Transcript 157-Trophic Relationships

BIOLOGY 157:
LIFE SCIENCE: AN
ENVIRONMENTAL APPROACH
(Trophic Relationships)
ENERGY
• Energy is the ability to do work.
• It has many forms (kinetic, potential;
electrical, chemical, heat, light, etc.).
• Every organism must have energy in order to
function.
• To understand about energy it is useful to
look at a paraphrasing of the TWO ‘LAWS’
OF THERMODYNAMICS.
THE LAWS OF
THERMODYNAMICS
• (1) Energy can be changed from one form to another
but is never created or destroyed (assumes matter
and energy are interchangeable).
• (2) No energy transformation is 100% efficient.
Some energy always goes off as unusable or
unavailable forms (e.g. - when burning something to
get heat, we get some light; or when metabolizing
foods to get chemical energy for the running of the
cells we also get some heat).
EARTH’S ENERGY SOURCES
• 1) the energy stored in its core
• 2) the sun
The equation for photosynthesis (one of the
most important chemical reactions on earth):
6CO2 + 12H2O    C6H12O6 + 6H2O + 6O2
chlorophyll
sunlight
glucose
HOW ORGANISMS GET ENERGY
 AUTOTROPHS or PRODUCERS ( = self-nourishing)
Photoautotrophs
Chemoautotrophs
 HETEROTROPHS (= other nourishing)
CONSUMERS
• Herbivores
• Carnivores
• Omnivores
DECOMPOSERS (= REDUCERS or SAPROTROPHS)
“FOOD” DEFINED
• A “FOOD” is an energy rich organic compound
used to fuel the metabolism of an organism.
• Autotrophs make foods using simple inorganic
compounds and an energy source.
• Examples of inorganic compounds: water, carbon
dioxide, iron, nitrates, phosphates
• Examples of foods: proteins, fats, alcohols,
carbohydrates such as sugars and starch
TROPHIC RELATIONSHIPS (I)
• TROPHIC (from the Greek meaning to
nourish):
essentially “Trophic Relationships” refers to
energy relationships between organisms (how
energy is transferred from one organism to
another).
• TROPHIC LEVEL:
the organism’s place in the energy flow pattern
in relation to the ultimate energy source. (It
usually is expressed as a whole number.)
TROPHIC RELATIONSHIPS (II)
• The flow of energy from organism to organism
(usually by eating and being eaten) forms a linear
energy flow system known as a FOOD CHAIN.
• In nature food chains are always interconnected to
form FOOD WEBS.
• The number of trophic levels in an energy flow
system is limited by the ENERGY BUDGET which
itself is the result of the Laws of Thermodynamics.
HYPOTHETICAL FOOD CHAIN
Trophic Level
1
Producer
2
Herbivore
(= primary consumer)
3
4
5
6
Carnivore
(= secondary consumer)
(= primary carnivore)
Green Plants

Rabbits

Snake

Carnivore
(= tertiary consumer)
(= secondary carnivore)
Hawk
Carnivore
(= quartenary consumer)
(= tertiary carnivore)
Wolf
Carnivore
(= pentenary consumer)
(= quartenary carnivore)
Human


EXAMPLES OF FOOD CHAINS
EXAMPLE OF A FOOD WEB (I)
EXAMPLE OF A FOOD WEB (II)
WHAT LIMITS THE NUMBER
OF TROPHIC LEVELS ?
THE ENERGY BUDGET !
ENERGY TRANSFER IN A FOOD
CHAIN (see your last page)
TROPHIC COMPLEXITY
• trophic complexity = community complexity
• simple systems are usually less stable
• In other words, COMPLEXITY of energy
flow pattern (= food web complexity),
generally makes for a more stable system
• WHY?
ADDITIONAL things from
chapter 2 for YOU to investigate
• What is Entropy?
• What is the connection between food and
potential energy?
• Which pyramid type (biomass, energy or
numbers) always gives the best ‘picture’ of
the trophic structure of a system? Why?
• What trophic level can’t a scavenger occupy?
• Most extremophiles are what type of
organism?