L. 28 - Assemblages and Ecosystems

Question 1

LO

Answer 1

• Communities as definable entities; comparison with assemblages
• Understand spatial and temporal changes in communities
• Understand succession and resilience
• Role of disturbance in community structure
• Ecosystems and productivity – global and local cycles
• Case study - trophic cascades and carbon cycles
• The science behind this ecological knowledge and understanding

Question 2

Community definition

Answer 2

2 or more species that occur together in the same area and time
- There has to be interactions between species

Question 3

Assemblage definition

Answer 3

Less defined community which may not interact together
- There are no assumptions that the species interact

Question 4

Communities over time

Answer 4

• Stable communities maintain consistant species and richness
• Changes in species composition is normal
• Predictable patterns of change occur due to disturbance
• Classic models are underpinned by succession of species

Question 5

Succession

Answer 5

Changes in species composition and abundance
Dominant species in systems change, and new ones come in
- growth rates in lower canopy and grounf level stara after a tree falls
- Pioneer species come in

Question 6

Pioneer species

Answer 6

• Grow in sun
• Fix nitrogen
• Small seeds
• Poor competition
• Short germination time
• Rapid growth
• Good dispursal

Question 7

Climax species

Answer 7

• Shade tolerant
• Slow growth
• Long-lived
• Good competitors

Question 8

Types of succession

Answer 8

Primary:
- Bare area without soil
- Sand-dune, bare rock

Secondary:
- In a habitat modified by other species
- Forest gap, abandoned agricultural field

Question 9

Models of succession

Answer 9

Facilitation:
- Early arriving species make env. favourable to later species

Tolerance:
- Neither negative or positive interactions between early and late species

Inhibition:
- Early species inhibit later species

Question 10

Intermediate Disturbance Hypothesis

Answer 10

• Comes from tropical rainforests and reefs
• When there is low disturbance, there is low numbers of species as there is no opportunites for new species
• Intermediate amount of disturbance leads to higher species variety
• Too much disturbance means no species at all

Question 11

Resilliance

Answer 11

how long before a community returns to an equilibrium state after disturbance
- Comes down to scale of disturbance in time and spacial extent

Question 12

Biogeochemical cycles

Answer 12

Energy flows through biosphere and all materials are recycled

Global Cycles:
- Materials transported through air
- Water cycle
- Nitrogen cycle
- Carbon cycle

Local Ecosystem Cycles:
- P, K, Ca, Mg all move through soil

Question 13

The water cycle

Answer 13

Global Cycle
~97% of water on earth is oceans
- Evaporation, condensation, precipitation into ground water, runoffs, lakes etc.

Question 14

Nitrogen Cycle

Answer 14

• Global Cycle
• Abundant in atosphere, plants cannot absorb atmospheric N
• Absorbed as ammonium or nitrate after bacteria in soil fix nitrogen
• Electrical storms may also fix nitrogen

Question 15

Carbon Cycle

Answer 15

• Global Cycle
• Most carbon is in rocks and fossil fuels
• Extremely important for photosynthesis
• CO2 makes oceans more acidic, but ocean is a good sink for carbon

Question 16

Phosphorus Cycle

Answer 16

• Local cycle
• Essential to all life, in ATP
• Taken up by plants as phospahte from soil
• Aussie plants have adapted to low P & N in soil
• Symbiosis of plant roots and mycorrhisal fungi to enhance P supply