Community Characteristics & Natural Selection

Question 1

What’s an ecological community

Answer 1

Consists of populations of different species living together and interacting

Question 2

Community characteristics

Answer 2

Biodiversity: species richness and diversity
Growth form and structure
Relative abundance of species
Trophic structure

Question 3

What is the word for succession in community structure

Answer 3

Temporal

Question 4

What is succession

Answer 4

When ground that previously had live is destroyed by floods, fire etc. life returns.
The first colonisers alter the environment, allowing additional species to become established.

Question 5

What is natural succession

Answer 5

The process by which an ecosystem forms in a lifeless terrestrial or aquatic system.

Question 6

What’s primary succession

Answer 6

Ecosystem forms in previously barren terrain or water body.

Question 7

What is secondary succession

Answer 7

Development of ecosystem after complete or partial destruction of previously existing communities

Question 8

What are stages in the succession process known as

Answer 8

Seral stages

Question 9

What alternative mechanisms are proposed to drive succession

Answer 9

Facilitation
Tolerance
Inhibition

Question 10

Explain facilitation

Answer 10

Pioneer species modify environment (soil nutrients, moisture & OM) making it less suitable for themselves and favoring the establishment of new species

Question 11

Explain tolerance

Answer 11

Earlier species neither d’avoir if inhibit the colonisation of later species, it’s just a question of who gets there first.

Question 12

Explain inhibition

Answer 12

Competitive interactions between species will determine which species dominate at each successional stage.

Question 13

What traits do the first species to colonize an area in succession have

Answer 13

Good dispersers (carried by wind, birds)
Have low nutrient requirements
Don’t need thick soil or substrate
Grow rapidly- need lots of sunlight for photosynthesis
Can tolerate exposed conditions

Question 14

Pioneer and intermediate communities consist of

Answer 14

Low species diversity
Simple food webs: most biomass flows through grazer food chain.
Volatile populations

Question 15

Describe the later colonisers in the succession process

Answer 15

Are slower disperses (carried by mammals)
Higher nutrient requirements
Can tolerate low sunlight and high shade

Question 16

What’s in a climax community

Answer 16

High species diversity
Complex food webs: most biomass flows through décomposér food chains
Stable population
More efficient cycling of nutrients

Question 17

Where are good areas to study succession

Answer 17

Recent glacial retreats provide excellent opportunities for studying primary succession.
In northern hemisphere glaciers have been retreating over last 200 years exposing bare ground or moraines where direct observation can occur to see what grows on them

Question 18

Where was the best studied example of primary succession on a glacial moraine.

Answer 18

Glacier Bay southeastern Alaska.
By 1894 had retreated 30-40km
Long range studies of natural succession began in 1916 (Prof. William C. Cooper)

Question 19

Describe pioneer community in primary succession of glacier bay

Answer 19

Thin nutrient poor soils
Algal growth stabilisés silt, retains water
Misses, lichens and herbs colonize
Dryas - nitrogen fixation

Question 20

Describe intermediate community in primary succession of glacer bay

Answer 20

Small shrubs colonize
Further nitrogen fixation
Light competition
Willow -> Alder -> Spruce

Question 21

Describe climax community in primary succession of glacier bay

Answer 21

Hemlock/spruce forest in well drained areas
Big in poorly drained areas

Question 22

When is the ecosystem restored by secondary succession

Answer 22

After ecological disturbances remove or reduce a climax community.
.

Question 23

Why does secondary succession happen more rapidly than primary succession

Answer 23

Soil already contains seed bank
Root system remain in soil, plants can regenerate
The fertility and structure of the soil has already been substantially modified by previous organisms

Question 24

Where can natural succession be observed

Answer 24

Sand dunes
Plant communities facilitate dune building by binding sand as dunes grow environment changes and pioneer plant species are replaced.

Question 25

What’s an embryonic dune

Answer 25

Youngest stage in dune development
Unstable mounds of sand rarely exceed 1m high
Hostile environment for plants due to high salinity and pH 8-9

Question 26

What plants are found in embryonic dunes

Answer 26

Elymous juncea (sand couch)
Leymus arenarius (Lyme grass)

Question 27

What are marram dunes

Answer 27

Occur behind embryonic dunes
Partially stabilized hills ridges of sand
Height 15-20m
Vegetation cover loose and incomplete

Question 28

What are fixed dunes

Answer 28

Stabilises ridges or hills of sand
Complete cover vegetation
Exposed sand generally <10%

Question 29

What is Machair in terms of dune systems

Answer 29

Machair develops in places with cool moist and windy climate. In Ireland found along west coast from Galway bay to malin head in Donegal.
Level stable coastal dune grassland over calcereaous soils

Question 30

How many ha does Machair cover

Answer 30

25,000 world wide
7,500 Ireland

Question 31

What’s the stages of dunes

Answer 31

Pioneer stage (embryonic dunes)
Building stage (Marram dunes)
Grey (fixed) dune stage
Dune slacks
Dune heath/woodland stage