Lec 28 (Disturbance) Flashcards
Succession?
a gradual change in communities
in an area following a disturbance or the
creation of new substrate
Disturbance?
any relatively discrete event that disrupts an
ecosystem, community, or population structure
and changes resources, substrate availability,
or the environment
The type of succession that occurs depends on
how extreme the disturbance was…
Primary succession= When disturbance creates/exposes new substrate (gradual change)
Secondary succession= Disturbance removes most organisms (but leaves/doesn’t destroy the soil)
Succession can?
cycle indefinitely, or end with stability (until the next disturbance)
Climax community?
Disclimax community?
Climax community: a community that occurs
late in succession and whose population
remains stable until disrupted by disturbance
Disclimax community: a community whose
species composition is maintained through
frequent disturbances
What is The Intermediate Disturbance Hypothesis?
The theory that “intermediate” levels of disturbance allow for the greatest species diversity.
Levels of disturbance are defined by?
– Frequency of the disturbance
– Intensity of the disturbance
Intermediate levels of disturbance promote higher
diversity.
True or False
True
Intermediate levels of disturbance promote higher
diversity….but why?
At Intermediate Disturbance:
– A moderate amount of change
– Sufficient time between disturbances for species
to colonize, but not enough time to allow
competitive exclusion.
– So, community contain organisms that are good
competitors AND organisms that are good
colonizers
What about low disturbance?
• Little change
• Contain mostly organisms that are good competitors
– Also called ‘climax
species’
– K-selected species
What about high disturbance?
• Lots of change
• Contain mostly organisms that are good colonizers
– Also called pioneer
species
– r-selected species
Evidence Supporting the Intermediate
Disturbance Hypothesis: Grasslands…
Grasslands can experience a lot of disturbance (Grazing, Fire and Drought)
Burrowing by prairie dogs can lead to patchiness,
creating patches of grass, grass with a few forbs, and forbs with a little grass.
How much evidence is there for the
intermediate disturbance hypothesis?
Some ecologists have NOT found support when looking at different ecosystems
Some ecologists have NOT found support when looking at different ecosystems… Why?
Ecosystems are complex: effect of disturbance depends on the biology of the organisms in the system and the details of the disturbance.
…. So not all communities will change equally due to
disturbance.
Why would communities NOT change when
disturbed?
Community Stability
Stability: the ability of a community to withstand
or recover from a disturbance
What Drives Stability?
Resistance and Resilience
What is Resistance and Resilience?
Resistance: The capacity of a community or ecosystem
to maintain structure and/or function in the
face of potential disturbance.
Resilience: The capacity to recover structure and/or function after disturbance; a highly resilient community or ecosystem may be completely disrupted by disturbance, but quickly return to its former state.
Evidence for Stability… Park Grass Experiment
- Long term experiment (started in 1856!)
* Originally intended on testing the effects of fertilizer on hay yield
-What were the results of the park grass experiment?
- Without fertilizer, grasses dominated
- With fertilizer, other species like legumes increased in frequency
- Whether a community is stable depends on how we view it!
-Scale is very important when measuring any
ecological phenomenon
Increased _________leads to
greater stability.
diversity (both genetic diversity within
species and a high diversity of species)
Insurance hypothesis?
theory that increased diversity increases community stability due to an increased probability of there being some species present in the community able to cope
with any particular disturbance.
-What temperature results in the most diversity?
Average temperatures
Biodiversity, stability and the insurance
hypothesis on coral reefs…
- Algae competes with coral for space
- Herbivory reduces competition
- Many types of herbivores on reefs
- High herbivore diversity and evenness supports coral community stability!
