Population Ecology

Population

Def. a group of individuals of a __________ species living in the same area

Characteristics of a popl’n1) Size2) Density3) Dispersion4) Age StructureDynamic Population PyramidUS vs. Swaziland

single

Measuring Density

Mark and Recapture Method

3

45

1

x

How would you find the value of x? Set up a proportion

=4

3

1

x4x = 3

x = 4/3

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?

=9

45

40

N

=

# of recaptures in 2nd catch

Total in 2nd catch

# of captures

Total Popl’n (N)

9N = 1800

N = 200

Demography

Def. The study of factors that affect the growth and decline of populations.

Factors that affect growth:

Factors that affect decline:

Birth and Immigration

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 age before mortality rates increase; few offspring (high care of young)

Type II: constant death rate; likelihood of death is equal at all ages

Type III: most individuals die while still young; few survive to reproductive age

Life Histories

Characteristics that describe an organism’s survival and reproductive schedule

1. Big Bang Reproduction / SemelparityEx. Salmon Spawning• Lower rate of offspring survival• Unpredictable env’ts

2. Repeated Reproduction / InteroparityEx. 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 J-shaped 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?

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

Logistical Growth Model

Deriving Equations to Growth Models

We will now derive the mathematical equations for both models

First let’s define some variables:

N = Population sizeK = Carrying capacityT = timer = reproductive rateB = # of birthsD = # of deaths