1. Chapter 4: Population Biology

2. Population
group of organisms, all of the same species, that live in a specific area

3. How fast do populations grow?
Not linear growth – so it is not a straight line
Graph- starts to increase slowly, then resembles a J-shaped curve
Initial increase slow, b/c # of organisms that reproduce is small
Increases b/c the total # of individuals that can reproduce has increased

4. Is Growth Limited?
J-shaped growth curve illustrates exponential population growth
Exponential Growth – means that as a population get larger, it also grows at a faster rate

5. What Can Limit Growth? Population growth does have limits
Limiting Factors – food, disease,
predators, or lack of space will
Cause population growth to SLOW
Under these conditions the population may stabilize in a S-shape growth curve

6. Carrying Capacity
the number of organisms of one species that an environment can support indefinitely
 Developing population – more births than deaths and the population increases until the carrying capacity is reached or passed
When a population overshoots the carrying capacity, limiting factors come into affect
Deaths begin to exceed births and the population falls below the carrying capacity

8. Reproduction Patterns
Life-History Pattern- organisms reproduction pattern
Slow life-history pattern – slow rate of reproduction and produce relatively few offspring
  Ex. Elephant
Fast life-history pattern – reproduce rapidly and produce many offspring in a short period of time
Ex. Mosquito

9. Rapid Life- History Patterns
Common among organisms in changeable or unpredictable environments
Organisms have:
Small body size
Mature rapidly
Reproduce early
Short life span
reproduction rises rapidly then decline when environment becomes unsuitable
population survives and will reproduce again when the environment is favorable

10. Slow Life- History Patterns
large species that live in more stable environments
Elephants, Bears, Whales, Humans, and plants (trees)
reproduce and mature slowly
long-lived
maintain population sizes at or near carrying capacity

11. Density Factors and Population Growth
3 Patterns of Dispersal:
1. Random
2. Clumped
3. Uniform

12. Density-Dependent Factors
disease
competition
predators
parasites
food

13. increasing affect as the population increases
Example- corn fields
Crops grow close together
Disease can spread rapidly and kill off the whole crop

14. Density-Independent Factors
can effect most populations regardless of their density
Most are abiotic factors
  Volcanic eruptions
Temperature
Storms
Floods
Drought
Chemical Pesticides
Major habitat destruction
Usually affect smaller organisms more
Example – Mosquitoes – severe winters kill the adults of most species

15. Population Size limited by abiotic and biotic factors
controlled by various interactions among organisms that share a community
Predation – can effect population size in minor and major ways

16. Locusts eat acres of lettuce on a farm
Brown snake introduced into Guam, there were no native predators, and it preyed freely on native birds – drastic effect on the population size

17. predator- prey relationships are known to experience cycles or changes in their numbers over periods of time
prey population increases and there is more food for the predator, so the predator population increases
predator population increase and predation increase, therefore – the prey population declines.
With less food, the predator population decrease.
Cycle starts again

18. Competition within a Population
density dependent factor
few individuals compete for resources, usually no problems
When population increase and the demand exceeds the supply, the population size decreases

19. Crowding and Stress
populations become crowded, individuals exhibit stress
stress symptoms
Aggression
decrease in parental care
decreased fertility
decreased resistance to disease
all have negative effects on a population

20. Human Population Demography – study of human population size
density and distribution
movement
Birth and death rates

21. Human Population Growth
Humans change their environment
Developed methods for producing
more food
infant mortality rate decreased
clean water
All enable people to live longer and produce more offspring
Population Grows

22. Calculating Growth Rate
Birthrate – number of live births per 1000 population in a given year
Death rate – number of deaths per 1000 population in a given year
Immigration – movement of individuals into a population
Emigration – movement of individuals out of a population

23. Calculate a population’s growth rate by
(Birthrate + Immigration Rate) – (Death rate + Emigration Rate) = Population Growth Rate
PGR = (B + I) – (D + E)
Immigration and emigration are not always accurate use:
PGR = Birthrate – Death rate

24. Positive Growth Rate
unless the growth rate becomes negative the population continues to grow, just slower
Doubling Time
time needed for a population to double in size
Age Structure
refers to the portions of the population that are in the different age levels