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Section I: General Principles
of Ecology
ECOLOGY – how organisms interact with one
another and with their environment
ENVIRONMENT – living and non-living
components
• ABIOTIC – non-living component or
physical factors as soil, rainfall, sunlight,
temperatures
• BIOTIC – living component are other
organisms.
Environment of an Organism
ABIOTIC components BIOTIC components
Heat
Light
Water
Substrate
physical
chemical
Atmosphere
Four elements of ancient Greek
philosophy:
Earth, air, fire, water
Conspecifics
Food (prey)
Predators
Symbionts
parasites
commensals
mutualists
Competitors
Modifiers of the Abiotic
Environment
ECOLOGICAL ORGANIZATION
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INDIVIDUAL – individual organisms
POPULATION – organisms of same
species in same area (biotic factors)
COMMUNITY – several populations in
same area (biotic factors)
ECOSYSTEM – community plus abiotic
factors
BIOSPHERE – all ecosystems on earth
ECOLOGY OF INDIVIDUALS
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Homeostasis – delicate balance of a stable
state
Components
 Physiological Ecology
 Temperature and Water Balance
 Light and Biological Cycles
 Physiological Ecology and
Conservation
INTERACTIONS AMONG
SPECIES
Interactions
 Interspecific competition
 Predation
 Exploitation
 Symbiosis
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Niches and Habitats
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The place where an animal lives is
called its habitat.
An animal lives where it can find food,
water, shelter and a mate. Combined,
these characteristics are called the
organism’s “niche”
The Niche is the organisms way of
life within an ecosystem.
Niche
The niche of a species consists of:
 Its role in the ecosystem (herbivore,
carnivore, producer etc)
 Its tolerance limits (e.g. soil pH,
humidity)
 Its requirements for shelter, nesting
sites etc etc, all varying through time
The niche as a two-dimensional
shape
Species A
Niche represented
by a 2-dimensional
area
Separate niches
Species A
Species B
No overlap of
niches.
So coexistence is
possible
Overlapping niches
Species B
Species C
Interspecific
competition
occurs where the
niches overlap
Specialisation avoids
competition
Species C
Species B
Evolution by
natural selection
towards
separate niches
Species B’
Species C’
Specialisation into two separate niches
This niche is not big enough for
the both of us!
Species A
Species D
Very heavy competition leads to
competitive exclusion
One species must go
Total exclusion
Species A has a
bigger niche it is
more generalist
Species E has a smaller
niche it is more specialist
Specialists, however, do
tend to avoid competition
Here it is total swamped
by Species A
Example: Squirrels in
Britain
The Red Squirrel (Sciurus
vulgaris) is native to Britain
Its population has declined
due to:
 Competitive exclusion
 Disease
 Disappearance of hazel
coppices and mature
conifer forests in lowland
Britain
The Alien
The Grey Squirrel
(Sciurus carolinensis)
is an alien species
Introduced to Britain in
about 30 sites between
1876 and 1929
It has easily adapted to
parks and gardens
replacing the red squirrel
Today’s distribution
Red squirrel
Grey squirrel
Carnivores
Some animals, like the kingfisher, eat
only other animals. These animals are
called “carnivores”.
Herbivores
Some animals do not eat other animals.
They survive on plants and are known
as “herbivores”.
Omnivores
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Some animals, like us, eat both plants
and animals.
These animals are called “omnivores”.
Consumers
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“Consume” means “eat”.
Animals are consumers because they
“eat” (consume) food provided by
plants or other animals.
Producers
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Plants are living organisms. They need
nourishment to survive.
But…
Plants do not eat other plants or
animals.
Plants are called producers, because
they make their own food inside
themselves.
Predator
A predator eats other animals.
Cats eat fish.
So do bears!
Prey
Any animal which is hunted and killed by
another animal for food is prey.
Predator
Prey
Types of Species Interactions
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Neutral – two species do not interact
Mutualism – both benefit
Commensalism – one benefits, other
neutral
Parasitism – one benefits, one harmed
but not killed
Predation – one benefits, other killed
Predator - Prey Relationship
Biogeochemical Cycles
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Hydrologic Cycle
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Phosphorus Cycle
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Nitrogen Cycle
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Carbon Cycle
Hydrologic (Water) Cycle
Phosphorus Cycle
Nitrogen Cycle
Carbon Cycle
Food Chain
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rose plant  aphids  beetle  chameleon  hawk
Producer
1st order Consumer or Herbivore
2nd order Consumer or 1st order Carnivore
3rd order Consumer or 2nd order Carnivore
4th order Consumer or 3rd order Carnivore
Decomposers – consume dead and decaying
matter
Food Web
ECOLOGY OF ECOSYSTEMS
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Energy Flow
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Energy Flow Pyramids
Bio-mass Pyramids
Community Succession and
Stability
Nutrient Recycling – nutrient
cycles
Energy vs Nutrient
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Nutrients –
cyclic
(Biogeochemical
Cycles)
Energy flow –
one way
Ecologic Pyramids
Ecological pyramid - a graph representing
trophic level numbers within an ecosystem.
The primary producer level is at the base of
the pyramid with the consumer levels above.
 Numbers pyramid - compares the number of
individuals in each trophic level.
 Biomass pyramid - compares the total dry
weight of the organisms in each trophic level.
 Energy pyramid - compares the total amount
of energy available in each trophic level. This
energy is usually measured in kilocalories.
Numbers Pyramid
Biomass & Energy Flow
Pyramids
Limiting Factor
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Any factor which limits a population’s
growth
Growth Curves
Human Population
An Introduction to Biomes
Aquatic and terrestrial biomes
(Biome = major ecosystem type)
Climate
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Four abiotic factors determine climate
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Macroclimate
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Sunlight
Temperature
Wind and Ocean currents
Precipitation
Global, regional, local climate
Microclimate
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Details of environmental conditions in small
spaces
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Forest floor
Under rock or log
Climate
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Temperature
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Affected by sunlight
But much more so by: Ocean currents
Climate
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Precipitation
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Warm moist air carried by winds
Condensation
Biomes
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Distribution of major habitat types
strongly influenced by climate
Aquatic biomes cover about 75% of the earth’s surface
- Wetlands
- Lakes
- Rivers, streams
- Intertidal zones
- Oceanic pelagic biome
- Coral reefs
- Benthos
Wetlands: includes marshes, bogs, swamps, seasonal ponds.
Among richest biomes with respect to biodiversity and
productivity. Very few now exist as they are thought of often
as wastelands.
Marine environment with zonation.
Coral Reefs occur in neritic
zones of warm, tropical
water, dominated by
cnidarians (corals); very
productive, protect land
from storms; most are now
dying from rise in global
temperatures
Deep-sea vent: Occurs in benthic zone; diverse, unusual
organisms; energy comes not from light but from
chemicals released from the magma.
Terrestrial biomes
- Tropical forest
- Savanna
- Desert
- Chaparral
- Temperate grassland
- Temperate deciduous forest
- Coniferous forest
- Tundra
Tropical Forest: Vertical stratification with trees in
canopy blocking light to bottom strata. Many trees
covered by epiphytes (plants that grow on other plants).
Example of Tropical, Dry
Forest
Savannah: exotic grassland with larger
animal species more common than a
temperate grassland (more energy coming in
= more energy going up the food chain)
Desert: Sparse rainfall (< 30 cm per year), plants and
animals adapted for water storage and conservation. Can
be either very, very hot, or very cold (e.g. Antarctica)
Chaparral: Dense, spiny, evergreen shrubs, mild rainy
winters; long, hot, dry summers. Periodic fires, some
plants require fire for seeds to germinate.
Temperate Grassland: Marked by seasonal drought and
fires, and grazing by large animals. Rich habitat for
agriculture, very little prairie exists in US today.
Temperate Deciduous Forest: Mid-latitudes with moderate
amounts of moisture, distinct vertical strata: trees,
understory shrubs, herbaceous sub-stratum. Loss of
leaves in cold, many animals hibernate or migrate then.
Original forests lost from North America by logging and
clearing.
Coniferous forest: Largest terrestial biome on earth, old
growth forests rapidly disappearing, usually receives lots
of moisture as rain or snow.
Tundra: Permafrost (Permanent frozen ground), bitter
cold, high winds and thus no trees. Has 20% of land
surface on earth.