Lecture 23: Secondary Production

1. Lecture 23: Secondary Production EEES 3050

2. Secondary Production • Last week: looked at primary production – • Today: Where does the energy/nutrients from primary production go? • Consumed • Growth • Decay • Respiration • Egestion • Definition: • Production by herbivores, carnivores, and detritivores.

3. How is energy partitioned? Energy removed from lower trophic level Energy not used Energy Consumed (Gross Intake) Egested Energy Digested Energy Urinary waste Assimilated Energy Maintenance: Respiration and activity Production: Growth and Reproduction

4. Measures of secondary production • Metabolic rate (Assimilation rate) = • Respiration + Net productivity. • Laboratory: fairly easy to measure. • Measure oxygen consumption, CO2 output, calories consumed, etc.

5. Field: • Using doubly labeled water: 3H2O18 • Where does H and O go in metabolic activity? • Labeled water mixes with body water. • Respiration results in H2O and CO2. • Can use the different rates of H and O elimination to calculate CO2.production.

6. What are the metabolic rates for different taxonomic groups?

8. Measures of secondary production • Can analyze changes in biomass over time. • Production = • growth + natality • Or • Production = • net change in biomass + losses by mortality.

9. Measures of secondary production • Can analyze changes in biomass over time. • Production = growth + natality • = 20 + 10 + 10 + 10 + 30 – 10 – 10 = 70 • Production = net change in biomass + losses by mortality. • = 30 + 10 + 10 + 20 = 70

10. Production example: elephants • Life Table 26.1 • Can measure: • Food consumed, Egestion, Growth • Maintenance = Food – egestion – growth. • For energy dynamics of elephants: • Region has ~ 3125 kj/m2/yr in primary production • Consumed • 299 kj/m2/yr • Egestion • 168 (56%) • Maintenance • 130 (43%) • Growth • 1.44 (0.5%)

11. Problems in estimation secondary production. • Difficult to assign species to a specific trophic level: • a lot of omnivores out there • What about detritus? • Not eaten by herbivores • Often complex • Difficulty in sampling complex ecosystems.

12. Example: What do birds eat? • Plants: • Leaves, fruit, seeds • Animals: • Insects, rodents, fish • For North American Birds, what percent of species are strict carnivores (strict herbivores)?

14. Ecological Efficiency • Production efficiency = • Net productivity / assimilation • Or P/(R+P) • How efficient are animals? • Not very • Which animals are most efficient?

16. Trophic efficiency • The amount of energy transferred from one trophic level to the next.

17. Trophic efficiency: Example

18. Differences in ecosystems • How much net primary production goes to animal consumption? • Aquatic systems vs. terrestrial? • Tropical rain forest vs. temperate forest? • Is there a link to what is limiting NPP? • My hypothesis: Aquatic systems, particularly the ocean is limit by nutrients. When plants produce, immediately eaten.

19. How much net primary production goes to animal consumption? (in percent consumed) • Tropical rain forest 7% • Temperate deciduous forest 5% • Grassland 10% • Open Ocean 40% • Oceanic upwelling zones 35%

20. Deciduous Forest Example:

21. Deciduous Forest Example:

22. Deciduous Forest Example:

23. Percent of NPP removed by herbivores.

24. Ecological efficiency: Tropical forest. • When efficiency is low, organisms at the based of the food chain dominate. (an Eltonian pyramid)

25. What limits secondary production? • 2nd law of thermodynamics? • Process of energy conversion is never 100% efficient. • What else?

29. What limits secondary production?Example 1: NA Grasslands • Grasslands ~ 25% of earths land surface • NPP increases with precipitation. • Aboveground NPP ranges from 100 to 600 g dry weight/m2/yr. • (Most annual plants are ~90% water). • So 600g dry weight ~ 12 lbs of plant material.

35. What about below ground? • The above ground biomass for a tall grass prairie is about 1000 g/m2. This included living, dead and litter material. How much biomass is below ground?

36. General components of primary and secondary production in prairies. • Tallgrass • Shortgrass • What are the differences?

37. What are the differences between tallgrass and shortgrass praries? • In both prairies • Large animals not important energetically. • Nematodes are a major factor energetically. • They consume more than half of all plant tissue consumed. • Differences. • Shortgrass has less above ground NPP but almost as much below ground. • Less energy in nematodes in shortgrass prairie.

38. Test of grassland limitations • Observations: • Shortgrass has less above ground NPP but almost as much below ground. • Less energy in nematodes in shortgrass prairie. • Hypothesis: • Shortgrass above ground production could be limited by nematodes, soil water, or competition for water and light. • Experiment: • Add water and nitrogen to shortgrass prairie.

39. Test of grassland limitations • Results: • To increase NPP both water and nitrogen needed. • Nematode abundance increased by 4 fold. • Small mammal abundance increased. • Shortgrass prairie limited by both water and nitrogen.

40. Example 2: Are the animals that evolved in an ecosystem the most productive? • African ungulates

41. Example 2: Are the animals that evolved in an ecosystem the most productive? • Observations: • African ungulates are suited to particular ecosystems, thus should have a higher sustained yield than domesticated animals. • Hypothesis: • Wildlife areas will have higher production than managed areas.

42. Results: Taken from Table 26.5 Wildlife Pastoral

43. Why are cattle more productive? • One explanation depends on the differences between ecological and economic ideas of maximized production. • Or rather what are the differences between ecological and economic carrying capacity? • Ecology: Carrying capacity is the maximum sustainable population that can be supported by a given area. • Economic: Maximum sustained harvesting.

44. Is carrying capacity important when concerned about harvesting? • Remember logistic curves…. • When trying to achieve maximum harvest what are we interested in? • Reproductive rate, not K.

45. Comparison of agricultural vs. natural systems in SA. • Question: What systems are most productive, natural or agricultural systems? • Hypothesis: • Agricultural systems are more productive. • Methods: • Looked at 51 natural and 67 agricultural systems. • No additions, such as water or nutrients, i.e. “free range” cattle.

46. Comparison of agricultural vs. natural systems in SA. • Results: • Ag land more productive.

47. In summary: • Secondary production is very inefficient • Secondary production often limited by net primary production. • Don’t forget about the importance of below ground processes. • Agriculture typically more productive than natural systems. • Systems have different “goals”.