BIO 1O1 Chapter 15
“Communities” Overview
1. What is a community?
2. Factors that shape a Community
3. Interactions within the Community
4. Creative Defense Mechanisms.
5. Development of New Communities
What is a Community?
1. All of the species—plants, animals, protists, bacteria, fungi . . . – that share the same Habitat.
2. Habitat: the physical environment of a community—forest, lake—where species coexist.
3. Niche: The position or role into which a species fits within a habitat—the part of the habitat
occupied, the resources utilized and the services performed for community.
Community + Habitat = Ecosystem
1. The living organisms work together as a food chain/web to convert natural resources to
usable nutrients.
2. These nutrients get passed up the chain.
3. This defines an Ecosystem.
Six Factors Affecting Communities
1. Climate & Topography of Habitat.
2. Available Natural Resources.
3. Physical Disturbances within Habitat.
4. Variations in Population sizes.
5. Adaptive traits of Species.
6. Species Interactions.
Species Interactions: Six Types
1. Neutral interactions.
2. Keystone species.
3. Interspecies competition.
4. Predation.
5. Symbiotic Interactions.
a. Commensalism.
b. Mutualism.
c. Parasitism.
Keystone Species
1. Dominant species that dictates community structure; interacts with many different species
in necessary ways.
2. Examples:
a. Saguaro cactus.
b. Lions.
c. Wolves.
Interspecies Competition
1. Two or more species trying to use the same limited resource.
2. Competitive Exclusion: One species dominates and others are eventually eliminated from
the community.
3. Resource Partitioning: Species utilize different subsets of the resource.
Predation
1. Predation: Animal eating another animal.
2. Predator Carrying Capacity: Dynamic, depends on available prey populations.
Symbiotic Interactions
1. Mutualism (+/+): Interactions between species that are beneficial to both.
2. Examples:
a. Bee & Flowering Plants.
b. Lichens.
c. Ants & Acacia tree.
3. Commensalism (+/0): Interactions between species that are beneficial to only one species and
the other is unaffected.
4. Examples:
a. Birds nesting in trees.
b. Dung beetle and elephants.
5. Parasitism (+/-): A species that lives in or on another and feeds on the tissues or nutrients of the
host which may or may not result in the death of the host.
6. Examples:
a. Leeches, ticks & flees.
b. Social Parasites: Cow bird.
c. Bacteria & viruses.
Question???
1. How do you distinguish a predator from a parasite???
Creative Defenses
1. Predator/Prey & Herbivore/Plant demonstrate many interesting defense/response mechanisms.
a. Camouflage.
b. Warning Coloration.
c. Mimicry.
d. Chemical defenses.
e. Projectile defenses.
Creative Responses
1. Predator Responses:
a. Camouflage.
b. Stealth.
c. Immunity to toxins.
d. Technique Adjustments.
Ecological Succession-General
How do communities become established in uninhabited areas?
1. Cleared areas.
a. Glacier.
b. Volcanic Island.
c. Human beings.
Primary Succession
1. Step 1—Pioneer Species: Opportunistic colonizers.
a. Hardy organisms, fast lifecycle, wide dispersal mechanisms.
b. Lichens, mosses & other simple plants.
c. Help improve environment.
1. Break down rocky areas.
2. Add nutrients to soil.
3. Become food source for future species.
Primary Succession
1. Step 2—More species—insects, plants, fungi etc.
a. Feed on Pioneers and each other.
b. Beginning stages of food web.
c. More species, larger species continue to be added.
Primary Succession
1. Final step—Climax Community: A stable group of species that is self-sustaining.
a. Depends on the environment.
b. Examples:
1. Washington National Forest.
2. Amazon Rain Forest.
3. Sonoran Desert.
2. Secondary Succession: Clearing within community (i.e. fire)
Ecological Succession-Example
1. Alaskan Glacier Bay Succession:
a. Glacier retreat leaves barren rock landscape.
b. Pioneer (lichens, horsetails, & Dryas spread over area.
c. 20 years later, alder cottonwood and willow seedlings have joined.
d. 50 years later, alder trees have formed thickets with cottonwood, hemlock and spruce.
e. 80 years later, cottonwood and spruce trees begin to crowd out the smaller alder trees.
f. 100+ years later, stable dense forests of sitka spruce and western hemlock.
