1. Chapter 8 Understanding Populations
Section 1: How Populations Change in Size

2. What is a Population?
Members of the same species living in the same place at the same time.
A reproductive group.
Examples:
bass in an Iowa lake
palm trees on an island

3. Properties of Populations
Size
Density= number of individuals
per unit area or volume
example: 14 birds = 7 birds per acre
2 acres
3. Dispersion- the relative distribution or arrangement of individuals within a given amount of space. —3 types….

4. Clumped Dispersion
Individuals live close together in groups for mating purposes, protection, or food resources
Clumped
dispersion

5. Uniform Dispersion
Individuals live at specific distances from one another
Uniform dispersion 

6. Random Dispersion Individuals are spread randomly within an area

7. Factors determine the size of a population
Immigration: movement of individuals into a population
Emigration: movement of individuals out of a population
Births: increase the size of a population
Deaths: decrease the size of a population

8. positive growth rates: more births, less deaths
zero growth rates: births = deaths
negative growth rates- more deaths, less births

9. Reproductive Potential:
biotic potential: the fastest rate at which a population can grow---this is limited by reproductive potential.
Reproductive potential: maximum number of offspring that a given organism can produce.
Some species have higher reproductive potential than others.-- Ex. Bacteria and insects have a high reproductive potential , while elephants have a low one

10. Reproductive potential increases when individuals produce more offspring at a time, reproduce more often, and reproduce earlier in life.
Reproducing earlier in life has the greatest effect on reproductive potential.
Reproducing early shortens the generation time, or the average time it takes a member of the population to reach the age when it reproduces.

11. Reproductive Potential con’t.
Small organisms, such as bacteria and insects, have short generation times and can reproduce when they are only a few hours or a few days old.
As a result, their populations can grow quickly.
In contrast, large organisms, such as elephants and humans, become sexually mature after a number of years and therefore have a much lower reproductive potential than insects.
Most organisms have a reproductive potential that far exceeds the number of their offspring that will survive. Ex. sea turtles, frogs

12. Population growth is based on available resources
2 types of population growth
- exponential growth
- logistic growth

13. Exponential Growth
Population grows rapidly due to abundant resources
bacteria or molds grow on a new source of food.
J-shaped curve

14. Logistic Growth
Population begins with slow growth followed by exponential growth then levels off due to limited resources
S-shaped curve

15. What Limits Population Growth?
a. resources being used up
b. environment changes
c. deaths increase or births decrease
d. Natural selection

16. Carrying Capacity:
maximum amount of individuals that an environment can support
A population may increase beyond this number but it cannot stay at this increased size.
Reached when a particular natural resource is consumed at the same rate at which the ecosystem produces the resource = limiting resource

17. Carrying Capacity
Example of carrying capacity: rabbits in Australia page 214

18. Ecological factors regulate population growth
Limiting factor: something that keeps the size of a population down
2 types of limiting factors
1. density-dependent
2. density-independent

19. Density-dependent limiting factors affect a population that has become overcrowded
Competition
Predation
Parasitism &
disease
The greater the population, the greater effect these factors have.
Ex. Black plague in the Middle Ages – more deaths in cities
Page 216- beetles spreading disease to pine trees

20. Density-independent limiting factors limit a population’s growth regardless of the density.
Unusual weather
Natural disasters
Human activities
-Most are abiotic factors
-Page 216- winter storm freezing crops and fruiting trees (regardless of density)

21. Section 2: How Species Interact with Each Other

22. A habitat differs from a niche.
Habitat: where an organism lives
includes
- biotic factors
&
- abiotic factors

23. - food (type, how it gets it, where is it in the food web)
Niche: includes all of the factors that a species needs to survive, stay healthy, and reproduce
- food (type, how it gets it, where is it in the food web)
- abiotic conditions (temp., amount of water it needs)
- behavior (when is it active, when does it reproduce)
**A habitat is where a species lives and a niche is how it lives within its habitat.

24. A lion must hunt and kill its
prey in order to survive on
the African savannah. Its
role as a top predator is
part of the lion’s niche. The lion may use the tall grass as camouflage, and hunt primarily at dawn or dusk. It also spends afternoons in the shade. All of this helps define its “ecological niche”.

25. Competition occurs when organisms fight for the same limited resources
Two types of competition:
- Interspecific: 2 different species compete for a limited resource
- Intraspecific: individuals from the same species compete for a limited resource

26. Ways some species adapt to competition:
Competitive Exclusion Principal- states that when two species are competing for the same resources, one species will be better suited to the niche, and the other species will be pushed into another niche or become extinct. (Also known as niche restriction)

27. potential niche- total niche a species can occupy
realized niche- where species is actually found

28. Another example:
North American gray squirrel
European red squirrel

29. Predation occurs when one organism captures and eats another

30. When predators eat only specific types of prey, the sizes of each population tend to increase and decrease in linked patterns, as shown below.
Ex. Canadian
Lynx and snowshoe
hare

31. Symbiosis
means “living (biosis) together (sym)” = It is a close ecological association between two or more organisms of different species.
3 Types of symbiosis:
- mutualism
- commensalism
- parasitism

32. Mutualism: both organisms benefit
- Bat eats cactus and spreads
seeds to new locations

33. bees get nectar from the plant and the plant is pollinated

34. Acacia tree and red ants: ants provide protection from other organisms trying to feed on the tree and the ants receive a home and nectar.

35. Tickbird feeds off insects on rhinos
Back; rhino gets irritating bugs picked
off hide = both benefit

36. Commensalism: one organism benefits, the other is unaffected
Human Our eyelashes are home to tiny mites
that feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle.
Demodicids Eyelash mites find all they need to survive in the tiny follicles
of eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope. +
Organism benefits Ø
Organism is
not affected
Commensalism

37. Sea anemone and clown fish- Fish feeds on scraps of food that come out the anemones mouth. The sea anemone receives nothing in return

38. Orchids growing in tops of trees- The orchids grow around the tree trunks and do not harm the tree. The orchid is exposed to sunlight and rain.

39. Parasitism: one organism benefits (parasite), the other is harmed (host)+ _
Organism is harmed
Hornworm caterpillar
The host hornworm will eventually die as its organs are consumed
by wasp larvae.
Braconid wasp
Braconid larvae feed on their host and release themselves shortly before reaching
the pupae stage of development.
Parasitism

40. Other examples of parasites: ticks, fleas, tapeworms, leeches, mistletoe.