Productivity and Biological Pyramids

Biological Pyramids Biological pyramids are graphical models of the quantitative differences that exist between the trophic levels of a single ecosystem.

Biological Pyramids There are 3 kinds of biological pyramids.  Productivity  Biomass  Number

Biological Pyramids--Productivity Productivity can be expressed in terms of a pyramid because of the 2 nd law of thermodynamics.  There is less energy available as you go up the food chain. In other words it takes many oak tree leaves to support one caterpillar, many catepillars to support one bluetit, and many bluetits to support one sparrowhawk.

Biological Pyramids--Productivity 10% Rule  Only about 10 % of the energy in one consumer level is represented the next higher level.  In other words 90% is lost.

Biological Pyramids--Productivity Pyramids of productivity refer to the flow of energy through a trophic level and show a decrease along the food chain. Pyramids of productivity are expressed in units of flow J m -2 y -1 (Joules/meter 2 /year ) or g m -2 y -1 (grams/meter 2 /year 1 )

Aquatic ecosystems tend to have more trophic levels, thus top carnivores are more vulnerable.

Productivity Productivity is one of the most important properties of an ecosystem.  There are 2 kinds of productivity: Primary productivity  Basis for almost all growth in an ecosystem.  Autotrophs (Photosynthesizers) are responsible for the primary productivity in an ecosystem. Secondary productivity  The manufacture of biomass (biological material) by organisms that eat plants.

Productivity Gross productivity is the amount of energy trapped in organic matter during a specified interval at a given trophic level.  (Gross means before deduction, for example, gross income which is a person’s income before taxes are deducted). Think TOTAL energy

Productivity Net productivity is the amount of energy trapped in organic matter during a specified interval at a given trophic level less that lost by the respiration of the organisms at that level

Productivity Gross primary productivity and net primary productivity  Class definition:

Productivity Calculations Net Primary Productivity can be calculated from the following equation:  NPP = GPP – R Where NPP = net primary productivity GPP = Gross primary productivity R = respiratory loss

Productivity Gross secondary productivity and net secondary productivity  Class definition:

Productivity Calculations Net Secondary Productivity can be calculated from the following equation:  NSP = GSP – R Where NSP = net secondary productivity GSP = food eaten – fecal loss R = respiratory loss

Primary Productivity and Ecological Succession What happens to biodiversity during ecological succession?

Biomagnification The pyramid structure affects the functioning of the ecosystem.  Limited length of food chain  Vulnerability of top carnivores  Concentration of non-biodegradable toxins in food chains—biomagnification.

Biomagnification Bioaccumulation is the process of accumulating higher and higher amounts of material within an organism’s body. Many persistent pesticides are fat soluble and build up in fat tissues. Biomagnification is the process of acquiring increasing levels of a substance in bodies of higher trophic-level organisms. DDT, mercury, and PCBs are all known to accumulate in ecosystems. DDT was banned in the U.S. in the early 1970s.

Biomagnification

The biomagnification of DDT. Numbers shown are in ppm. The amount of DDT in the bodies of the organisms increases as we go from producers to herbivores to carnivores. Because DDT is persistent it builds up in the trophic levels of the food chain