Population and Community Dynamics

Question 1

The Hardy Weinberg principle

Answer 1

Shows that allele frequencies WILL NOT change from generation to generation as long as certain conditions are met.

1. The population is infinitely large
2. No migration occurs
3. No mutations occur
4. No natural selection occurs
5. Mating is random

Question 2

Factors that cause diversity in a gene pool.

Answer 2

Natural selcetion: survival of the fitest - does not influence the entire population unless a significant benefit is provided

Mutations: changes to the DNA

Competition: intraspecific competition - within a species (ex. tigers competing)

Interspecific competition - between species (ex. lions and hyennas competing for food)

Founder effect: when a small group of individ. leave a large pop. to start a new population, change in allele frequencie

Bottle neck effect: decrease genetic variation, when a sever event resulting in a reduction in the nymber of organisms

Genetic drift: A change in the make up of a population, small pop. influenced by chance ecent which causes large changes in allele frequencies

Non - random mating: sexual selection, any variation that favours the selection of an individual to mate

Gene flow: movement alleles from one population to another

Migration: traveling of long distances in search of a new habitat

Question 3

Preditor prey

Answer 3

The size of both populations fluctate together. This keeps the population numbers from significantly increasing and the prey population by feeding on the old, weak and ill.

Herbavour

Carnicour

Omnivour

Question 4

Realationship among organisms

Answer 4

Mutualism - both organisms benefit (bacteria living in humans)

Comensalism - one organism benefits while the other one is unaffect (voltures)

Parasitism - one organism benefits while the other one is harmed (tape warm)

Symbiosis - interaction among organisms = both organisms benefit

Question 5

Succession

Answer 5

Primary succession - development of a new community in a previously barren area (no soil is present)

Secondary succession - regrowth of previously existing community after an ecological disturbance differ from primary succession in the presence of soil, which is not usally destroyed. (forest fire)

Climax community - final stage of succession in the area; may remain stable if no major change

Question 6

Changes in gene pool

Answer 6

Population is small

Migration occurs

Mutations occur

Mating is not random

Natural selection occurs

Question 7

Defense mechanism

Answer 7

Used to avoid predation

Mimicry - the close external resemblance of an organism

Protective coloration AKA camouflage - allows animals to blend with its environment

Toxins, and behaviour

Question 8

Growth of population

Answer 8

Carrying capacity (K): theoratical max population size the environment can sustain

Biotic potential (r): max rate at whicha population can increase it size

Environmental resistance - all of the limiting factors that keep a population from growing at its biotic potential

Minimum viable population - smallest a population can be to ensure it survives for a given time frame

Question 9

If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous(Ss) for the sickle-cell gene?

Answer 9

9% =.09 = ss = q2

(¦)s = q = Square root of .09 = .3

p = 1 - .3 = .7

2pq = 2 (.7 x .3) = .42 = 42% of the population are heterozyotes (carriers)

Question 10

After graduation, you and 19 friends build a raft, sail to a deserted island, and start a new population, totally isolated from the world. Two of your friends carry (that is, are heterozygous for) the recessive cf allele, which in homozygotes causes cystic fibrosis.

A. Assuming that the frequency of this allele does not change as the population grows, what will be the instance of cystic fibrosis on your island?

B. Cystic fibrosis births on the island is how many times greater than the original mainland. The frequency of births on the mainland is .059%

Answer 10

There are 40 total alleles of the 20 people of which 2 alleles are cystic fibrosis causing.

2/40 = .05 the ¦ of the cystic fibrosis allele

thus cc or q2 = (.05)2 =.0025 or .25% of the population will be born with cystic fibrosis.

B.

0.25/.059 = about 4 times greater occurrence

Question 11

Gene pool

Answer 11

Hardy-Weinberg principles ensure that a gene pool of a
population will not change from generation to generation

The 5 principles:

1. The population is small
2. Migration occurs
3. Mutations occur
4. Natural selection occurs
5. Mating is not random

Question 12

Mutations

Answer 12

Randomly occurring events that alter the genetic
material of an individual

A mutation has the potential to alter the gene pool or
allele frequency of the population

It will not influence the entire population unless it
provides a significant benefit

Question 13

Gene Flow

Answer 13

• The movement of alleles from one population to
another
• Occurs frequently in wild populations
• New alleles are added or rare alleles can be lost in
gene flow events
• Reduces differences between populations

Question 14

Non - random mating

Answer 14

Sexual selection – any variation that favors the selection of
that individual to mate

Because of this males will compete with one another for the
right to mate or females will chose a preferred mate

Sexual dimorphism – when males and females of the
same species look very different from one another

Question 15

Genetic drift

Answer 15

Genetic drift – a change in the genetic makeup of a
population
small populations are influenced by chance events
which causes large changes in the allele frequency
can lead to fixation of alleles and increase the
incidence of homozygous individuals which
decreases genetic diversity

Bottleneck effect - when a severe event results in a
drastic reduction in numbers
If this occurs there is a chance that certain alleles
may be present in higher ratios than before
Decreases genetic variation

Founder effect – when a small group of individuals
leaves a large population to start a new population
elsewhere
The allele frequency of the new population will not
be the same as the original

Question 16

Growth rate

Answer 16

Growth rate (gr) – the change in population
size over time (how quickly it is growing or
shrinking)
gr = ΔN/Δt
gr = growth rate
ΔN = change in population numbers
Δt = change in time

Question 17

Per capita growth rate

Answer 17

cgr = ΔN/N
cgr = per capita growth rate (change in
population size relative to initial population
size)
ΔN = change in population numbers
 N = initial population
Percentage growth rate = cgr x 100

Question 18

Population density

Answer 18

Dp = N/A or Dp = N/V

Dp = population density
N = total numbers counted
A = area occupied
V = volume occupied

Question 19

Exponential growth

Answer 19

Exponential growth – populations that grow
continuously at a fixed rate
J-shaped growth curve

Question 20

Logistic growth

Answer 20

Logistic growth – shows the effect of
carrying capacity on the growth of a
population
Most common growth pattern seen in nature
It takes into account that most populations do
not grow infinitely as resources are limited

Lag phase – initial stage where the
population is small and increasing slowly
Log phase – the next stage where the
population grows very rapidly
Stationary phase – the population has
stopped growing as it has started to reach its
carrying capacity

Question 21

r - selected

Answer 21

Individuals are usually small in size
Have a short life-span
High reproductive rate
Offspring grow rapidly with little parental care
Are able to survive in constantly changing
environments

i.e. flies, locusts, mice

Question 22

K - selected

Answer 22

individuals are usually large in size
Young are slow-growing and may require care
Reproduction rate is low
Population sizes tend to change slowly
Do well in environments that are stable

i.e. elk, bears, elephants, humans