2.  A population is a group of organisms belonging to the same species and living within a certain area.  The number of organisms within the group is the population size.  Under ideal conditions, unlimited food, absence of disease etc, the size of a population would increase indefinitely.

3.  Increase in the size of a population over time is termed population growth.  Here is an example of a J-shaped growth curve.

4.  Under ideal conditions, many species of bacteria can double their population size every 20 minutes.  In 36 hours, one bacterium could give rise to enough bacteria to cover the Earth with a layer 30 cm deep.  The highest rate of reproduction under ideal conditions is called a population’s biotic potential.

5.  Most organisms never reach their biotic potential.  Limiting factors are circumstances that keep organisms from reaching their biotic potential.  Temperature, disease, predators, habitat, and lack of food can all be considered limiting factors.

6.  How do we know how populations grow and respond to the environment?  In a lab, growth can be studied easily because conditions can be controlled.  To study a population of yeast cells, a culture medium can be inoculated with a few yeast cells and growth can be measured.

7. Population Age (Hours)Number of CellsIncrease in Number 010 22919 47142 6175104 8351176 10513162 1259582 1464146` 1665615 186626

9.  When a population arrives at a point when its size is no longer increasing, it has reached its carrying capacity of the environment at that particular time.  This number is not definite or permanent.  What do you think this means?  At carrying capacity, the birth rate for a population will roughly equal the death rate, (everything else being equal.)

10.  Limiting factors for organisms that follow an S-shaped growth curve are almost always density-dependent.  This means the influence of any limiting factor varies with the size of the population density.  Example: Frogs in a pond.

11.  Insects usually show a different kind of population growth. Resembles a J curve at first, then crashes. Ex:  DI factors, like temp, fire, oxygen supply, hurricanes, etc. are generally physical aspects of the environment.

12.  Questions 1-5 page 766

13.  DD limiting factors are more often biological rather than physical.  Predation and food: Often hard to determine what effect predation has on a population.  Predation as a DD factor: we will work on an activity with this.  Is predation beneficial?

14.  Parasites can be limiting factors for a population.  They usually harm their host, but do not kill it.  If they killed the host, they would be without a home.  Why is parasitism a DD factor?  What about disease and populations? Are they DD as well?

15.  When populations of different species compete for same food source.  Its DD.  When it occurs, three things may happen: › Extinction (local) › Movement – warblers and spruce trees. › Adaptation – Darwin’s finches – seeds vs. insects. Virtual Lab involving Paramecium caudatum and Paramecium aurelia.

16.  Competition between members of the same species.  More severe, because all members of the same species have same requirements to survive.  Also DD: how organisms adapt › Life cycles and life spans – tadpoles and frogs; insects, dispersal of plant seeds by wind. › Dominance and social hierarchy – wolves. Increases order and decreases aggression throughout the species. If not all can mate due to poor conditions, dominant ones will and lesser ones will not.

17.  Role separation – ants and bees  Behavioral and physiological changes – birth and death rates can be affected by stress in populations.  Emigration – move out to a new area.  Territoriality – song birds, coyotes, fox, howler monkeys. Reduces conflict within species and can help keep populations in check.

19.  Right now, it appears to be a J curve growth.  Growth rates are declining in developed countries.  Not the case in undeveloped countries. › More sanitary populations › Antibiotics › Technology has expanded the limits

20.  Thomas Malthus wrote an essay on population growth.  Dealt with people’s tendency to take care of what they owned, and not take care of what they did not.