Lecture 8.docx

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18 Apr 2012
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Lecture 8: metapopulations, plant community composition
Fender blue butterfly
- .5 percent of habitat left, rest turned to agriculture
- rediscovered in 1989 nd people wanted to help it
- it is known from 13 small fragments of prarie
- can only feed on kincaids lupin
- pulses of population occur every year. Cyclic
Andy Smith Pika research
- bodie is mining town
- pikas live in tailings pathces
- he took metapopulation approach
- north patch consistently occupied
- southern patch has decreasing population
- middle patch has cyclic
stochastic versus deterministic models
-fixed
- one outcome
- paramters include chance
-better than deterministic models
- ex.
Deterministic: l=.5 of x=100, then 50 newborns live
Stochastic: flip coin 100 times, some time itll be 46 living etc… some years good,
some bad
Stochastic model for pika
North zone: Source. High Stable. By itsekf, it can maintain its pikas, even better than
before because none can leave
Middle Zone: sink, needs source to survive . depends on import. Low, stable. By itself
it goes to extinction quickly
South Zone: Sink, needs stream to survive. Unstable. Doesnnt do well on its own
Conclusions on stability and coexistence
Model pops can bedriven to extinction
- chaos
- unstable competition
- unstable predator prey (disease- host)
- Alee effects at low density
But these things can be countered
By nine equilibrium conditions, habitat patchiness, rescue by migration, variation in
life strategies
Plant community ecology
- Some species have robust association with other association
- Seen as community types. Mostly descriptive
2 different views as to why associations exist
1. Holistic- they have to be together because they are dependent on each other.
The man who created idea named it also organismal approach because he
saw interactions similar to an organism which work together (Frederick
clement)
2. Individualistic- species are distributed independently. They may be near
each other because the belong to same biome… (henry gleason) “plant
association is dependent on coincidence of environmental selection ans
migration”aka environment just needs to be right. Abiotic environments
-Initially clement one, but later on data was collected and viewed in “gradient
analysis”. Robert whittaker direct gradient analysis saw:
plotted abundance of plants across ecological gradients which included soil
moisture.
If clement Is right, the it’s a, it Gleason is right It be D. D was looked upon to be right.
Maragret davis showed through fossil data that trees moved upwards after glacier
by themselves, not in specific packs.
Curtis also used indirect gradient to prove clement wrong