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POPULATION GROWTH & MEASUREMENT. AP Environmental Science Chapter 6. WHAT IS A POPULATION?. A group of interbreeding individuals within a geographical location. POPULATION SIZE is determined by: #of births (based on fertility rates) # of deaths # of indiv that

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POPULATION GROWTH & MEASUREMENT

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## POPULATION GROWTH & MEASUREMENT

AP Environmental Science

Chapter 6

### WHAT IS A POPULATION?

A group of interbreeding individuals within a geographical location.

POPULATION SIZE is determined by:

• #of births (based on fertility rates)

• # of deaths

• # of indiv that

enter or leave the population

### Population Graphs measure status of populations

J-curve or Exponential Growth Curve

S-Curve or Logistics Curve

### POPULATION DENSITY

DENSITY: number of individuals per unit area or volume

Ex: Suppose there are

150 bullfrogs living in a

pond that covers an

area 3 square km.

What is the population density?

### Population density

Population Density =

Number of Individuals (150 frogs)

Unit Area (3 sq KM)

= 50 bullfrogs per square kilometer!

### Populations Dynamics

• Population Modeling

http://www.hippocampus.org/course_locator?course=AP%20Biology%20II&lesson=63&topic=1&width=600&height=454&topicTitle=Population%20Ecology:%20Overview&skinPath=http://www.hippocampus.org/hippocampus.skins/default

### CARRYING CAPACITY

P

R

E

D

A

T

O

R

S

F

O

O

D

D

I

S

E

A

S

E

D

I

S

A

s

T

E

R

S

=

Max population that a habitat can support

(Level line)

### Carrying Capacity Factors

These limiting pressures keep a population in check such as carrying capacity:

• 1. # of Predators

• 2. Amount of Food & Water Resources

• Disease

• Natural Disasters

• Reproductive ability

### Other factors – H I P P O can decrease in population!!

• H=Habitat

• I= Invasive species

• P= Pollution

• P=Other interacting populations

• O=Overconsumption

### Exponential Increase (J-curve)

In a J-curve,

the popul keeps

growing

quickly

(exponentially over time).

### What causes J-curve to occur?

Conditions:

• No enemies

• No competition.

• Plenty of food & water

4. Low % of disease

J-curve is usually a temporary situation=Population crash.

### Exponential Growth Math Model

Change in N

Initial Population

Change in time

Rate of reproduction

Time

### dN/dt = rN

N=2 cockroaches (male and female)

r= 2 cockroaches can produce 20 offspring in 3 months

a. The rate of growth (r) 20/2 adults or 10 per 1 adult.

b. The growth rate (r) equals 10

### Exponential Growth can Crash

• When population can no longer sustain itself without food resources, pop decrease beneath the carrying capacity.

### Population Crash

Isle Royale, Michigan

National Park

Moose pop

quickly in 1991-1995.

Wolf pop due to

Parvovirus passed on from domesticated dogs visiting the National Park.

Moose population

Due to tick infestation.

### S-curve or Logistics Population

1. Population at equilibrium.

• S-curve may change (increase & decrease) slightly, but is constant near the carrying capacity.

• May be considered “restricted growth”.

Migration

### Logistics Curve Model

• dN = rN 1-N

dt K

dN = change of population over time

dt

N = Population

K= Current Carrying Capacity

r= rate of change or reproductive rate of a speciesd

### Logisitics/Carrying Capacity Connection

If the carrying capacity (K) = 100 wolves

If the N = 100 wolves (wolves bred successfully to increase population)

Look at the 1-N/K part: 1 - 100

100

1- 1 = 0

dN/dt = rN(0)=0!!!

### Logistics & CC (continued)

There is no change in dN/dt-no population growth!

What if N=50? Plug it into 1-N/K to see how it affects the reproductive rate for a population.

1-50/100 = 1-1/2 = 1/2rN or half of the maximum reproductive rate for the wolves.

### Logistics & CC (continued)

• If N = 10…plug into 1-N/K

(1- 10) = (1-.10) = .90

100

dN = rN(.90) or dNis at a rate of

dtdt

90% as fast as the max possible reproductive rate for the wolves!

### Lincoln Peterson Population Estimate Model

Estimating population size by random sampling an ecosystem.

Focus on population density or animal abundance.

Model: n1 = m2 OR N= n1 x n2

N n2 m2

n1=#animal marked & released 1st time

n2=# animals captured during 2nd session

m2-# animals captured during 2nd session & are marked.

Est Population

### Population Equilibrium

Equilibrium: the balance between births and deaths within a population

### Environmental Resistance

Factors/pressures that limit a population’s ability to increase (CC)

### Population Dispersal Definition

Different patterns of how a species or

population will inhabit a certain

geographical location.

Population Dispersal is determined by:

### POPULATION DISPERSAL

A. RANDOM:

1. Least Common

2. Found anywhere in envir.

3. High mobility such as wind blown

Ex: Dandelions

### POP DISPERSAL

B. Uniform

• Rare Occurrence but does occur in nature! (Hawks, wolves)

• Can indicate human impact

a. Plantations, orchards, etc.

Red-Tailed Hawk

Orchards

### CLUMPED POP DISPERSAL

C. CLUMPED:

• Patchy, most common

• Protection, avail of natural resources, to survive

• Ex: Allelopathy, fish, plants, trees, etc.

### Reproductive Potential

…Is an organism’s ability to grow at the fastest rate.

(To replenish the species—innate!)

R-selected

Hint: Rapid Repro

Early reproduction

Short life span

Hi mortality

Little/no parental care

Large # of offspring produced

Inhabit lower trophic levels (1st order consumers)

2. K-selected

Hint: Longer Repro

Late reproduction

Long life span

Low mortality

High parental care

Small # of offspring produced

K-SELECTEDTYPE

R-SELECTED TYPES

### Reproductive potential – “R”

Bacterium can produce 19 million descendants in a few days!!

Mosquitoes live 10-14 days laying eggs every 3 days.

Mosquito rafts have 200-300 eggs;. hatch in 48 hours

### Reproductive potential – “K”

Some species have higher reproductive potential!!

K-Potential Gestation

Times:

Human= 9 months

Elephants= 22 months

Oppossum = 12-13 days (marsupial)

### CRITICAL NUMBERS

Survival & recovery of population depends on a minimum population base—its critical number.

### Factors Affecting Critical Number

C1. IMMIGRATION:

movement of indiv into an area

C2. EMIGRATION:

movement of individuals which leave an area.

Plus

Environmental Resistance Factors

### Critical Numbers

If pop falls below critical number, breeding may fail and extinction could occur.

Threatened: species whose pops are declining rapidly

Endangered: near critical number and may become extinct.