POPULATION DYNAMICS CHAPTER 4

LET’S TALK ABOUT HOW POPULATION SIZE 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 LIVE IN AN AREA AT THE SAME TIME. RECALL THAT….

THE SIZE OF A POPULATION IS AFFECTED BY: BIRTHS, 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 TIME, 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).

-BIOLOGY GURU’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.”

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

FOR EXAMPLE: A large population of lions needs more food than a small population. If there are not enough resources, some lions will move out or die. Therefore, their food 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 LIMITING FACTORS: Density-Dependent Factors Density-Independent Factors

DENSITY- DEPENDENT LIMITING FACTOR A limiting factor that DEPENDS on the size of a population living in a certain amount of space.

DENSITY DEPENDENT LIMITING 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 LIMITING FACTORS CAN HAVE A GREATER EFFECT IN A DENSE POPULATION IN WHICH ORGANISMS ARE CROWDED TOGETHER! THIS IS CALLED POPULATION DENSITY.

EXAMPLE OF DD LIMITING 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 LIMITING 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 LIMITING 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 SIZES OR EVEN WIPE OUT POPULATIONS!