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Population Dynamics.

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Presentation on theme: "Population Dynamics."— Presentation transcript:

1 Population Dynamics

2 Population Characteristics
All populations have three main characteristics that are used to classify the population. Population density Spatial Distribution Population ranges Growth Rate

3 Population Characteristics
1. Population Density- Number of organisms per unit area Example: pg 92 Three birds per square meter, closer to water buffalo Fifty meters from water buffalo, density is zero

4 Population Characteristics
2. Spatial Distribution Dispersion- the pattern of spacing a population within a certain area. 3 types: See page 93 and draw a diagram to show the different patterns. a. Uniform- ex: Black bear b. Clumped- ex: American Bison c. Random- ex: White-tailed Deer

5 Population Characteristics
Population Ranges There is no population that occupies all habitats in the biosphere Population ranges can be limited by abiotic factors such as temperature range, humidity, annual rainfall and sunlight Biotic factors may be predators, competitors and parasites

6 Population-Limiting Factors
Limiting factors- biotic or abiotic factors that keep a population from increasing indefinitely. Ex: food supply increases population increases, food supply decreases population decreases Two Categories of Limiting factors: Density-Independent Factors 2. Density- Dependent Factors

7 Limiting Factors Density-independent factors:
Any factor in the environment that does not depend on the number of members in a population per unit area Usually abiotic Natural phenomena (weather events)-drought, flooding, extreme heat or cold, tornadoes, hurricanes, and wild fires Human Activities- such as air, land and water pollution

8 Limiting Factors Density-dependent factors:
Any factor in the environment that depends on the number of members in a population per unit area Usually biotic factors Predation, disease, parasites and competition

9 Density-Dependent factors Disease
1. Outbreak of disease occurs when population has increased and population density is high 2. Disease is transmitted easily when pop density is high because contact is more frequent 3. Disease spreads easily and quickly

10 Density-Dependent factors Competition
Competition increases when density increases Individuals must compete for resources Competition can occur within a species or between other species Could result in population decrease because of starvation or individual leaving the area As population size decreases, competition decreases

11 Density-Dependent factors Parasites
1. Similar to disease, as population density increases parasites can negatively affect population growth

12 Population Growth Rate (PGR)
Definition: Explains how fast a given population grows. Dependent on the following factors: 1. Natality-birth rate 2. Mortality-death rate Emigration-individuals moving away from population Immigration-individuals moving into a population *******Birthrate and death rate are usually most important when figuring out the PGR because emigration usually equals immigration.

13 Exponential Growth Model
**No limits placed on growth rate by environment Population grows slowly at first –lag phase Population rate soon begins to increase rapidly because number of organisms that can reproduce has increased J-shaped curve- Figure 7 All populations grow exponentially until some limiting factor slows the pop growth

14 Logistic Growth Model A S-shaped curve (figure 8)
Occurs when the populations growth slows or stops following exponential growth, at the populations carrying capacity. Carrying capacity-The maximum number of individuals in a species that an environment can support for the long term Limited by energy, water, oxygen and nutrients available. The reasons why many populations stabilize

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