Succession

Question 1

What is a
succession?

Answer 1

the change in an ecological
community over time

Question 2

What is a
primary
succession

Answer 2

a succession with a pioneer
species colonising bare rock or
sand
the first time the land is
colonised

Question 3

Describe the
process of
succession

Answer 3

Pioneer species colonise a hostile, abiotic
environment
they change the conditions making the
environment less hostile
new species outcompete the pioneers and
become established
Over time, biodiversity and stability increase
A climax community is eventually reached,
stable and in equilibrium with the
environment

Question 4

Pioneer
species

Answer 4

The first species to colonise an
area
e.g. lichen

Question 5

Climax
community

Answer 5

The final seral stage in
succession
the most stable stage

Question 6

Conservation of
habitats

Answer 6

• Protecting habitats as a means
  to protect species
• maintains habitats and food
  sources

Question 7

What is the
advantage of
managing succession?

Answer 7

• Conserves a range of habitats
  and a range of food sources
• enabling a wider range of
  species to survive

Question 8

Describe the
process of
speciation

Answer 8

Genetic variation exists in a population due to
mutations
A barrier (e.g. geographical or reproductive)
causes reproductive isolation or populations
different selection pressures act on each
population
different alleles are favoured by natural selection
in each group
over time, allele frequencies change due to
selection, mutation, and possibly genetic drift
Eventually, the populations become genetically
different and can no longer interbreed
→ They are now separate species

Question 9

What creates
genetic
variation?

Answer 9

mutations
crossing over in meiosis
independent segregation in
meiosis
random fertilisation of gametes

Question 10

Selective
advantage

Answer 10

Individuals with alleles that
make them more likely to
survive in that environment

Question 11

Effects of
stabilising
selection

Answer 11

• the middle (median) trait has a
  selective advantage and
  continues to be the most
  frequent in the population
• range decreases as the extreme
  traits are lost over time

Question 12

Effects of
directional
selection

Answer 12

one of the extreme traits has a
selective advantage
occurs when there is a change
in the environment
the modal trait changes

Question 13

Effects of
disruptive
selection

Answer 13

Individuals with extreme
phenotypes have a selective
advantage.
→ middling phenotype becomes
less common
→ can lead to two distinct
populations and eventual
speciation.

Question 14

Evolution

Answer 14

a change in allele frequencies in
populations
over many generations

Question 15

Why is genetic drift
important in small
populations?

Answer 15

• the impact of allele frequency
  changes has a bigger impact
  proportionally
• results in evolution occurring
  more rapidly

Question 16

Describe the
changes you would
see in a succession

Answer 16

Abiotic factors become less
hostile
biodiversity increases
becomes more stable