Lecture 15

Question 1

Mount St Helens Eruption

Answer 1

• 1980
• Largest avalanche in recorded history
• New habitats devoid of living organisms
• Effects of the eruption: varied depending on the distance from the volcano and habitat type

Question 2

Many Animals Survived the Eruption Because

Answer 2

• Some were still dormant (animals hiding from the cold underground)
• Animals that live in burrows (under ice-covered lakes)
• Or plants with underground parts

Question 3

Mechanisms Responsible for Primary Succession

Answer 3

1. facilitation
2. lupines
3. tolerance

Question 4

Facilitation

Answer 4

• By dwarf lupines on the Pumice Plain
• They trap seeds and detritus
• Have nitrogen-fixing bacteria

Question 5

Lupines

Answer 5

• Inhibited by insect herbivores
• Which controlled the pace of succession

Question 6

Tolerance

Answer 6

• Douglas fir and herbaceous species lived together in some habitats

Question 7

Agents of Change

Answer 7

• Act on communities across all temporal and spatial scales
• Vary in frequency and intensity

Question 8

Agents of Change Example

Answer 8

• Coral reef community
• Abiotic features interact, such as predation, competition, and other interactions between organisms
• Slow, subtle changes, as well as catastrophic ones have occurred over the last few decades

Question 9

Sucession

Answer 9

• The directional change in species composition over time as a result of abiotic and biotic agents of change
• Studies of succession often focus on vegetative change
• The roles of animals, fungi, bacteria, and other microbes are equally important
• Agents of change vary in frequency and intensity

Question 10

Two Types of Succession

Answer 10

1. Primary Succession
2. Secondary Succession

Question 11

Primary Succession

Answer 11

• Ex. Volcanic Rock
• involves the colonization of habitats devoid of life
• Very slow due to inhospitable conditions

Question 12

Secondary Succession

Answer 12

• involves the reestablishment of a community in which some, but not all, organisms have been destroyed
• Occurs after fires, storms, logging, etc
• Legacy of the preexisting species and their interactions with colonizing species play larger roles than in primary succession

Question 13

The First Colonizers

Answer 13

• Tend to be stress-tolerant
• Transform habitat in ways that benefit their growth

Question 14

Henry Cowels

Answer 14

• 1899
• Studied succession on sand dunes along Lake Michigan
• Assumed plant assemblages farthest from the lake’s edge were the oldest
• Ones nearest to the lake were the youngest
• Representing a time series of successional stages

Question 15

Frederick Clements

Answer 15

• 1916
• Believed plant communities are like “superorganisms”
• Groups of species working together toward some deterministic end
• succession is similar to the development of an organism
• Each community reaches a stable endpoint called the “climax community”
• composed of dominant species that persist over many years and provide stability that can be maintained indefinitely

Question 16

Henry Gleason

Answer 16

• 1917
• thought communities are the random product of fluctuating environmental conditions acting on individual species
• Communities are not predictable and repeatable
• result of coordinated interactions among species; each community is unique

Question 17

Charles Elton

Answer 17

• 1927
• Organisms and the environment interact to shape the direction succession will take
• Animals can affect the timing and sequence of succession

Question 18

Connell and Slayter

Answer 18

• 1977
• Reviewed the literature on succession and proposed three models:
  1. Facilitation Model
  2. Tolerance Model
  3. Inhibition Model

Question 19

Facilitation Model

Answer 19

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

Question 20

Tolerance Model

Answer 20

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

Question 21

Inhibition Model

Answer 21

• assumes early species modify conditions in negative ways that hinder later successional species

Question 22

Mechanisms of Succession

Answer 22

• Glacier Bay, Alaska one of the best-studied examples of primary successions
• Glaciers scrap everything clear
• Melting glaciers have led to a sequence of communities that reflect succession for centuries
• Organic material provides substrates that hold water and nutrients (bacteria)
• Pioneer stage doesn’t have much bacteria seen compared to spruce stage

Question 23

Nitrogen

Answer 23

• an important limiting factor

Question 24

Glacier Bay illustrated all Three Mechanisms in Connell and Slyater’s Models:

Answer 24

• early stages showed facilitation
  - changes in habitat
• inhibition seen through species such as alders having a negative effect on later successional species
• succession was driven by life history characteristics, a signiture of the tolerance model

Question 25

Rocky Intertidal Zone

Answer 25

• 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 26

Sousa

Answer 26

• 1979
• Studied algal succession on the boulders

Question 27

Alternate Stable States

Answer 27

• The theory of alternative stable states can be depicted as a topographic surface
• Different communities follow different successional paths
• Develop in the same area under similar environmental conditions
• A community is thought to be stable when it returns to its original state after some perturbation

Question 28

2 Different Stable Communities Seemed to Result

Answer 28

• One dominated by Styela, a solitary tunicate
• One dominated by Schizoporella, a bryozoan, on tiles placed out in late summer
• Both were impervious to colonization by other species
• Styela can escape predation once it reaches a certain size
• The system might show hysteresis given that it does not shift back to the original community type once the original conditions are restored

Question 29

Regime Shifts

Answer 29

• caused by the removal or addition of strong interactors that maintain a community-type
• It is unclear whether the results can be reversed