Week 22 Flashcards
What is succession?
Describes species change over time.
It is started, directed and redirected by disturbance
What are the two types of succession?
Primary Succession
Secondary succession
What does primary succession describe?
Succession from sterile beginnings. (No life there at that time)
EG: Volcanoes and glaciers (for example Earths evolution of the origins of life)
What is secondary succession?
When origin of succession starts on previously colonised land after major disturbance
For example: landslides, fires, floods, cultivation, land abandonment, etc.
Usually due to propagules (eg seeds) and sources of new colonisers
What are the two processes of succession?
Autogenic (species change due to activities of organisms themselves - biotic) eg competition, interactions, etc.
Allogenic (species change due to external, non biological factors - abiotic) eg climate change, silting of waters, etc.
What are the general trends of early succession species - colonisers “r-selected”?
Small, fast growing
Produce many, small seeds (dispersal)
Often no dormancy requirement (germinate if conditions favourable)
Often N fixers (lichens, cyanobacteria, dryas)
Allocate more energy to reproduction than biomass
What are the two general trends and selection types of succession?
‘R-selected’ = Colonisers (early successional species) - eg Dandilions
‘K-selected’ = Competitors (late successional species) - eg Oak tree
What are the general trends of latesuccession species - competitors “k-selected”?
Large, slow growing (Trees)
Dormancy
Large seeds, animal dispersal (few)
Competitive (canopy species)
Allocate more energy to biomass than reproduction
Describe the r-K continuum graph?
x-axis = competitive ability
y-axis = colonisation ability
R selected starts high on y-axis as fast growth rate, high investment in reproduction (dispersor). This reduced as K selected starts to colonise and colonisation ability decreases but competitive ability increases due to slow growth rate, long-live, investment in biomass production
What are the patterns of diversity (succession)?
- Short term diversity
- Diversity
- Productivity
Why are glaciers beneficial to see succession processes?
Can see the process of succession by creating a plant-soil successional chronosequence from 1760 to present day. As Glaciers retreat at a rate of 0.4km/yr
Examples of pioneer communities?
Microbes - Bacteria, archaea, fungi
Algae, lichens, liverworts, bryophytes
What types of plant species may dominate after pioneer species in succession?
Dryas sp (10-20yrs ice free) - R selected
Alder dominated (75yrs ice free) - R
Alder-spruce transition (125yrs ice free) - R
Spruce forest (200yrs ice free) - K selected species begin!
In terms of succession, what is seres?
Successional stages with characteristic vegetation types and associated biota
Mechanisms that drive succession?
- Colonisation
- Species replacement over time
What are pioneer species?
The earliest form of colonists during a succession process in primary succession, (making the land more colonisable for other species to then later form)
What are the two species replacement models (proposed by Connell and Slater 1977)?
Inhibition model
Facilitation model
What is the inhibition model of species replacement?
Early arrivals competitively inhibit (e.g. light competition)
Spread rapidly (thickets) and monopolise resources
What is the facilitation model of species replacement?
Succession is a series of sequential invasions, each dependant on site amelioration by earlier colonist
Species die out since changes in environment better suited for later colonists
Primary versus secondary succession in severe and favourable conditions uses what model of species replacement?
Facilitation = Primary as severe conditions.
Facilitation less important = secondary as conditions are more favourable
primary succession at Glacier Bay – driven by alder cause changes in soil pH. What does this mean?
N fixation acidify soil, so plant species that prefer acidic soil will have a competitive advantage (now K selected). Such as Spruce trees.
Succession remains a central concept in ecology today. Why is this?
- Impact of climate change
- Invasive species
- Restoration
