7. Ecological Succession

Question 1

What is succession?

Answer 1

The changes over time in the species that occupy a particular area.

Question 2

What is the first stage of succession?

Answer 2

Colonisation of an inhospitable environment by a pioneer species

Question 3

Give examples of features of pioneer species that make them suited to colonisation.

Answer 3

• Produce a large number of wind dispersed seeds or spores so they can easily reach isolated situations
• Rapid germination of seeds so they don’t require a period of dormancy
• Ability to photosynthesise as food will not be readily available whereas light most likely will be
• Tolerance to extreme conditions
• Ability to fix nitrogen as the soil (if there is any) will most likely contain very little nitrates

Question 4

What is a climax community?

Answer 4

A stable equilibrium where there is very little change in the species and number of individuals of the species inhabiting the environment

Question 5

What results emerge as a result of succession?

Answer 5

• Environment becomes less hostile
• Greater number and variety of habitats
• More complex food webs
• Increased biomass (especially mid succession)

Question 6

What is a type of succession that does not begin with a pioneer species?

Answer 6

When there is a change in environment eg. due to a fire or deforestation
The sequence of succession is the same but it is much more rapid (usually). Also, it does not start with a pioneer species but with a species that already existed and survived

Question 7

What are the main reasons for conservation?

Answer 7

• Ethical- respect for living things
• Economic-long term productivity is increased if ecosystems are maintained in their natural balanced states. Also plants etc may produce substances which may be useful for us in the future
• Cultural and aesthetic- entertain and fulfill us

Question 8

How can habitats be conserved by managing succession?

Answer 8

-Climax communities can be prevented from being reached which means more species present in mid succession do not get out competed and die as a climax community is reached

Question 9

What is secondary succession?

Answer 9

Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat.

Question 10

(1 mark)
Investigating the stages of succession with algae species on a concrete block placed near the sea
The scientist used percentage cover rather than frequency to record the abundance of
algae present. Suggest why.

Answer 10

-Difficult/too many/too many to count /
individual organisms not identifiable /
too small to identify / grows in
clumps;

Question 11

(1 mark)
Investigating the stages of succession with algae species on a concrete block placed near the sea

Some scientists reviewing this investigation were concerned about the validity of the
results because of the use of concrete blocks.
Suggest one reason why these scientists were concerned about using concrete blocks
for the growth of algae.

Answer 11

Any described feature of concrete eg
texture / flat / composition chemicals
/ nutrients etc;

Question 12

(4 marks)
Investigating the stages of succession with algae species on a concrete block placed near the sea

Use the results of this investigation to describe and explain the process of succession.

Answer 12

1. Pioneer species 
increases then decreases;
2. Principle of a species
changing the conditions / a
species makes the conditions
less hostile;
3. New/named species better
competitor /
previous/named/pioneer
species outcompeted;
4. G. coulteri/Gelidium (don't worry about the names as the graph is not available)
increases and other/named
species decreases;

Question 13

(3 marks)

Explain the increase in the diversity of birds as the woodland developed through succession.

Answer 13

1. Greater variety/diversity of plants/insects / more
   plant/insect species;
2. More food sources / more varieties of food;
3. Greater variety/more habitats/niches;

Question 14

Measuring succession using a line transect from sections A to E, from A to E, the species diversity of plants increases
The diversity of animal species is higher at E than A. Explain why.

Answer 14

1. Greater variety of food / more
   food sources;
2. More/variety of habitats/niches;

Question 15

(2 marks)
Marram grass is a pioneer species that grows on sand dunes. It has long roots and a
vertically growing stem that grows up through the sand.
Sand dunes are easily damaged by visitors and are blown by the wind. Planting
marram grass is useful in helping sand dune ecosystems to recover from damage.
Use your knowledge of succession to explain how.

Answer 15

1. Stabilises sand / stops sand
   shifting;
2. Forms/improves soil / makes
   conditions less hostile;