Populations & Populations & Hardy WeinbergHardy Weinberg

Alex HoagAlex Hoag

Populations Populations

Outline how population size is affected by Outline how population size is affected by natality, immigration, mortality and natality, immigration, mortality and emigrationemigration

NatalityNatality: increases population size as : increases population size as offspring are added to the population.offspring are added to the population.

ImmigrationImmigration: increases population size as : increases population size as individuals have moved into the area from individuals have moved into the area from somewhere else and so this adds to the somewhere else and so this adds to the population. population. 

MortalityMortality: decreases the population as some : decreases the population as some individuals get eaten, die of old age or get sick.individuals get eaten, die of old age or get sick.

EmigrationEmigration: decreases the population as : decreases the population as individuals have moved out of the area to go individuals have moved out of the area to go live somewhere else.live somewhere else.

Draw and label a graph showing a Draw and label a graph showing a sigmoid (S-shaped) population sigmoid (S-shaped) population

growth curvegrowth curve

Explain the reasons for the exponential Explain the reasons for the exponential growth phase, the plateau phase and the growth phase, the plateau phase and the

transitional phase between these two transitional phase between these two

phases.phases.  Exponential phase:Exponential phase: Rapid increase in population Rapid increase in population

growth. growth. Natality rate exceeds mortality rate. Natality rate exceeds mortality rate. Abundant resources available. (food, Abundant resources available. (food,

water, shelter) water, shelter)

Diseases and predators are rare.Diseases and predators are rare.

Traditional phaseTraditional phase::•Natality rate starts to fall and/or Natality rate starts to fall and/or mortality rate starts to rise. mortality rate starts to rise. •There is a decrease in the number of There is a decrease in the number of resources. resources. •An increase in the number of predators An increase in the number of predators and diseases. and diseases. •Population still increasing but at a Population still increasing but at a slower rate. slower rate.

Plateau phase:Plateau phase:•No more population growth, No more population growth, population size is constant.  population size is constant.  •Natality rate is equal to mortality Natality rate is equal to mortality rate. rate. •The population has reached the The population has reached the carrying capacity of the carrying capacity of the environment.  environment.  •The limited resources and the The limited resources and the common predators and diseases common predators and diseases keep the population numbers keep the population numbers constant.constant.

List three factors that set List three factors that set limits to population limits to population

increaseincrease Shortage of resources (food) Shortage of resources (food) Increase in predators Increase in predators Increase in diseases and parasites Increase in diseases and parasites

Population Ecology Population Ecology

Distinguish between r-strategies and K-Distinguish between r-strategies and K-strategiesstrategies

An An r-strategyr-strategy involves investing more involves investing more resources into producing many offspring, resources into producing many offspring, having a short life span, early maturity, having a short life span, early maturity, reproducing only once and having a small body reproducing only once and having a small body size size

K-strategyK-strategy involves investing more resources involves investing more resources into development and long-term survival. This into development and long-term survival. This involves a longer life span and late maturity, involves a longer life span and late maturity, and is more likely to involve parental care, the and is more likely to involve parental care, the production of few offspring, and reproducing production of few offspring, and reproducing more than once more than once

Discuss the environmental Discuss the environmental conditions that favour conditions that favour

either r-strategies or K-either r-strategies or K-strategies strategies In a predictable environment, it pays In a predictable environment, it pays

to invest resources in long-term to invest resources in long-term development and long life (K-development and long life (K-strategy) strategy)

In an unstable environment, it is In an unstable environment, it is better to produce as many offspring better to produce as many offspring as quickly as possible (r-strategy) as quickly as possible (r-strategy)

Hardy WeinbergHardy Weinberg

Describe an adaptation in terms of the Describe an adaptation in terms of the change in frequency of a gene's alleleschange in frequency of a gene's alleles

If an allele increases the chances of survival If an allele increases the chances of survival and reproduction of individuals that possess and reproduction of individuals that possess it, the frequency of the allele in the gene it, the frequency of the allele in the gene pool will tend to increase. pool will tend to increase.

Ex: A moth inherits an allele of a gene that Ex: A moth inherits an allele of a gene that would make it bright pink in a dark brown would make it bright pink in a dark brown

environment - it would stand out in its environment - it would stand out in its environment and be eaten. This would environment and be eaten. This would

cause the bright pink allele to decline in cause the bright pink allele to decline in frequency. frequency.

Explain how the Hardy-Weinberg Explain how the Hardy-Weinberg equation (p squared + 2pq +q equation (p squared + 2pq +q

squared = 1) is derivedsquared = 1) is derived In a population where two alleles occur, p represents the In a population where two alleles occur, p represents the

frequency of the dominant allele and q the frequency of the frequency of the dominant allele and q the frequency of the recessive allele. Thus the combined frequency of the alleles recessive allele. Thus the combined frequency of the alleles must account for 100% of the genes for that particular locus in must account for 100% of the genes for that particular locus in the population. the population. p + q = 1 p + q = 1

When gametes combine their alleles to form zygotes, When gametes combine their alleles to form zygotes, the probability of AA (A dominant allele) is p the probability of AA (A dominant allele) is p squared. The probability of aa is q squared. There squared. The probability of aa is q squared. There are two ways in which an Aa genotype can arise, are two ways in which an Aa genotype can arise, depending on which parent contributes the dominant depending on which parent contributes the dominant allele. Thus, the frequency of heterozygous allele. Thus, the frequency of heterozygous individuals is 2pq. frequency of genotypes add to 1. individuals is 2pq. frequency of genotypes add to 1.

p² + 2pq + q² = 1 p² + 2pq + q² = 1

AA + Aa + aA + aa = 1 AA + Aa + aA + aa = 1

Describe one example of transient Describe one example of transient polymorphism and sickle cell anemia polymorphism and sickle cell anemia as an example of balanced as an example of balanced polymorphismpolymorphism

Polymorphism is when two or more Polymorphism is when two or more forms of a phenotype are forms of a phenotype are represented in high enough represented in high enough frequencies to be readily noticeable. frequencies to be readily noticeable. A balanced polymorphism is when A balanced polymorphism is when frequencies of the characteristics frequencies of the characteristics remain fairly constant over time. A remain fairly constant over time. A transient polymorphism is one that is transient polymorphism is one that is changing in frequency over time. changing in frequency over time.

Sickle Cell Anemia Sickle Cell Anemia