Energy and the Ecosystem

Questions for Today:

• How does energy flow in Ecosystems?

• What happens to usable Energy as it travels through a food chain or web?

• Why is it important to analyze the amount of plant matter in an ecosystem?

• What is the difference between Gross Primary Productivity and Net Primary Productivity?

Review

• Life on Earth Depends on three interconnected factors:1. The one-way flow of high quality energy.

2. The cycling of matter or nutrients.

3. Gravity

Food Chains and Food Webs

• Energy in the Ecosystem is transferred through the different trophic (feeding) levels.– Food Chain – a sequence of organisms, each of

which serves as a source of food or energy for the next.

– Food Webs – a series of interconnected Food Webs.

– Chemical energy and nutrients travel through trophic levels primarily through photosynthesis, feeding, and decomposition.

Food Chains and Food Webs

• As chemical energy travels through trophic levels, some useful energy is lost to the environment as heat. – This would result in the collapse of the

ecosystem or biosphere if it weren’t for the Sun.

Food Chains and Food Webs

Energy Efficiency

• The Chemical Energy in Ecosystems are stored in biomass.– Biomass – the dry weight of all organic matter

contained in its organisms.• Energy transfer through food chains is not

very efficient and a lot of the energy is lost as heat.– The percentage of usable chemical energy

transferred as biomass from one trophic level to the next is called Ecological Efficiency.

• 10% is usually the normal Ecological Efficiency

Energy Efficiency Question

• Assuming 10% ecological efficiency, if green plants capture 10,000 units of energy, how much chemical energy will be available to support herbivores and carnivores?

Energy Efficiency

Energy Efficiency

• Energy pyramids help explain how:– The earth can sustain populations better if

they eat at lower trophic levels.– Ecosystems usually only have 4 or 5 Trophic

levels.

The Importance of Producers

• Producers are the source of all nutrients or chemical energy in an ecosystem.

• In order to quantify the energy captured through producers in ecosystems, Scientists analyze the Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).

The Importance of Producers

• Gross Primary Productivity is defined as the rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass found in their tissues.

• Their unit is kcal/m2/yr

The Importance of Producers

• Remember, that plants can create their own food, but they also must eat that food.

• When calculating NPP, we have to subtract the energy loss due to the consumption of that food.

• NPP = GPP – R– R is the energy used in respiration

The Importance of Producers

• Different areas in the planet both terrestrial and aquatic have variable NPPs due to the amount of sun and nutrients available.– The further you are away from the equator,

the less NPP in that ecosystem.– In aquatic zones, the further you are away

from the surface or a nutrients source, the less NPP in that life zone.

Importance of producers

• As consumers, the NPP in an ecosystem is important for us to know because only the biomass represented in the NPP is available to us as nutrients.

• Therefore, the planet’s NPP ultimately limits the number of consumers that can survive on the earth.