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ECOSYSTEMS

A. INTRODUCTION

Biogeography

        Biome: a large assemblage of ecosystems with similar characteristics

        Ecosystem: a community of plants and animals and their non-living physical environment

        Ecosystem components linked by functions related to:

• productivity and energy cycling

• sequences of consumption

• nutrient cycling

B. ECOSYSTEM PRODUCTIVITY

Autotrophs

• organisms that synthesize organic matter from inorganic matter with aid from an external energy source (usually sunlight)

Photosynthesis

• CO₂ + H₂O + sunlight CH₂O + O₂

• carbon dioxide + liquid water + sunlight carbohydrate + oxygen

• gross primary productivity: total energy produced by photosynthesis

Respiration

• consumption of carbohydrates to maintain physiologic functions

Net Primary Productivity

• gross primary productivity - respiration

• carbohydrates contributing to plant growth; amount organic matter available for consumers

• biomass: mass of organisms per unit area; g/m²/year

• plants comprise majority of biomass in any ecosystem

• geographic patterns to NPP

June NPP

December NPP Image credit: NASA Earth Observatory (2003) NASA satellite measures earth’s carbon metabolism. http://earthobservatory.nasa.gov/Newsroom/NPP/npp.html

• geographic patterns to limiting factors

Image credit: NASA Earth Observatory (2003) Global garden gets greener. http://eobglossary.gsfc.nasa.gov/Study/GlobalGarden/

C. SEQUENCES OF CONSUMPTION

Producers

Consumers

primary consumers: herbivores



secondary consumers: carnivores & omnivores



tertiary consumers: top carnivore



scavengers

Decomposers

Trophic level

• level of an organism within a sequence of consumption

• significant energy loss at each higher trophic level

• food chain: one or very few sources of food for organism

• food web: multiple food sources for organisms

• keystone species: a principle consumer of food within a food web or a principle supplier of food within a food web

  • loss of keystone species may have far-ranging consequences

D. NUTRIENT CYCLING

Major Nutrients

O, C, H, N, Ca, K, Mg



nutrients cycle through biotic & abiotic components of ecosystems



nutrient sources



• weathering of soil parent material
  
  
• atmosphere
  
  
• legumes: symbiotic relationship between plant roots and nitrogen fixing bacteria
  
  
• decomposition of dead organic matter

Carbon Cycle (p. 294)

• atmosphere - gas
  
  
• oceans - dissolved gas & marine shells
  
  
• lithosphere - sedimentary rocks & fossil fuels
  
  
• biosphere: organic matter in soil, and living & dead organisms
  
  

E. SUMMARY

• Ecosystems: communities of interacting biotic and abiotic components

• Photosynthesis adds energy ecosystems

• Net primary productivity indicates amount energy available for consumption

  • limited by temperature, moisture, solar radiation

  • available energy decreases as trophic level increases

• Nutrients: essential for all organisms in addition to energy

  • cycle through the biotic & abiotic components of ecosystems