POPULATION DYNAMIC S

CHAP T ER 4

LET ’S TALK ABOUT HOW POPULATION S IZE CHANGE HELPS HUMANS PRESERVE HEALTHY ECOSYSTEMS.

ABIOTIC FACTORS

• All the nonliving components of an ecosystem.

• Sunlight

• Temperature

• Precipitation

• Soil type

• Salinity

• Materials: Water, Nitrogen, and Oxygen

BIOTIC FACTORS

• All the living things in an environment.

• All the organisms with which an organism may interacts: Bacteria, plants, animals, fungi, and protists.

BIOTIC FACTORS CONTINUED…• May include: Other organisms

that the organism eats or tries to eat

• organisms that compete against one another

• any other organism with which the organism has a symbiotic relationship.

A POPULATION IS MADE UP OF ALL THE ORGANISMS OF A SPECIES THAT L IVE IN AN AREA AT THE SAME T IME.

RECALL THAT….

THE S IZE OF A POPULATION IS AFFECTED BY: B IRTHS, DEATHS, IMMIGRATION, AND EMIGRATION

IMMIGRATION

• The movement of organisms into an area.

• Births and immigration increase population size.

EMIGRATION

• Moving out of an area.

• Deaths and emigration decrease population size.

BIRTH AND DEATH RATES OF HUMANS ARE AFFECTED BY MANY FACTORS:

• For example: Birth rates in underdeveloped nations tend to be much higher than those in developed nations.

• This higher birth rate is due to a need for more people to do work such as farming.

AT THE SAME T IME,

• death rates in many developing nations are higher than those in developed nations.

• This is due to a lack of food and water, medical care, and sanitary conditions (clean water).

-B I OLOGY G UR U ’ S

“Overall, changes in either abiotic or biotic factors can greatly affect

population sizes. If a population cannot adapt to changes in its environment, some members will die or move away

and the population will decrease. Likewise, if organisms are well adapted

for a changed environment, their numbers may increase.”

L IMIT ING FACTORS

• Anything in the environment that can “limit” the size of a population.

FOR EXAMPLE:

A large population oflions needs more food than

a small population. If there are notenough resources, some lions

will move out or die. Therefore, theirfood supply is limited.

• Limiting Factors also include the following in addition to food…

• Water

• Oxygen

• Sunlight

• Relationships with other organisms

THERE ARE 2 MAIN TYPES OF L IMIT ING FACTORS:

• Density-Dependent Factors

• Density-Independent Factors

DENSITY-DEPENDENT L IMIT ING FACTOR

• A limiting factor that DEPENDS on the size of a population living in a certain amount of space.

DENSITY DEPENDENT L IMIT ING FACTORS INCLUDE:

• Competition- competing for the same resource

• Predation-One kills and eats another

• Parasitism- One organism benefits at the expense of another

• Diseases- Spread by pathogens

ALL OF THESE L IMIT ING FACTORS CAN HAVE A GREATER EFFECT IN A DENSE POPULATION IN WHICH ORGANISMS ARE CROWDED TOGETHER!

THIS IS CALLED POPULATION DENSITY.

EXAMPLE OF DD L IMIT ING FACTOR:

• Dutch Elm Disease

• Caused by fungus

• Beetles spread the fungus

• Because the trees were so close together, the disease spread rapidly and killed almost half the elm trees in the northern U.S.

ANOTHER EXAMPLE OF DD L IMIT ING FACTOR:

• Tuberculosis (TB)

• caused by bacteria that affects lungs

• spread through the air when coughing, sneezing, or exhaling while talking.

• Can spread rapidly in dense populations

DENSITY-INDEPENDENT L IMIT ING FACTOR

• limits the growth of a population regardless of its density.

EXAMPLES OF DENSITY-INDEPENDENT FACTORS INCLUDE:

• Abiotic factors such as: weather, natural disasters such as forest fires, droughts, tsunamis, and pollution produced by humans.

THESE EVENTS CAN REDUCE POPULATION S IZES OR EVEN WIPE OUT POPULATIONS!