Interspecific competition Flashcards
What is intraspecific competition?
Competition within a species.
What are the 2 types of intraspecific competition? Briefly describe them.
- Exploitation - direct and symmetrical.
2. Interference - indirect and asymmetrical.
What is another name for intraspecific competition?
Conspecific.
What is interspecific competition?
Competition between species.
What is another word for interspecific competition?
Heterospecific.
What is the ‘competitive exclusion principle’, also called Gause’s Law?
Two species cannot coexist on the same limiting resource. The resource must be limiting to both species.
Gause’s Law is dependent on population size. True or false?
False - ‘the species that is largest in isolation does not necessarily prevail’.
What was Tilman’s experiment to demonstrate Gause’s Law in 1981?
Grew 2 different algae species in monoculture to find the limiting factor, then grew them together.
What were the 2 algal species used in Tilman’s experiment in 1981?
Synedra and Astrionella.
What was the limiting factor for both algal species in monoculture in Tilman’s experiment in 1981?
Silica.
In Tilman’s experiment in 1981, which species drove silica down to a lower level in monoculture? Why was this important?
Synedra, even though their population size was smaller than astrionella.
In Tilman’s experiment in 1981, what happened when the 2 algal species were grown together?
Synedra outcompeted astrionella.
Gause conducted an experiment to prove his law with 2 species of paramecium, what were they?
P. Aurelia and P. caudata.
In Gause’s experiment, with paramecium species was better at exploiting the resource?
P. Aurelia.
When 2 species are under the competitive exclusion principle, which one succeeds?
The species that is able to exploit the (limiting) resource the best, regardless of their population size.
What was Tansley’s experiment in 1917?
He grew 2 bacterial species in monoculture and found that although they could both grow on either calcareous or acidic soil, they each preferred a soil type. When he grew them together, they each only grew in the soil type they preferred - they had competitively excluded each other.
Lokta-Volterra is a logistic growth model. What kind of time does this use?
Continuous.
What does Lokta-Volterra do?
It describes and predicts the relationship of 2 interacting populations.
In Lokta-Volterra, what is α(12)?
The per capita effect of a species. ‘α(12) means the ‘effect of species 1 on species 2’.
If it were α(21) it would mean ‘the effect of species 2 on species 1’ etc.
dN1/dt = N1[r1 - α11N1 - α12N2]
This is a simplified version of Lokta-Volterra. Explain each term, using 1 as ‘species 1’ and 2 as ‘species 2’.
dN1/dt = the rate of change in species 1 at time t N1 = density of species 1 r1 = net fecundity of species 1 (births - deaths) α(11) = intraspecific competition, the effect of species 1 on species 1 α(12) = interspecific competition, the effect of species 1 on species 2. N2 = density of species 2.
In this example of Lokta-Volterra, which terms are variable?
dN1/dt = N1[r1 - α11N1 - α12N2]
N and dN/dt.
In this example of Lokta-Volterra, which terms are fixed?
dN1/dt = N1[r1 - α11N1 - α12N2]
r, α11 and α12
dN/dt represents population change. What does it say about a population if the right hand side of the equation is negative?
The population is shrinking.
dN/dt represents population change. What does it say about a population if the right hand side of the equation is positive?
The population is growing.
dN/dt represents population change. What does it say about a population if the right hand side of the equation is zero?
The population is at equilibrium.
Invasion analyses are conducted to assess the impact of invading species. What is the first step and the assumption it follows?
Grow species 1 in a monoculture and assume it reaches equilibrium of dN/dt = 0.
Invasion analyses are conducted to assess the impact of invading species. What is the second step?
Add a low density of species 2.
After the addition of species 2 in an invasion analysis, the simplified equation of Ň1 = r1/α11 is created. How?
Species 2 is in such low density that it can be omitted from the Lokta-Volterra equation, which is then simplified to Ň1 = r1/α11. This means we can work out the density of species 1 ‘in the absence of’ species 2.
In invasion analyses our only interest lies in the initial phase of invasion of species 2. True or false?
True, we do not care about long-term population dynamics.
If we only care about the initial phase of invasion, is it okay to make assumptions when formulating equations?
Yes.
In an invasion analysis, with regards to species 2 the only equation we are concerned with is dN2/dt = N2[r2 – α21Ň1]. Explain this.
dN2/dt = change in density of species 2 N2 = density of species 2 r2 = net fecundity of species 2 α21 = effect of species 2 on species 1 Ň1 = effective density of species 1 in the absence of species 2.
In order for species 2 to invade, dN2/dt = N2[r2 – α21Ň1] must be what?
Greater than 0.
We have just added species 2, thus we know N2 > 0. This means that r2 > α21Ň1, otherwise dN2/dt = N2[r2 – α21Ň1] would equal 0. True or false?
True, otherwise the inside of the brackets would be 0 or negative.
We already know Ň1 = r1/α11. If we combine this with r2 > α21Ň1, we get r2 > α21(r1/α11). What does this simplify to?
r2/α21 < r1/α11
In order for species 2 to invade, we need α21 < α11. What does this mean?
The interspecific competition, specifically the effect of species 2 on species 1, to be greater than the intraspecific competition within species 1.
What is the whole principle of invasion analyses?
To assess whether a species can invade, the interspecific competition is compared to the intraspecific competition.
In invasion analyses what must be true for a species to invade?
The interspecific competition, i.e. the effect of the invader species on the existing species, must be greater than the intraspecific competition within the invading species.
You can perform invasion analysis to see if ‘species 1’ can invade ‘species 2’. How do you assess whether ‘species 2’ can invade ‘species 1’?
Change the equations so that they focus on species 2, essentially to the opposite of what you have just done.
Define coexistence in terms of invasion.
Both species can invade each other, then live together and thrive independently.
For coexistence to work, which kind of competition must be strongest?
Intraspecific competition must outweigh interspecific competition
How does intraspecific become more important than interspecific competition?
The two species differentiate into separate niches.
Define exclusion in terms of invasion.
One species can invade the other, but not vice versa.
For exclusion to work, which kind of competition must be strongest?
Interspecific competition must outweigh intraspecific competition.
Define Founder Control.
Neither species can invade the other, but the one that thrives is either the one that arrives first or the largest.
Define a fundamental niche.
The full range of environmental conditions, both biotic and abiotic, under which an organism can exist.
Define a realised niche.
The niche an organism actually lives in that is restricted by competition.
Chance can affect niches. True or false?
True.
Why are overlapping niches not often observed in nature?
They cause fierce competition which is only solved by extinction of one species or by coevolution.
Define coevolution.
Evolution driven by the close association of another species, causing niche differentiation.
