Chapter Chapter 16: 16:

PopulationPopulationss

16.116.1 Population: all the individuals of Population: all the individuals of

a species that live together in a species that live together in an area (Ex: ____)an area (Ex: ____)

Demography: the statistical Demography: the statistical study of populations, make study of populations, make predictions about how a predictions about how a population will changepopulation will change

Three Key Features of Three Key Features of PopulationsPopulations

1. Size 1. Size Small populations are most likely to Small populations are most likely to

become extinct. WHY?become extinct. WHY? Natural disturbances –fire, disease, floodNatural disturbances –fire, disease, flood Inbreeding-homozygous for harmful Inbreeding-homozygous for harmful

recessive traits (Ex: dog inbreeding may recessive traits (Ex: dog inbreeding may produce deafness, underbite) produce deafness, underbite)

reduces diversity reduces diversity

2. Density- # of individuals that live in a given 2. Density- # of individuals that live in a given areaarea

3. Dispersion-how individuals are arranged in 3. Dispersion-how individuals are arranged in spacespace clumped, even, or randomclumped, even, or random –FIGURE 16-3 –FIGURE 16-3

DRAWDRAW

Which dispersion pattern Which dispersion pattern are these?are these?

A.A. B.B. C.C.

Growth Rate Growth Rate = Birth Rate - = Birth Rate - Death RateDeath Rate

1. In Cedar Grove, 15 babies were born 1. In Cedar Grove, 15 babies were born in 2000, 4 residents died. What is the in 2000, 4 residents died. What is the growth rate for Cedar Grove?growth rate for Cedar Grove?

2. In Springfied, 1500 babies were born 2. In Springfied, 1500 babies were born in 2000, 1550 residents died. What is in 2000, 1550 residents died. What is the growth rate?the growth rate?

http://2010.census.gov/2010census/datahttp://2010.census.gov/2010census/data//

Growth CurvesGrowth Curves J - Shaped (exponential growth)J - Shaped (exponential growth)

Population is steadily increasing FIGURE Population is steadily increasing FIGURE 16-4 DRAW16-4 DRAW

S - Shaped (logistic model) S - Shaped (logistic model) Population size that the Population size that the

environment can sustain FIGURE 16-5 environment can sustain FIGURE 16-5 DRAWDRAW

Populations are limited by space, Populations are limited by space, food, predators, disease, resources. food, predators, disease, resources.

That limit is called the CARRYING That limit is called the CARRYING CAPACITY-CAPACITY-

The graph shows a (J or S) curve at the The graph shows a (J or S) curve at the beginning, then over time it is (J or S)beginning, then over time it is (J or S)

Place a circle on the line where limiting Place a circle on the line where limiting resources stopped population growth.resources stopped population growth.

Place an X on the graph where the deer Place an X on the graph where the deer reach CARRYING CAPACITY.reach CARRYING CAPACITY.

What Limits Population SizeWhat Limits Population Size

Density-dependent factors: limited Density-dependent factors: limited resources- space, food, water, air, resources- space, food, water, air, shelter, nesting sitesshelter, nesting sites

Density-independent factors: random Density-independent factors: random occurrences that can limit occurrences that can limit population - earthquake, bad population - earthquake, bad weather, fire, etc.weather, fire, etc.

Is disease density dependent, or Is disease density dependent, or density independent?density independent?

Growth StrategiesGrowth StrategiesR StrategistsR Strategists short life span short life span reproduce quickly reproduce quickly have many young have many young little parental care little parental care Ex: cockroaches, Ex: cockroaches,

weeds, sea turtles weeds, sea turtles

K StrategistsK Strategists long life span long life span reproduce slowly reproduce slowly have few young have few young parental care parental care Ex: elephants, Ex: elephants,

humans; Some humans; Some endangered Sp. endangered Sp. (tigers, whales, (tigers, whales, rhinos, gorillas)rhinos, gorillas)

r or K strategist?r or K strategist?

a.a. b.b.

c.c.

Population PyramidsPopulation Pyramids

Population of a Stable Country

Ways To Estimate Ways To Estimate PopulationsPopulations

1. Random Sample-sunflowers in a field1. Random Sample-sunflowers in a field

2. Mark & Recapture2. Mark & Recapture

16.2 How Populations 16.2 How Populations EvolveEvolve

1.1. Populations change over time as a Populations change over time as a result of environmental pressure result of environmental pressure (evolution)(evolution)

2.2. Allele frequences in population Allele frequences in population change if evolutionary forces act change if evolutionary forces act upon them (Hardy Weinberg upon them (Hardy Weinberg Principle)Principle)

3.3. Mutation is the source of variationMutation is the source of variation

Evolution of Populations Evolution of Populations continuedcontinued

Gene Flow: the movement of individuals Gene Flow: the movement of individuals to and from a population, migrationto and from a population, migration Immigration (IN) adds allelesImmigration (IN) adds alleles emigration (OUT) takes them awayemigration (OUT) takes them away

Non random mating: individuals mate Non random mating: individuals mate with others living nearby OR are of their with others living nearby OR are of their own phenotype OR have certain traitsown phenotype OR have certain traits The probability that two individuals will mate The probability that two individuals will mate

in a population is not the same for all in a population is not the same for all individualsindividuals

Genetic Drift: occurs in isolated Genetic Drift: occurs in isolated populations, they become more alike populations, they become more alike (cheetahs)(cheetahs)

Natural selection acts only on:Natural selection acts only on: phenotypesphenotypes Traits that are expressedTraits that are expressed Peppered MothPeppered Moth

What about recessive alleles?What about recessive alleles?-NOT eliminated by natural selection-NOT eliminated by natural selection Heterozygous individuals carry allele Heterozygous individuals carry allele

but do not express it. but do not express it. R R r r

SEE Punnett Square RSEE Punnett Square R

rr

Natural Selection Causes Natural Selection Causes Changes in PopulationsChanges in Populations

Directional Directional Selection: evolution Selection: evolution favors an extreme favors an extreme trait, more and trait, more and more individuals more individuals have the trait. have the trait.

Ex: Rats get longer Ex: Rats get longer and longer tailsand longer tails

Stabilizing Stabilizing selection: selection: extremes are extremes are selected against, selected against, favors the favors the averageaverage

WHICH type of selection?WHICH type of selection?A.A. B.B.

A parasitic insect lays its eggs at the base of the cacti's spines. When the grubs hatch, they bore into the cacti to eat the soft inner pulp, to grow, to pupate, and to emerge as new adults later in the year.

Peccaries naturally choose to consume those cactus plants with the fewest spines. Even with their tough mouths, they prefer to eat the cacti with 70 spines first, before going on to tackle the plants with 80 spines.