Trophic Levels & Ecological Pyramids

1. Trophic Levels & Ecological Pyramids Energy Flow in Ecosystems

2. Trophic Levels • Each step in a food chain or food web is called a trophic level. • Primary producers always make up the first trophic level. • Various consumers occupy every other level. Some examples are shown. Energy Flow in Ecosystems

3. Energy Flow Trophic Levels Quaternary Consumers Tertiary Consumers Secondary Consumers Primary Consumers Producers Energy Flow in Ecosystems

4. Ecological Pyramids • Ecological pyramids show the relative amount of energy or matter contained within each trophic level in a given food chain or food web. • There are three different types of ecological pyramids: • pyramids of energy, • pyramids of biomass, and • pyramids of numbers Energy Flow in Ecosystems

5. Ecological Pyramids • What do the three types of ecological pyramids illustrate? • Pyramids of energy show the relative amount of energy available at each trophic level. • A pyramid of biomass illustrates the relative amount of living organic matter at each trophic level. • A pyramid of numbers shows the relative number of individual organisms at each trophic level in an ecosystem. Energy Flow in Ecosystems

6. 1. Pyramids of Energy • There is theoretically no limit to the number of trophic levels in a food web or the number of organisms that live on each level. • However, only a small portion of the energy that passes through any given trophic level is ultimately stored in the bodies of organisms at the next level. • Organisms expend much of the energy they acquire on life processes, such as respiration, movement, growth, and reproduction. • Most of the remaining energy is released into the environment as heat—a byproduct of these activities. Energy Flow in Ecosystems

7. Pyramids of Energy • On average, about 10 percent of the energy available within one trophic level is transferred to the next trophic level (trophic efficiency) • The more levels that exist between a producer and a consumer, the smaller the percentage of the original energy from producers that is available to that consumer. Energy Flow in Ecosystems

8. Pyramids of Energy Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers 1,000 kcal 10,000 kcal Producers Energy Flow in Ecosystems

9. Pyramids of energy • Advantages • Takes into account the PRODUCTIVITY • Addresses the fact that weight for weight, two species do not necessarily have the same energy content • Disadvantages • Very difficult to obtain data • Destructive • Problems identifying trophic level Energy Flow in Ecosystems

10. 2. Pyramids of Biomass • The total amount of living tissue within a given trophic level is called its biomass. • The amount of biomass a given trophic level can support is determined, in part, by the amount of energy available. Energy Flow in Ecosystems

11. 2. Pyramids of Biomass • Illustrates the relative amount of living organic matter at each trophic level. • Indicates the total dry mass of the organisms in each trophic level • Typically, the greatest biomass is at the base of the pyramid, as is seen in the field ecosystem modeled here. Energy Flow in Ecosystems

12. Pyramids of Biomass • How might this data be collected? • Individual organisms weighed and counted. • Dry mass should be compared to eliminate errors due to water content • Advantages • The data is more accurate. • Eliminates misleading problems of producer size differences • Disadvantages • Laborious and expensive • Destructive • Can also be misleading in some circumstances Energy Flow in Ecosystems

13. 3. Pyramids of Numbers • A pyramid of numbers shows the relative number of individual organisms at each trophic level in an ecosystem. 3rd level carnivore 2nd level carnivore 1st level Carnivore Herbivores Producers Log numbers Energy Flow in Ecosystems

14. 3. Pyramids of Numbers In most ecosystems, the shape of the pyramid of numbers is similar to the shape of the pyramid of biomass for the same ecosystem, with the numbers of individuals on each level decreasing from the level below it. Energy Flow in Ecosystems

15. 3. Pyramids of Numbers • In some cases, however, consumers are much smaller than organisms they feed upon. • Thousands of insects may graze on a single tree, for example. The tree has a lot of biomass, but represents only one organism. • In such cases, the pyramid of numbers may be turned upside down, but the pyramid of biomass usually still has the normal orientation. 2nd level carnivore 1st level carnivore herbivores Producers numbers Energy Flow in Ecosystems

16. Pyramids of Number • Advantage • Data relatively easy to collect using simple sampling • Disadvantages • Producers vary in size • Large range of numbers • Trophic level difficult to work out Energy Flow in Ecosystems

17. Associated terms with energy production and energy flow. • Primary production: • Fixation of energy by autotrophs in an ecosystem. • Rate of primary production: • Amount of energy fixed over a given period of time. • Gross primary production (GPP): • Total amount of energy fixed by autotrophs. • Net primary production (NPP): • Amount of energy leftover after autotrophs have met their metabolic needs. Energy Flow in Ecosystems

18. Primary Productivity in Ecosystems • Gross primary productivity (GPP) • The rate at which an ecosystem's producers capture and store a given amount of chemical energy as biomass in a given length of time. • Net primary productivity (NPP) • Rate at which all the plants in an ecosystem produce net useful chemical energy; equal to the difference between the rate at which the plants in an ecosystem produce useful chemical energy (gross primary productivity) and the rate at which they use some of that energy through cellular respiration. • (NPP = GPP – Respiration) Energy Flow in Ecosystems

19. Coral reefs and Marine ecosystems have the highest primary productivity? WHY? • Highest rates of primary production by marine phytoplankton are generally concentrated in areas with higher levels of nutrient availability. • Highest rates found along continental margins. • Nutrient run-off from land. • Sediment disturbance • Open ocean tends to be nutrient poor. • Vertical mixing main nutrient source. Energy Flow in Ecosystems

20. What controls primary productivity? • Terrestrial primary production generally increases with moisture and temperature • Rosenwitz studied net primary production across biomes • Compare NPP to actual evapotranspiration Energy Flow in Ecosystems

21. What controls primary productivity? • Terrestrial and aquatic primary production is also limited by nutrient availability Energy Flow in Ecosystems