Lecture 7.docx

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18 Apr 2012
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Lecture 7- species interactions. Two species population models to community
structure
Classification of who gains who looses: (consumer resource +/-)
a) Predator+,-Prey
b) Plant+,-Herbivore
c)
Competition (-/-)
Mutualism (+/+)
Focci of study:
- Effects on Population dynamics
- Coevolution, reciprocal changes of genetic makeup of species. Reaction of
species to each others presence
1) Lotka Voltera Model of competition: extension of logistics
- alpha 12 is the effect of species 1 on species 2
- pair of differential equations which show impact of animals on each other.
Large alpha means lots of competition
- Equations evaluated by outcomes. Graph cant be drawn but end result of
competitive interaction is know.
- There are 4 different end results
a) species 1 always wins b) species 2 can always win c) two species might
coexist indefinitely. Each cut into each other species pop size d) unstable
situation where we don’t know who will win because of different starting
situation.
- Coexistence requires species to inhibit there own growth more than
they inhib each others growth.
2) Criteria for coexistence in competitors
- law of competitive exclusion stated that in competition, one species would loose.
3) Empirical testing: gause experiments with protozoa
Used protozoa and saw lotka voltera outcomes where he saw competition exclusion
and coexistence.
- with paramecium he saw competitive exclusion. With green red species he
saw coexistence
Competitive effects manifested in nature
- Species unlikely to completely die out. They may just get smaller in numbers
and distribution altered
- Soil conditions (environmental conditions) affects competition
4) LV Model of predation predator -prey cycles
- Similar to competition models: two differential equations
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