1. Populations and Community Ecology
Chapter 19 and 20
Populations and Community Ecology

2. Why is it important to study Populations?
Let’s consider the human specie population…
Currently: about 6.1 billion
Projected growth: 9.3 billion by 2050
Have other species increased or decreased?
Can human population increase faster than food production?
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3. What is a population? all the fish in a pond All the birds in NYC
A group of organisms that belong to the same species and live in a particular place at the same time.
(Should be isolated and not interact with others)
Question: Which of the following is a population?
all the fish in a pond
All the birds in NYC
All the members of a family of humans
All the fish of the same species in a lake.
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4. Dispersion (Distribution)
Population Size
Number of individuals that population contains
Population Density
the average number of individuals in a population per unit of area
Dispersion (Distribution)
describes how the individuals are distributed
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5. 1. Dispersion Spatial distribution of individuals Clumped Uniform
Random
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6. Continuation on Dispersion
Clumped
Allows organisms to hunt or defend themselves more efficiently
Uniform
Maximize the distance from all of the neighbors
Random
Individuals do not interact strongly.
Most populations show clumping or uniformity
Benefits to each?

7. 2. Population Equilibrium
Affected by: birth rate and death rate.
When birth rate equals the death rate, the population remains at a constant level. =
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8. 3. Birth Rate 4. Death Rate (Natality) Number of live births
(Mortality)
Number of deaths
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9. 5. Growth Rate The amount by which a population changes
Rate of increase is represented by:
Birth rate – death rate = Growth Rate
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10. What affects growth rate?
6. Factors that affect GROWTH RATE
1. Immigration
2. Emigration Nasality
3. Birth Rate
4. Death Rate Immigration (+) Emigration (-)
Mortality
Growth Rate
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11. 8. Emigration 7. Immigration vs.
Movement of individuals into a population
Movement of individuals out of a population
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12. How do population grow????? 9. Exponential Growth (J)
10. Logistic Growth (S)
The exponential form is used when populations reproduce continually
Actually, the human population has shown faster-than-exponential growth, but is now exhibiting a gradual slowing of the growth rate
Population will exhibit an initial exponential phase followed by slowed growth.
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13. What causes growth to slow down????
11. Carrying Capacity (k)
The maximum population size that can be supported by the available resources
There can only be as many organisms as the environmental resources can support!!!!!
Food supply
Disease
Predation
Buildup of toxic waste
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14. Chapter 20
Community Ecology
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15. This chapter focuses on the five major types of interactions among species
1.Predation
2. Competition
3. Parasitism
4.Mutualism
5. Commensalism

16. 12. Predation
An individual of one species, called the predator, consumes a prey.
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17. 13. Adaptations in animals vs. plants
Animal avoid being eaten by:
Fleeing
Chemical defenses
Mimicry (Harmless king snake mimics a venomous snake)
Plants avoid being eaten by:
Thorns
Spines
Tough leaves
Secondary compounds
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18. 14. Competition
Type of interaction in which two or more species use the same resource.
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19. 15. Symbiosis
Any of the several living arrangements between two different species.
Includes:
Parasitism
Mutualism
Commensalism
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20. Examples of Symbiosis 16. Parasitism 17. Mutualism 18. Commensalism
Host is harmed while parasite benefits
Doesn’t lead to immediate death
17. Mutualism
Both species will result in a benefit
18. Commensalism
One specie is affected while the other isn’t affected
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21. Use the following adjectives to describe each specie: “benefited” “harmed” or “unaffected”
Interaction
Species A
Specie B
Example
Predation
Rattlesnake hunt and feed on mice
Competition
Barnacles compete for space in intertidal zones
Parasitism
Tapeworms are endoparasites in humans
Mutualism
Bees pollinate plants
Commensalism
A bird nests in a tree
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22. 19. Latitude and Specie Richness
The closer a community is to the equator, the more species it will contain.
Due to more stable climate
Due to tropical habitats weren’t disturbed in the last Ice Age as the habitats closer to the poles.
Specie Richness is the number of species in a community.
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23. Disturbances are events that change communities
One of the most important characteristics of a community is how it responds to disturbances. Change communities by removing/destroying organisms; altering resources.
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24. 20. Ecological Succession
The gradual, regrowth of a community of species.
Lichens will colonize rock and secrete acids that break down the rock and start the soil-production process.
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25. There are 2 types of Succession…..
21. Primary Succession
22. Secondary Succession
Development of a community that has not supported life previously
Very slow!!!!!!
Replacement of species that follows disruption of an existing community
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26. 23. Pioneer Specie First species that predominate early in succession
When lichens die, they provide some organic matter that also contributes to soil.
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27. 24. Climax Community
Series of stages until a community proceeds to its stable endpoint
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