Energy in Ecosystems

Here Comes The Sun• Of the incoming solar radiation,

only 1% is used for photosynthesis. • The amount of energy

produced is known as the Gross Primary productivity.

GPP

• This energy will be used by the producer to meets its needs. • Needs = Respiration • Rest will be stored as biomass. Biomass = mg of C

Starting Energy• The net primary productivity is the energy that becomes available

for the rest of the food chain.

NPP = GPP - Respiration

GPP Calculation• Light bottle:

• Initial = 4.6 ppm of oxygen • Final = 6.1 ppm of oxygen

• Dark bottle: • Initial = 4.6 ppm of oxygen • Final = 3.4 ppm of oxygen

NPP Respiration

• To calculate the NPP, we need to see how much carbon was produced. • Find the amount of oxygen produced.

NPP = 6.1 - 4.6 ppm = 1.5 ppm

GPP Calculation• According to our known information, an increase of 1 ppm of

oxygen is equal to 1 mL of oxygen if we have 1 L of water. • We had less than 1 L, so to account for the smaller bottles, we

can think about it as a percentage.

= 0.40 mL/L of oxygen 1.5 ppm = 1.5 mL/L x 0.266

266 mL1000 mL

=0.266

0.40 mL/L of oxygen = 0.40 mg/L of oxygen

0.40 mg/L of oxygen 0.375 mg of C

1 mg of O2x = 0.15 mg/L of C

GPP Calculation• Light bottle:

• Initial = 4.6 ppm of oxygen • Final = 6.1 ppm of oxygen

• Dark bottle: • Initial = 4.6 ppm of oxygen • Final = 3.4 ppm of oxygen

NPP = 0.15 mg of C Respiration

• Now we need to know how much energy is used for respiration!

Respiration = 4.6 ppm - 3.4 ppm = 1.2 ppm

GPP Calculation

= 2.7 ppm

2.7 ppm = 2.7 mL/L x 0.266

0.72 mL/L of oxygen = 0.72 mg/L of oxygen

0.72 mg/L of oxygen 0.375 mg of C

1 mg of O2x = 0.27 mg/L of C

GPP = NPP + Respiration

• Units must match when doing the calculations!

GPP = 1.5 ppm + 1.2 ppm

How Valid Is this?

= 56% x 1000.15 mg of C0.27 mg of C

• The NPP of ecosystems ranges from 25 - 50% of GPP. • Commonly we say that 40% is passed up the food chain.

Check Your Math!Then answer the conclusion questions!

Let’s Model Energy Flow in An Ecosystem!

Thermodynamics• When energy is transferred from

one trophic level to the next, some of the energy must become unusable.

• Because of this loss in useable energy, it is better to represent our trophic levels as a pyramid.

2nd Law of Thermodynamics

Energy Efficiency

1%

60% 40%

• If we look at the transfer between trophic levels, we follow the 10% rule. • 10% is transferred up, the rest is lost as heat.

Consider This…• Vegetarians need as much

land as needed to grow the crops they eat.

• Meat Eaters need the land to grow the crops they eat + the land to grow the crops that the cows eat, and the land needed to raise the cows.

Energy Efficiency• Vegetarians act as primary

consumers, so they get 10% of the energy from the producers.

• Meat eaters act as secondary consumers, so they only get 1% of the energy from the producers.• Need to consumer more to

meet their energy needs!

Biomass• The biomass at each trophic level follows a similar shape.

• Lowest level will have the greatest biomass.

• Standing crop - the amount of biomass present in an ecosystem at a particular time. • Productivity measures the

rate of energy production.

Differentiating between them…

Standing Crop

Slow growth forest

Productivity

High

Low

Ocean

Standing Crop

Productivity

Low

High

Other Producers• The starting energy in our pyramid comes from the producers.

• They do not have to be photosynthetic!

• Chemosynthesis is performed by bacteria in locations where light is not available. • Hydrothermal vents!

What limits productivity?

Limits to Productivity• Excluding the amount of light, there are three main factors that

limit productivity.

Temperature

Amount of Water

Nutrient Availability

• Which factor is the most limiting depends on the type of ecosystem.

Terrestrial Ecosystems• Excluding the amount of light, the main limiting factors of

productivity in terrestrial environments are…

Temperature

Amount of Water

Nutrient Availability

• Areas that are warm and wet tend to be more productive.

Aquatic Ecosystems• Excluding the amount of light, the main limiting factors of

productivity in aquatic environments are…

Temperature

Amount of Water

Nutrient Availability

• The two nutrients needed for photosynthesis are phosphate and nitrate. • Of the two, phosphate is

usually the most limiting. Nutrients enter from rivers and runoff!

Aquatic Ecosystems

• Areas closest to the shore line, will have the most nutrients.