The Components of Ecosystems: Food Webs

In the previous lecture, we discussed the abiotic factors contributing to the formation of biomes (each of which is composed of many ecosystems). We now turn our attention to the biotic, or living components of those ecosystems, and how they interact to effect energy flow through those ecosystems.

All organisms interact with one another (we'll go through this in a later lecture), and the most basic way they do this is by feeding on one another. We have defined the different levels of feeding ("trophism" - from the Greek word troph, meaning "to eat") by how many levels they are from the first level, plants

PRIMARY PRODUCERS - Organisms that can perform photosynthesis, harnessing the energy of sunlight by placing it into the chemical bonds of sugar, which they manufacture from water (from the soil and surroundings) and carbon dioxide (from the atmosphere).

PRIMARY CONSUMERS (1o)- (first trophic level) - Organisms that feed on primary producers. Also called herbivores, frugivores (fruit eaters), seed eaters, etc.

SECONDARY CONSUMERS (2 o)- (second trophic level) - Organisms that feed on primary consumers. These are carnivores, insectivores, etc.

TERTIARY CONSUMERS (3 o) - (third trophic level) - You guessed it.

QUATERNARY CONSUMERS (4 o) - (fourth trophic level) You guessed it again.

DECOMPOSERS - digest organic molecules and break them down into their inorganic components

As you might guess, most organisms eat more than one kind of food, and a particular species isn't always eating at the same trophic level (Can you think of an example of this, even using yourself?).

In times past, the trophic interactions of these different levels were called the "food chain":

However, trophic levels do not form a straight line, or "chain" from one level to the next. Rather, they interlace to form more of a WEB. Ecologists call these complex feeding relationships the FOOD WEB, and every ecosystem is characterized by a specific type of food web.

These complex interactions are what drive the flow of energy and chemicals through ecosystems, between living and non-living components of the earth. That will be our next topic. Stay tuned!