Chapter 16: Populations

16.1 Population: all the individuals of a species that live together in an area (Ex: ____) Demography: the statistical study of populations, make predictions about how a population will change

Three Key Features of Populations 1. Size Small populations are most likely to become extinct. WHY? Natural disturbances –fire, disease, flood Inbreeding-homozygous for harmful recessive traits (Ex: dog inbreeding may produce deafness, underbite) reduces diversity 2. Density- # of individuals that live in a given area 3. Dispersion-how individuals are arranged in space clumped, even, or random –FIGURE 16-3 DRAW

Which dispersion pattern are these? A. B. C.

Growth Rate = Birth Rate - Death Rate 1. In Cedar Grove, 15 babies were born in 2000, 4 residents died. What is the growth rate for Cedar Grove? 2. In Springfied, 1500 babies were born in 2000, 1550 residents died. What is the growth rate? http://2010.census.gov/2010census/data/

Growth Curves J - Shaped (exponential growth) Population is steadily increasing FIGURE 16-4 DRAW S - Shaped (logistic model) Population size that the environment can sustain FIGURE 16-5 DRAW Populations are limited by space, food, predators, disease, resources. That limit is called the CARRYING CAPACITY-

The graph shows a (J or S) curve at the beginning, then over time it is (J or S) Place a circle on the line where limiting resources stopped population growth. Place an X on the graph where the deer reach CARRYING CAPACITY.

What Limits Population Size Density-dependent factors: limited resources- space, food, water, air, shelter, nesting sites Density-independent factors: random occurrences that can limit population - earthquake, bad weather, fire, etc. Is disease density dependent, or density independent?

Growth Strategies K Strategists R Strategists long life span reproduce slowly have few young parental care Ex: elephants, humans; Some endangered Sp. (tigers, whales, rhinos, gorillas) R Strategists short life span reproduce quickly have many young little parental care Ex: cockroaches, weeds, sea turtles

r or K strategist? a. b. c.

Population Pyramids

Population of a Stable Country

Ways To Estimate Populations 1. Random Sample-sunflowers in a field 2. Mark & Recapture

16.2 How Populations Evolve Populations change over time as a result of environmental pressure (evolution) Allele frequences in population change if evolutionary forces act upon them (Hardy Weinberg Principle) Mutation is the source of variation

Evolution of Populations continued Gene Flow: the movement of individuals to and from a population, migration Immigration (IN) adds alleles emigration (OUT) takes them away Non random mating: individuals mate with others living nearby OR are of their own phenotype OR have certain traits The probability that two individuals will mate in a population is not the same for all individuals

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

Natural Selection Causes Changes in Populations Natural selection acts only on: phenotypes Traits that are expressed Peppered Moth What about recessive alleles? -NOT eliminated by natural selection Heterozygous individuals carry allele but do not express it. R r SEE Punnett Square R r

Directional Selection: evolution favors an extreme trait, more and more individuals have the trait. Ex: Rats get longer and longer tails Stabilizing selection: extremes are selected against, favors the average

WHICH type of selection? A. B. 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. 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.