1. Chapter Eight: Understanding Populations

2. Section One: How Populations Change in Size
What is a population?
Population: all the members of a species living in the same place at the same time
Population Density: the number of individuals per unit area or volume
Population Dispersion: relative distribution or arrangement of a population’s individuals within a given amount of space

3. Section One: How Populations Change in Size
How does a population grow?
Growth rate: a change in a population’s size over a given period of time
Growth rate= births – deaths
When the number of births = number of deaths, the growth rate is 0

4. Section One: How Population Change in Size
How fast can a population grow?
Reproductive potential: the maximum number of offspring that each member of a population can produce
Exponential growth: populations grow exponentially, or faster and faster
Only happens when there is plenty of space and food in nature

5. Section One: How Populations Change in Size
What limits population growth?
Carrying capacity: the maximum population that an ecosystem can support indefinitely
Difficult to predict because ecosystems are always changing
Resource Limits
Competition within a Population
Members of population use the same resources in the same way and compete for that resource
Territories may be established

6. Section One: How Populations Change in Size
Population Regulation
Density dependent
Populations are large and there are not enough resources for everyone
Density independent
A certain amount of individual die regardless of population size
Such as weather and natural disasters

7. Section Two: How Species Interact with Each Other
An Organism’s Niche
Niche: the unique role of a species within a ecosystem
Includes their home, environmental factors needed for survival, and all interactions with other animals

8. Section Two: How Species Interact with Each Other
Ways Species Interact
Competition
Predation
Parasitism
Mutualism
Commensalism
Symbiosis and Coevolution

9. Section Two: How Species Interact with Each Other
Competition
When different individuals or populations attempt to use the same limited resource
Can occur within and between species
When different species compete for the same resource it is called a niche overlap
Indirect competition: species compete but do not come in direct contact with one another
Niche restriction: each species uses less of the niche than it is capable of using
Adaptations reduce competition

10. Section Two: How Species Interact with Each Other
Predation
When a predator feeds on a prey
Some organism have adaptations to avoid or defend against predation
Predator-prey populations are usually similar because the predator depends on prey for food

11. Section Two: How Species Interact with Each Other
Parasitism
When one organism lives in or on another and feeds on it
Examples: ticks, tapeworms, fleas, leaches, mistletoe
Parasites do not kill their host but often weaken it

12. Section Two: How Species Interact with Each Other
Mutualism
A close relationship between species in which both receive a benefit from the other
Examples: gut bacteria

13. Section Two: How Species Interact with Each Other
Commensalism
A relationship in which one species benefits while the other is not harmed or helped
Example: epiphytes

14. Section Two: How Species Interact with Each Other
Symbiosis and Coevolution
Symbiosis: a relationship in which two species live in close association
Usually describes relationships where atleast one species benefits
May lead to coevolution