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

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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”.
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

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.

UNIFORM POPULATION DISP.

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

REPRODUCTIVE POTENTIAL COMPARISON
REPRODUCTION TYPES

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.