1. How Populations Grow
Ms. Simons 2015

2. 3 important characteristics of a population
Its geographic distribution
Its density
Its growth rate

3. Geographic distribution
Is the area inhabited by a population.
This can vary in size
A few cm for bacteria living on a rotting apple
Millions of kilometers for a population of whales.

4. Population Density The number of individuals per unit area.

5. 3 factors that affect population size
# births
# deaths
# of migrations (entering or leaving)
A population will increase or decrease in size depending on how many individuals are added or removed from it.

6. Population Growth Birth rate > death rate = Growth
Birth rate < death rate = Pop shrinks
Birth rate = death rate = Pop stays the same

7. Immigration- the movement of individuals into an area.
Emigration- the movement of individuals out of a population.

8. Exponential Growth
Occurs when the individuals in a pop reproduce at a constant rate.
At 1st the growth is slow
Over time the growth increases at a faster rate.
Under ideal conditions with unlimited resources, a pop will grow exponentially.

9. Rabbit population after 10 years shows exponential growth

10. Looking back Look at your graph from the deer population activity.
At which point did the deer, lion, and resource populations grow exponentially?

11. Logistic Growth (S shaped curve)
Occurs when a pop’s growth slows (or stops growing exponentially)
-As resources become less available, the growth of population slows or stops.

13. Looking back Look at your graph from the deer population activity.
At which point did the deer, lion, and resource populations show logistic growth?

14. Carrying Capacity
This is the largest # of individuals an environment can support.
This is where the growth levels off
When the carrying capacity is reached the growth rate is zero.

15. Looking back Look at your graph from the deer population activity.
At which point did the deer, lion, and resource populations reach carrying capacity?

16. Biotic Factors
Biotic factors are the biological influences on organisms within an ecosystem.
These are living influences, such as prey, predators, producers, and other cohabitating organisms.

17. Density-dependent factors
Factors that influence the growth rate of a population
Density of the population matters
Usually biotic factors
Examples: predation, disease, food availability, migration, & parasitism
The density dependent factors are factors whose effects on the size or growth of the population vary with the population density. There are many types of density dependent limiting factors such as; availability of food, predation, disease, and migration. However the main factor is the availability of food. For example when the food supply of jack rabbits get depleted, they start to die or migrate to another places causing the foxes or the secondary consumers to have a shortage of food; also causing them to die or migrate. 

18. Abiotic Factors
Abiotic factors are physical nonliving factors that shape an ecosystem.
Ex. Climate (temperature, precipitation), sunlight, wind, limiting nutrients, etc.

19. Density-independent factors
Any factor limiting the size of a population whose effect is not dependent on the number of individuals in the population
Usually abiotic factors
Examples: natural disasters, climate, precipitation

21. A Habitat A habitat is the area where an organism lives.
A habitat includes both the biotic, and abiotic factors.
Together biotic and abiotic factors determine the survival of both an organism and the productivity of the organism’s ecosystem.

22. Community Interactions
Competition
Predation
Symbiosis
Mutualism
Commensalism
Parasitism

23. Competition
Competition occurs when two organism (of the same or diff species) attempt to use a resource in the same space at the same time.
A resource is any life necessity. (food, water, light, shelter, etc.)

24. Competitive Expulsion Principle (CEP)
CEP states that no 2 species can occupy the same niche in the same habitat at the same time.

25. Predation
Predation is when one organism captures and feeds on another organism.
The organism that does the killing is called the predator.
The organism that gets killed is called the prey.

26. Symbiosis
Symbiosis is any relationship in which 2 species live closely together.
There are 3 main types of symbiosis.
Mutualism- both species benefit from the relationship.
Commensalism- One organism is helped by the relationship, the other, is neither helped nor harmed.

27. 3. Parasitism- One organism lives on or inside another organism, and harms it.
The parasite receives all or part of its nutrition from the host organism.
The host is weakened, but not usually killed. Ex. tapeworm