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