EVS 411 Exam 3

Lecture 19 - Disturbances

Hypoxia - low levels of oxygen (related to eutrophication) vs. anoxic - no oxygen levels.

Once the population goes above the impact threshold, systems are less likely to recover from disturbances.

Intermediate disturbance hypothesis (IDH):

• At intermediate levels of disturbances, you will have the maximum number of species.

• Low disturbances, leads to less recovery from disturbances due to there being low diversity.

• (5) diversity is highest when there is a healthy pool of recruits, aiding in the recovery of an area.

• When competition is equivalent, there will be a high level of diversity.

• Depth: in shallow areas, there are crests. Species that grow and outgrow others, there will be less diversity. (depending on the physical area of the habitat, the results of diversity will be different)

Reef community development:

• Bare substrate → colonization → succession → → → (multiple events) climax community.

Disturbances on reefs: (each operates on a different scale, with different frequency and intensity)

• Hurricanes

• Acanthaster

• Oil spills

• Bleaching

• Disease epizootic

• Blast fishing (poor fishing practices)

• flood/runoff sedimentation

Hurricanes:

• Important for coral reefs.

• (12) there are a number of variables/stressors that are impacting coral reefs that are leading to their decline, not just hurricanes, such as bleaching and diseases.

Cyclone effects at Heron Island:

• Depending on where coral is, outside of the crest or in the lagoon, decline was different. Depending on where it is, some populations might be more susceptible to desiccation, impacting their recovery.

• Exposed crests populations are more likely to recover

(17): if there is resiliency, the ball is going to stay in its hole, no matter what events occur. Overfishing and extra nutrients, brings that wall down, that leads to the ball falling into another state (different states of degradation). Resiliency continues to decrease over time.

Can corals cope?

• Resistance (individual and population) to experience change without changing, and resilient (population) even though the system changes, the population can come back, depends on: intensity of event, duration, frequency, and species.

Adaptation and acclimation:

• Adaptation: genotypic changes over time, selection for more favorable genotypes.

• Delays adaptation: long life span, long generations, and backcrossing (with other colonies)

• Accelerates adaptation: short life spans, large genetic variation, and limited backcrossing.

• Potential outcome: new species and local adaptations.

• Acclimation: phenotypic change in response to environmental change. Ex: squirrels in US vs canada. In the US they are grey and in Canada they are black.

1. Usually compensatory

2. Occurs during the organism's lifetime

3. Limits set by genotype.

4. Usually reversible. Once conditions change, they can change to a different phenotype.

5. Not inherited