Unit 8: Biosphere Note Packet By: Mrs. Barbee If you remember populations are groups of individuals of the same species that live in the same area.

Characteristics of Populations Geographic distribution – location where a population lives Density – Concentration of organisms in an area Growth Rate – Speed a population grows Geographic distribution or range – describes the area inhabited by a population. The range can vary in size from a few centimeters occupied by bacteria eating a rotten apple to millions of square miles occupied by migrating whales in the Pacific Ocean. Population density- number of individuals per unit area. Population density can vary. A low population density would be cacti in the desert versus a high density of fruit flies on a orange. Growth Rate- how quick or slow a population grows or increases.

Population Size Populations will increase or decrease in size depending on how many individuals are added or removed. The factors that affect population size: # of births # of deaths # of individual that enter or leave a population

Population Size Terms Births: Offspring born Deaths: Individuals that die Immigration: movement of individuals to an area Emigration: movement of individuals out of an area

Exponential Growth or J Curve What does this graph show? Exponential Growth occurs when the individuals in a population reproduce at a constant rate. Why might a population increase exponentially? Unlimited resource, constant birth rates, no predators

Exponential Growth or J Curve A J curve is exponential growth depicted on the graph. Do you see the resemblance to a J in the graph?

Logistic Growth or S Curve How is this graph different than the exponential growth graph? What events might cause a population to level off? Increase and then levels off This graph levels off. When resource become less available, the growth of a population slows down or stops. Reduction in resources

Logistic Growth or S Curve A S curve depicts a logistic growth graph. The logistic growth curve occurs when a population’s growth slows or stops following a period of exponential growth.

Logistic Growth or S Curves You can see populations grow and decrease in this logistic growth curve. If you notice the population number changes after the initial exponential growth. The population hovers above and below the carrying capacity. Once the organisms or (fish) population in this case. Population estimates are based on estimated population growth. Japan populations growth include the tsunami

Carrying Capacity The largest # of individuals that a given environment can support. What do you think happens once a population reaches carrying capacity? Organisms in the population will die.

Carrying Capacity Under ideal conditions with unlimited resources, a population will grow exponentially. Yet, there are not unlimited resources on Earth. Every population eventually will reach a carrying capacity. It is just of matter of when. Do you think humans are close to reaching a carrying capacity?

Human Pop. Growth Human Population Growth has increased with time! Around 500 years ago, the human population began growing. Why do you think the human population has exponentially increased in the last two hundred years? What are some causes?

Human Pop. Growth The human population cannot continue to grow exponentially. The question is when will humans hit a carrying capacity? Demography is the study of human population growth. It attempts to examine the characteristics of human populations and to explain how human population changes over time.

Patterns of Human Pop. Growth The populations of the U.S., Japan, and most of Europe have slowed dramatically. Demographers hypothesize that these countries have undergone demographic transition. In the past, birth and death rates were a lot higher. Today birth rates are still high but death rates have slowed. Demographers hypothesis that these countries have a demographic transition or a dramatic change in birth and death rate. IN the past birth rates and death rates equaled each other. However today, death rates have decreased and birth rates has stayed the same. This increases the population size of these countries. Demographic transition is complete when birthrate falls to death rate.

Population Growth in Real Time http://www.census.gov/main/www/popclock.html A cool website you could go to is http://www.worldometers.info/