Populations

A population is a group of organisms of the same species living in the same place at the same time.

Populations evolve according to their own self interest in a particular environment.

Factors which can limit the Factors which can limit the growth of a population growth of a population

include:include: Predation Shortage of food Disease Lack of water Lack of space Disaster

Carrying Capacity

Look at the picture. How do you think this is an analogy for carrying capacity?

Carrying CapacityThe largest number of individuals in a

species that an environment can support

ActivitiesActivities Question sheet (page 4)Question sheet (page 4) Activity Activity

Competition Ecosystems have limited resources.

Organisms with similar needs must compete to get the resources they need.

Competition occurs between: Members of the same species = Intraspecific

competition Members of different species = Interspecific

Competition

Activity Time!

Follow UpFollow Up After we combined tweezers and After we combined tweezers and

tongs, did you get more or less tongs, did you get more or less beans? Why?beans? Why?

What are the challenges of What are the challenges of intraspecific vs interspecific intraspecific vs interspecific competition?competition?

Limiting Factors An organisms’ need for space depends on

their size, environment, and way of life.

This need for space determines the carrying capacity of a specific organism.

Factors affecting population size may be:1. Density-Dependent Factors2. Density-Independent Factors

Density Dependent FactorsIf population density increases, it can cause a

decrease in the population.

Population density measures the # of individuals of a particular species per unit of area or volume

Some examples of density dependent limiting factors:

CompetitionCompetition PredationPredation DiseaseDisease Intrinsic factors (mice)Intrinsic factors (mice)

Density Independent Factors

Events that can decrease population size that are not related to how many individuals are in the population to begin with: Pollution Forest fire Flood Volcano Extreme weather

ActivityActivity Hand out limiting factors assignment Hand out limiting factors assignment

Characteristics Characteristics of Populationsof PopulationsPopulation Size and DensityPopulation Size and Density

Size vs DensitySize vs Density Population size measures the # of

individuals of a particular species in a given region

Population density measures the # of individuals of a particular species per unit of area or volume

Population dispersion measures the general pattern in which individuals are distributed throughout a given region

Population DensityPopulation Density Density (D) = # of

individuals (N)/unit total area (S) S

ND

ExampleExample During the Walking Dead, During the Walking Dead,

Atlanta, a city 342.9 kmAtlanta, a city 342.9 km2 2 , , was was populated with 4000 zombies. populated with 4000 zombies. What is the population density of What is the population density of zombies in Atlanta?zombies in Atlanta?

Activity SheetActivity Sheet

Population DispersionPopulation Dispersion Additionally, the Additionally, the

population can disperse population can disperse in different waysin different waysRandomRandomClumpedClumpedUniformUniformLet’s model each type with volunteers

Population Dispersal Patterns of distribution are usually species-specific but may derive Patterns of distribution are usually species-specific but may derive

from a variety of causes: from a variety of causes: Uniform dispersal Uniform dispersal pattern is likely to result from direct pattern is likely to result from direct

competition or territoriality. Penguins often exhibit uniform competition or territoriality. Penguins often exhibit uniform spacing by aggressively defending their territory among their spacing by aggressively defending their territory among their neighbors neighbors

Random distribution Random distribution the lack of any strong social interactions the lack of any strong social interactions between species (dandelions seeds dispersed by the wind)between species (dandelions seeds dispersed by the wind)

Clumped pattern Clumped pattern could result from behavior (pack animals), or a could result from behavior (pack animals), or a very spotty arrangement of suitable habitat (animals need certain very spotty arrangement of suitable habitat (animals need certain resources to survive. When resources are rare animals tend to resources to survive. When resources are rare animals tend to “clump” together around these resources “clump” together around these resources

Population Growth (r)Population Growth (r) If unlimited resources are If unlimited resources are

present, growth will be present, growth will be exponentialexponential

It will proceed very quickly It will proceed very quickly for rapidly reproducing for rapidly reproducing organisms and more slowly organisms and more slowly for slowly reproducing onesfor slowly reproducing ones

The curve, however, will The curve, however, will always be a “J” curve or an always be a “J” curve or an exponential growth curveexponential growth curve

Population Growth 2Population Growth 2 Resources are never Resources are never

unlimited, though. unlimited, though. As population rises, As population rises,

resources decline.resources decline. If the growth is too rapid, If the growth is too rapid,

resources are rapidly resources are rapidly depleted and a depleted and a population population crashcrash can occur can occur

This pattern occurs often This pattern occurs often with many populations with many populations (including humans)(including humans)

For example...For example...

Gypsy moth caterpillar

Population Growth 3Population Growth 3 More often what happens More often what happens

is that the resources is that the resources slowly decrease, the slowly decrease, the growth rate slowly growth rate slowly decreases, and they decreases, and they meet.meet.

This point that they This point that they oscillate around is the oscillate around is the carrying capacitycarrying capacity of the of the environment for that environment for that particular organismparticular organism

So when would you So when would you “harvest” these “harvest” these individuals? (1,2,3,4,or 5)individuals? (1,2,3,4,or 5) S - shaped curve

ActivityActivity Work sheetWork sheet Rabbit activity Rabbit activity

Factors That Affect Population Growth

Populations experience natural hourly, Populations experience natural hourly, daily, seasonal, and annual fluctuations daily, seasonal, and annual fluctuations in numbers.in numbers.

Population size changes due to:Population size changes due to: BirthsBirths DeathsDeaths = POPULATION= POPULATION Immigration Immigration DYNAMICSDYNAMICS EmigrationEmigration

Which country looks like it is Which country looks like it is experiencing exponential experiencing exponential growth?growth?

Which country looks like it has Which country looks like it has

reached its carrying capacity?reached its carrying capacity? Because it has reached its Because it has reached its

carrying capacity, describe the carrying capacity, describe the relationship between its birth relationship between its birth rates and death ratesrates and death rates

Describe what is happening to Describe what is happening to

Europe’s population size in Europe’s population size in terms of birth rates and death terms of birth rates and death rates.rates.

Which country or countries Which country or countries

could be experiencing: could be experiencing: • • emigration: emigration: • • immigration: immigration:

rr - Selected Species - Selected Species BacteriaBacteria Pest insectsPest insects Diatoms Diatoms Small Rodents Small Rodents

K - Selected Species K - Selected Species Most birdsMost birds Most predatorsMost predators ElephantsElephants WhalesWhales OaksOaks ChestnutsChestnuts AppleApple CoconutCoconut

In groupsIn groups Based on the examples of r selected Based on the examples of r selected

and k selected species from the and k selected species from the previous slides, brainstorm previous slides, brainstorm characteristics you think are shared characteristics you think are shared amongst each type of species. amongst each type of species.

r – selected Species In In unstable or unpredictableunstable or unpredictable environments environments

rr-selection predominates-selection predominates

Traits that are thought to be characteristic Traits that are thought to be characteristic of of rr-selection include: -selection include: high fecundity (potential for reproduction in one high fecundity (potential for reproduction in one

lifetime), lifetime), small body size, small body size, short generation time, short generation time, ability to disperse offspring widely. ability to disperse offspring widely.

k-selected Species In In stable or predictable environmentsstable or predictable environments kk--

selection predominatesselection predominates Typically are very constant and close to the Typically are very constant and close to the

maximum that the environment can bearmaximum that the environment can bear. .

Traits that are thought to be characteristic Traits that are thought to be characteristic of of kk-selection include: -selection include: large body size, large body size, long life expectancy, long life expectancy, production of fewer offspring that require production of fewer offspring that require

extensive parental care until they mature. extensive parental care until they mature.

VideoVideo http://highered.mcgraw-hill.com/http://highered.mcgraw-hill.com/

sites/9834092339/student_view0/sites/9834092339/student_view0/chapter55/animation_-chapter55/animation_-_r_and_k_strategies.html_r_and_k_strategies.html

Group DiscussionGroup Discussion Why are pest species likely to be Why are pest species likely to be

extreme r-selected species?  extreme r-selected species?  Why are many endangered species Why are many endangered species likely to be extreme K-selected likely to be extreme K-selected species.species.

Journal EntryJournal Entry Given current environmental Given current environmental

conditions, if you had a choice would conditions, if you had a choice would you rather be an r-strategist or a K-you rather be an r-strategist or a K-strategist?  Explain your answer.  strategist?  Explain your answer.  What implications does your decision What implications does your decision have for your current lifestyle?have for your current lifestyle?