Chapter 5.1 Energy flow in Ecosystems

Sustaining Life on Earth Life depends on these interconnected factors: One-way flow of energy from the sun through ecosystems Cycling of water and nutrients

Energy flows through ecosystems due to trophic interactions Trophic interactions = feeding interactions Food chains – one way flow of energy as one thing feeds on another Energy came from the sun, but the sun isn’t part of the food chain itself

Food webs – more realistic representation of an entire community’s trophic interactions because most organisms feed on and are eaten by more than one thing Arrows show the direction of energy flow

Trophic terms to know Know the words in this column (see textbook for definitions if you do not remember them from biology)

Trophic terms to know

The label for an organism depends on what it is eating – it may have more than one label in a food web For example, the fox is both a secondary and tertiary consumer because it feeds on mice and grasshoppers

Photosynthesis and Cellular Respiration Let’s start with what you learned in biology – the process of photosynthesis takes up carbon dioxide from the atmosphere and converts it into glucose Photosynthesis: Cellular respiration: Cellular respiration takes the glucose molecule and breaks it down for energy, releasing carbon dioxide as a waste product Energy is stored when glucose is formed and released when glucose is broken down.

Trophic pyramids: We can represent information about trophic relationships by diagrams called trophic pyramids – three types: 1.Pyramid of energy 2.Pyramid of biomass 3.Pyramid of numbers Each one is discussed on the following slides

Pyramid of Energy This diagram shows the amount of energy in each trophic level. There is the most energy in the producers’ level and less as you go up the food chain. Why is this? Go on to the next slide…

Pyramid of Energy Only about 10% of the energy available at one trophic level is passed on to the next because some energy is: lost as heat some energy is used to carry out cellular processes some energy is used for reproduction Also known as the 10% Rule

Pyramid of energy and the “10% rule” Therefore, not all calories consumed go to make up the organism’s body (meal for next level) Notice that 3500 kcal are in the producer level and only 10% of that, or 350 kcal, are in the next level (herbivores)

Pyramid of Numbers Due to the loss of energy with each trophic level, there are fewer and fewer individuals as you go up the food chain. We can represent this with a pyramid of numbers….here are two examples:

Pyramid of Biomass Biomass is defined as the amount of mass of living things in a given area. We can measure the biomass of producers, the biomass of primary consumers, etc. There is more biomass of plants than primary consumers, and more of primary consumers than secondary consumers, etc. Biomass of plants>biomass of grasshoppers>biomass of birds Then we can make another pyramid to represent this information….

Pyramid of Biomass The most biomass is in the producer level

Trophic pyramids explain three concepts… 1. They show why there are usually only four or five trophic levels in a food chain 2. They show why there are so few large top predators 3. They show why the earth can support more people if they eat at lower trophic levels (eat less meat)