Interspecific competition

Question 1

What is intraspecific competition?

Answer 1

Competition within a species.

Question 2

What are the 2 types of intraspecific competition? Briefly describe them.

Answer 2

1. Exploitation - direct and symmetrical.

2. Interference - indirect and asymmetrical.

Question 3

What is another name for intraspecific competition?

Answer 3

Conspecific.

Question 4

What is interspecific competition?

Answer 4

Competition between species.

Question 5

What is another word for interspecific competition?

Answer 5

Heterospecific.

Question 6

What is the ‘competitive exclusion principle’, also called Gause’s Law?

Answer 6

Two species cannot coexist on the same limiting resource. The resource must be limiting to both species.

Question 7

Gause’s Law is dependent on population size. True or false?

Answer 7

False - ‘the species that is largest in isolation does not necessarily prevail’.

Question 8

What was Tilman’s experiment to demonstrate Gause’s Law in 1981?

Answer 8

Grew 2 different algae species in monoculture to find the limiting factor, then grew them together.

Question 9

What were the 2 algal species used in Tilman’s experiment in 1981?

Answer 9

Synedra and Astrionella.

Question 10

What was the limiting factor for both algal species in monoculture in Tilman’s experiment in 1981?

Answer 10

Silica.

Question 11

In Tilman’s experiment in 1981, which species drove silica down to a lower level in monoculture? Why was this important?

Answer 11

Synedra, even though their population size was smaller than astrionella.

Question 12

In Tilman’s experiment in 1981, what happened when the 2 algal species were grown together?

Answer 12

Synedra outcompeted astrionella.

Question 13

Gause conducted an experiment to prove his law with 2 species of paramecium, what were they?

Answer 13

P. Aurelia and P. caudata.

Question 14

In Gause’s experiment, with paramecium species was better at exploiting the resource?

Answer 14

P. Aurelia.

Question 15

When 2 species are under the competitive exclusion principle, which one succeeds?

Answer 15

The species that is able to exploit the (limiting) resource the best, regardless of their population size.

Question 16

What was Tansley’s experiment in 1917?

Answer 16

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.

Question 17

Lokta-Volterra is a logistic growth model. What kind of time does this use?

Answer 17

Continuous.

Question 18

What does Lokta-Volterra do?

Answer 18

It describes and predicts the relationship of 2 interacting populations.

Question 19

In Lokta-Volterra, what is α(12)?

Answer 19

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.

Question 20

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’.

Answer 20

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.

Question 21

In this example of Lokta-Volterra, which terms are variable?

dN1/dt = N1[r1 - α11N1 - α12N2]

Answer 21

N and dN/dt.

Question 22

In this example of Lokta-Volterra, which terms are fixed?

dN1/dt = N1[r1 - α11N1 - α12N2]

Answer 22

r, α11 and α12

Question 23

dN/dt represents population change. What does it say about a population if the right hand side of the equation is negative?

Answer 23

The population is shrinking.

Question 24

dN/dt represents population change. What does it say about a population if the right hand side of the equation is positive?

Answer 24

The population is growing.

Question 25

dN/dt represents population change. What does it say about a population if the right hand side of the equation is zero?

Answer 25

The population is at equilibrium.

Question 26

Invasion analyses are conducted to assess the impact of invading species. What is the first step and the assumption it follows?

Answer 26

Grow species 1 in a monoculture and assume it reaches equilibrium of dN/dt = 0.

Question 27

Invasion analyses are conducted to assess the impact of invading species. What is the second step?

Answer 27

Add a low density of species 2.

Question 28

After the addition of species 2 in an invasion analysis, the simplified equation of Ň1 = r1/α11 is created. How?

Answer 28

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.

Question 29

In invasion analyses our only interest lies in the initial phase of invasion of species 2. True or false?

Answer 29

True, we do not care about long-term population dynamics.

Question 30

If we only care about the initial phase of invasion, is it okay to make assumptions when formulating equations?

Answer 30

Yes.

Question 31

In an invasion analysis, with regards to species 2 the only equation we are concerned with is dN2/dt = N2[r2 – α21Ň1]. Explain this.

Answer 31

``` 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. ```

Question 32

In order for species 2 to invade, dN2/dt = N2[r2 – α21Ň1] must be what?

Answer 32

Greater than 0.

Question 33

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?

Answer 33

True, otherwise the inside of the brackets would be 0 or negative.

Question 34

We already know Ň1 = r1/α11. If we combine this with r2 > α21Ň1, we get r2 > α21(r1/α11). What does this simplify to?

Answer 34

r2/α21 < r1/α11

Question 35

In order for species 2 to invade, we need α21 < α11. What does this mean?

Answer 35

The interspecific competition, specifically the effect of species 2 on species 1, to be greater than the intraspecific competition within species 1.

Question 36

What is the whole principle of invasion analyses?

Answer 36

To assess whether a species can invade, the interspecific competition is compared to the intraspecific competition.

Question 37

In invasion analyses what must be true for a species to invade?

Answer 37

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.

Question 38

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'?

Answer 38

Change the equations so that they focus on species 2, essentially to the opposite of what you have just done.

Question 39

Define coexistence in terms of invasion.

Answer 39

Both species can invade each other, then live together and thrive independently.

Question 40

For coexistence to work, which kind of competition must be strongest?

Answer 40

Intraspecific competition must outweigh interspecific competition

Question 41

How does intraspecific become more important than interspecific competition?

Answer 41

The two species differentiate into separate niches.

Question 42

Define exclusion in terms of invasion.

Answer 42

One species can invade the other, but not vice versa.

Question 43

For exclusion to work, which kind of competition must be strongest?

Answer 43

Interspecific competition must outweigh intraspecific competition.

Question 44

Define Founder Control.

Answer 44

Neither species can invade the other, but the one that thrives is either the one that arrives first or the largest.

Question 45

Define a fundamental niche.

Answer 45

The full range of environmental conditions, both biotic and abiotic, under which an organism can exist.

Question 46

Define a realised niche.

Answer 46

The niche an organism actually lives in that is restricted by competition.

Question 47

Chance can affect niches. True or false?

Answer 47

True.

Question 48

Why are overlapping niches not often observed in nature?

Answer 48

They cause fierce competition which is only solved by extinction of one species or by coevolution.

Question 49

Define coevolution.

Answer 49

Evolution driven by the close association of another species, causing niche differentiation.