Lecture 16 Flashcards
Disturbances are events that affect
The physical environment and therefore resource availability
These events change community properties (such as:
Interactions among species and overall biodiversity
Disturbances can be categorized as _______ or __________
Physical or biological
Examples of physical disturbances
Glacial advance and retreat
Volcanic eruptions
Fire
Flood
Drought
Tornado
Examples of biological disturbances
Bark beetle infestation
Root rot of fungus
Overgrazing
Algal blooms
How is pollution categorized?
Chemical pollutants (physical), but human-caused (biological)
Disturbance regime
A community’s disturbance regime is the historical pattern of different disturbances to which organisms in the community are adapted
The disturbance regime of a Southern California forest would include:
Frequent drought and bark beetle infestation, and less frequent fire
Novel disturbance
A new kind of disturbance to which organisms in a community are not adapted
OUTSIDE the disturbance regime
Example of novel disturbance
Pollution
Succession
Involved a directional change in the species composition of a community over time following a disturbance
Primary succession
Occurs on substrate without soil, such as rock or lava
Severe disturbances such as a volcanic eruption or glacial retreat initiate primary succession
Secondary succession
Occurs after a disturbance that has left the soil intact
Fires, floods, and abandoned farmlands initiate secondary succession
After a severe disturbance, only a few certain _______ are able to colonize the disturbed site and initiate primary succession
Pioneer species
Pioneer species are ____________ organisms
r-selected
Pioneer species change:
The composition of the substrate, making it suitable for others to follow
___________ are the most common pioneer species
Lichens and mosses
Lichens and mosses convert the rock into soil that will support _____________-
Vascular plants with roots
Vascular plants are more ________ than lichens and mosses
K-selected
Once these new species begin to arrive, the original colonizers (the pioneer species) are ______________-
Less able to compete and are gradually eliminated
Over time, the vegetation develops in a sequence of series/stages called
Seres
First sere
The seral community
The early colonizing community of pioneer species following the disturbance
Final sere
Climax community
The stable, self-perpetuating community that consists of (in a forest community) tree species such as pine or oak
Between the seral and climax communities, there is frequently a __________ followed by a _________ followed by a sere with _____________-
Grass sere, shrub sere, sere with different tree species
It is not just the __________- that changes during succession, but the _________________________ as well
Plant composition, composition of animals and microorganisms
___________, in the early 1900s, described communities as ___________
Frederick Clements, “superorganisms”
“Superorganisms”
All of the species in a community are equivalent to all of the interacting organs within an individual organism’s body
Succession represents a community developing “from infancy to maturity”
____________ believed communities to be much more random
Henry Gleason
How often is a climax community (“maturity”) reached?
If there is another disturbance, the community must start over
