Lecture 5: Ecosystems & Global Change

What is primary productivity?

The rate at which solar/chemical energy is captured and converted into chemical bonds by photosynthesis or chemosynthesis. 

What is the equation for photosynthesis?

6CO₂ + 6H₂O + E(sunlight) → C₆H₁₂O₆ + 6O₂

What 3 things do producers use solar/chemical energy for?

Respiration, growth, reproduction.

What is the equation for respiration?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + E(ATP)

What is gross primary productivity (GPP)?

The total amount of solar energy that is captured via photosynthesis.

What is net primary productivity (NPP)?

The amount of energy remaining for growth and reproduction after respiration (R).

NPP = GPP - R

What is ecological (food chain) efficiency?

% Net production from one trophic level compared to the next lower tropic level. Ecological efficiencies typically range from 5%-20%.

How to calculate ecological efficiency?

Ecological efficiency = Net production energy (J) / Net production energy of the next lower trophic level (J)

Why can’t we have 10 trophic levels?

There isn’t enough energy in the system to support more than 4 or 5 trophic levels.

What is the difference between standing stock vs primary productivity?

Primary productivity = the amount of energy/biomass converted from solar energy for a period of time.

Standing stock = biomass of producers present in an ecosystem in a given area and a given time. 

Areas of high PP may have high or low standing stock.

Are producers bigger in terrestrial or aquatic environments?

Producers are much bigger and more long-lived in terrestrial environments.

Why is standing stock lower in in aquatic systems?

It is all converted into biomass at higher trophic levels.

How to calculate biomass residence time?

Biomass residence time (years = biomass present in a trophic level (kg/m²) / net productivity (kg/m²/year)

What is the difference between bottom up and top down control?

Top-down control = when the abundance of trophic groups is determined by the existence of predators at the top of the food web. 

Bottom-down control = when the abundance of trophic levels is determined by the existence of producers at the bottom of the food web.

What is a trophic cascade?

Indirect effects initiated by predators.

How do greenhouse gases cause global warming?

Certain gases (like CO2) act like window panes in a greenhouse – trapping energy in the lower atmosphere – creating a warm earth.

Warmer atmospheric temperatures = due primarily to burning of fossil fuels (which has increased the greenhouse effect).

What is causing ocean acidification?

Increased atmospheric CO2 is causing ocean acidification (which is the decrease in pH of oceans) due to increased absoprtion of atmospheric CO2.

What is biomagnification?

How not just energy and nutrients move up the food chain, but chemicals and minerals as well. 

What is DDT?

A good example of bioaccumulation and biomagnification of toxic chemicals in the ecosystem.

What is bioaccumulation?

The buildup of absorbed chemicals in an organism over time.

What is eutrophication?

When water bodies have too much nutrients.