PopulationsPopulations

• Population- the number of individuals of a species that inhabit a particular area at the same time.

2 characteristics of populations

1. Population Density

2. Population dispersal

Population Density

• The number of individuals of a population that inhabit a certain area (land or water)

• Example) there is a population of 10 million people in los angeles

• Give 3 examples of population density

Population Dispersal

• How individuals in a population are dispersed or spread out in an area.

3 ways populations can be dispersed

1. Random- location of organisms is random and not dependent on other

members of the species

Ex) dandelion seeds being randomly spread in a field

VERY RARE

2. Clumping – Individuals of a population clump or flock together ** most common kind**

Ex) fish swim in schools or groups

In this kind of dispersion animals “clump” near resources

3. Uniform- members of population are uniformly spread out in region or area

• results from competition for resources,

members of a population need to spread out because of limited resources

• Farmers create artificial uniform distribution

Factors Controlling Distributions

In eastern Connecticut, The Black-capped Chickadee’s moves its geographic range south in winter (summer left, winter right; darker colors are denser populations) because its physiological need for a warmer climate is better met there.

Summer Winter

You do!

• What are two important characteristics of populations- explain each

• Name and describe three kinds of population dispersion & explain them

• Population density and dispersal• Random, uniform, clumping

Population Growth

Questions we need to be able to answer

• How do populations grow?• What determines if populations grow or

not?• What patterns are there for population

growth?

2 Factors that regulate population growth

• Density-dependent factors- certain factors limit growth. These include disease and availability of food and living space. As populations increase, mortality increases

• Density-independent factors- other factors influence populations regardless of their size. These include storms, forest fires, geologic events, minimum winter temperatures and snowfall amounts.

Two main kinds of populations:r and K Strategists/organisms

r-selected/ r-strategist K-selected/k-strategist

Reproduce early in lifeHigh reproductive growthDon’t care for young(bacteria, amoebas)

Reproduce late in lifeHave few youngDevote much time and energy to survival of youngHumans, tigers, dogs

• Biotic Potential-The amount that a population would grow if there were unlimited resources in the environment

• Are there unlimited resources in an environment? What keeps populations from reaching their biotic potential?

Words and concepts we need to know:

• Resources ARE limited in ecosystems so populations DO NOT reach their biotic potential.

• Organisms reach “carrying capacity”

Carrying Capacity (K)

»The maximum population size that can be supported by the available resources in an area.

»Different ecosystems have different Carrying capacities for different species because all species have different requirements for life!

You do

• In a forest what populations would have a high carrying capacity? Why

• What is the difference between biotic potential and carrying capacity?

• Give an example of an r-strategist• Give an example of a K-strategist

• What species would have a lower carrying capacity- why?

4 stages of population growth

• 1. Lag phase- population grows slowly• 2.Exponential Phase- population grows

rapidly/ exponentially (growth exceeds death rate)

• 3.Stationary Phase – Population stops growing and stays relatively stable. (equal numbers of birth and death)

• 4.Death phase- more members are dying than being born or moving in (immigration) so the population is decreasing

Showing carrying capacity

RULE OF 70

• The rule of 70 tells us how long it will take a population to double in size

• Formula - 70 divided by the current growth rate • Example) The growth rate of a population is 5%

per year. How long will it take for the population to double

• 70/5= The population will double in.

Practice

• US population =311 million, growth rate is 0.883 How long will it take US to double?

• World population is 7 billion growth rate is 1.2 How long till we double?

• What happens then?

Patterns of Population Growth1. Logistic Population Growth- population grows

fast at first then becomes stable and remains at carrying capacity- S shaped curve

Population Growth

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Population cycles in ecosystems

In nature populations generally follow one of two patterns

Boom and Bust cycleCommon among r-strategists Rapid increase followed by rapid decrease- cyclical

Predator prey cycle

Predator Prey Cycle

• Populations of predator and prey influence each other

• Prey population grows rapidly• Predator population grows after prey is

established• Prey begin to die out• Predators die out• Cycle continues.

• Find the doubling rate for a population that has a growth rate of 1.5

• What two cycles of population growth exist in nature

• Name the 4 stages of population growth and give an example of each

Human Population Dynamics

7 billion

• Video – how did we grow so fast?

Notes in bold:How do populations change

• Immigration – movement of people or species into a population

• Emmigration – movement of people or other species out of a population

** In general these are not significant factors in population size& DO NOT affect global population ***

Fertility Rates

• Replacement level fertility (RLF)

– Number of children a couple must have to replace themselves

– 2.1 in developed countries (DCs) 2.5 in some less-developed ones (LDCs)

– Have to take infant mortality into account

• Total Fertility RateThe number of children a woman will bear during her lifetime.

• Total Fertility Rate is decreasing globally however world population is still increasing.

*** TFR = most significant addition to human population******

Projected Birth Rates by Region

Which one of these countries is

experiencing the most population growth?

World Population Growth Rate

Goal

• Total fertility rate = replacement rate

• Still does not equal zero population growth because of people living longer

Factors that affect the growth rate of Human Populations

Anything that impacts TFR (total fertlility rate) impacts population growth.

Examples>Availability of birth controlDemand for children in the labor forceUrbanization (rural communities have children for

labor) Base level of education for womenReligious beliefs, customs and traditions

You do – with your partners and be ready to share in ______

• Identify and describe two factors that affect TFR(total fertility rate)

• Explain the difference between TFR and RLF (replacement level fertility)

Factors not related to TFR that affect population

DEATH RATE ALSO AFFECTS population!!!!

The reason the worlds population has grown in the past 100 yrs is due more to later death rate than higher birth rate

Why are people living longer?

• Industrial Revolution improved standard of living

• Clean water• Better sanitation (fewer diseases) • Dependable food supply• Better health care

2 generalization about population

• The more industrialized or developed the nation the longer the life span

• Overall health of a population can be estimated by looking at lifespan AND mortality rate of infants.

Life span: Afghanistan = 44yrs. Japan = 80yrsInfant Mortality: Afghanistan=121/1000

US= 6/1000

You do! – think pair share

• What are two generalizations you can make about populations?

• Why are people living longer?

Endangered/extinction

The reason so many big cats (and other species) are endangered

• Habitat destroyed• Prey dies • Predator has no food• Species without food go extinct

Are you typical

• video

Human Population growth Lab

• Lab is due for a grade• You may work with your groups • You may write on the lab

You have to complete _your graph_________ by the end of the period.