Lecture 4- Succession Flashcards
What is succession a measure of?
Biodiversity changes across temporal scales
What process controls successional processes?
DISTURBANCE
WHAT ARE THE TWO MODES OF SUCCESSION?
Primary and secondary
When does primary succession occur?
From a COMPLETELY sterile beginning, eg. Volcanic eruption
When does secondary succession occur?
From a disturbance on ALREADY COLONISED land
What are the two succession processes classed as?
Autogenic or allogenic
Describe AUTOgenic succession
Species change from BIOTIC interactions
Decribe ALLOgenic succession
Species change due to ABIOTIC interactions
What type of species are early successional species?
R selected species
Describe the characteristics of r selected species that enable them to be successful colonisers (4)
- produce many seeds with high dispersal ability
- no dormancy in germination(quick)
- often n-fixers which allows them to live in regions with low resource avaliability
- allocate more energy to reproduction than biomass (which allows rapid population growth)
What type fo species are late successional species
K selected species
What are the properties of k selected species that makes them successful in later successional stages?
- large,slow growing (allows monopolisation of light)
- send dormancy, dispersed by animals
- large, containing more resource for growth
- allow more energy to biomass than reproduction
Which type of species are more at risk to extinction? Why?
K selected species as they have lesser adaptations to fluctuating environments
Describe the r-k continuum
Initially, species have high rates of colonisation and low competitive ability. However,as the community switches from being r to k dominated, the rates of competitively outweigh those fo colonisation
How does biomass change throughout succession
Initially a low biomass as early colonisers have low LIFE HISTORY STRATEGIES,but biomass gradually increases with the arrive of large K selected species. However, as competitive exclusion begins (from k selected species), biomass falls from its peak and stabilises
Explain how species diversity changes throughout succession
Diversity is initially low as only specialised r selected species can handle unfavourable conditions (eg. Nitrogen fixers), however this rapidly increases until dominant species become prevalent, outcompeting others and stabilising biodiversity at a constant level
What are the two mechanism of succession?
Colonisation
Replacement
What are the mechanism of succession driven by?
COMPETITIVE EXCLUSION
How does colonisation differ between primary and secondary succession
Low in secondary succession as species are already present in the environment. High in primary succession as new species immigrate.
What are the two models of species replacement?
- Inhibition model
2. Facilitation model
Outline the inhibition model
Early successional species monopolise resources and completely inhibit the arrival of later species, until something ounces (eg, change in conditions) that allow later species to also access these resources
Out line the facilitation model
Each invasive species involved in succession is dependant on site AMELIRATION from earlier colonists. These earlier species make the conditions optimal for the next step in succession (eg. By providing enough nutrients to the soil), and then die as conditions are no longer best suited to them
What is a plagioclimax community?
One that is prevented from reaching climax state by human activities
