Honors Biology – Chapter 5 Populations Honors Biology – Chapter 5

What is a Population? A group of the same species living in a given area It is populations of organisms that interact in ecosystems Example:

An Introduction – Sea Otters of the Pacific Northwest Life in kelp forest community

An Introduction – Sea Otters of the Pacific Northwest Sea urchins as food Sea urchins eat kelp Sea otters nearly eliminated due to hunting Sea urchin populations rise Kelp forests decline Restoring balance: Sea otters declared endangered – protected from hunting

Predator/Prey Population Relationships Hare / Lynx Hare population goes up Lynx population goes up Lots of food (hares) available Causes hare population to go down More lynx = more predation on hares Causes lynx population to go down Hare population decrease means less food for lynx and they die

Hare/Lynx

4 Characteristics of Populations Geographic distribution Range Area inhabited by a population Density Number of individuals per unit area Growth rate Age structure

Population Growth 3 factors affect population size Number of births natality Number of deaths mortality Number of individuals that enter or leave a population Immigration - enter Emigration - leave

Population Growth A population will increase or decrease in size depending on how many individuals are added to it or removed from it Growth occurs if More individuals are born than die If birth rate equals death rate the population will stay near the same size

Movement into or out of a population May be caused by Young animals mature and leave the area Shortage of food in an area

Exponential Growth Individuals in a population reproduce at a constant rate Initially, growth is slow Overtime the population becomes larger and large until it approaches an infinitely large size Ideal conditions with unlimited resources required

Bacteria Fastest rates of reproduction among living things 20 minutes for population to double Why don’t they take over the Earth? NOT unlimited resources

Logistic Growth Growth pattern that occurs when a population’s growth slows or stops following a period of exponential growth. Things that slow a population’s growth Natality (birth rate) decreases Mortality (death rate) increases Rate of immigration decreases Rate of emigration increases

Logistic Growth Also, when birth and death rates are the same, the population growth will slow or even stop for a time Even when a population stops “growing”, the population is still rising and falling somewhat – though the ups and downs average out to the same population size.

Logistic Growth Curve Slow growth Exponential growth Growth levels off Carrying Capacity K Dotted line The maximum number of individuals that an environment can support

Limits to Growth Limiting Factors Factors that cause population growth to decrease Competition Predation Parasitism Drought Human disturbance

There are TWO types of limiting factors Density Dependent Density Independent

Density Dependent Limiting Factors Depends on the size of a population Usually greatest impact when the population is large and dense Include Competition Predation Parasitism Disease

Density Independent Limiting Factors Affects all populations (large or small) in similar ways. Unusual weather Natural disasters Human activities Like Habitat Destruction

Human Population Growth Like other populations of organisms, the human population tends to increase with time.

Human Population Growth Curve Initially slow Food scarce Life harsh 500 years ago More rapid growth Currently EXPONENTIAL Why? Agriculture and industry advances Food supply increased Improved sanitation Medicine

Human Population Growth Curve

Demography The study of human populations Examines human populations and tries to predict how they will change over time.

Demographic Transition Population growth in some countries has slowed U.S. Japan Much of Europe Why? Hypothesis: These countries have completed the “demographic transition

Demographic Transition A dramatic change in birth and death rates What happens Initially both birth and death rates high Advances in nutrition, etc. lower death rate Population increases rapidly Societies modernize – increase education, etc. Families have fewer children Birthrate falls to meet the death rate Population growth stops

Populations that have NOT completed the demographic transition Most countries India China

Age Structure Diagrams Shows how many people of different ages and genders are in a population Useful in predicting future population growth

Age Structure Diagram

Predicting Future Population Growth Factors to consider Age structure of each country Prevalence of life-threatening diseases Predictions for 2050 9 billion people on Earth

Effects of Human Population Growth Some scientists suggest if human population growth rate does not become LESS than 0 (deaths outnumber births) Serious damage to environment Serious damage to global economy Some economists say that technology advances and changes in societies can control negative impacts