Energy in Ecosystems

Four Criteria for Sustainability

Sustainable Ecosystems

Need:

Nutrient Cycling

Reliance on Solar

Energy

High Biodiversity

Population Control

This note set

aligns with this

concept.

The Ultimate Source of Energy • Almost all energy on Earth is derived from

the sun!

– Either organisms use the sun directly to

create energy (food) or organisms get the

energy indirectly (eating others that made the

energy)

• To show how energy moves around the

environment, scientists use food chains

and food webs

Food Chains • Food Chain -- Linked series showing a one-

way set of feeding relationships .

– Rule 1: Arrows always point to the predator.

– Rule 2: Producers ALWAYS start a chain.

– Terrestrial food chains are typically shorter than

aquatic food chains.

What’s wrong with this one? (screw you, Encyclopedia Brittanica!)

Hey Swedish Natural History

Museum! Really?

Food Webs • Show ALL the connections and potential

food chains of a set of organisms.

Make a Food Web • Create a food web from the following

wetland creatures:

Eagle Algae

Snail Fish

Make a Food Web • Create a food web from the following

wetland creatures:

Eagle Algae

Snail Fish

Trophic Levels In Food Chains/Webs

• Trophic Level –

An expression of an organism’s feeding status in a food chain/web

• Expressed as a number or with correct terminology – Example:

Trophic Level 2 OR Primary Consumer

Other Trophic Level Vocabulary

• Organisms can also be identified by the

type of food they consume:

– Herbivores (Plants)

– Carnivores (Meat)

– Omnivores (Plants/Meat)

– Scavengers (Carcasses)

– Detritivores (Debris)

– Decomposers (All Dead Material)

Rules of Energy Transfer

• The 1st Law of Thermodynamics (Law of

Conservation of Energy)

– When energy is converted from one form to another, no

energy is created or destroyed…it is simply converted!

– However, energy in the conversion may NOT be usable

for the task at hand (in the case of a food chain, the

energy may not be used in the body that consumed it)

Rules of Energy Transfer • The 2nd Law of Thermodynamics

– Explains that energy transfer between trophic

levels reduces the amount of usable energy

available to the higher trophic level • Metabolism of food releases some energy as heat (not

usable), so predator efficiency is NOT 100%

Energy is NOT

lost though!

1000 J of energy

enters plant

990 J + 10 J of

energy exits plant

= 1000 J

Rules of Energy Transfer

• The 2nd Law of Thermodynamics

– What is the average efficiency of eating? OR How

much of the energy that you ate actually stays in

the next trophic level?

• 10% Rule -- generally, 10% of the energy in a lower

trophic level is usable in the next level

The 10% rule applies to

consumers.

The efficiency of plants

taking sunlight and

converting it to food is

only 1%, on average!

What do you notice about this actual food pyramid?

What do you notice about this actual food pyramid?

The average of all 3 levels is 10%!!!

5%

energy

transfer

16%

energy

transfer

9%

energy

transfer

Vegetarianism • It is said that

vegetarianism is one of

the top three things

that someone could

personally do to be

more “green” in their

life that has the most

impact.

• WHY???? --- Think

about this in terms of

the ecological

efficiency rule just

mentioned! CREEPY!!!

• Meat-Eating Food Chain

Human Walleye Minnow Duckweed

100 kcal ______ kcal _______ kcal _______ kcal

• Vegetarian Food Chain

Human Duckweed

100 kcal ______ kcal

– Each time you go up a trophic level in a food

chain, most of the starting energy is lost in the

form of heat. The more levels up, the more

cycles of energy loss.

• Meat-Eating Food Chain

Human Walleye Minnow Duckweed

100 kcal 1,000 kcal 10,000 kcal 100,000 kcal

• Vegetarian Food Chain

Human Duckweed

100 kcal 1,000 kcal

– Each time you go up a trophic level in a food

chain, most of the starting energy is lost in the

form of heat. The more levels up, the more

cycles of energy loss.

What Can You Do? • Try and not eat meat

every dang minute of the

dang day!

– Try Meatless Mondays!

• When eating meat, eat

lower on the food chain!

– Example: Eat mussels

instead of tuna in this

chain! (or even sardines!)

Algae Mussels Sardine Tuna

How Does Energy Even Get

Into the Food Chain? • Generally, plants and algae are KEY to life on

Earth, as they start most food chains. (except for

deep ocean ecosystems)

• How do plants do it? PHOTOSYNTHESIS!!

6 CO2 + 6 H2O + light C6H12O6 + O2

What Happens With The Food?

• All life, even plants, take their food

(glucose) and can make energy out of it.

• This is called cellular respiration. Aerobic

respiration looks like this:

C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy

Hmmmm…is there a pattern to

these processes?...Hmmm

Some Ecosystems Make More Plant

Matter (Biomass) Than Others

• Two Ways to Measure Ecosystem Productivity

– GPP (Gross Primary Productivity) – measures how

fast producers turn solar/chemical energy into

biomass (organisms).

– NPP (Net Primary Productivity) – measures how

much leftover energy is made, after you subtract out

the energy needed for cellular respiration

– Think of these in business terms:

• GPP is your gross salary in a year ($60,000/year)

• NPP measures the leftover money you have after you pay

expenses ($60,000 – $40,000 in expenses = $20,000 net).

Which have the highest GPP

(simply make a lot of biomass)?

Oceans make the most biomass

– thus allowing these things to

exist!!

What ecosystems have the highest NPP (highly

productive and efficient systems – have energy

left over to grow extensive food webs)?

Who cares about NPP?

• NPP is the limiting factor

determining how many

consumers can be on Earth.

• Humans use 20-30% of Earth’s

NPP.

• Humans only represent 1% of

biomass of Earth’s consumers.

• This is main reason the

environment is out of balance.