ch 4: population biology 4.1 population dynamics
TRANSCRIPT
Ch 4: Population BiologyCh 4: Population Biology
4.1 Population Dynamics
4.1 Population Dynamics
Lets Calculate the number of bacteria there would be if the population were allowed to grow for 24 hours.
Assume that there were two to start with, they divide once every 20 minutes, and none of them died.
What factors might keep them from taking over the world?
Principles of Population Growth
Principles of Population Growth
Section 4.1Section 4.1
Linear Growth
Suppose you work at a some job
You get paid $10 per hour
How much would you have in 10 hours?
Section 4.1Section 4.1
How do Populations Grow?How do Populations Grow?
This is NOT how populations grow
Exponential Growth
The initial phase of population growth is slow because the number of available organisms is limited at first.
Soon the growth becomes very fast as the organisms reproduce.
How do Populations Grow?How do Populations Grow?
Section 4.1Section 4.1
J shaped curve – unchecked
growth2, 4, 8, 16, 32, 64,
128, 256, 512
Is growth unlimited?
Can a population of organisms grow indefinitely?
Limiting factors
Space to grow
Availability of food
The number of organisms that an environment can support is called the Carrying Capacity.
Limits of the EnvironmentLimits of the Environment
Section 4.1Section 4.1
The graph of the carrying capacity is a S curve.
Populations start out slow and then experience a period of exponential growth, followed by a stabilizing growth rate.
Populations go above the carrying capacity then fall below, only to rise above again.
Carrying CapacityCarrying Capacity
Section 4.1Section 4.1
If the population overshoots carrying capacity, limiting factors will come into effect and deaths will exceed births and the population will fall below carrying capacity.
Carrying CapacityCarrying Capacity
Section 4.1Section 4.1
Why do some populations of organisms seem to thrive at certain times of the year and then dwindle at other times?
In order to answer this question biologists study the reproductive pattern (aka life history pattern) of animals.
Patterns of Population GrowthPatterns of Population Growth
Section 4.1Section 4.1
Two extreme organisms for population growth rates are elephants and mosquitoes.
Mosquitoes are rapid reproducers over a short time.
Elephants are slow reproducers over a long time.
Ranges of Population GrowthRanges of Population Growth
Section 4.1Section 4.1
Mosquitoes are successful in environments that are unpredictable and unstable.
Organisms with this type of life-history pattern tend to:
Be small
Mature rapidly
Reproduce early
Have a short life span
The Mosquito StrategyThe Mosquito Strategy
Section 4.1Section 4.1
Organisms that tend to live in a more stable environment have a different life-history pattern. They tend to:
Be large
Reproduce and mature slowly
Live for long periods of time.
The Elephant StrategyThe Elephant Strategy
Section 4.1Section 4.1
• The type of reproductive pattern that an organism has depends on the environment they are in.
• Limiting factors in an environment can be biotic or abiotic and may include limited food supply, space, chemicals, temperatures …
• How organisms are dispersed can also be important.
Why the Different Types of Reproductive Cycles?
Why the Different Types of Reproductive Cycles?
Section 4.1Section 4.1
Population Density
The number of organisms per
unit areaSpatial Distribution
Chapter 4
Population Ecology
Dispersion is the pattern of
spacing of a population.
Spatial DistributionSpatial Distribution
• 3 types of dispersion
• Dependent on the availability of resources such as food.
Plant, bat, resources clumpedCompeting for a resource; territories
Neutral interactions
between organisms
Density-DependantE.g. Disease, Competition, Parasites, Food
(effects get bigger as population size increases)
Density-IndependentTemperature, Storms, Floods, Drought
(effects not influenced by population size – mostly abiotic)
Two Limiting Factors that affect Dispersal
Two Limiting Factors that affect Dispersal
Section 4.1Section 4.1
Organism InteractionsOrganism Interactions
• Population sizes are also controlled by interactions among organisms that share a community -- biotic factors
Organism Interactions Limit Population Size
Organism Interactions Limit Population Size
The population of the prey in a community will affect the population of the predators.
Likewise the opposite is true.
This relationship is referred to as the Predator-Prey Relationship
e.g. Lynx and Hare
Predation increases the chance that resources will be available for the remaining individuals in a prey population!
Predation Affects PopulationPredation Affects Population
Section 4.1Section 4.1
The more organisms in the same population you have struggling for the same resource the less resources there are for each individual organism.
Competition for resources such as food, water and territory increases with increased population = density dependent
Competition for ResourcesCompetition for Resources
Section 4.1Section 4.1
As a population grows the amount of stress increases in a population.
Stress can cause:
Aggression
Decrease in parental care
Decreased fertility
Decreased resistance to disease
Crowding and StressCrowding and Stress
Section 4.1Section 4.1
