Changing Ecosystems

Question 1

Differentiate between the two main modes of succession

Answer 1

Primary succession occurs over broad time scales where bare areas are colonised for the first time (e.g. lava flows, new sand dunes, new coral reefs, land exposed by retreating glaciers)

WHEREAS

Secondary succession occurs over short time scales where there has been a disturbance (e.g. Natural disasters like wildfires and floods, human events or a tree falling) that resets the community to an earlier stage of succession.

Question 2

identify the features of pioneer species that make them effective colonisers

Answer 2

• be tolerant of extreme abiotic conditions.
• be able to photosynthesise.
• fix nitrogen from the air (as substrate is often nutrient poor).
• reproduce quickly, have short life cycle and produce many offspring.
• disperse seeds easily and have seeds germinate quickly.

Question 3

Differentiate between pioneer species and the climax community (Type of species present, biomass, biodiversity, biotic interactions, abiotic interactions, soil quality)

Answer 3

Pioneer species vs Climax community:

Type of species present: Small size organisms, fast growing, r-selected organisms VS larger size organisms, slow growing, k-selected organisms

Biomass: low VS high

Biodiversity: low VS high

Biotic interactions: simple interactions (food chains/ small food webs) VS complex interactions (large food webs)

abiotic interactions: conditions unstable, harsh VS conditions stable, less harsh

soil quality: poor quality, no soil or low quantity, low nutrients, no initial seed store and relatively low microbial content VS good quality, higher quantity, high nutrients, is seed store and microbial content

Question 4

explain the concept of ecological succession (refer to pioneer, intermediate and climax communities and seres)

Answer 4

Ecological uccession refers to the change in an ecosystem or biological communities structure over time.

pioneer species: colonise new or recently exposed substrate (e.g. grass, lichens, ferns) and are unstable

Intermediate species: Regrow or seeds germinate/ grow from seed stored in soil (e.g. shrubs, wattles, she oaks)

Climax community: Develop as nutrient levels and micro-habitats develop overtime (mature, stable)

Each of the community stages shown above has recognisable characteristics which are termed a sere.

A seral community: is the intermediate stage of ecological succession as it advances towards the climax community