Lecture 5, Chapter 54 - Ecosystems and Global Change

Ecosystem Ecology

the study of the sum of all the organisms living in a given area and the abiotic factors with which they interact

most energy comes from the sun via photosynthesis

What do major ecosystem processes include?

1. primary production

2. energy transfer

3. decomposition

Primary Productivity

the rate at which solar/chemical energy is captured and converted into chemical bonds by photosynthesis/chemosynthesis (converting energy using oxidation of inorganic molecules instead of sunlight)

Community Ecology vs Ecosystem Ecology

community ecology = who is interacting with who
ecosystem ecology = where is this energy/matter going to?

What do producers use energy for?

• respiration

• growth

• reproduction

Gross Primary productivity (GPP)

the amount of solar energy that is captured via photosynthesis (gained)

Net Primary Productivity (NPP)

the amount of energy for growth and reproduction after respiration (accounts for matter lost)

NPP = GPP - R

Photosynthesis Equation

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

Cellular Respiration Equation

C₆H₁₂O₆ + 6O₂ + ATP (energy) → 6CO₂ + 6H₂O

Describe the difference in energy transfer of Terrestrial v. Aquatic Systems

Terrestrial Systems → standing stock (total of biomass (amount of weight/energy stored in organisms like trees) at a specific moment

• high standing stock (land plants build up massive amounts of living biomass/woody structure that lasts for years)

• bigger and long-lived producers

Aquatic Systems → NPP is quickly converted to biomass at higher trophic levels
(image for aquatic systems)

T/F: High productivity does NOT equal to high standing stock

True: areas of high primary production (the speed/amount of energy converted from sunlight) may have high or low standing stock (total weight or mass of living producers/land)

think of it like this: consumers could remove the new biomass just as fast as it is created

Terrestrial Systems ~ Standing Stock

biomass of producers present in a given area/specific time (a snapshot amount)

Biomass Resident Time (+ formula)

length of time biomass spends in a specific trophic level

Describe the difference in Top Down vs Bottom Up control

Top down → higher trophic levels (apex predators) control the lower trophic level populations

• changes in predator numbers can cause alternate increases/decreases in the food chain (trophic cascade).

• Example: tigers/wolves keep deer populations in check. without them, too many deer eat all the plants

Bottom Up → nutrient availability + primary producer limit drive predator populations of higher trophic levels (the base controls the top)

• if the base lacks nutrients, the whole food chain stays small because there is less energy to go around.

• Example: adding a fertilizer (nutrients) to a lake to increase algae growth, which feeds zooplankton, which feeds more fish

Name 3 reasons why having more nutrients isn’t better

1. Greenhouse gases cause global warming

2. Ocean Acidification

3. Eutrophication

Trophic Cascade

indirect effects caused by (apex) predators

Ocean Acidification

increase CO₂ = decrease of pH in oceans (more acidic) = more absorption of CO₂ in the form of ion bicarbonate, which many organisms need for growth/shells (example of when the gastropods have softer shell because lack of carbonate)

Eutrophication

too many nutrients in the waters (nutrients being nitrogen & phosphorus) leading to rapid plant growth & suffering aquatic life

• occurred naturally but drastically changed as humans dump industrial waste into the water

• affects terrestrial/aquatic ecosystems → ocean acidification, harmful algal blooms

Carbon Cycle

1. CO₂ is captured by photosynthesis and turned into sugars and bioavailable forms of carbon

2. plant biomass turn into soil carbon and be stored or decompose by soil microbes/detritivores (getting food from dead organisms)

3. plants and microbe respiration release CO₂

4. in the oceans, CO₂ the air diffuses into the water, becoming bicarbonate ions (which the photosynthetic algae take

5. Humans change this cycle now by taking deep stores of carbon and extracting them for their use, releasing more CO₂

List the Limiting Nutrient in terrestrial ecosystems, freshwater ecosystems, open ocean, and major ocean regions

terrestrial = nitrogen (N)

freshwater = phosphorus (P)

open ocean = nitrogen (N)

some major ocean regions = iron (Fe)

General Compartment model

nutrients are present either in organic material (living/dead tissues of organisms) or in inorganic material (rocks, soil)

Why can’t we have 10 trophic levels?

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

Biomagnification

the concentration of toxic chemicals increases in living tissues as organisms move up the food chain

→ toxins enter the base, absorbed by producers, passed up the chain, concentration increases

* this is why pregnant women cannot have fish/sushi because it contains mercury

Another Example: DDT and how birds kept dying (Rachel Carson: Silent Spring)

What happens if we have too much of carbon, nitrogen + phosphorus?

1. Carbon

+ essential for photosynthesis

- excess → global warming + ocean acidification

2. Nitrogen + Phosphorus

+ essential for growth

- excess → eutrophication

Secondary Production

the total amount of energy consumed by herbivores in a given area that is used for respiration, growth, and reproduction

Carbon Cycle

• ecological food chain efficiency → % of net production from one trophic level compared to the next lower trophic level

• ecological efficiencies typically range from 5-20%

• this means that eating meat requires much more carbon to be processed by the environment to give you the same amount of energy as eating plants (because eating plants take CO₂ out of the air directly and convert it to energy efficiently)

  • eating meat uses a lot of the carbon for cellular respiration and only some is left for the environment (inefficient)