend on population size? (climate )

Population Growth 3 factors affecting population size are- - number of births -number of deaths -number of individuals that enter/leave a population Immigration-movement of individuals into a population, this can cause a population to grow Emigration-movement of individuals out of a population, can cause a population to decrease in size

Exponential Growth  Given abundant space, resources, & protection, a population could potentially grow exponentially.  Which would you prefer: 1. On the first day of the month, Be given $1,000,000 to live on, or 2. Get 1 cent on the first day of the month, then have that doubled for day 2, then doubled for day 3, and so on until the end of the month? It’s no contest! That is exponential growth!!!

Exponential Growth (J shaped curve) Exponential growth does not occur in natural populations for very long. What slows the growth down? Birthrate decreases Death rate increases Immigration decreases Emigration increases

The J- shaped Curve Population growth vs. Time Exponential growth J shaped curve

Logistic growth As resources become less available, the growth of a population will slow or even stop As growth levels off, the “carrying capacity” is reached Logistic growth is shown with an S-shaped curve

Logistic growth of yeast Carrying Capacity Time (hours) Number of yeast cells

Logistic growth

Population Concept Map Population Growth can be represented bycharacterized by represented by which cause a Exponential growth Logistic growth Falling growth rate S-shaped curve Limits on growth No limits on growth J-shaped curve Constant growth rate Unlimited resources

Limiting factors A limiting factor is a factor that causes population growth to decrease A limiting nutrient(more specific/narrow) would be an example of a limiting factor (less specific/broad) Molasses Lab: What were limiting factors in the growth of the yeast?

Density-dependent Limiting Factors Density-dependent limiting factors only become limiting when the population density (organisms per unit area) reaches a certain level. Usually this applies when the population is large and dense Density-dependent factors are a factor in organisms evolving into different niches Examples of density-dependent limiting factors include: competition, predation, parasitism & disease

Competition When a population is crowded, organisms may compete for resources Resources=food, water, space, sunlight, nutrients Competition may be intra-species (wolf packs) or inter-species (wolves/coyotes/bears)

A Density-dependent Limiting Factor (Competition for resources) Exponential Growth Steady Population Size Peak Population Size Rapid Decline Steady Population Size

Wolf & Moose Populations on Isle Royale (Density- dependent/ predation) MooseWolves

Predation Predator-prey relationships fluctuate with time

Parasitism & Disease Parasites range from microscopic (bacteria) to macroscopic (tapeworm/30 cm long) Parasites act somewhat like a predator in that they derive nourishment from the host

Density-Independent Factors Density-Independent Factors are not influenced by population size These include- Weather (drought, flood, heat, cold) Human activities (clear cutting forest, dams on river, )

Human Population Growth 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. The rate of human population accelerated until about Today, the world’s human population is greater than 6.7 billion people, and it continues to grow, but at a slower rate than in However, we are still feeling the results of humans who were born in that time as they are still reproducing today and their children are now reproducing. How fast are we growing?

Human Population Graph Agriculture begins Plowing and irrigation Bubonic plague Industrial Revolution begins

World Vital Events Per Time Unit: 2008 (Figures may not add to totals due to rounding) Natural Time unit Births Deaths increase Year 135,330,281 55,205,782 80,124,499 Month 11,277,523 4,600,482 6,677,042 Day 369, , ,919 Hour 15,406 6,285 9,122 Minute Second

1.The human population is increasing by about 1.4 percent each year. Sometime in the year 1999, it was estimated that the world population reached 6 billion (6,000,000,000). How large will the population be in one year 2000? 6,000,000,000 X = 6,084,000, If the human population continues to grow at a rate of 1.4 percent per year, the population would double in size (to 12 billion people) in only 51 years! What effect might this increase in population have on the environment and on other people? (Doubling rate??? Learn about the rule of 70)

Here is how you determine the doubling rate of a population growing exponentially: Divide the number 70 by the growth rate that is in the form of a percent. Therefore, a country that has a growth rate of 1 % will take 70 years to double its current size while a country growing at 2 % will take 35 years to double its size: 70/1 = 70 years70/2 = 35 years

Demography-the study of human populations Demographic Transition: change in birth and death rates due to modernization and improvements in medicine, sanitation, and nutrition Demographic transition has lowered the death rate among humans

U.S. PopulationRwandan Population Males Females

T The table and bar chart that follows shows world human population in millions, in 50-year intervals, since the year year million million ,260 million ,650 million ,555 million ,080 million (data from United Nations and Bureau of Census - other source(s)may give slightly different numbers)

Does the “lifeboat” analogy apply here? Are there natural controls on human population? What are the consequences? What are the solutions?

Doubling rate and the Rule of 70 Doubling time of a population = 70/r r = the rate of growth expressed as a percent