Competition Flashcards
What is competitions effect on sp 1 and sp 2?
Both negative
What is competition?
Interactions in which two species negatively influence each other’s population growth rates
3 types of competition?
Exploitation competition
Compete for a shared resource
Interference competition
Behaviour that reduces resource exploitation by other individuals/species
Pre-emptive competition
Compete for limited space
Barnacles on rocks
Interspecific and infraspecific competition.
Intraspecific competition:
Among individuals within a population
Captured by models with density-dependence (e.g., logistic)
Interspecific competition
Among individuals of different species
Population growth is affect by other species’ population size
(e.g. Lotka-Volterra)
Whats competition coefficients?
- Apha
- How much each individual of species 2 reduces carrying capacity of species 1
Which colour box is sp 1 and sp2?
-Red box:
species 1 individual (size = 1)
-Blue box:
species 2 individual (size = α12)
Whats the frame?
carrying capacity of species 1
What does more individuals of N2 result in?
Less N1 at equilibrium
What does a larger alpha result in?
Steeper growth isocline
What are the 4 possible outcomes?
-Sp2 win- N2 isocline above N1
-Sp1 win- N1 isocline above N2
-Co existence- N1 K below N2 on x axis and N2 K below N1 on y axis
-Founder control (unstable)
N1 K above N2 on x axis and N2 K above N1 on y axis
How to be a successful competitor?
- Achieve positive growth when competitor at K
- More efficient at exploiting resources
- Lessen effect of competition
What does stable coexistence require?
Both species can invade one another
Criticisms of Lotka-Volterra competition
Unclear “how” species compete
→ what they are competing for?
α only measure pair-wise competition, not among >2 species (“higher-order interactions”)
Hard to measure parameters
Predictions only confirmed in simple lab experiments
“Resource competition” theory
Predicts what species wins without observing them together
What s a resource?
- Something in the environment that
(1) contributes positively to population growth, and
(2) is consumed in the process
-Examples: Light, nutrients, food
Not examples: Temperature, air
Assume per-capita biomass growth depends on what?
The concentration of some resource R
What is stable competition equilibrium?
If R < R*, then B(biomass) ↓, consumption ↓, and R ↑
What happens when biomass increases?
R is reduced to lowest R*
Whats an example of competition for a single resource?
2 species of diatoms (algae) competing for Si
Where is the optimum Growth os Species?
Where the growth rate intersects the R*
What happens when there are two resources?
Resources not substitutable Positive growth only if R1 > R1* and R2 > R2*
What happens when neither R is < R*?
Species at equilibrium
Whats the consumption vector?
(c)
Relative rate at which species consumes R1 and R2
Points in direction from (R1,R2) to origin
Whats the supply point?
(S): Total amount of R1, R2 that can exist in the environment (without consumption)
Whats the supply vector?
(U): Rate of resource replenishment
Points from current (R1,R2) back to S
Whats ZNGI?
Zero net growth isocline
What happens if S is below ZNGI?
Species can’t persist
What happens if S is above ZNGI
- Species can persist
- Equilibrium occurs along ZNGI where consumption vector is opposite supply vector (c = -U)
- Resource that is at R* at this point is the most limiting
What does the competition of 2 sp with 2 resources depend on? Which sp will win if they don’t cross?
- The zero net growth isocline
- Species with lower R will win
What happens if ZNGI cross?
- Outcome depends on consumption vectors and supply point
- S before any isocline- both go extinct
- S infront of sp 1 isocline- sp 1 wins
- S infront of sp 2 isocline- sp 2 wins
- S infront of both (directly infront of sp 2)- Sp 1 wins
- S infront of both (directly infront of sp 2)- Sp 2 wins
Why is coexistence possible?
- Species 2 consumes more of, and is limited by, R1
- Species 1 consumes more of, and is limited by, R2
- Stronger competition with themselves than each other
How many species can persist with one resource? 2?
One
Two
When is coexistence possible?
Co-existence possible when:
- Each species can survive on less of one resource than the other species
- Environment provides adequate supply of both resources
- Each species consumes more of the resource that is limiting to it
