Topic 25

Question 1

Linkage density

Answer 1

average number of actual links (arrows) per species in a food web

Question 2

Connectance

Answer 2

number of links divided by the number of possible links

Question 3

Food chain length

Answer 3

number of trophic levels

Question 4

Most food webs have how many trophic levels

Answer 4

4 levels

Question 5

Food web complexity

Answer 5

defined by a combination of food chain length, species richness, linkage density, connectance

Question 6

General pattern

Answer 6

higher food web complexity (species richness) –> higher community ‘stability’ (resistance to change)

Question 7

More complex food webs have ..

Answer 7

lower resilience; if the structure of a complex food web changes, it will take longer and be harder to return to original state

Question 8

Typical patterns in communities

Answer 8

many rare moderately abundant species (weak interactors) few common species (strong interactors)

Question 9

Evidence shows that the removal of a strong interactor results in..

Answer 9

changes to community structure

Question 10

2 conceptual weak interactors models

Answer 10

• redundancy model

- rivet model

Question 11

Redundancy model

Answer 11

species = passengers on a plane. few key passengers (species) required to fly plane. loss of any one passenger = no effect. lost of key passengers (pilot) = doesn’t fly. DOMINANCE EFFECT

Question 12

Redundancy model implies

Answer 12

species within functional groups are redundant

Question 13

Rivet model

Answer 13

species = rivets on airplane. each rivet (species) plays a small but significant role. lots of a rivet weakens plane, loss of many rivets –> plane falls apart. COMPLEMENTARY EFFECT

Question 14

Rivet model implies

Answer 14

all species within functional groups are important

Question 15

Evidence (small scale)

Answer 15

higher stability in species rich (vs species poor) communities under changing environmental conditions. high number of weak interactors results in higher stability

Question 16

Observational (large scale)

Answer 16

phase shifts (=instability) often follow gradual loss of species richness

Question 17

Suggests high species richness is essential for..

Answer 17

stable community structure under changing environmental conditions.

Question 18

Species within a functional group (perform the same roles in the food web) are not…

Answer 18

redundant

Question 19

Diversity stability (insurance) hypothesis

Answer 19

species richness provides insurance and buffers or minimizes chances of changes in structure under environmental change

Question 20

Response diversity

Answer 20

variation in responses to environmental change among species within a functional group

Question 21

Response diversity is critical because species with ..

Answer 21

respond differently to environmental change, these different responses will maintain community structure in its original state

Question 22

Coral/algal phase shift

Answer 22

free living algal species will readily outcompete coral species if left unchecked. in coral dominated communities several herbivores exist that consume algae. as herbivores re removed from community response diversity eroded. some point community becomes particularly prone to irregular changes in environmental conditions