3.2.3 - Changing Ecosystems: Resources

Question 1

what is a community and how does this relate to succession?

Answer 1

• a community consists of all the plants and animals that occupy a particular area
• the community is a constantly changing and dynamic unit, which passes through a number of stages from its origin to its climax
• the transition from one stage to the next is called succession

Question 2

what is succession?

Answer 2

• a process by which communities of plants and animals colonize an area and then, over time, are replaced by other, more varied organisms
• a seral community (or sere) is an intermediate stage in an ecosystem advancing through these different stages
• there are two types of succession:
  
  • primary –> plants growth where no plants have grown before
  • secondary –> plants grow where there has been a previous population that were destroyed by something like a fire

Question 3

describe primary succession

Answer 3

• starts from bare rock or water
• occurs in an environment that is devoid of vegetation, organisms and soil (such as a lava flow or area left from retreated glacier)
• basically, it’s the gradual growth of an ecosystem over time
  
  • sand dunes are one of the few places where it takes place
  • volcanic islands

Question 4

how do pioneer species start primary succession?

Answer 4

• the first species to colonise an area, and tend to be lichen
• they are opportunistic species which are able to rapidly exploit a sudden new opening in ground plant cover
• they are able to withstand desiccation, extremes of temperature and low levels of nutrients
• they must be able to grow quickly, but are usually short lived

Question 5

why are pioneer species effective colonisers?

Answer 5

because of some specific features:
- ability to fixate nitrogen
- tolerance to extreme conditions
- rapid germination of seeds
- ability to photosynthesize

Question 6

how do pioneer species evolve primary succession?

Answer 6

• the pioneer species penetrate and break up the rock
• as they die and decompose, humus builds up
• this allows other simple plants such as mosses and ferns to now grow

Question 7

how do mosses and ferns evolve primary succession?

Answer 7

• mosses and ferns cast shade to stop
• their roots are longer and so further break up the rock
• the organic matter gradually increases as these bigger plants die
• more water is retained by this, so grasses, small flowering plants and shrubs can grow

Question 8

how do the growth of larger plants and the animals evolve primary succession?

Answer 8

• growth of larger plants and the animals which inhabit them will cause further changes in soil and light conditions
• the shading effect of the larger plants kills some of the smaller ones

Question 9

how is the climax community reached in primary succession?

Answer 9

• eventually the area is colonised by dominant plant species and a climax community is reached
• eg. rainforest

Question 10

how does primary succession occur (summary)?

Answer 10

• the plants present at each seral stage modify the environment making it more favorable for other plant species to colonise and out compete the current plants

Question 11

what is secondary succession?

Answer 11

• occurs when the current stage is is removal abruptly
• this may be due to a natural disaster such as a fire, deforestation

Question 12

describe how secondary succession starts?

Answer 12

• there is already soil and seeds present
• hence, succession will happen more rapidly than primary succession
• the pioneer plants are tolerant to high levels of sun and grow fast
• fast growing trees then develop, while shade-tolerant species develop in the understorey

Question 13

summarise primary vs secondary succession

Answer 13