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Ch 27
Ch 28
Unit 14—Ecology
Populations, Communities,
& Ecosystems
• Population
– A group of organisms of the
same species living in an area
at the same time
• Community
– All the different populations
living & interacting in an area
• Ecosystem
– Interaction of community with
the non-living environment
Visualizing population structures &
predicting future changes
•population pyramids (a.k.a. age structure diagrams)
–basic shape can help us predict what’s going to happen
to the population in the future
How Population Pyramids Are Made Video
Animated Population Pyramid
Rapid Growth
Guatemala
Nigeria
Saudi Arabia
Ages 0-14
Slow Growth
U. S.
Australia
Canada
Ages 15-44
Zero Growth Negative Growth
Spain
Germany
Austria
Bulgaria
Greece
Sweden
Ages 45+
Population
growth rate by
country
Population Pyramids
(Age Structure Diagrams)
Developing Countries
Developed Countries
– Wide base
– High #s of reproductive/
pre-reproductive age
– High birth rates
– slightly wider base, width ~
same, or inverted pyramid
– fewer people of reproductive
age or younger
• the higher educational level of – low birth rates
women, the lower the birth rate
– Population will grow fast
• slow growth, zero growth,
negative growth (pop. shrinks)
•Population clock
•http://www.census.gov/main/www/popclock.html
Population Growth
• Limiting factors: circumstances or resources
that limit growth, reproduction, or distribution of
organisms (provide environmental resistance)
– prevents population from growing indefinitely
• “carrying capacity”
– can be:
• abiotic or biotic
Examples of Abiotic Factors
Organisms have optimal ranges of
abiotic factors in which they thrive
• Is temperature a limiting factor for these
fish species?
Optimal
temperature
Biotic Factors
• Living factors in an ecosystem
– Usually described in terms of interactions
• especially who eats whom or trophic levels
Energy Flow: Food Chains
Fourth trophic level
Tertiary consumers
Carnivores/omnivores
Third trophic level
Secondary consumers
carnivores
Second trophic level
Primary consumers
herbivores
Decomposers
Heterotrophs
Break down
dead material
& recycle
nutrients
First trophic level
Primary producers
autotrophs
Autotrophs vs. Heterotrophs
• Another name for autotrophs?
– How do they get nutrients?
 Another name for
heterotrophs?
 How do they get nutrients?
 What categories can we break
heterotrophs into?
 herbivores
 carnivores
 scavengers
 omnivores
 decomposers
 Part of EVERY ecosystem
Energy Flow: Food Chains
• Does energy only flow through
Where do
individual organisms?
almost all
–No… through community
• food chains & webs
***Arrow always points toward organism
taking in the energy & away from the
organism “giving up” the energy.***
communities get
their energy?
Energy Flow: Energy Pyramids
• 10% Rule of Ecological Efficiency
– ~10% passed to next level
• Nutrients are recycled
– Ex. carbon cycle
• Energy is transferred & degraded.
– ~90% is lost as heat
Carbon Cycle
Other relationships - Symbiosis
• When two
species live
closely
together in a
relationship
that lasts
over time
symbiosis
occurs.
Commensalism
• One partner benefits from the relationship
& the other neither benefits, nor is harmed
Mutualism
• Both partners benefits from the relationship.
Parasitism
• One partner benefits, the other is harmed.
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