Unit5：Population Growth&Extinction 人口增长与灭绝的联系

Birth or Death Rate
dlow
Klow
K
Khigh
Population Size
Fluctuating Environment
Merlin
Paramecium
Khigh
Khigh
Klow
Klow
At Khigh there is ____ feedback from environment that increases ____ At Klow there is ____ feedback from environment that increases ____
Populations: Growth & Extinction
Population Ecology
What is a population?
“A group of individuals of the same species living together in the same place at the same time.”
A. B. 10 yrs 35 yrs
C.
50 yrs
D. 100 yrs
Attendance exercise- not a clicker question
Bacterial Biotic Potential
One bacterium weighs 1 10-12 grams. Say we start with one individual and a division occurs every 20 min. Assuming no mortality and that growth follows Nt = N0 ert, how many bacteria exist after 2 days?



Doubling time = time until Nt/N0 = 2
ln(Nt/N0) = ln(ert ) = ln(2)
rt = .7 t ~ .7/r
If r = 10%/yr then doubling time = ? t = .7/.10 = 7 yrs
A population is growing at 1.4% per year. What is the doubling time?
Limited Short
Short High
Equlibrial Species (K)
Often extensive Long
Long Low Few
# of young/reproductive episode Many
# of reproductions per lifetime
Age at 1st reproduction Eggs or offspring size Parental care
G = rN
•G is the growth rate of the population (# of new individuals added per time interval) •N is the population size at a particular time
•r is the per capita rate of increase
346 2
Data from C.J. Krebs, Ecology, 3rd ed. (New York: Harper & Row, 1985)
Size and Population Density
Population Declines
Handouts
Characteristics of Opportunistic (r) & Equilibrial Species (K)
Characteristic
Homeostatic capability Maturation time
Lifespan Mortality rate
Opportunistic Species (r)
• Mass of earth is 5.98 1027 g
• Is such growth possible?
What sets population size?
• Biotic potential • Environmental resistance
The Logistic Equation
House mouse Blue whales
Dandelions
Horses
House flies Coconut trees
Per capita rate of increase varies with the organism
rbacterium
>
rrabbit
>
relephant
Video: Reproducing
Exponential Growth in a rabbit population: per capita rate of increase
In this example r (per capita rate of increase) is 0.3. This value for r is due to # of births minus the # of deaths. For these rabbits with r = 0.3, there were 50 births and 20 deaths in one month with an initial population of 100 or r = 30/100 = 0.3.
&
decreases ______. decreases ______.
&
r & K Selection: The Logistic Model and Life Histories
r & K Selection: examples
Many offspring - high r Few offspring - low r
Biotic factors?
• Food • Habitat • Interactions:
– – – – Predation Competition Parasitism Disease
Physical factors?
• • • • • • Light Nutrients Water Temperature Space pH
Major Questions in Population Ecology
•
What factors determine the distribution & abundance of individuals in a population?
•
Why are some populations stable while others exhibit regular oscillations or chaotic fluctuations?
Organism
Soil arthropods Barnacles (adult) Trees Field mice Woodland mice Deer Human beings Netherlands Canada
Density/km2
5,000,000,000 2,000,000,000 50,000 25,000 1,200 4
Exponential Growth Model assumes ideal growth conditions and r is at the maximum capacity of the members to reproduce
Equation to calculate the rate of population increase is:
Phytoplankton
Population Growth
Some populations show exponential growth but this is not sustainable under normal conditions
What factors affect population size?
Bacterial Biotic Potential
• After 48 hours how many doublings?
3 per hr x 48 = 144
• How many cells?
• Total weight?
(2)144 = 2.2 1043 cells 2.2 1043 cells x 10-12 g/cell = 2.2 1031 g
Why are some populations extinction prone while others survive much longer?
•
Population Stability

Some populations have stable abundances
Nortne
Several
Late Large Extensive
rmax and Generation Time
Generation Time, d
Size and Rate of Increase
Representative Population Densities

*(1 – N/K) dN/dt = rN

What happens as N approaches K?
Logistic Growth Examples
Paramecium
Merlin
Fluctuating Environment- density dependent factors