BIOSCI 109: Lecture 11 - Ecosystem III: Nutrient Cycling & Energy

Energy Transfers

They underly all the biological intractions within an ecosystem. Food chains show linear energy transfer while food webs show interconnected transfers. Energy is typically transfered by the consumption of another organism.

Primary Producers

Organisms that capture energy (light or from chemicals) and convert it into something they and other organisms can use as energy.

Photoautotrophs use lights while chemoautotrophs use chemicals and compounds.

Consumers

Organisms that need to consume or eat something else to gain its energy. There are different levels of consumers depending on what they prey on.

Primary consumers consume plants, secondary consumers consume herbivores, tertiary consumers then consumer them and so on.

The same organism can be a part of many consumer groups.

Detritivores

Organisms that use dead and decaying matter as a source of energy. They’re under the umbrella term of decomposers.

They’re extremely important in the nutrient cycling of the ecosystem and tend to work better in warmer damp conditions.

Energy Loss During Transfers

As energy is transfered, it is typically lost as heat, cellular respiration, and waste. Only a small chunk of energy (~10%) is actually available for use.

We can see this when comparing the dry mass of different trophic levels. There tends to be a lot more primary producers than consumers. In some aquatic ecosystems, a small producer population can also support a larger consumer population.

Gross Primary Production

The total amount of energy that primarh producers make (chemical energy/unit time)

Net Primary Production

The difference between GPP and respiration, the energy that is leftover and available for use.

Terrestrial Ecosystems & GPP

Tend to be more productive than aquatic ecosystems.

Higher temperatures and moisture are the main factors affecting GPP and tends to increase GPP. In extreme values, GPP tends to plateau though. Rainforests are the most productive terrestrial ecosystem.

Nutrients are also important but they tend to be limiting factors. Adding nutrients may temporarily increase productivity, but that or another nutrient will become limiting again. Excess nutrients tend to be dangerous for ecosystems.

Decomposers help cycle the nutrients and ensure that there are enough nutrients in the soil to support producer growth and fungi assimilation.

Aquatic Ecosystems & GPP

Tend to be not as productive than terrestrial ecosystems. However, it’s size makes the total productive about the same.

Aquatic ecosystems are limited by solar radiation as the sun can’t penetrate waters as deep and they tend to be nutrient limited as well. Coral reefs are the most productive aquatic ecosystem.

Nutrients are brought into the system when upwelling occurs, bringing deep cold nutrient-rich waters to the surface.

The biological pump is also another way nutrients are distributed. As organic waste and matter sinks, it brings its nutrients to organisms in deeper waters. As some deep diving organiams traverse to the surface, they excrete waste that is high in nutrients.

Decomposers tend to be slower in aquatic ecosystems due to the conditions and how nutrients are typically already usable in the waters.

Ecosystem Conditions & Productivity

The conditions of an ecosystem greatly affects how productive it is, whether it is terrestrial or aquatic.

Conditions have been changing globally due to climate change and these changes in conditions tend to bring in implications for those ecosystems too. It may introduce new interactions between old and introduced species, more biodiversity, eutrophication, and so much more.

Seasonality also affects productivity as ecosystems tend to be more productive during summer and spring, where there’s a lot of solar radiation and moisture.

Net Ecosystem Production

Refers to the total biomass accumulation over time. It gives us an idea of how the system is doing.

Typically we’d look at whether it is gaining or losing CO2 and O2. When a system has more CO2 going into it than coming out, it can be considered a carbon storage sink. The same can also occur with oxygen.

However, most systems have been losing more CO2 than gaining it, which is a main driver of climate change