Topic 27: Assemblages and ecosystems

Question 1

Differentiate assemblages and communities

Answer 1

• Assemblages: a group of taxonomically related species occurring or living in the same space without any assumption about interactions
• Communities: a group of two or more species that occur together in a space at any time

Question 2

Identify the features of pioneer species and climax community in succession

Answer 2

• Pioneer species:
  + Grow in sun
  + Shot generation time -> rapid growth by high dispersal of large numbers of small seeds
  + Able to fix nutrients for the soil
  + Poor competitors
  + Shade-intolerant
  –> Create favourable environment for later species
• Climax community:
  + Tend to be shade-tolerant
  + Good competitors -> long-lived
  + Slow growth

Question 3

What are some models of succession that pioneer/early species can exert influence on later ones?

Answer 3

• Facilitation: pioneer species are able to fix nutrients for the soil -> facilitate a favorable environment for later species
• Inhibition: presence of early species may inhibit emergence of later ones until they are destroyed (e.g. too dense, not enough space)
• Tolerance: early and late species have no positive or negative interactions

Question 4

How important disturbance is to the diversity of an ecosystem?

Answer 4

A controlled intermittent/intermediate frequency of disturbance increases the diversity of an ecosystem by creating the space for new species to come in.

Question 5

Explain the concept of resilience and the difficulty in determining the degree of resilience of each ecosystem

Answer 5

• Resilience: the time it takes fr an area to recover after a disturbance
• There is a reference of pre-disturbance conditions, but it is hard to determine pinpoint this.

Question 6

Explain the concept of ecosystem

Answer 6

A community of living organisms which has to be considered in conjunction with all abiotic components. Biotic and abiotic elements together make up a system.

Question 7

Differentiate between global and local ecosystem cycles

Answer 7

• Global cycles involve the transportation of matter in the atmosphere.
• Local cycles only involves recycling matter through soil.

Question 8

Describe the nitrogen, carbon and phosphorus cycles

Answer 8

• Nitrogen cycle:
  
  • Present a lot in the atmosphere
  • Fixed by nitrogen-fixing bacteria in soil → nitrate (NO3-) and ammonium (NH4)
  • Converted into gaseous form by denitrifying bacteria
    → relies a lot on activity of bacteria → limited N if bacteria activity is inhibited
• Carbon cycle:
  
  • Most C is locked up in the rock as CO3 2-
  • Burning fossil fuels releases carbon into the atmosphere much faster than it can be cycled.
  • Large amounts of CO2 are absorbed by the ocean.
  • Can be affected by trophic cascade
• Phosphorus cycle:
  
  • Not common in Earth’s crust or in atmosphere
  • Taken by platns as phosphate (PO4 3-) from sparingly soluable soil storage pool
  • Roots of green plants and mycorrhizae establish symbiosis to enhance phosphorus supply.

Question 9

What is one of the most important drivers for succession?

Answer 9

The capacity of that area for new species to establish or come in.