Community Characteristics & Natural Selection Flashcards
What’s an ecological community
Consists of populations of different species living together and interacting
Community characteristics
Biodiversity: species richness and diversity
Growth form and structure
Relative abundance of species
Trophic structure
What is the word for succession in community structure
Temporal
What is succession
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.
What is natural succession
The process by which an ecosystem forms in a lifeless terrestrial or aquatic system.
What’s primary succession
Ecosystem forms in previously barren terrain or water body.
What is secondary succession
Development of ecosystem after complete or partial destruction of previously existing communities
What are stages in the succession process known as
Seral stages
What alternative mechanisms are proposed to drive succession
Facilitation
Tolerance
Inhibition
Explain facilitation
Pioneer species modify environment (soil nutrients, moisture & OM) making it less suitable for themselves and favoring the establishment of new species
Explain tolerance
Earlier species neither d’avoir if inhibit the colonisation of later species, it’s just a question of who gets there first.
Explain inhibition
Competitive interactions between species will determine which species dominate at each successional stage.
What traits do the first species to colonize an area in succession have
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
Pioneer and intermediate communities consist of
Low species diversity
Simple food webs: most biomass flows through grazer food chain.
Volatile populations
Describe the later colonisers in the succession process
Are slower disperses (carried by mammals)
Higher nutrient requirements
Can tolerate low sunlight and high shade
What’s in a climax community
High species diversity
Complex food webs: most biomass flows through décomposér food chains
Stable population
More efficient cycling of nutrients
Where are good areas to study succession
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
Where was the best studied example of primary succession on a glacial moraine.
Glacier Bay southeastern Alaska.
By 1894 had retreated 30-40km
Long range studies of natural succession began in 1916 (Prof. William C. Cooper)
Describe pioneer community in primary succession of glacier bay
Thin nutrient poor soils
Algal growth stabilisés silt, retains water
Misses, lichens and herbs colonize
Dryas - nitrogen fixation
Describe intermediate community in primary succession of glacer bay
Small shrubs colonize
Further nitrogen fixation
Light competition
Willow -> Alder -> Spruce
Describe climax community in primary succession of glacier bay
Hemlock/spruce forest in well drained areas
Big in poorly drained areas
When is the ecosystem restored by secondary succession
After ecological disturbances remove or reduce a climax community.
.
Why does secondary succession happen more rapidly than primary succession
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
Where can natural succession be observed
Sand dunes
Plant communities facilitate dune building by binding sand as dunes grow environment changes and pioneer plant species are replaced.
What’s an embryonic dune
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
What plants are found in embryonic dunes
Elymous juncea (sand couch)
Leymus arenarius (Lyme grass)
What are marram dunes
Occur behind embryonic dunes
Partially stabilized hills ridges of sand
Height 15-20m
Vegetation cover loose and incomplete
What are fixed dunes
Stabilises ridges or hills of sand
Complete cover vegetation
Exposed sand generally <10%
What is Machair in terms of dune systems
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
How many ha does Machair cover
25,000 world wide
7,500 Ireland
What’s the stages of dunes
Pioneer stage (embryonic dunes)
Building stage (Marram dunes)
Grey (fixed) dune stage
Dune slacks
Dune heath/woodland stage
