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Chapter 56
Community Ecology
Why knowing about ecosystems is important?
Scientific knowledge as ‘models’
Basic ecological concepts
Biotic interactions in an ecosystem
Question
Chapter 56 -- Community Ecology
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Why understanding ecosystems is important
DDT (dichloro-diphenyl-trichloroethane)
1874: discovery
1934: Paul Müller, Swiss chemist
“polychlorinated hydrocarbon”
DDT is a potent insecticide ...
Low toxicity for humans (mammals)
Many Agricultural uses
e.g., corn earworm, cotton bollworm
tobacco budworms
Control of diseases
malaria, typhus
WWII
Dutch elm disease
Cotton bollworm
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By the 1950s other people were seeing other,
unintended effects . . .
Fish
-- trout, sunfish, suckers, etc
-- higher toxicity than to mammals
Birds of prey
-- eagles, osprey, hawks, etc
-- Reproductive effects
Songbirds
What was impact of Rachel Carson’s “Silent Spring”?
-- 1962
Tranforms U.S. environmental consciousness
pairs (in 1000s)
Nat. Envr. Prot. Act (NEPA)
CAA & CWA
7
DDT banned in 1973
6
5
4
Number of bald eagle pairs
in lower 48 states
3
2
1
0
1960
Question
Chapter 56 -- Community Ecology
1970
1980
1990
2000
3
Why did we misjudge effects of DDT?
An incomplete understanding of ecosystems . . .
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•
•
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How do organisms interact with their surroundings?
How do organisms interact with each other?
How do nutrients (and pollutants) move & change in an ecosystem?
How do ecosystems change over time?
Our answers to these form a ‘model’ of ecosystem function
What is a scientific ‘model’?
How does it differ from traditional ‘fact-based’ knowledge?
1) Recognized to be incomplete
2) simplified version of reality
3) explain all current information
4) are modified over time
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A ‘food chain’ and ‘food web’ illustrate two models with different levels of detail
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Some Basic Concepts
What is an Ecosystem?
“A community of organisms and the physical
surroundings with which they interact.”
What are the two components of an ecosystem?
-- “Biotic” vs “abiotic”
What are some abiotic factors that define a habitat?
What are 3 levels at which biologists study the organisms of an ecosystem?
Species:
Population:
Community:
Question
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How big is an ecosystem?
Depends on model being studied . . .
microecosystems
organisms
forests
biomes
Why are ecosystems said to
be “open systems”?
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What is an
ecological niche?
“ The sum of all the resources
an organism requires”
What is a ‘fundamental’ niche?
… ‘realized’ niche?
How do species interact
within an ecosystem?
Competition
Predator-prey
Symbiosis
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Competition
What are two forms of competition?
Intraspecific competition
Interspecific competition
Interactions cascade through an ecosystem
Why did removing seed-eating
rodents from desert ecosystem
favor then diminish ant populations?
Question
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What happens when two
species compete for the same
resources?
What is the “Competitive Exclusion
Principle”?
Classic Paramecium experiment
How does “Resource Partitioning” prevent
competitive exclusion?
e.g. Caribbean anoles
Question
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Why does introduction of exotic
species often disrupt ecosystems?
Examples:
Zebra mussels
Japanese knotweed
Grey Squirrel
Emerald Ash Borer
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Predator-Prey relationships
Many animal defense mechanisms
Vigilance, e.g., Flocking ostriches
Concealment, e.g., Chuckwalla lizard
Warning Coloration, e.g., Skunk
Camouflage (cryptic coloration)
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Animal defense mechanisms, con’t
Mimicry
Batesian mimicry
Müllerian mimicry
How are mimicry and cryptic coloration different?
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Some other really neat defense mechanisms. . .
Read National Geographic article
on reserve in library
“The Art of Deception”
By Natalie Angier
http://mclib.marietta.edu/search~S0?/rbiol+101/rbiol+101
/1,1,1,B/l856~b1233151&FF=rbiol+101&1,1,,1,0/startrefe
rer//search~S0/rbiol+101/rbiol+101/1,1,1,B/frameset~1233
151&FF=rbiol+101&1,1,/endreferer/
Self-quiz is available
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Predators evolve strategies also
Predators and prey “co-evolve’
Angler fish
Snake
Common stargazer fish
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What are the types of symbiosis?
Mutualism
Commensalism
Parasitism
external
internal
These relationships are not always what they
seem…
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What type of symbiosis does each of
these relationships represent?
How is each organism benefited or harmed?
Rhino and tick bird
Mistletoe on pine
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Let’s test our knowledge…
Symbiosis
Question
Defense mechanisms
Question 1
Question 2
Types of Mimicry
Question
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Species Distribution (from chapter 55.2)
You are not responsible for:
-- logistic growth curve equation
-- r & k selected species
Geographic range
How are populations dispersed?
What factors determine how individuals are dispersed?
“Clumped”
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What causes population growth cycles?
(from chapter 55.2)
e.g., central European larch bud moth
-- periodic outbreaks every 8-10 years
Similar cycles occur here for tent caterpillars
Question
Zimmer, 1999. Science 284:86; Ranta, et al, 2002. Science 298:973
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Ecosystems change
geographically
Gradients of physical conditions
Create an “Ecotone”
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Read about human population
growth (Chapter 55.7)
Exponential trends
Population pyramids
Doubling times
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How do Ecosystems change over time?
Succession
primary vs secondary
pioneer species
climax community
Why does succession occur?
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Secondary Succession
Disturbances -- Fire in Yellowstone
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Old Field Succession
Question
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