The nature of community: patterns in space and time lectures

Question 1

community

Answer 1

an assemblage of species populations that occur together in space and time

Question 2

how can a community be defined?

Answer 2

at any scale within a hierarchy of habitats (communities within communities)

Question 3

what defines community assemblage?

Answer 3

• dispersal constraints (can get there)
• environmental constraints (can survive there)
• internal dynamics (interact with organisms present there)

Question 4

species richness

Answer 4

number of species present (S)

Question 5

what is species richness a function of?

Answer 5

non-linear sampling effort

Question 6

what does a non-linear sampling effort lead to?

Answer 6

more sampling eventually leads to no more species being discovered

Question 7

what does species richness ignore?

Answer 7

community structure

Question 8

Species Diversity

Answer 8

richness and equatability combined (D)

Question 9

Species Diversity (D) formula

Answer 9

D = 1 - E(n(n-1))/N(N-1)

Question 10

Measurement of equitability

Answer 10

E = D/Dmax

Question 11

Gradient analysis

Answer 11

1) subjective mapping of the vegetation - implying hard boundaries
2) distribution of abundance of species along a moisture gradient - no sharp boundaries

Question 12

Primary succession

Answer 12

large disturbance or completely new environment created

Question 13

Secondary succession

Answer 13

more minor disturbances

Question 14

Example of secondary succession

Answer 14

Watt (1947)

disturbance caused by severe rain-storms in Borneo forests

Question 15

Implications of patch dynamics perspective

Answer 15

• disturbance opens up gap in community
• gaps/patches recolonised by individuals of various species
• disturbance ‘resets’ the community
• migration/dispersal between habitat patches are important processes
• the order of arrival and relative recruitment of different species may be important

Question 16

Dominance-controlled communities

Answer 16

some species strongly competitively superior, leading to ecological successions

Question 17

Founder-controlled communities

Answer 17

all species have similar competitive abilities, leading to ecological successions

Question 18

Connell’s Intermediate Disturbance Hypothesis

Answer 18

• importance of time since disturbed
• importance of spatial scale or intensity of disturbance
• importance of frequency of disturbance

Question 19

Connell’s Intermediate Disturbance Hypothesis

- importance of spatial scale or intensity of disturbance

Answer 19

LOW LANDSCAPE DIVERSITY - large scale disturbances that are synchronised over extensive areas

HIGH LANDSCAPE DIVERSITY - unphased small-scale disturbances that create a mosaic of patches at different stages of succession

Question 20

What circumstances are likely to lead to founder-control?

Answer 20

• high diversity of coexisting species
• only a proportion of diversity attributable to resource partitioning
• vacant space crucial limiting factor
• vacant space unpredictable in space and time

Question 21

Three tests of the Intermediate Disturbance Hypothesis

Answer 21

Sousa 1979 - inter-tidal algae communities, southern California
Townsend et al. 1997 - stream-bed insect communities, New Zealand
Molino & Sabatier 2001 - tropical tree communities in French Guiana

Question 22

What circumstances are likely to lead to dominance-control?

Answer 22

• light sensitive (aware of openings in canopy)
• pioneer species specially adapted (10% of community species)
• highly competitively superior species