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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
1. What is a food chain? Ex: midwest deciduous forest & Artic & 1 other ecosystem.
  • Gulf of Mexico: Osprey as top carnivore
ex 3 for each example be able to list 2 3 food chains
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
2.  What is a food web? 
  • 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
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
5. Keystone Species
  • If keystone species reduce likelihood of competitive exclusion, their activities would increase the number of species that could coexist in communities.
5 keystone species10
5. Keystone species
  • 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
5. Keystone example – yellowstone Nat. Park
  • 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
Effects of Predation by Birds on Herbivory
  • 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
Effects of Predation by Birds on Herbivory
  • 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
Keystone Species: Summation
  • Power :Keystone species exert strong effects on their community structure, despite low biomass.
6 consumers effects on local diversity
6. Consumers’ Effects on Local Diversity
  • 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
6. Consumers’ Effects on Local Diversity
  • 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
6. Consumers’ Effects on Local Diversity
  • 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
6. Con’t Example: Consumers’ Effects on Local Diversity
  • 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
7. Exotic Predators
  • 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
7. Exotic Predators

Species diversity decreased after nile perch introduced.

exotic predators
Exotic Predators
  • 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
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
9. What is AET? How do ecosytems compare?
  • 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
9. Con’t
  • Draw
  • Compare ecosystems
10 why do coral reefs and marine ecosytems have the highest primary productivity
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
10. Marine productivity con’t
  • Highest marine productivity.
10 con t grasslands
10. Con’t grasslands
  • 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
10. Con’t
  • Primary Production in the Serengeti
11 what is lindeman s efficiency concept
11. What is Lindeman’s efficiency concept?
  • 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
12. Calculate Energy flow in an ecosystem
  • 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
12. Energy flow con’t
  •    sun           
  • 30% reflected, 20% absorbed by atmosphere
  • 50% absorbed by ground, water or vegetation
  • 1% left for photosynthesis
producer level
Producer level
  •    Producer      ex 2.
  • 15,000 stored                     10,000 calories
  • 60% of 15,000 =9000 stored ____________
  • 40%  waste (6000)                    ____________  
primary consumer
primary consumer
  • 20% of 9000 = 1800 eaten              ____________
  • 10% stored = 180                            ____________
  • 90% lost = 620                                ____________
secondary consumer
secondary consumer
  • 30% of 180 = 54 cal       ____________
  • 10% stored = 5.4 cal ____________
tertiary consumer
  tertiary consumer 
  • 30% of 5.4 = 1.6  cal         ____________
  • 10% stored = .16           ____________
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