An ecological pyramid is a chart representing the trophic level numbers within an ecosystem. The producer level is always at the base of the pyramid with the consumer levels above.

Common types of pyramids:

• Energy pyramids compare the total amount of energy available in each trophic level.
• Biomass pyramids compare the total dry weight of the organisms in each trophic level.
• Numbers pyramids compare the number of individuals in each trophic level. Normal
  Inverted

 
The total of all species populations inhabiting the same area forms a community. A community can be any natural biotic unit, regardless of size.

Communities are not static; they respond to environmental disturbances both slowly or quickly.

• Through evolutionary changes, species within an community can adapt over a long period of time.
   
• Through successional changes, communities within an ecosystem can adapt over a relatively short period of time.
   
  • Ecosystem Resistance - the capacity of an ecosystem to remain relatively unchanged when confronted by a disturbance.
     
  • Ecosystem Resilience - the speed at which an ecosystem returns to its former state following a disturbance.

 
Ecological succession is a progression of communities appearing on a site over time. Each of these communities has its own dominant plant species and animals that depend on them.

• Young communities quickly accumulate biomass, causing rapid change.
   
• Climax communities are relatively stable and will remain basically unchanged for hundreds of years, if not disturbed.

• Primary succession is a slow process because the physical environment must be modified by the community to produce soil.
   
• Pioneering plants are the first to grow in a disturbed area. They are usually short, fast growing plants that produce large numbers of seeds.
   
• Soil building is primarily a biological process as dead organic matter increases the amounts of nutrients in the soil. As the depth and richness of the soil increases, larger plants are able to grow.

 
Succession also occurs In Ponds.

 
Biogeochemical Cycles: the process by which abiotic materials move from the atmosphere or soil into organisms and back again.

Unlike energy, chemical materials called nutrients move in cycles within an ecosystem. These cycles are homeostatic (self-regulating) systems. Under normal conditions, if one part of the cycle becomes overloaded, another part of the cycle will become more or less active to relieve the stress in the cycle. Both energy flow and nutrient cycling are important factors determining the success of an ecosystem.

 
The Nitrogen Cycle: converts atmospheric nitrogen, N₂ , into a form plants and animals can use.

Nitrogen makes up about 78% of the atmosphere. However, most living things cannot use atmospheric nitrogen and must rely on nitrates (NO₃⁻) and nitrites (NO₂⁻) in the soil.

Steps of the Nitrogen Cycle:

1. Nitrogen fixation - nitrogen-fixing bacteria, primarily living on the roots of legumes, convert nitrogen gas into NH₄OH.
    
2. Ammonification - bacteria decomposers break down amino acids from dead animals and animal wastes into NH₄OH.
    
3. Nitrification - chemosynthetic bacteria oxidize NH₄OH to produce nitrates and nitrites.

   The energy of lightning also causes atmospheric oxygen and nitrogen to combine to form nitrate ions.
    

4. Denitrification - anaerobic bacteria break down nitrates, releasing N₂ back into the atmosphere.

 
Carbon-Oxygen Cycle: is the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth.

The "Short" Carbon Cycle:

• Photosynthesis removes CO₂ from the air and adds O₂.
   
• Cellular respiration removes O₂ from the air and adds CO₂.
   
• Photosynthesis and respiration usually balance out.
   
• Decomposers break down organic material releasing CO₂.

• Coal, oil, and natural gas are the remains of prehistoric plants and animals.
   
• This energy from the Sun has been locked away for millions of years.
   
• By burning fossil fuels, we are releasing the carbon back into the atmosphere, in effect recreating the hot, steamy world of millions of years ago.