L9 Tosh Interspecific competition

Question 1

What are the 5 basic interactions 2 species have on each other?

Answer 1

1. +- = predators and parasites
2. ++ = mutualism
3. – = interspecific competition
4. -0 = ammensalism
5. +0 = commensalism

Question 2

Give 2 examples of competitive exclusion

Answer 2

1. Flour beetle
   - 2 species of flour beetle grown in containers with and without parasites
   - with parasites one has a competitive advantage over the other, but this is reversed when the parasite is removed
2. Gallium study
   - 2 species - both can grown on either limestone or peat (base and acid) soil when grown alone
   - when growth together, one outcompetes the other, one is better in acid the other in basic soil

Question 3

What is Niche theory?

Answer 3

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 4

What is a species Fundamental Niche and realised niche?

Answer 4

FN: the one niche in which a species can live in, the absence of all competitors (it is a large niche)

RN: with competition the niche becomes smaller

Question 5

What are the 2 mechanisms operating in niche partitioning?

Answer 5

1. Change the components of the niches (resource partitioning)

OR

2. Change themselves morphologically (character displacement)
   - radical - involves changing the physical form of the animal to avoid competition
   E.g. mud snails change their shell

Question 6

What are the effects of niche partitioning?

Answer 6

• It reduces the amount of interspecific competition
• niche requirements for each species are now narrower
• restricts the individual members of the population
• the narrower the niche the more fierce the competition between members of the same species for resources

IE: the playoff between reducing interspecific competition at the expense of increasing intraspecific competition

Question 7

Give an example of niche partitioning

Answer 7

Darwin’s Finches

2 sizes of seeds on the islands where 2 types of finches live alone - they have bigger bills than expected

Where they love together on Santa Cruz, one has a smaller beak so there isn’t a size overlap

Question 8

Give an example of Niche Partitioning

Answer 8

Seed eaters in desert environments - between rodents and ants