Population Ecology
Population
single
Def. a group of individuals of a __________
species living in the same area
Characteristics of a popl’n
1) Size
2) Density
3) Dispersion
4) Age Structure
Dynamic Population Pyramid
US vs. Swaziland
Measuring Density
Mark and Recapture Method
4
1
=
3
x
4x = 3
5
4
x = 4/3
x
3
How would you find the value of x?
1
Set up a proportion
Apply same strategy of proportion for mark and recapture method
Mark and Recapture
40 fish are marked,
captured and
released. In 2nd
capture, 45 fish are
caught, 9 of which
were marked
(recaptured) What is
the estimated number
of individuals in the
population?
# of recaptures in
2nd catch
# of captures
=
Total Popl’n (N)
Total in 2nd catch
9
40
=
45
N
9N = 1800
N = 200
Demography
Def. The study of factors that affect the
growth and decline of populations.
Factors that affect growth: Birth and Immigration
Factors that affect decline: Death and Emmigration
Survivorship Curves
Describe how mortality of individuals in a
species vary over time; gives survival
pattern of popl’ns
Type I: most
survive to middle
Type
III:
most
Type
II:
constant
age before
individuals
die
death
rate;
mortality rates
while
still young;
likelihood
of death
increase; few
few
survive
toages
is
equal
at
all
offspring (high care
reproductive age
of young)
Life Histories
Characteristics that describe an organism’s
survival and reproductive schedule
1. Big Bang Reproduction / Semelparity
Ex. Salmon Spawning
• Lower rate of offspring survival
• Unpredictable env’ts
2. Repeated Reproduction / Interoparity
Ex. Lizards, humans
• Higher rate of offspring survival
• More dependable env’ts w/ limited resources
Population Growth Models
2 Models
1) Exponential Growth Model
2) Logistical Growth Models
What population do you think this is?
Exponential Growth Model
1) Also called geometric growth or Jshaped growth.
2) 1st growth phase is slow (lag phase)
3) 2nd growth phase is rapid (the
exponential phase)
So, what do you think is going to
happen to the human population?
• We will probably reach our carrying
capacity.
• Our growth rate will start to look like most
organisms, which is the Logistic Growth
Model
Carrying Capacity (k)
What letter does this curve
kind of look like?
Logistical Growth Model
1) Often called the S-shaped growth curve
2) Growth slows or stops following exponential growth
at the population’s carrying capacity
3) Populations stop increasing when:
•
•
Birth rate < Death rate
Emigration > Immigration
4) Carrying capacity can be raised or lowered. How?
•
•
Ex. 1: Artificial fertilizers have raised k
Ex. 2: Decreased habitat can lower k
Deriving Equations to Growth
Models
We will now derive the mathematical equations for
both models
First let’s define some variables:
N = Population size
K = Carrying capacity
T = time
r = reproductive rate
B = # of births
D = # of deaths