Succession Flashcards
What is succession central to
Ecology as evolution is to biology
What is succession
Species change over time (turnover)
What effect does disturbance have on succession
It is started directed and redirected by it. Climate events, landuse change, conversion of rainforests etc
What is the incorrect thought about succession
It is thought to progress towards climax but in reality it is complex and multidirectional
What are the types of succession
Primary succession
Secondary succession
What is primary succession
From sterile beginnings with no existing communities
Example of primary succession
Volcanoes
Glaciers
Facts about volcanoes
3000 active ones.
60-70 erupt annually affecting 500 million people.
Facts about glaciers
10% earths surface
90% of that in Greenland and Antarctica.
75% of glaciers in retreat - get primary terrain left to look at succession over time
How do glaciers create disturbance
As they move through landscapes they peel vegetation away, grinding it up and creating a less biodiversity environment but there are microbes under them.
How much are glaciers retreating
20m per year
What is secondary succession
On previously colonised land after major disturbance
Examples of secondary succession
Landslides Fires Cultivation Land abandonment Wind throw
What are the source of new colonisers in secondary succession
Propagules (seeds) organism in the soil, bacteria, fungi, plants that can recover
What are the two types of succession processes
Autogenic
Allogenic
What is autogenic process
Species change due to activities organisms themselves - biotic. Competitive and interactions for niches and water
What is allogenic process
Species change due to external, non biological factors - abiotic. Like climate change and silting of waters
What are the two general trends for plant community succession
Early successional species
Late successional species
Characteristics of early successional species
Colonisers ‘ruderals’. Small and fast growing. Produce many small seeds for dispersal. No dormancy requirement. Often N fixers. Allocate more energy to reproduction than biomass.
Example of N fixers
Lichens
Cyanobacteria
Dryas
What can colonisers ‘ruderals’ cope with
Desecration
Drought
Warm and cold conditions
Examples of dormancy periods
Some seeds have to be eaten by animals, some have to be frozen to be colonisers
What is an advantage in a nutrient limited enivonrkwbt
Ability to fix atmospheric nitrogen and turn it to an amino acid
Why do early successional species allocate energy to reproduction not biomass
To increase chances they have successful next generations
What are early successional species classed as
R-selected
What are late successional species classed as
Competitions ‘k-selected’
Characteristics of late successional species
Large, slow growing (trees) Dormancy. Dominate. Late seeds, animal dispersal sometimes. Competitive (canopy species) Allocate energy to biomass not reproduction.
What are canopy species
Dominate and control light resource. Plants that dominate resources like light has impact on other plants - selection process goes on e.g plants that tolerate lower light.
Early advantage in late successional species
Big seeds. More energy for seed to produce energy and grow quickly
Model for r selected and k selected plants
R selected have fast growth rate, high investment in reproduction (Dispersor). High colonisation, low competitive ability.
K selected have slow growth rate, long lived, investment in biomass production (competitor). Low colonisation, high competive ability.
What are the patterns of diversity
Short term diversity
Longer term diversity
What is short term diversity
Things changing rapidly e.g mt st Helens with huge pyroxlastuc flow wip e out vegetation on the mountain and created new surface for succession.
In Mt St Helens why was there a rapid increase in species after the pyroclasic flow
Because the species that are colonising are not the species found at the end of successional process (strategists). Trees and forests are at the end of succession due to their forest cover.
What do ribosomes do
Concert atmospheric nitrogen for pea and bean plants which can turn co2 into sugar for the bacteria y the roots who are converting the nitrogen
What is longer term diversity
Limited life historic strategies.
Maximum number of niches and resources.
Competitive exclusion due to resource limitation Means diversity drops over time.
Pathogens and parasites are critical.
What is productivity
Production of biomass in a community. Relationship eternal productivity and succession over time.
Example of longer term diversity
Glacier bay, south east Alaska
Facts about glacier bays longer term diversity
Glacier retreat at a rate of 0.4km.
Creating a plant soil succession chronosequence from 1760 to present day.
What are pioneer communities
Microbes - bacteria, archaea, fungi
Algae, lichens, liverworts, bryophytes (can dry to nothing or freeze or be saturated and okay)
Exposed environments, can still thrive.
How to pioneer species move to colonisers plant species
Overtime they bring organic material into the environment.
Protosoil will begin to form once these die, facilitate next stage of succession (10-20 years ice free)
What are the stages of succession
Pioneer species Coloniser plant species Alder dominated Alder-Spruce transition Spruce dominated forest
Example of coloniser plant
Dryas.
Speed dispersal by wind.
When do dryas dominate in the successional stage
25 years ice free
When do alder dominate in the successional stage
75 years ice free
What is the alder dominated stage
Small shrubs trees, associated with bacteria that can fix nitrogen
What is the alder Spruce transition
125 years ice free.
Facilitation and inhibition. Excluding some species from the space until you get the dominating species.
What is the spruce dominated forest
200 years and >300t/ha
What are seres
Successional stages with characteristic vegetation types of associated biota
Case study for successional stages glaciation
Rootmos glacier, Austria
Glaciated in 2006 are lichen on rock, biological weathering.
Spatial chronosequence.
Glaciated in 1970 and 1953, 1950.
Alpine meadow, lots of species, diverse but no dominance.
Individual species have characteristic ecological traits.
Sand dune case study
Cooloola, Australia.
Monocotyledons, graminoids (grasses and sedges), xerophytes (desecration)
What does Cooloola look like after 100 years
Xerophyte woody shrubs
What does Cooloola look like after 200 years
Eucalyptus forest
What does the volcanic islands in Hawaii look like 100 years after eruption
Things can grow in the cracks of the dried lava.
What does the volcanic islands in Hawaii look like 300 years after eruption
Some trees are growing
What does the volcanic islands in Hawaii look like 12,000 years after eruption
Lots of treees dominate
What is the primary/secondary succession of the slate quarries in Wales
Lichens and microbes. Bryophytes, Moses and liverworts - enough resources for seed germinates. Heterogenous and patchy. Grasses, sedges and rushes. Shrubs - broom and gorse. Trees - silver birch and holly
What are the mechanisms of succession
Getting there - colonisation.
Species replacement over time.
Concurrent interactions between them lead to competitive exclusion.
Basics of early colonists (pioneers)
Light seeds, wind dispersal.
High seed production.
E.g 97u seed, early. For dryas
What is the general trend on role of colonisation
Successful immigration is lower bc of competitor for secondary succession. High for primary
Why are microbial colonists important
For first stage of biological weathering and first stage of succession for protosoil e.g black algal crusts in Glacier Bay is tough, flexible, organic mat.
How does black algal crusts in Glacier bay help
Consolidate surface 1-2cm.
Reduce rain impact/particle movement due to freeze thaw.
N fixers - limiter resource for heterotrophs
What are the two species replacement models
Inhibition model
Facilitation model
Who came up with the species replacement models
Connell and Slayter (1977)
What is the inhibition model
Early arrivals competitively inhibit (light competition)
Spread rapidly and monopolise resources.
What is the facilitation model
Succession is a series of sequential invasions, each dependant on site amelioration by early colonists.
Species die out since changes in environment suited for later colonists.
Example of facilitation
N-fixers e.g alder in glacial deposits and lupins on volcanic ash improve soil N status for later colonists
What percentage of primary seres has N fixers as dominant vegetation
77%
In glacier bay how did alders help succession
Changes in soil conditions e.g increased soil N making the soil acidify by liberating H+ Ions. Spruce prefer acidic soil so have a competitive advantage.
