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Lecture 23: Secondary Production. EEES 3050. Secondary Production. Last week: looked at primary production – Today: Where does the energy/nutrients from primary production go? Consumed Growth Decay Respiration Egestion Definition:

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Lecture 23: Secondary Production

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Lecture 23 secondary production l.jpg

Lecture 23: Secondary Production

EEES 3050


Secondary production l.jpg

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.


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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


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Measures of secondary production

  • Metabolic rate (Assimilation rate) =

    • Respiration + Net productivity.

  • Laboratory: fairly easy to measure.

    • Measure oxygen consumption, CO2 output, calories consumed, etc.


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  • 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.


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What are the metabolic rates for different taxonomic groups?


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Measures of secondary production

  • Can analyze changes in biomass over time.

    • Production =

      • growth + natality

    • Or

    • Production =

      • net change in biomass + losses by mortality.


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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


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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%)


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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.


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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)?


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Ecological Efficiency

  • Production efficiency =

    • Net productivity / assimilation

    • Or P/(R+P)

  • How efficient are animals?

    • Not very

  • Which animals are most efficient?


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Trophic efficiency

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


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Trophic efficiency: Example


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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.


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  • How much net primary production goes to animal consumption? (in percent consumed)

    • Tropical rain forest7%

    • Temperate deciduous forest5%

    • Grassland10%

    • Open Ocean40%

    • Oceanic upwelling zones 35%


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Deciduous Forest Example:


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Deciduous Forest Example:


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Deciduous Forest Example:


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Percent of NPP removed by herbivores.


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Ecological efficiency: Tropical forest.

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


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What limits secondary production?

  • 2nd law of thermodynamics?

    • Process of energy conversion is never 100% efficient.

  • What else?


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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.


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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?


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  • General components of primary and secondary production in prairies.

  • Tallgrass

  • Shortgrass

  • What are the differences?


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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.


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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.


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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.


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Example 2: Are the animals that evolved in an ecosystem the most productive?

  • African ungulates


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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.


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Results: Taken from Table 26.5

Wildlife

Pastoral


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  • 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.


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  • 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.


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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.


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Comparison of agricultural vs. natural systems in SA.

  • Results:

  • Ag land more productive.


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  • 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”.


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