Chapter 7 Community Interactions. 7-1 COMMUNITY STRUCTURE AND SPECIES DIVERSITY.
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Transcript of Chapter 7 Community Interactions. 7-1 COMMUNITY STRUCTURE AND SPECIES DIVERSITY.
Chapter 7Chapter 7
Community Community InteractionsInteractions
7-1 COMMUNITY STRUCTURE AND SPECIES
DIVERSITY
Community
• Community: populations of all species living and interacting in an area at a particular time
Four Characteristics of Community Structure
• Physical Appearance: size and distribution of its population and species
• Species Diversity/Richness: number of different species
• Species Abundance: number of individuals of each species
• Niche Structure: number of niches, how they compare, and how they interact
Differing Physical Appearances
• Patch Effects: most large communities usually consist of a mosaic of vegetation “patches”
• Edge Effects: differences in physical appearance at boundaries between ecosystems
Species Diversity• Species Rich Environments
– Tropical Rain Forests– Coral Reefs– Deep Sea– Large Tropical Lakes– Tend to have high species diversity but low
species abundance
• Factors that Affect Diversity– Latitude (terrestrial) – distance from equator– Depth (aquatic)– Pollution (aquatic)
Species Abundance
• Determined by:– Rate at which new species immigrate – Rate at which species become extinct
Niche: role an organism plays in an ecosystem
•niche is like an "occupation“ – a species’ interactions with habitat and other organisms (their role in food web)
Ecological Niche vs. HabitatHabitat: actual location where an organism lives
•habitat is like an "address"
7-2 GENERAL TYPES OF SPECIES
GENERAL TYPES OF SPECIESGENERAL TYPES OF SPECIES
•Generalist Species
•Specialist Species
•Native Species
•Nonnative Species
•Indicator Species
•Keystone Species
Generalist vs. SpecialistGeneralist vs. Specialist
© Brooks/Cole Publishing Company / ITP
•Generalist Species have broad niches, can live many places, use a variety of resources
e.g., dandelions, cockroaches, coyotes, humans
•Specialist Species have narrow niches, live only in specific places
e.g., spotted owls, giant pandas
Native vs. Nonnative SpeciesNative vs. Nonnative Species
• Native Species: species that normally live & thrive in a particular ecosystem
• Nonnative Species:
•also called exotic, invasive, or alien species
•originate in other ecosystem
•deliberate or accidental introduction by humans causes problems
•may thrive and crowd out native species
The Case of the Killer Bees
• 1957 Brazil imported wild African bees to help increase honey production
• Displaced domestic honeybees• Actually reduced honey
production• Moved north in Central America• Established populations in
Texas, Arizona, New Mexico, Puerto Rico, and California
Snakehead Fish
CANE TOADS!
Indicator SpeciesIndicator Species
• Indicator Species: species that serve as early warnings that a community or ecosystem is being damaged
•Birds are good indicator species
•Found everywhere
•Respond to environmental change quickly
•northern spotted owls are indicators of healthy old–growth forest
•Fish are good indicator species in aquatic ecosystems (i.e. trout)
Keystone SpeciesKeystone Species
Keystone Species: species that play a critical role in an ecosystem
•Ex: sea otters are keystone species because they prevent sea urchins from depleting kelp beds
•Ex: flying foxes are keystone species because they pollinate tropical trees and disperse seeds, such as durian fruit trees
“The loss of a keystone species is like a drill accidentally striking a power line. It
causes lights to go out all over.”– E.O. Wilson
7-3 SPECIES INTERACTIONS:
COMPETITION AND PREDATION
Species InteractionsSpecies Interactions
• The effects of one species on another may be negative, positive, or neutral
• Five kinds of interactions:
•Interspecific competition
•Predation
•Parasitism
•Mutualism
•Commensalism
Intra- vs. Inter- specific Intra- vs. Inter- specific competitioncompetition
• Intraspecific Competition – members of the SAME species compete for resources
•Interspecific Competition – members from 2 or more DIFFERENT species compete for resources
•When two or more species use the same limited resource (food, space, etc.) they may adversely affect each other
•niche overlap
•Ex: fire ants & native ants in North America
High
Low
Rela
tive p
op
ula
tion
den
sit
y
0 2 4 6 8 10 12 14 16 18
Days
Each species grown alone
Parameciumaurelia
Parameciumcaudatum
No CompetitionNo Competition
High
Low
Rela
tive p
op
ula
tion
den
sit
y
0 2 4 6 8 10 12 14 16 18
Days
Both species grown together
Parameciumaurelia
Parameciumcaudatum
Interspecific Competition
Resource PartitioningResource Partitioning
Species with similar resource requirements can coexist because they use limited resources:
•at different times
•in different ways
•in different places
© Brooks/Cole Publishing Company / ITP
Resource Partitioning
Where are the 2 species competing?
Why is there no competition here?
Resource PartitioningResource Partitioning
© Brooks/Cole Publishing Company / ITP
Resource Partitioning ExampleResource Partitioning ExampleFive species of insect–eating warblers coexist in spruce forests of Maine:
•feed in different portions of trees
•consume somewhat different insects
© Brooks/Cole Publishing Company / ITP
PredationPredation•Members of one species (predator) feed on another species (prey);
•+ / –
•Ex: lion feeding on zebra
© Brooks/Cole Publishing Company / ITP
Predator-Prey Relationship
• What do predators do to increase their chances of getting a meal?
• What do prey do to avoid being eaten?
Predator-Prey Relationship
• Predators get better at catching prey
• Prey get better at avoiding capture
• Similar to an “arms race”– Ex: During the Cold War,
the US and the USSR tried to intimidate the other with bigger and better weapons
Predators
• Pursuit– Faster (cheetahs)– Better eyesight (eagles)– Hunting in packs (wolves)
• Ambush – Camouflage (praying mantis)– Mimicry (alligator snapping turtles)
Prey
• Camouflage • Ex: walking stick
• Chemical warfare • Ex: skunk
• Warning colors • Ex: poison dart frog
• Mimicry • Ex: king snake
• Behavior• Ex: blowfish
7-4 SPECIES INTERACTIONS:
PARASITISM, MUTUALISM, AND COMMENSALISM
ParasitismParasitism
One organism (parasite) lives on part of another organism (host)
•+ / –
•Ex: flea living on a dog
© Brooks/Cole Publishing Company / ITP
MutualismMutualism
Two species interact in a way that benefits both
•+ / +
•Ex: lichens (algae & fungi)
•Ex: clownfish & anemones
•Ex: ants & acacias
© Brooks/Cole Publishing Company / ITP
CommensalismCommensalism
One organism benefits from another, but neither helps nor harms the other organism
•+ / 0
•Ex: epiphyte growing on a tree
© Brooks/Cole Publishing Company / ITP
Species InteractionsSpecies Interactions
• The effects of one species on another may be negative, positive, or neutral
• five kinds of interactions:POPULATION A POPULATION B
COMPETITION - -PREDATION + -PARASITISM + -
COMMENSALISM + 0MUTUALISM + +
7-5 ECOLOGICAL SUCCESSION: COMMUNITIES
IN TRANSITION
Ecological SuccessionEcological Succession
Succession: gradual & fairly predictable change in species composition over time
© Brooks/Cole Publishing Company / ITP
Primary SuccessionPrimary Succession
© Brooks/Cole Publishing Company / ITP
Primary Succession• Type of succession that
occurs where there was no ecosystem before
• Occurs on rocks, cliffs, and sand dunes
• Pioneer species: the first organism to colonize any newly available area and begin the process of ecological succession
Primary SuccessionPrimary Succession
Primary Succession: gradual establishment of biotic communities in an area where no life existed before
•Ex: succession on newly formed islands & after the retreat of a glacier
•Early Communities: lichens & mosses colonize bare rock
•Mid Communities: small herbs & shrubs colonize
•Late Communities: tree species colonize
Lichens
Mosses
Parking Lot
Secondary SuccessionSecondary Succession
© Brooks/Cole Publishing Company / ITP
Secondary SuccessionSecondary SuccessionSecondary Succession: gradual reestablishment of biotic communities in an area where a biotic community was previously present
•Ex: "old field succession"
Secondary Succession: Mount St. Helens
• Erupted in 1980
• 44,460 acres were burned and flattened
• After the eruption, plants began to colonize the debris
DisturbanceDisturbance
Disturbance: a distinct event that disrupts an ecosystem or community
•disturbance initiates secondary succession
•Natural disturbances: fires, hurricanes, tornadoes, droughts, & floods
•Human-caused disturbances: deforestation, overgrazing, plowing
Intermediate Disturbance Hypothesis: moderate disturbances in communities promote greater species diversity than
small or major disturbances
Climax Community
• Climax community: the final and stable community in an ecosystem
• Will continue to change in small ways, but will remain primarily the same over time (unless disturbed)
The Circle of Life in Secondary Succession
7-6 ECOLOGICAL STABILITY AND SUSTAINABILITY
Stability - complex networks of positive and negative feedbacks loops
Ecosystem Stability
• Inertia/Persistence: the ability of an ecosystem to resist being disturbed
• Constancy: the ability of a living sysmte such as a population to keep its numbers within the limits imposed by available resources
• Resilience: the ability of an ecosystem to “bounce back” after it has been disturbed
Precautionary Principle• We should try to prevent potential
harm to an ecosystem even though we don’t understand all of the cause-and-effects
• “better safe than sorry”