Lecture 15: Change in communities

Question 1

Blow down zone

Answer 1

trees knocked down

Question 2

Scorch zone

Answer 2

trees dead but stems still intact

Question 3

Mount st. Helens

Answer 3

• new habitats devoid of living organisms
• enormous debris avalanche
• Some survived in burrows, or under ice-covered lakes, or were plants with underground parts
• Gophers survived in their tunnels and their preferred habitat, expanded after the eruption

Question 4

Facilitation by dwarf lupines on the Pumice Plain

Answer 4

they trap seeds and detritus, and have nitrogen-fixing bacteria

Question 5

Agents of change

Answer 5

act on communities across all temporal and spatial scales

Question 6

Coral bleaching

Answer 6

• Temp rises, or stresses
• Algae gets kicked out of coral, lose important symbiosis
• Gradual, large scale change

Question 7

Tsunami

Answer 7

• Went through and stripped coral reefs
• Dramatic effect

Question 8

Abiotic Factors

Answer 8

• waves, currents, wind, water supply chemical composition, temperature, volcanic activity

Question 9

Biotic Factors

Answer 9

• negative interactions
• Ex. Competition, predation, herbivory, disease, parasitism

Question 10

Succession

Answer 10

• the directional change in species composition over time as a result of abiotic and biotic agents of change.
• often focus on vegetative change, but the roles of animals, fungi, bacteria, and other microbes are equally important

Question 11

Primary Succession

Answer 11

• involves the colonization of habitats devoid of life
• Low frequency events with massive change (volcano, hurricane, etc.)
• can be very slow and Initial conditions are very inhospitable

Question 12

Secondary succession

Answer 12

• Involves re-establishment of a community in which some, but not all, organisms have been destroyed (forest fire)
• high disturbance but leaves organisms that can rebuild
• The legacy of the pre-existing species and their interactions with colonizing species play larger roles than in primary succession.

Question 13

Climax stage

Answer 13

• final stable stage a community can reach (controversial, not sure if its real)

Question 14

superorganisms

Answer 14

• groups of species working together toward some deterministic end. Thus, succession is similar to the development of an organism

Question 15

climax community

Answer 15

composed of dominant species that persist over many years and provide stability that can be maintained indefinitely.

Question 16

Facilitation model

Answer 16

• Early species modify the environment in ways that benefit later species. The sequence of species facilitations leads to a climax community

Question 17

Tolerance model

Answer 17

• also assumes the earliest species modify the environment, but in neutral ways that neither benefit nor inhibit later species

Question 18

Inhibition model

Answer 18

assumes early species modify conditions in negative ways that hinder later successional species
- something needs to be removed for succession

Question 19

Glacier Bay, Alaska example

Answer 19

• primary succession
• Melting glaciers have led to a sequence of communities that reflect succession over many centuries
• Get young vegetation close to the glacier and much older vegetation (spruce forests) further from glacier

Question 20

Intact spruce system, shady, seed predators

Answer 20

very competitive but have a lot of germination as they drop a lot of seeds

Question 21

New England Salt Marsh

Answer 21

• Salt marshes have different species compositions and physical conditions at different tidal elevations.
• A common disturbance is tidal deposition of wrack (dead plant material) that smothers and kills plants, leaving patches where secondary succession occurs
• Spike grass, Distichlis spicata, colonizes the patches first. It is eventually outcompeted by both Spartina and Juncus in their respective zones

Question 22

Rocky intertidal zone

Answer 22

• Disturbance is created mostly by storms— waves and debris rip out the organisms
• Low tides expose organisms to high or low temperatures which can kill them or cause them to detach.

Question 23

What happens as succession progresses?

Answer 23

• larger, slow growing and long-lived species begin to dominate
• Competition probably plays a more dominant role later in succession
• In mid- to late successional stages, an array of both positive and negative interactions are operating

Question 24

Alternative stable states

Answer 24

• different communities follow different successional paths develop in the same area under similar environmental conditions
• can be depicted as a topographic surface.

Question 25

valley/ball analogy

Answer 25

• Valleys represent different community types; a ball represents a community.
• The ball can move from one valley to another, depending on presence or absence of strongly interacting species
• If stable, push ball it’ll go back to where it’s meant to be
• If big enough change, can roll over edge, if it is the same, wont be able to get back to old species composition

Question 26

Are human activities shifting communities to alternative states?

Answer 26

Yes
- These regime shifts are caused by the removal or addition of strong interactors that maintain a community type.