Describe the difference between r and k species.
R species grow fast and reproduce early - allocate more resources to reproduction than growth so not strongly competitive
K species have vigorous growth, thrive in competition but at the expense of delayed reproduction - produce fewer large progeny.
What characterises discrete environments?
individuals / organisms respond in similar ways to environmental factors.
What is Clements view of succession?
The evolution of communities over time towards the climax community
What is Gleason’s view of succession?
Species respond individualistically to env factors. Environment is constantly changing on all time and space scales, there is no end point to succession, only dynamic equilibrium.
What are vegetation dynamics affected by?
Frequency and type of disturbance, area affected
What characterises early succession?
biomass small, photosynthetic efficiency low, good seed dispersal, plant longevity short, resource consumption fast, open/rapid biogeochemical cycling, high primary productivity, low ecosystem stability.
What id diversity the product of?
Richness (number of species)
Eveness (how evenly these are represented)
What is allopatric speciation?
Biological populations separated by a physical barrier, which develop to the extent that is the barrier was removed, they would not be able to interbreed. Most common in animals.
What is sympatric speciation?
When a new species develops from an ancestral one, occupying the same geographic area. Most common in plants. May occur rapidly by polyploidy as polyploids are sterile in crosses with parent species.
What is the species richness of an island determined by in the short term?
Immigration, extinction
Describe the latitude gradient of organisms species diversity compared to microbes.
Organisms diversity decreases from tropics to poles, whilst microbes not affected as disperse and colonise easily.
What is the latitude gradient the result of?
- Lower extinction rate (larger area, stability of climate = higher population number, larger species range, lower chance of extinction)
- Diversification and speciation rates higher in tropics
- Time for diversification higher in tropics (env is older and dispersal of clades from tropics relatively recent)
What makes diversification higher in the tropics?
- Genetic drift
- Climate variation = higher speciation at tropics
- Sympatric speciation more likely
- larger area = more likely to be isolated
- narrower physiological tolerance = reduces dispersal to unfavourable environments
- higher temps = increased evolutionary speed
- stronger biotic interactions = faster speciation / greater specialization
What are the three mechanisms of species richness accumulation over time
- Tropics and temps dont differ in diversification rate, but in ecological factors such as niche availability
- tropics have higher diversification rate so accummulate richness faster
- tropics have had more time for diversification, as without ice for longer.
What is diversification calculated by?
Speciation - extinction
In clements view, what was secondary succession?
after disturbance, remnants may alter resulting community
What did clements see as the 6 processes to control community development?
- Nudation (creating bare surface)
- Migration
- Ecesis (establishment so complete life cycle can occur)
- competition
- Reaction (modification of habitat by vegetation)
- Stabilization (climax community)
Why are species poor islands more subject to invasion?
- Less occupied niches
- conservation / farming creates more favourable environment
What do short term disturbances create?
high species richness
Why is competition greatest between similar species?
Niches more likely to overlap
