Ecosystems and Energy Structure

Ecosystems An ecosystem comprises a community and its physical environment Both biotic and abiotic components make up an ecosystem

Energy Flow and Chemical Cycling One way to look at ecosystems is as systems that cycle life-sustaining chemicals and allow energy to flow between trophic levels Trophic levels describe the levels of the food chain

Energy Flow All energy used for life must originally come from autotrophs Autotrophs obtain carbon from inorganic compounds Photoautotrophs obtain energy from light Chemoautotrophs obtain energy from inorganic compounds

Primary production Autotrophs are responsible for primary production, the creation of sugars and other energy-rich compounds from inorganic matter

Heterotrophs Heterotrophs obtain carbon from organic sources Chemoheterotrophs obtain energy from sources such as carbohydrates Photoheterotrophs obtain energy from light

Consumers Heterotrophs act as consumers Organisms that eat primary producers are primary consumers Organisms that eat primary consumers are secondary consumers, and so on (tertiary, quaternary)

Decomposition Decomposers (also called saprotrophs) include fungi, bacteria. Primary difference between decomposers and consumers is that decomposers break down dead matter while consumers eat still living or recently deceased matter. Similar to detritivore

Decomposers play a vital part in chemical recycling, allowing producers to continue producing. Fungi (rot) and some bacteria are the only known organisms able to digest lignin, a primary component of wood.

Laws of Physics The laws of physics still apply when dealing with biology Of particular importance are the Laws of Thermodynamics and Conservation of Mass

Laws of Thermodynamics 1st – Energy cannot be created or destroyed, only transformed. 2nd – Energy transformations are never completely efficient. Combined the two laws have a variety of implications for life. Life could not exist without the constant addition of energy, primarily from the Sun, to our ecosystems.

Law of Conservation of Mass Mass cannot be created or destroyed, only converted into new forms For ecosystems the implication of this law is that carbon, nitrogen, phosphorus, and other nutrients cannot be destroyed and will be continuously recycled

Primary Production The sun provides approximately 1022 J (2.39 x 1021 cal) of energy to the Earth per day However most of this energy is absorbed or deflected by Earth’s atmosphere, or land places without any photosynthetic organism around In the end, approximately 1% actually makes it into chemical energy

Gross vs Net Gross primary productivity (GPP) is the total about of light energy converted into chemical energy in a given time period Net Primary Productivity (NPP) = GPP – R (energy used by primary producers for respiration) NPP is the amount of energy that is available to consumers

Measuring energy production Most commonly energy production is measured by biomass added to the ecosystem in a given time Note that it’s the biomass added. The total biomass (called the standing crop) is not a useful indicator of energy production,

What limits productivity? The limiting nutrient is the nutrient that most limits primary production Put another way, the limiting nutrient is the nutrient that most increases production when added to an ecosystem

The limiting nutrient depends upon the ecosytem in question In ocean ecosystems the limiting nutrients tend to be either light or nitrogen Light limits productivity in deep water where little light penetrates Near the ocean surface nutrients, such as nitrogen, limit productivity

Nitrogen is the most common limiting nutrient in open water Addition of nitrogen to open water often results in eutrophication and algal blooms

Upwelling can cause natural increase in nutrients Wind driven motion of water can cause nutrient rich upwellings

Freshwater tends to lack phosphorus

Terrestrial ecosystems Water can be a very important limiting nutrient in terrestrial systems Temperature also varies more on land than in water and can limit growth in colder months Nitrogen and phosphorus may be local limiters on productivity.