Lecture 15 Flashcards
1
Q
Mount St Helens Eruption
A
- 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
2
Q
Many Animals Survived the Eruption Because
A
- Some were still dormant (animals hiding from the cold underground)
- Animals that live in burrows (under ice-covered lakes)
- Or plants with underground parts
3
Q
Mechanisms Responsible for Primary Succession
A
- facilitation
- lupines
- tolerance
4
Q
Facilitation
A
- By dwarf lupines on the Pumice Plain
- They trap seeds and detritus
- Have nitrogen-fixing bacteria
5
Q
Lupines
A
- Inhibited by insect herbivores
- Which controlled the pace of succession
6
Q
Tolerance
A
- Douglas fir and herbaceous species lived together in some habitats
7
Q
Agents of Change
A
- Act on communities across all temporal and spatial scales
- Vary in frequency and intensity
8
Q
Agents of Change Example
A
- 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
9
Q
Sucession
A
- 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
10
Q
Two Types of Succession
A
- Primary Succession
- Secondary Succession
11
Q
Primary Succession
A
- Ex. Volcanic Rock
- involves the colonization of habitats devoid of life
- Very slow due to inhospitable conditions
12
Q
Secondary Succession
A
- 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
13
Q
The First Colonizers
A
- Tend to be stress-tolerant
- Transform habitat in ways that benefit their growth
14
Q
Henry Cowels
A
- 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
15
Q
Frederick Clements
A
- 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
16
Q
Henry Gleason
A
- 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
17
Q
Charles Elton
A
- 1927
- Organisms and the environment interact to shape the direction succession will take
- Animals can affect the timing and sequence of succession
18
Q
Connell and Slayter
A
- 1977
- Reviewed the literature on succession and proposed three models:
1. Facilitation Model
2. Tolerance Model
3. Inhibition Model
19
Q
Facilitation Model
A
- inspired by Clements
- Early species modify the environment in ways that benefit later species
- The sequence of species facilitations leads to a climax community
20
Q
Tolerance Model
A
- assumes the earliest species modify the environment, but in neutral ways that neither benefit nor inhibit later species
21
Q
Inhibition Model
A
- assumes early species modify conditions in negative ways that hinder later successional species
22
Q
Mechanisms of Succession
A
- 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
23
Q
Nitrogen
A
- an important limiting factor
24
Q
Glacier Bay illustrated all Three Mechanisms in Connell and Slyater’s Models:
A
- 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
25
Q
Rocky Intertidal Zone
A
- 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
26
Q
Sousa
A
- 1979
- Studied algal succession on the boulders
27
Q
Alternate Stable States
A
- 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
28
Q
2 Different Stable Communities Seemed to Result
A
- 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
29
Q
Regime Shifts
A
- caused by the removal or addition of strong interactors that maintain a community-type
- It is unclear whether the results can be reversed
