T10.3 - Changes In Ecosystems

Question 1

State what is meant by the term colonisation

Answer 1

The process in which a species spreads to new areas.

Question 2

State what is meant by the term succession

Answer 2

The process by which the communities of organisms colonizing an area change over time.

Question 3

State what is meant by primary succession

Answer 3

The establishment and development of an ecosystem in an area that was previously uninhabited.

Question 4

What are pioneer species?

Answer 4

The first species to colonise an area

Question 5

What is a climax community?

Answer 5

A self-sustaining, stable community with constant biodiversity and species range

Question 6

Give examples of pioneer species

Answer 6

Mosses, lichens, algae, small annual plants; grasses, herbs

Question 7

Describe the process of primary succession

Answer 7

● Bare rock is colonised by pioneer species, which break up the rock
● When they die they add humus/organic matter to the ground as they decompose; this provides mineral ions, water and anchorage for higher plant species.
● When these plants die they add more humus so soil becomes deeper
● this holds onto more water and minerals which can support herbaceous plants/ shrubs / trees.
● until eventually a climax community is established.

Question 8

State what is meant by secondary succession

Answer 8

The recovery of a damaged ecosystem (flood, fire, human activity) in an area where the soil was left intact

Question 9

Describe the process of secondary succession

Answer 9

● As soil is more developed more complex pioneer plant species colonise.
● When these plants die they add more humus so soil becomes deeper;
● this holds onto more water and minerals which can support shrubs / trees,
● until eventually the climax community is restored

Question 10

What are the differences between primary and secondary succession?

Answer 10

● Primary succession starts on bare ground / rock, whereas secondary succession starts on disturbed ground / soil which was previously colonised.
● In primary succession pioneer species are simple species like algae / moss / lichen which get succeeded, whereas in secondary succession pioneer species are more complex species like fast growing grasses / small shrubs.
● In primary succession a climax community is established for the first time, whereas in secondary the climax community is restored;
● Primary succession takes hundreds of years, whereas secondary succession takes approx 50-150 years.

Question 11

What are biotic factors?

Answer 11

Living factors that affect an ecosystem

Question 12

Give examples of biotic factors

Answer 12

Predation, competition, herbivory, parastism, disease, food supply, availability of mates, pollination

Question 13

How does predation affect population sizes?

Answer 13

Predator numbers always less than prey.
Predator numbers track peaks and troughs of prey numbers later in time.

Question 14

What is intraspecific competition?

Answer 14

Competition between individuals of the same species

Question 15

How does intraspecific competition affect population sizes?

Answer 15

Stabilises population size as numbers limited by availability of resources

Question 16

What is interspecific competition?

Answer 16

Competition between individuals of different species.

Question 17

How does interspecific competition affect population sizes?

Answer 17

Competitive exclusion - one species can out compete others and exclude from habitat.

Resource partitioning / niche differentiation- competition can affect distribution, with species found in different areas to avoid competition.

Question 18

How does availability of mates affect population size?

Answer 18

Inability to find mate reduces abundance as no reproduction.
If lots of mates available then abundance increases as more reproduction.

Question 19

How does disease / parasitism affect population size?

Answer 19

Disease reduces abundance but populations recover.
Parasites usually tolerated at specific levels.

Question 20

How does food supply affect population size?

Answer 20

Food shortage reduces abundance.
Good food availability increases abundance.

Question 21

How does pollination affect population size?

Answer 21

Higher number of pollinators will increases abundance.
Reduction in pollinators will reduce plant species abundance as not able to reproduce.

Question 22

What are abiotic factors?

Answer 22

Non-living factors in an ecosystem

Question 23

Give examples of abiotic factors

Answer 23

Light intensity/wavelength, temperature, wind speed, pH, salinity, edaphic factors, water availability

Question 24

What are soil edaphic factors?

Answer 24

Soil structure and mineral content

Question 25

Explain how light intensity affects population size and distribution of plant species

Answer 25

Plant growth increases in higher light areas;
light is required for LDRs of photosynthesis;
photons excite electrons from chlorophyll during photoactivation,
which leads to production of NADPH and ATP via
Chemiosomosis;
low light reduces production of NADPH and ATP for LIRs.

Question 26

Explain how high temperatures affects population size in plants

Answer 26

Reduces population due to;
denaturing enzymes such as RUBISCO,
which reduces rate of LIRs e.g. reduces carbon fixation, reducing photosynthesis and therefore plant growth.
Increases rate of transpiration which may cause plasmolysis of plant cells

Question 27

Explain how low temperatures affects population size in plants

Answer 27

Reduces poulation size due to:
slow plant growth;
as slow rate of enzyme-controlled reactions
e.g. carbon fixation slow;
so slow rate of photosynthesis

Question 28

Explain how wind speed affects population size

Answer 28

High wind speed reduces population size due to;
increased evaporation,
cooling effect so organisms live where wind speed is low.
Increases transpiration

Question 29

Explain how water availability affects population size

Answer 29

Chemical reactions happen in solution - so organisms found where water is available unless specially adapted.

Question 30

Explain how oxygen availability affects population size

Answer 30

Oxygen required for aerobic respiration - terminal electron acceptor during oxidative phosphorylation- organisms found where O2 levels are high