Lecture 31: Energy, Nutrients and Food webs

1. What is a community?

 

 

2. Species interactions in communities

a. Interactions are more complex, multiple species at different trophic (feeding)

levels è Food web. (Fig. 54.1, 54.2)

b. Levels

i. decomposers

ii. plants parasites

iii. herbivores

iv. carnivores (may be several levels of these) pathogens

c. Simultaneous interactions

i. Within levels-- competition
    1. between levels -- consumption (e.g., predation, parasitism, disease)

d. Interactions may be complex, removals (or additions) may have surprising

results

i. "trickle down effects"

-- how did attempts to control mosquitoes lead to houses falling

down and outbreaks of plague??

 

3) Communities and their physical environment are linked to form an ecosystem

Biotic and abiotic aspects of the environment are linked in ways that control

flow of energy and cycling of nutrients and water

 

4) What cycles and what doesn't?

5) Energy flows (see Figs. 54.4, 54.5)

a) Primary producers (plants) capture sun's energy in photosynthesis

i. Energy flows through the food web -- some lost at every level by metabolism (i.e., as heat).

b) Food webs in different environments look different, but all have common elements:

    1. decomposers and detritivores,
    2. primary producers (plants) herbivore,
    3. Consumers (carnivores).

c) Productivity, energy and biomass are highest at the lowest levels in the web, decline up the web–pyramids.

6) Nutrient cycles: carbon, nitrogen, phosphorous etc. are continually recycled on earth

    1. Carbon-- carbon chains are backbone of all organic molecules (Fig. 54.10).

      2. i. Captured ("fixed") by plants--Transferred up through food web

       

    2. Nitrogen -- crucial element in proteins (see 54.11)
    1. N2 in air fixed by nitrogen fixing bacteria in legume roots and soil
    2. Converted to proteins that go through the food web

 

iii. Decomposers eventually break dead organisms and waste products

down into N2 (don't worry about complex series of steps)

 

7) Hydrological cycles: Water-we all need it (54.9).

 

 

 

We really ARE all on this earth together-- hard to alter the earth without having huge, possibly irreparable effects.