Chapter 2 Principles of
Ecology
2.1 Organisms and Their
Relationships
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What is ecology?
 Oikos
Greek for “homestead”
 Ology means “study of”
 Scientific study of interactions among
organisms and their environment
 Reveals relationships among living
things (biotic) and nonliving (abiotic)
parts of the world
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What is ecology?
Uses both quantitative and descriptive
research
 Combines information and techniques
from many scientific fields:

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Mathematics
Chemistry
Physics
Geology
And many others
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Aspects of Ecological Study

Biosphere: portion of
the Earth that
supports life
– High in atmosphere to
bottom of ocean
– Extends several
kilometers above the
Earth’s surface and
several kilometers
below the surface of the
ocean
– Comparable to peel of
an apple
– Very diverse climate
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Living thing affected by:

Abiotic factors
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Air currents
Temperature
Moisture
Light
Soil composition
Terrain
And many others
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Living thing affected by:

Biotic factors
– Same species for
protection,
competition, food,
and reproduction
– Other species for
all but reproduction
Tree decay
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Levels of Organization in Ecology
Need to study
more than just an
individual to get
the whole story
 Need to study
relationships or
interactions among
organisms of the
same and different
species
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Levels of Organization in Ecology
 Biosphere
–Ecosystem
Community
–Population
Organism
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Populations

A group of
organisms of one
species that
interbreed and live
together in the
same place at the
same time
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Populations
 Compete
with each other for food,
water, space, light and other
resources in short supply
 How organisms share resources
determines how far apart they live
and how large a population gets
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Populations

Some species
reduce competition
by larvae and adult
stages living in
different
environments and
using different
resources as food
(frogs and many
insects)
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Individuals Interact within
Communities
 Community:
collection of interacting
populations (all the populations at
one place and time)
 Change in one population will cause
change in another population
– Small changes
– Large changes
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Interactions among living things
and abiotic factors
 Ecosystem:
interaction of populations
in a community and nonliving
(physical) surroundings
 Three kinds of ecosystems
– Terrestrial (land)
– Fresh water
– Marine: 75% of the earth
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Organisms in Ecosystems

Habitat: place where an organism lives its
life (home)
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Organisms in Ecosystems
 Niche:
the role and position a species
plays in its environment
– All the interactions with abiotic and
biotic factors
– Everything the species does
– How it uses resources
– Its job
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Organisms in Ecosystems
 Even
though two species occupy the
same habitat, they do not occupy the
same niche because resources (food,
shelter) are used in different ways
 It is an advantage for a species to
occupy a different niche, unique
strategies are important to reduce
competition
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Organisms in Ecosystems
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Symbiosis
 Permanent,
close association
between two or more organisms of
different species
 Three types of symbiosis
– Commensalism
– Mutualism
– Parasitism
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Commensalism
 One
species benefits, other species
not harmed or benefited
 Few examples because further study
usually reveals mutualism or
parasitism
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Commensalism
Cattle egrets follow
cattle to feed on
the insects stirred
up by the grazing
cattle.
 Egret benefits as it
gets more food
 Cattle is neither
helped nor harmed

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Commensalism
Orchids growing on
trees have a home
and moisture
 Orchids benefit
while the tree is
not affected

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Mutualism
 Both
species benefit
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Mutualism
A remarkable 3-way
mutualism appears to
have evolved between an
ant, a butterfly
caterpillar, and an acacia
in the American
southwest. The
caterpillars have nectar
organs which the ants
drink from, and the
acacia tolerates the
feeding caterpillars. The
ants appear to provide
some protection for both
plant and caterpillar.
Research of Diane Wagner, American Museum of
Natural History Southwestern Research Station
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Mutualism

Ants “tending” soybean aphids
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Parasitism

One organism
benefits the other
is harmed but
usually not killed
Ticks
Ring Worm
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Chapter 2 Principles of
Ecology
2.2 Flow of Energy in an
Ecosystem
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How Organisms Obtain Energy
 Ultimate
source of energy is the sun
 Producers use the sun’s energy to
make food
 Consumers eat producers of other
consumers
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How Organisms Obtain Energy
 Autotrophs:
energy
“auto” = self; “troph”=
– Most are photoautotrophs: organisms
that use the sun’s energy to make food
in the process of photosynthesis; all
have chlorophyll
– Some are chemoautotrophs; make food
by using energy stored in chemical
bonds (some Archaebacteria)
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Photoautotrophs
Cyanobacteria
Plants
Algae
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How Organisms Obtain Energy
 Heterotrophs:
“hetero”= other;
“troph”= energy
– Can’t make food so must feed on other
organisms
– Herbivores: only eat autotrophs
– Carnivores: only eat other heterotrophs
– Omnivore: eat both autotrophs and
heterotrophs
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How Organisms Obtain Energy
 Heterotrophs:
“hetero”= other;
“troph”= energy, cont.
– Scavengers: feed on dead (carrion and
refuse)
– Decomposers: breakdown and absorb
nutrients from dead organisms (fungi,
protozoans, many bacteria)
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Heterotrophs
Carnivore
Decomposer
Scavenger
Herbivore
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How Organisms Obtain Energy

Detritivores
– Eat fragments of
dead matter in an
ecosystem, and
return nutrients to
the soil, air, and
water where the
nutrients can be
reused by
organisms.
– Also considered
heterotrophs
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Matter and Energy Flow
Food Chains: simple model to show
energy flow in an ecosystem; one possible
route
 Food web: several interconnected food
chains

– shows that an organism occupies more than
one trophic level
– Expresses more possible feeding relationships
at each trophic level
– More realistic than a food chain
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Food Chain
 Arrows
indicate direction energy
flows
 Usually 3 to 5 trophic (energy) levels
 On average only 10% of energy is
transferred to next trophic level
– Most energy is lost as heat
– Also lost as urine, feces and other
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Food Chain
Top Carnivore
Carnivore
Omnivore
Herbivore
Producer
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Food Web
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Food Web
 Trophic
level is one step in a food
chain
 Organisms can occupy more than
one trophic level
 Important part of organism’s niche is
how it obtains energy
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Energy and Trophic Levels
Energy Pyramid
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Energy Pyramids

Pyramid of Numbers
– Count the number of
organisms at each
level
– Numbers decrease as
move up the pyramid
– Not always reveals
true relationship as
one tree (producer)
could support 50,000
insects (herbivore)
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Energy Pyramids

Pyramid of Biomass
– Use dry weight of
organisms at each
level
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Energy Pyramids
Pyramid of Numbers
Pyramid of Biomass
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Chapter 2 Principles of
Ecology
2.3 Cycling of Matter
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Cycles in Nature
Energy flows, nutrients cycle
 Atoms of carbon, nitrogen and other
elements in your body today made up the
bodies of other organisms
 Matter including nutrients are constantly
recycled
 The cycling of nutrients in the biosphere
involves both matter in living organisms
and physical processes found in the
environment such as weathering.

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Nitrogen Cycle
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Phosphorus Cycle
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