- Biomes
- Trophic levels
- Producers, consumers, and decomposers
- Trophic levels and biomass


[SLIDE 1]

Biomes are ecosystems with a similar type of vegetation and climate conditions. A good example of this is a tropical rainforest biome. You can compare tropical rainforest biomes in the Philippines with those in the Amazon.

Studying ecosystems extends beyond understanding community interactions such as predation and prey relationships as well as the flow of energy through carbon, sulfur, nitrogen and phosphorus cycles. It also requires understanding trophic levels, productivity and consumption.


[SLIDE 2]

Every feeding level in a food chain is called a trophic level. Food chains describe the flow of energy and nutrients from one organism to another. Green plants that conduct photosynthesis are called autotrophs. They do not require consumption of other organisms to survive. They are also called producers.

Organisms that have to consume other organisms to survive are called heterotrophs. There are two types of heterotrophs - consumers and decomposers. Consumers eat living prey while decomposers eat dead organic material.


[SLIDE 3]

Producers capture energy from the sun or from chemical reactions to convert carbon dioxide into organic matter. Most producers are green plants. Plants use chlorophyll, a green pigment to capture light energy during photosynthesis.

Consumers rely upon organic matter for survival. Primary consumers or herbivores eat producers (green plants) directly. An example would be a mouse. Secondary consumers eat primary consumers. An example would be a snake. Carnivores eat secondary consumers and other consumers. An example is a wolf that eats other mammals. Omnivores eat both both plants and animals. Human beings are considered omnivores.

Decomposers break down and consume dead or decaying organic matter. Decomposers are essential to the food chain because they break down material. They are the biggest consumers in the food chain and range from scavengers like vultures to earthworms, termites and microbes.


[SLIDE 4]

In a typical terrestrial ecosystem, there are 3 or 4 trophic levels. Biomass or total combined dry weight is roughly 90% less at each higher trophic level. This means that if you dried all the grass in an acre of grassland for example, you could have a certain weight (let's say 2000 lbs for this example). Then the herbivores (ranging from grasshoppers to cattle) that consume this grass would weigh 200 lbs per acre. Following this, the weight of all the carnivores (wolves, coyotes, foxes and more) would be 20 lbs. 

Trophic levels will eventually end as you continue this process upward to higher-level consumers.

As you go further up the food chain, biomass keeps decreasing until you are finally at zero. If you graphed these levels, it would resemble a pyramid. The highest trophic level (3 or 4) would be at the summit or top of the pyramid.