Populations

Question 1

What are the assumptions made in the Hardy-Weinberg principle?

Answer 1

• no migration
• no mutations of genes
• population is large and individuals can interbreed freely
• no selection or genetic drift

Question 2

Hardy-Weinberg equation

Answer 2

p+q = 1
p^2 +2pq + q^2 = 1
where p and q are dominant and recessive alleles

Question 3

What are the two type of variation?

Answer 3

Continuous - can be measured on a scale and attributed numerical value (normal distribution curve) -> both genetic + environmental factors

Discontinuous - not measurable on a scale, instead grouped into categories (bar chart) -> genetic factors

Question 4

Stabilising selection

Answer 4

Extreme phenotypes selected against, when environment is stable
mean=median

Question 5

Directional selection

Answer 5

Extreme phenotype at one end of distribution are selected against

Question 6

Disruptive selection

Answer 6

Extreme phenotypes at both ends of distribution are selected for, mean (average) is selected against

Question 7

Genetic drift

Answer 7

change in allele frequencies in a population from generation to generation that occurs due to chance events - ratio of alleles is skewed

Question 8

Allopatric speciation?

Answer 8

ancestral population is physically sub-divided by geographical barrier -> prevents interbreeding between groups
Over time natural selection occurs on each group separately relative to env. conditions

Question 9

Sympatric speciation

Answer 9

groups of individuals in a population become reproductively isolated despite no physical barrier
seasonal, temporal + behavioural isolation

Question 10

What is the carrying capacity?

Answer 10

The maximum stable population size of a species that an ecosystem can support at a given time in a given area

Question 11

Factors affecting the final carrying capacity

Answer 11

Biotic
- food availability
- predation
- competition
- disease

Abiotic
- light intensity
- space/shelter availability
- water availability

Question 12

What are the two types of competition?

Answer 12

Intraspecific - between individuals of the same species (identical niches)

Interspecific - between individuals of different species (niches overlap)

Question 13

Competitive exclusion principle

Answer 13

If 2 species initially occupy same or very similar niches + resources are limited, one will increase in number and the other will be outcompeted (undergo death phase)

Question 14

Mark-release-recapture + its assumptions

Answer 14

Used to estimate abundance of motile organisms

• marked individuals released distribute themselves evenly amongst population + have enough time to do so
• no migration (definite boundary of population
• few deaths/birth
• marking is not toxic or dangerous/ not rubbed off or lost

Question 15

Stages of primary succession (Surtsey case study)

Answer 15

• pioneer species (eg. lichen) arrive on bare rock + colonise
• lichen causes weathering to form rock sediment which combines with dead organic matter -> basic soil
• conditions become less hostile -> new species able to colonise, outcompete pioneers
• cycle of erosion, death + decomposition continues -> bigger, more complicated species colonise
• final stable community reached (climax community)

Question 16

Why would secondary succession take place?

Answer 16

If a habitat that had previously been colonised becomes damaged or disturbed (soil remains so much faster process)

Question 17

Reasons for conservation

Answer 17

economic, social/aesthetic, ethical

Question 18

Why can conservation involve interrupting succession?

Answer 18

Prevents climax community being reached so that other species survive
eg. burning of moorland in UK to protect heather