Some ecologists divide the living parts into functional units such as trophic levels (feeding levels).

Sun-producer-consumer-predator-secondary predator.

Though this simplistic view is easy to comprehend. It misses much of the beauty and complexity involved in real ecosystems

A) Trophic levels

1.Producers: the green plants or autotrophs that produce organic compounds that feed life on earth.

Photosynthesis and respiration, biological production

Photosynthesis: Green plant are photosynthetic. They use a complex set of interactions to bind H2O and CO2 to form glucose. O2 is released as a byproduct.

6 CO2 + 6 H2O + light energy ----> C6H12O6 + 6 O2

Respiration breaks down the glucose and other organic molecules to provide chemical energy for work.

C6H12O6 + 6 O2 --------> 6 CO2 + 6 H2O + energy

Primary production: the amount of organic matter in an area that was produced by plants. It is measured as mass/unit area.

Gross primary productivity (GPP) : the total amount of organic matter in an area that was produced by plants. It is measured as mass/unit area/unit time. It is a rate function.

Respiration (R) consumes some of the GPP . By subtracting respiration from gross production, you get the Net primary productivity (NPP) = GPP -respiration.

GPP = NPP + R

Secondary productivity is the production of heterotrophic (consumer) biomass/unit area/unit time

Hetrotrophs are consumers because they get at least part of their food from other organisms.

Consumers are divided into several groups.

Primary consumers (herbivores): animals that eat plants

Secondary consumers (carnivores): animals that eat animals that eat plants

Tertiary consumers (carnivores): animals that eat animals that eat animals

Omnivores: animals that feed on more than one thing or trophic level.

Detritivores: organisms that consume dead organic matter.

Decomposers: Heterotrophic bacteria and fungi which breakdown the organic compounds of dead organisms. These organisms contribute greatly to cycles in ecosystems.

 B) Food chains:

The transfer of food energy through a series of organisms.

In the past it was assumed that food chain lentghs were severely limited by the laws of thermodynamics. Indeed this would be the case if all webs involved strictly linear chains.

The conversion of light energy to energy-containing foods by plants is quite inefficient (about 0.2%).

Efficiencies of energy transfers associated with feeding interactions typically range from

from 5% to 20%.

A ten percent transfer efficiency is normal. The remaining 90% of the energy transferred from on trophic level to another is lost as low-quality heat to the environment.

C). Complex food webs convey a different dynamic function and structure to ecosystems than would be predicted from simple foodchains.

D) However, laws of thermodynamics still apply, and this places constraints on populations of organisms.

E) Pyramids of numbers, mass, and energy.

 II. Community interactions

Types of species interactions

The members of two different species may directly affect each other in any one of several different ways (Interspecific interactions):

Neutralism 00

Mutualism++

Commensalism +0

Inhibition 0-

Competition--

Parasitism+-

Predation+-

Altruism-+

Indirect Effects