How do ecosystems work? Part 1! Chapter 41. Overview: Pathways of energy and nutrients Materials cycle Note complete cycles for purple arrows. Energy.

How do ecosystems work? Part 1!

Chapter 41

Overview: Pathways of energy and nutrients

Materials cycle Note complete cycles

for purple arrows. Energy flows one

way! Energy (red) arrows in

direction of energy flow

Note heat loss at each step.

Energy flow through communities

Energy enters communities through photosynthesis

Carbon dioxide, water and sun’s energy used directly for photosynthesis

Inorganic mineral nutrients needed to build other molecules (proteins, lipids, carbohydrates)

Energy flow through communities Trophic levels

Autotrophs Which Domains/Kingdoms include at least some autotrophs?

Heterotrophs or consumers Primary consumers = herbivores: consume primary

producers Secondary consumers and higher = carnivores: consume

other consumers… Detritus feeders and decomposers

Consume dead organic matter Convert organic molecules back to inorganic ones so primary

producers can use them (bacteria mostly do this step.) What if there were no decomposers?

Energy flow through communities Terrestrial food chain and trophic levels

What is missing here?

Energy flow through communities Marine food chain and trophic levels

What is missing here?

Energy flow through communities Trophic levels (cont.)

Many consumers cannot be strictly categorized Omnivores: Feed as both herbivores and carnivores Many carnivores feed at multiple levels

• Example: Leopard seal in Antarctic marine food web

Antarctic marine food web (simplified)

Energy flow through communities

Energy transfer is inefficient

On average, only 10% of energy gets transferred from one trophic level to the next (red arrows)

Most of the rest is lost as heat (yellow arrows)

Some converted to unusable form (i.e. indigestible for the consumer, such as cellulose for us.)

Energy pyramid shows inefficiency of energy transfer

Biomagnification: Unlike energy, toxins become concentrated up the food web

Top predators are most affected by toxins At the peak of DDT use, predatory birds contained

DDT concentrations up to 1 million times the concentration in water.

Cycling of nutrients: Carbon

CO2 sinks Primary

producers (via photosynthesis)

Terrestrial Marine (>50%)

Ocean water Ocean sediments Carbonification

Fossil fuels formed from phytoplankton (oil and gas) and plants (coal, peat)

Cycling of nutrients: Carbon

CO2 sources Respiration: All

organisms Decomposition Fires

Natural For agriculture

Burning of fossil fuels*

Use 1 million times as fast as it is formed!

In sum, decrease of CO2 sinks and increase of CO2 sources

Increase in global CO2 correlates with global warming

Highest temperature increases are along the Antarctic Peninsula