Energy Flow in an old field, MI:

1. Energy Flow in an old field, MI: • Sun 47.1 x 108 kcal/ha/yr strikes plants 58.3 x 106 kcal/ha/yr assimilated by plants or only 1.2 % of available energy = Gross Primary Productivity: total energy captured or assimilated for metabolism and growth of new tissue Assimilation Efficiency: how well an organism assimilates available (ingested or consumed) energy An/In = 1.2 % for plants above 58.3 x 106 47.1 x 108

2. Of Gross Primary Productivity, plants use 15 % for respiration and 85 % (49.5 x 106 kcal/ha/yr)for new tissue growth Net Primary Productivity: amount of energy assimilated that is used for new tissue growth by plants Production Efficiency: how well energy is used for net production from amount assimilated Pn/An = 85 % for plants 49.5 x 106 58.3 x 106

3. Of NPP, only 32 % (15.8 x 106 kcal/ha/yr) is edible tissue available for herbivores to ingest or consume Mice only consume 250 x 103 of this edible tissue (1.6 %) or only 0.5 % of NPP (49.5 x 106) Consumption Efficiency: amount of net production that is ingested or consumed by the next level up In/Pn-1 = 0.5 % in mice 250 x 103 49.5 x 106

4. Of the energy consumed by the mice (250 x 103 kcal), 68 % used for respiration 30 % lost (feces and undigested material 2 % (5170 kg) used for net secondary productivity Weasels at third trophic level consume mice, only 2.2 % of this energy goes into net tertiary productivity This last amount is only 0.00026 % of the original NPP (49.5 x 106 kcal) produced by plants!

5. These efficiencies will vary by trophic level e.g., carnivores can absorb their food better than herbivores Thus, AE is much higher in carnivores Herbivores have low AE—plant matter is difficult to digest Also, ectotherms have higher CE than endotherms --they don’t need to maintain constant Tb

6. 10 % Rule A general rule in ecology that only 10 % of energy on average is transferred from one trophic level up to the next level This means that ~ 90 % of energy is lost, not digestible and left behind

7. Logical Assumptions for Energy Flow A high NPP at first trophic level should allow for more trophic levels in the entire community Any trophic level with high productivity should have more levels above it There should be a threshold value of productivity above which no more trophic levels can be supported

9. Phytoplankton Zooplankton Zooplankton Zooplankton Fish Fish

10. Does any level with relatively high productivity have more levels above it? Ectotherm vs. endotherm communities Ectotherms have higher CE, so should have more levels above them Ecotherms: mean .583 levels above Endotherms: mean .625 levels Prediction #2 is false

11. Threshold value for more levels above? All but one (14) have 3-4 trophic levels Herbivore Biomass NPP

12. What other factors might control the number of trophic levels in a community? Ecological stability: how well a community maintains its structure following a disturbance -- assessed by complexity (links in food web) -- measured by persistence, or how well it retains species richness -- and by resilience, or how quickly a it returns to equilibrium

14. Detritivores in 1 m2 of temperate forest soil: ~ 1000 species, millions of individuals 10 million nematodes and protozoa 100,000 springtails and mites 50,000 other invertebrates

15. Microfauna, < 0.001 mm Mesofauna, 0.001 to 2.0 mm Macrofauna, > 2.0 mm

18. Feeding Guild A group of species feeding on the same resource in different ways