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Lecture 25

NATS 1940 Lecture Notes - Lecture 25: Paramecium Aurelia, Starfish, Competitive Exclusion Principle

Natural Science
Course Code
NATS 1940
Mark Vicari

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Lect 25: chapter 19.9 pg. 176-79
* Biodiversity Through Time: Mass Extinctions:
For a species survival every species requires a set of :
1. Resources:
Individuals compete for
Food, nesting sites
2. Conditions:
Non consumables
No competition
Certain temp, humidity, pH
The complete set of conditions and resources required is the niche of
the species
Competitive Exclusion Principle:
2 species cannot coexist in a community if their niches are the same
Lab experiments
Paramecium aurelia & P. Caudatum
Feed on same bacteria
Were put together in same dish
Both populations increased then leveled off at a high
Only P.Aurelia survives long term
P.Caudatum is completely excluded
Predators and the diversity of prey
When species competing for the same resources have predators
It is possible for those competitors to coexist
Sea star study
Sea star feeds on mussels in intertidal communities

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Mussels compete with other species for space
Mussels strongly dominant without sea stars to
keep it in check = exclude other species
Predation reduces population sizes of competing species
and therefore allows those species to coexist without
competitively excluding one another
In conclusion:
In recent geological time, species richness of the earth (gamma diversity) has
been higher than ever before due to
1. Configuration of the continents
Many opportunities for isolation
Allopatric speciation
Increase beta diversity
2. The tendency for diversity to beget more (alpha) diversity
More prey
More food types (ecological niches)
More predators
More predators
Less competitive exclusion
Fossil records show that 99% of all species that ever lived are extinct
The rate of extinction varies
Background extinction (normal)
Background rate varies for different groups taxa
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