28. Disturbance

Question 1

succession

Answer 1

the gradual change in communities in an area following a disturbance or creation of a new substrate

Question 2

disturbance

Answer 2

any relatively discrete event that disrupts an ecosystem, community, or population structure, and changes resources, substrate availability, or the environment - disturbance leads to succession

Question 3

types of succession

Answer 3

1. primary succession - disturbance creates/exposes new substrate
2. secondary succession - disturbance removes most organisms (but leaves soil)

Question 4

the cycle (or not) or succession

Answer 4

succession can cycle indefinitely, or end with stability (until next disturbance)

Question 5

climax community

Answer 5

a community that occurs late in succession and whose population remains stable until dispersed by disturbance

Question 6

disclimax community

Answer 6

a community whose species composition is maintained through frequent disturbances

Question 7

intermediate disturbance hypothesis

Answer 7

greatest species diversity at intermediate levels of disturbance (levels of disturbance defined by frequency and intensity)

Question 8

reasons for intermediate disturbance hypothesis

Answer 8

low disturbance: little change, contains mostly organisms that are good competitors (climax/K-selected species)
high disturbance: lots of change, contains mostly organisms that are good colonizers (pioneer/r-selected species)
intermediate disturbance: moderate amount of change, sufficient time between disturbances for species to colonize, but not enough to allow competitive exclusion –> contain organisms that are both good competitors and good colonizers –> high diversity because both types of species

Question 9

evidence for intermediate disturbance: intertidal pools

Answer 9

major disturbance: wave action that can dislodge organisms

• areas with larger boulders = less likely to be overturned = higher diversity
• areas with smaller boulders = more likely to be overturned = lower diversity

Question 10

evidence for intermediate disturbance: grasslands

Answer 10

disturbed by grasslands, drought, and burrowing

• shrub species resistant to burrowing do not change presence across levels of disturbance
• grass species thrive in little disturbance (competitively dominant)
• forb species thrive in high disturbance by nitrogen being brought to the surface
• -> highest total diversity at intermediate disturbance

Question 11

evidence against intermediate disturbance

Answer 11

• ecosystems are complex; effect of disturbance depends on biology of organisms in system and details of disturbance

Question 12

why would communities not change when disturbed

Answer 12

community stability

Question 13

stability

Answer 13

the ability of a community to withstand or recover from a disturbance in terms of diversity/abundance

Question 14

what drives stability

Answer 14

resistance or resilience

Question 15

resistance

Answer 15

the capacity of a community or ecosystem to maintain structure and/or function in the face of potential disturbance

Question 16

resilience

Answer 16

the capacity to recover stucture and/or function after disturbance; a highly resilient community may be completely disrupted by disturbance, but quickly return to its former state

Question 17

evidence for stability: park grass experiment

Answer 17

different amounts of fertilizer applied to different plots - data used to look at community composition and stability

• over time, within each treatment across time, community diversity is constant
• some species increased, some declined, some variable patterns across time period

Question 18

biodiversity and stability

Answer 18

increased diversity (both genetic and species) leads to greater stability

Question 19

insurance hypothesis

Answer 19

theory that increased diversity increases stability because of the increased probability of there being some species within the community that area able to cope with any particular disturbance

Question 20

biodiversity, stability, and the insurance hypothesis in coral reefs

Answer 20

• coral compete with macroalgae
• herbivores that graze on the algae reduce competition and allow reef to thrive
• high herbivore diversity and evenness = coral community stability