Ecosystems

A. Introduction to Ecosystem Ecology

1. What is an ecosystem?

-aquarium

-ocean

2. How do ecosystems direct energy flow and recycle materials?

-review trophic levels in a community

-generalized model for energy flow and nutrient cycling

Points:

• autotrophs are primary producers
• energy supplied by the sun*
• energy flow is one way
• materials are recycled

B. Primary Production in Ecosystems

1. What is primary production?

2. How efficient are producers in converting solar energy to organic compounds?

3. What is the difference between gross (GPP) and net primary production (NPP)?

C. Secondary Production in Ecosystems

1. What is production efficiency? How does it vary between endo and ectotherms?

-caterpillar example

2. How efficient is energy transfer between trophic levels?

Ecological pyramids:

-NPP

-Biomass

-Numbers

D. Nutrient Cycling

1. Life on earth depends on recycling essential chemical elements

Biogeochemical cycles:

Global Cycling

Local Cycling

2. The Nitrogen Cycle

a. What is the most common form of nitrogen?

b. How does nitrogen enter an ecosystem?

-Rain and dust

example: epiphytic plants

-Nitrogen Fixation

example: legumes

N₂ --> NH₃ + H⁺ --> NH₄⁺

The Cycle

Points:

• nitrogen from atmosphere is fixed by prokaryotes
• NH₄ in soil is converted by nitrifying bacteria to NO₂^- and NO₃^-
• NO₃ is taken up by plant roots and also denitrified by bacteria back to N₂
• death of plants and animals returns some ammonia to the soil
• soil nitrogen limits plant growth:

in agriculture (crop rotation)

in nature (N₂ fixing trees)