Productivity

1. Productivity

2. Energy flow through an ecosystem

3. ENERGY ENTERS THE ECOSYSTEM AS SUNLIGHT • Only 1-2% of the light energy falling on a tree is captured and turned into chemical energy by PHOTOSYNTHESIS • The rest is reflected, or just warms up the tree as it is absorbed

4. Gross Primary Productivity is a measure of total energy captured • It is measured in joules (J) • It is the energy captured or assimilated by an organism • for a plant, it is the sunlight actually fixed by the leaves during photosynthesis Energy is stored in leaf as sugars and starches, which later are used to form flowers, fruits, seeds,

6. Gross Primary Productivity: GPP • The total energy gain in biomass per unit time due to photosynthesis in plants.

7. Net Primary Productivity Plants • NPP • The gain in energy or biomass per unit time remaining after allowing for respiratory losses (R)

8. Net and Gross Primary Productivity • Gross primary productivity and net primary productivity are not the same • The plants produce biomass over time and then lose some of it due to respiration (R). • Does this make sense? NPP = GPP - R

9. NPP = GPP - R Net productivity = Gross productivity - Respiration Energy The productivity of a plant is called PRIMARY PRODUCTIVITY because plants are the first or primary organisms in the food web

10. Net primary productivity: NPP • Plants have to use some of the energy they capture to keep themselves growing: • they move water and stored chemicals around • they make hormones and enzymes to control their metabolism • they make flowers, fruits, new leaves and stems • the energy left over after they have used what they need is called the net productivity • the energy used by the plant for essential tasks is called respiration energy, and eventually it is released to the environment as heat

11. Chart of Net Primary Productivity for biomes

12. Secondary Productivity (animals)

13. Gross Secondary Productivity • GSP refers to the production of biomass over time by consumers. • It is also called assimilation

14. Gross Secondary Productivity • Animals must eat other organisms to obtain energy, unlike plants which photosynthesise • Animals may eat plants or animals or both • Not all the energy in food is absorbed (assimilated) into an animal’s body • Unassimilated food is ejected as faeces or droppings gross secondary productivity = food assimilated gross productivity = food eaten - energy in faeces

15. NSP

16. Net Secondary Productivity • Gross secondary productivity = Energy eaten - energy in faeces • As well as keeping themselves alive, animals must use energy to move and keep warm - plants need rather less energy- but in the end it, as in plants, it all turns to heat • Net secondary productivity (NSP) = food eaten - faeces - respiration energy so NSP = GSP- R (just like plants) ?

17. Net and gross productivity in the food web • In a food web diagram, you can usually assume that: • the energy input into an organism represents the Gross Productivity (GP) • the energy output from that organism to the next trophic level represents the Net Productivity • the difference between GP and NP = R (respiration energy ) and/or loss to decomposers ?

18. Remember: only 10% of biomass is transferred between trophic levels

19. Pyramid of Biomass Review

20. Pyramid of ProductivityCalculate the gross productivity, then draw the pyramid of productivity

21. Draw your own energy flow diagram, rather like the one on the previous slide to show energy flows through one of the animals named in your food web. You should include the following labels: • energy lost in faeces • food ingested • respiration loss, R • GSP, NSP • arrows showing energy moving to carnivores and decomposers