L13 - Commuities

Question 1

What does it mean that a species populations may be r or K selected?

Answer 1

r selected - species reproduce rapidly

K selected - species reproduce more slowly, they are near the carrying capacity

Question 2

Give 3 characteristics of r selected populations

Answer 2

1) have rapid population spurts free from intraspecific competition
2) are smaller, mature early, have numerous small young
3) unpredictable mortality rates

Question 3

Give 3 characteristics of K selected populations

Answer 3

1) live in constant/predictable habitats
2) delayed reproduction with larger fewer offspring
3) live in crowded populations with intraspecific competition

Question 4

Are K or r selected species typical for early succession?

Answer 4

r - fast population growth

Question 5

Are K or r selected species typical of late succession?

Answer 5

K - good competitors

Question 6

When might competition not be apparent?

Answer 6

• when previous competition has lead to niches to be formed
• when habitat is patchy
• unsuccessful species are extinct
• competition is only apparent at high population densities

Question 7

Describe how niche differentiation and negative association relate

Answer 7

If niche differentiation is absent one species should be present only where the other is absent = a negative association

Question 8

Often predation (by grazers, parasites etc.) or disturbance (by storm, fire etc.) restrain populations so resources are not limiting. If resources are limiting do we get competitive exclusion?

Answer 8

• in homogeneous systems yes

- in heterogeneous systems no - spatial and temporal variation

Question 9

What happens to the species diversity when predatorial disturbance is a) infrequent b) intermediate c) high frequency

Answer 9

a) competitive exclusion occurs and some species are squeezed out
b) high diversity
c) low diversity

Question 10

Give an example of a) a high scale disturbance b) a low scale disturbance

Answer 10

a) a forest fire

b) a mole hill

Question 11

What is speicies diversity of an island like compared to mainland?

Answer 11

Islands have a lower number of species the smaller the island, and compared to comparable areas of mainland

Question 12

What 3 reasons cause the lower number of species per area of an island compared to mainland. Describe each

Answer 12

• Habitat diversity - the larger the island the more varying the habitat the more species can live there. This is true for mainland as well
• Evolution - Isolated oceanic islands have a high proportion of endemic species. Evolution is more significant for communities that have been isolated for a long time
• immigration/extinction balance - The numbers of species on an island is determined by an equilibrium between immigration and extinction. Equilibrium effect doesn’t effect mainland