ECOSYSTEMS

A. INTRODUCTION

Ecosystem: a community of plants and animals (biotic component) and their non-living physical environment (abiotic component)

Biotic components: producers (autotrophs) consumers (heterotrophs) decomposers

Abiotic components: sunlight soil water air nutrients

Ecosystem components linked by various functions related to:

• productivity and energy cycling

• sequences of consumption

• nutrient cycling

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B. ECOSYSTEM PRODUCTIVITY

Autotrophs

• organisms that can create their own nourishment from inorganic compounds with the aid of an external source of energy

Photosynthesis

• CO₂ + H₂O + sunlight CH₂O + O₂

• carbon dioxide + liquid water + sunlight carbohydrate + oxygen

• sunlight provides source of energy

• gross primary productivity: total energy produced by photosynthesis; the gain of carbon stored in living organisms

Respiration

• consumption of carbohydrates to maintain physiologic functions

• loss of carbon

Net primary productivity

• gross primary productivity - respiration

• carbohydrates contributing to plant growth; measure of organic matter available for consumers (heterotrophs)

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

• plants comprise majority of biomass in any ecosystem

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

Limiting factors:

• temperature

• moisture

• sunlight

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

Impact of global warming on NPP

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

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C. FOOD CHAINS & FOOD WEBS

Producers

Consumers

• primary consumers: herbivores

• secondary consumers: carnivores & omnivores

• tertiary consumers: top carnivores

• scavengers

• decomposers

Trophic level: level of an organism within a food chain

• not all consumed energy goes towards tissue gain or towards maintenance

• significant energy loss at each higher trophic level

Sequences of consumption

• food chain: simple sequence of consumption; one or very few sources of food for organisms

• food web: complex sequence of consumption; 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

  • extinction and extirpation

  • introduced (invasive) species

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D. NUTRIENT CYCLING

Major nutrients

• O, C, H, N, Ca, K, Mg

• nutrients cycle through biotic & abiotic components of ecosystems

Abiotic sources of nutrients

• weathering of soil parent material

• atmosphere

Biotic sources of nutrients

• legumes: symbiotic relationship between plant roots and nitrogen fixing bacteria

• decomposition of dead organic matter

Carbon cycle

• atmosphere - gas

• oceans - dissolved gas & marine shells

• lithosphere - sedimentary rocks & fossil fuels

• organic matter in soil

• organic matter in living & dead organisms

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E. SUMMARY

• Ecosystems: communities of plants & animals & their non-living physical environment

• Energy is added to ecosystems through photosynthesis, which is partially dependent on solar radiation

  • Net primary productivity: a measure of energy available for consumption

  • limiting factors: temperature, moisture, sunlight

• Energy is lost at every step of the food chain/web

• Nutrients: essential for all organisms in addition to energy

• cycle through the biotic & abiotic components of ecosystems