Lecture 9

Question 1

The process of interaction between populations of different species may be very complex, but essentially only 3 basic effects. What are these?

Answer 1

. One species causes an increase in the survival, growth and fecundity of the other
. One species causes a decrease in the survival, growth or fecundity of the other
. One species has no apparent effect no the other

Question 2

What effect do the interactions between populations of different species have on each other for it to be interspecific competition?

Answer 2

Has a negative effect on individuals of both species

Question 3

What is commensalism?

Answer 3

When the presence of one species is a pre-requisite for another

Question 4

Predation is just one species killing another but also…

Answer 4

Parasites and parasitoids

Question 5

What ammensalism?

Answer 5

Where one species has an adverse effect on another, but to no advantage to itself

Question 6

Give categories of the results of interactions between populations of different species

Answer 6

. Predation 
. Commensalism 
. Ammensalism  
. Mutualism (both species benefit) 
. Interspecific competition (both species suffer- causes demonstrable decline in the fecundity, growth or survival of both species. Competition may be one-sided, with one species suffering more then the other

Question 7

What can competition exclusion be affected by? Give an example, explain how this can be demonstrated experimentally

Answer 7

Environmental conditions (e.g. flour beetles
This can be demonstrated experimentally with two species of flour beetle grown in containers with and withou parasites. With parasites, Tribolium confusum has a competitive advantage over Tribolium castaneum, but this is reversed when parasites are removed From Park (1948)

Question 8

What mediates competitive exclusion?

Answer 8

Abiotic and biotic factors

Question 9

Explain the Tansley’s Galium study of competitive exclusion on the species G. saxatile and G. sylvestre

Answer 9

Though G. saxatile is largely confined to acidic soils and G. sylvestre to basic soils.
. Both species can grow on either limestone (basic) or peat (acidic) soil when grown alone
. When grown together, G. sylvestre outcompetes G. saxatile on limestone soil and visa versa
So they can grow in the different soils by themselves but when they are put together one will enevetly outcompete the other (competitively exclude each other)

Question 10

What do competitive exclusion imply?

Answer 10

That no two species can use exactly the same resource(s) without one of them becoming extinct
(Easy to demonstrate in the laboratory- much rarer in the field. Must consider niche theory)

Question 11

Explain the niche theory

Answer 11

. Consider a single environmental variable, such as temperature
. A species can survive and reproduce only within a defined temperature range
. One-dimensional niche
. Add a second dimension, e.g. humidity
. Two-dimensional niche
. Add a third dimension e.g. food particle size
. Three-dimensional niche

Question 12

What is a fundamental niche?

Answer 12

Is the one in which a species can live in the absence of all competitors (so the organism isn’t excluded from any areas and so it is its widest niche.
It is a large niche. With competition (or predation) the niche becomes smaller: this is the realises niche

Question 13

What should natural selection favour?

Answer 13

Should favour species separating in terms of their requirements (to reduce competition) i.e. partitioning their niches (animal will shift its niche slightly so that it is not overlapping with another species)

Question 14

What are the two mechanisms of niche partitioning?

Answer 14

Animals can either:

1. Change the components of their niches (‘resource partitioning’)
   - e.g. change the foods that you eat, the places that you go to, so that you don’t overlap too much with another species
2. Change themselves morphologically (‘character displacement’)
   - evolve different beak shapes so that they don’t overlap too much

Question 15

Give an example of resource partitioning

Answer 15

Temperature- either quickly or evolutionary individuals will switch their niche slightly so there is less overlapping, less interspecific competition, narrower niche, increases intraspecific competition

Question 16

What are the effects of resource partitioning?

Answer 16

. Reduces the amount of interspecific competition
. Niche requirements for each species are now narrower
. Restricts the individuals members of the population
. The narrower the niche the more fierce the competition between members of the same species for resources
(i.e. playoff between reducing interspecific competition at the expense of increasing intraspecific competition)

Question 17

What does radical character displacement (e.g. morphological changes to reduce interspecific competition) involve? Give an example of a species that shows radical character displacement

Answer 17

Involves changing the physical form of the animal to avoid competition
E.g. mud snails (Hydrobia ventrosabajd H. ulvae)

Question 18

Explain character displacement in Hydrobia ventrosa and H. ulvae mud snails)

Answer 18

. Both species feed in algae found on detritus on the mud
. When found alone, both species are about 3.5mm long
. When together H. ulvae became larger (4mm) and H. ventrosa smaller (<3mm)
. The snails feed indiscriminately
. The size of food particles they eat is directly proportional to their body size
(Impact on fecundity?)

Question 19

Explain the character displacement shown in Darwin’s finches

Answer 19

. 2 species of seeds on the island where Geospiza fortis and G. fuliginosa live alone, they have larger bills than might be expected (bill size influences the sizes of the seeds the birds can eat)
. Where they live together on Santa Cruz, G. fulignosa has smaller beak size so no overlap
. Evolutionary response