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Food Webs and Energy Flow. Chapter 17. 1. What is a food chain? Ex: midwest deciduous forest & Artic & 1 other ecosystem. Gulf of Mexico: Osprey as top carnivore. Ex 2. Midwest. Ex 3. For each example, be able to list 2 – 3 food chains.

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1 what is a food chain ex midwest deciduous forest artic 1 other ecosystem l.jpg
1. What is a food chain? Ex: midwest deciduous forest & Artic & 1 other ecosystem.

  • Gulf of Mexico: Osprey as top carnivore


Ex 2 midwest l.jpg
Ex 2. Midwest Artic & 1 other ecosystem.


Ex 3 for each example be able to list 2 3 food chains l.jpg
Ex 3. For each example, be able to list 2 – 3 food chains.

  • Summerhayes and Elton studied feeding relations on Bear Island in High Arctic.

    • Primary producers were terrestrial plants and aquatic algae.

      • Fed on by several kinds of terrestrial and aquatic invertebrates.

        • Consumed by birds.

          • Attacked by arctic foxes.



2 what is a food web l.jpg
2.  What is a food web?  chains.

  • Make a food web for grasslands, using symbols provided in handout


3 describe each of the following trophic levels and give an example of each l.jpg
3.  Describe each of the following trophic levels  and give an example of each.

  • Trophic Level: Position in a food web determined by number of energy transfers from primary producers to current level:

    • Primary producers occupy first level. Autotrophic, energy from sun or chemicals.

    • Primary consumers occupy second level.

      • herbivores

    • Secondary consumers occupy third level.

      • Omnivore or carnivore

    • Tertiary consumers occupy fourth level.

      • Carnivore



5 keystone species l.jpg
5. Keystone Species used for?  Draw ex.

  • If keystone species reduce likelihood of competitive exclusion, their activities would increase the number of species that could coexist in communities.


5 keystone species10 l.jpg
5. Keystone species used for?  Draw ex.

  • A keystone species is a species that has a disproportionate effect on its environment relative to its abundance.

  • organism plays a role in its ecosystem that is analogous to the role of a keystone in an arch.

  • While the keystone feels the least pressure of any of the stones in an arch, the arch still collapses without it.

  • ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of biomass or productivity.


5 keystone example yellowstone nat park l.jpg
5. Keystone example – yellowstone Nat. Park used for?  Draw ex.

  • Before wolves after wolves

  • High coyote low coyote

  • High red fox low red fox

  • Low weasel several weasel sp.

  • Low rabbit higher rabbit

  • Low rodent more rodent species

    • (mice, rat)

  • High mule deer lower deer

  • High elk lower elk

  • Less diverse veg more diverse vegetation

  • Fewer hawks more hawks


Effects of predation by birds on herbivory l.jpg
Effects of Predation by Birds on Herbivory used for?  Draw ex.

  • Birds reduce densities of insect larvae feeding on dominant understory shrub.

    • Higher densities of insect larvae translated directly into higher levels of damage to shrubs.

  • Marquis and Whelan found higher densities of herbivorous insects on tress from which birds were excluded.


Effects of predation by birds on herbivory13 l.jpg
Effects of Predation by Birds on Herbivory used for?  Draw ex.

  • Atlegrim studied influence of birds on herbivorous insects and insect-induced plant damage.

    • Insectivorous birds may act as keystone species via effects on herbivorous insects.

      • Larval insect densities peak when many insectivorous birds are feeding their young.


Keystone species summation l.jpg
Keystone Species: Summation used for?  Draw ex.

  • Power :Keystone species exert strong effects on their community structure, despite low biomass.


6 consumers effects on local diversity l.jpg
6. Consumers’ Effects on Local Diversity used for?  Draw ex.

  • to resolve the effect herbivores have on plant diversity, you need to know:

    • Herbivore food preference.

    • Competitive relationships between plant species in the local community.

    • Variance in feeding preferences and competitive relationships across environments. (Lubchenko)



6 consumers effects on local diversity17 l.jpg
6. Consumers’ Effects on Local Diversity used for?  Draw ex.

  • When snails are present in high densities, Littorina grazes down Enteromorpha, releasing Chondrus from competition.

    • Green crabs (Carcinus maenus) prey on young snails, preventing juveniles from colonizing tide pools.

    • Populations of Carcinus are controlled by seagulls.

    • 1) Seagull --- green crabs --- algae species

    • 2) seagulls--- snails -----algae species


6 consumers effects on local diversity18 l.jpg
6. Consumers’ Effects on Local Diversity used for?  Draw ex.

  • Low snail density - Enteromorpha dominates tide pool.

  • Medium snail density - Competitive exclusion eliminated, and algal diversity increased.

  • High snail density - Feeding requirements are high enough that snails eat preferred algae and less-preferred algae.

    • Algal diversity decreased.


6 con t example consumers effects on local diversity l.jpg
6. Con’t Example: Consumers’ Effects on Local Diversity used for?  Draw ex.

  • Lubchenko studied influence of intertidal snail (Littorina littorea) on structure of an algal community.

    • Snails fed on green (Enteromorpha spp.) and red (Chondrus crispus) algae.

      • Under normal conditions, Enteromorpha out-competes Chondrus in tide pools, and Littornia prefers Enteromorpha.

        • In the absence of snails, Chondrus is competitively displaced.


7 exotic predators l.jpg
7. Exotic Predators used for?  Draw ex.

  • Exotic species have dramatic impacts on communities because they were outside the evolutionary experience of local prey populations.

    • Nile Perch (Lates nilotica) exotic fish predator in Lake Victoria.

      • Fish fauna dramatically reduced.

        Local examples: gobi, zebra mussels


7 exotic predators21 l.jpg
7. Exotic Predators used for?  Draw ex.

Species diversity decreased after nile perch introduced.


Exotic predators l.jpg
Exotic Predators used for?  Draw ex.

  • Kaufman pointed out changes in Lake Victoria fish community coincide with other ecosystem changes.

    • Dissolved oxygen concentrations significantly decreased.

    • Cultural eutrophication.


8 define terms associated with energy production and energy flow l.jpg
8. Define terms associated 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: Total amount of energy fixed by autotrophs.

      • Net primary production: Amount of energy leftover after autotrophs have met their metabolic needs.


9 what is aet how do ecosytems compare l.jpg
9. What is AET? How do ecosytems compare? energy flow.

  • annual actual evapotranspiration (AET).

    • AET: Annual amount of water that evaporates and transpires off a landscape.

      • Cold dry ecosystems tend to have low AET.

  • positive relationship between net primary production and AET.

    • east-west variation in primary production correlated with rainfall. (east = wetter)


9 con t l.jpg
9. Con’t energy flow.

  • Draw

  • Compare ecosystems


10 why do coral reefs and marine ecosytems have the highest primary productivity l.jpg
10.   Why do coral reefs and marine ecosytems have the highest primary productivity?

  • 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.


10 marine productivity con t l.jpg
10. Marine productivity con’t highest primary productivity?

  • Highest marine productivity.


10 con t terrestrial productivity l.jpg
10. Con’t terrestrial productivity. highest primary productivity?


10 con t grasslands l.jpg
10. Con’t grasslands highest primary productivity?

  • McNaughton estimated Serengeti grazers consume an average of 66% of annual primary production.

    • Rate of primary production in the Serengeti is positively correlated with rainfall quantity.

  • Found grazers can increase primary production.

    • Increased growth rate.

      • Lower respiration rate due to lower biomass.

      • Reduced self-shading.

      • Improved water balance due to reduced leaf area.


10 con t l.jpg
10. Con’t highest primary productivity?

  • Primary Production in the Serengeti


11 what is lindeman s efficiency concept l.jpg
11. What is Lindeman’s efficiency concept? highest primary productivity?

  • Lindeman concluded the ecosystem concept is fundamental to the study of energy transfer within an ecosystem.

    • Suggested grouping organisms within an ecosystem into trophic levels.

      • Each feeds on level immediately below.

        • As energy is transferred from one trophic level to another, energy is degraded.


12 calculate energy flow in an ecosystem l.jpg
12. Calculate Energy flow in an ecosystem highest primary productivity?

  • Gosz studied solar energy flow:

    • 15% reflected

    • 41% converted to heat

    • 42% absorbed during evapotranspiration

    • 2.2% fixed by plants as gross primary production

    • 1.2% used in plant respiration

    • 1% left for primary production


12 energy flow con t l.jpg
12. Energy flow con’t highest primary productivity?

  •    sun           

  • 30% reflected, 20% absorbed by atmosphere

  • 50% absorbed by ground, water or vegetation

  • 1% left for photosynthesis


Producer level l.jpg
Producer level highest primary productivity?

  •    Producer      ex 2.

  • 15,000 stored                     10,000 calories

  • 60% of 15,000 =9000 stored ____________

  • 40%  waste (6000)                    ____________  


Primary consumer l.jpg
primary consumer highest primary productivity?

  • 20% of 9000 = 1800 eaten              ____________

  • 10% stored = 180                            ____________

  • 90% lost = 620                                ____________


Secondary consumer l.jpg
secondary consumer highest primary productivity?

  • 30% of 180 = 54 cal       ____________

  • 10% stored = 5.4 cal ____________


Tertiary consumer l.jpg
  tertiary consumer  highest primary productivity?

  • 30% of 5.4 = 1.6  cal         ____________

  • 10% stored = .16           ____________


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