An ecosystem is a relatively closed system (more or less isolated from other ecosystems) whose limits are defined by two major processes, Energy Flow and Bio-Geo-Chemical Cycling. It consists of all the organisms (individuals, populations, communities), resources and abiotic conditions co-existing within a geographical area.

An ecosystem is the most inclusive, and usually the largest, of all ecological concepts. Ecosystems range in scale from small systems like ponds, small islands or mountain tops; through regional systems like the Serengeti Plains of Africa; up to the scale of the whole earth (or biosphere).

Properties of Ecosystems: These primarily build on and extend aspects of the trophic structure and trophic organization of the communities within the ecosystem.

There are several similar ways to describe the role of each individual, population or species within an ecosystem:

Producer: synthesizes new living tissues

Consumer: eats (or metabolizing) tissues

Decomposer: breaks tissues and/or biological molecules into inorganic materials.

Autotroph: fixes energy from abiotic sources.

Photo-autotroph: fixes solar energy (via photosynthesis) into organic molecules

Chemo-autotroph: uses chemical energy from inorganic molecules

Heterotroph: obtains energy by consuming and metabolizing organic molecules from

other organisms (i.e. all consumers and decomposers)

Plant: Uses inorganic nutrients, solar energy

Herbivore: Eats plant tissues

Carnivore (Predator): Eats animal tissues

Detritivore: Eats dead animal/plant tissues

Energy flow is a directional, irreversible process. However, the rate and timing of energy transfers are highly variable as a result of physiological and ecological processes. It is also inefficient, with

large amounts of energy radiated into space as heat at each step in the process:

Photo-autotrophic: sun è biotic (è abiotic ) è space

Chemo-autotrophic: abiotic è biotic (è abiotic ) è space

Productivity is the process by which energy (or carbon) is incorporated within the organic molecules of new living tissues. It is a Rate, measured in such units as: J m^-2 d^-1 or gC m^-2 d^-1

In analogous ways, Gross and Net Secondary Productivity measure the rates at which herbivores convert plant tissues into animal molecules and tissues; Gross and Net Tertiary Productivity measure the rates at which carnivores convert herbivore tissues; etc.

At each transfer between trophic levels, approximately 90% of the energy consumed is lost, mainly as heat during respiration. Hence energetic efficiency, measuring the proportion of energy at one trophic level than is retained in new production at the next trophic level averages about 10% (5% to 20%). The efficiency is lowest in decomposer transfers where vast amounts of heat are lost as organic molecules are broken into simple inorganic molecules.

Standing Crop or Biomass is used to measure the accumulated products of production present at each trophic level at a specified instant. Biomass is the total mass of tissue, usually expressed as dry weight ( e.g. g m^-2 ) or total carbon (e.g. gC m^-2 ). Changes in biomass equals NPP - NRR.

These pyramids may vary in form depending on turnover rate (average longevity and other LHC), efficiency of transfer, species composition and diversity, and recent history of each trophic level. Inverted pyramids indicate that turnover rate slows markedly as one moves up trophic levels

In accord with the Law of Conservation of Matter (atoms can be transformed in chemical reactions, but not created nor destroyed), materials remain within closed ecosystems, but may be cycled back and forth within and between the biotic and abiotic components of the ecosystem.

(abiotic ç è abiotic) ç è (biotic ç è biotic)

Biogeochemical cycling has up to five main compartments (Campbell Fig 49- 8)

Biogeochemical cycling is usually studied by concentrating on a single element or molecule, and following its chemical pathways within and between through the abiotic and biotic components. A particular cycle may not include all the components, and the rates, frequencies and forms of the pathways vary greatly for different elements, and among different kinds of ecosystems. Within each component the nutrient may be available or unavailable for use by the organisms

Ecosystem studies usually focus on essential or limiting nutrients, those that set upper limits on standing crop and productivity at each trophic level. Different nutrients have very different availabilities, recycling rates, and residence times within the biosphere

Water Cycle: (Campbell: Fig 49- 9)

Carbon Cycle: (Campbell: Fig 49- 10)

Oxygen Cycle: (usually treated as a subset of the carbon cycle)

Nitrogen Cycle: (Campbell: Fig 49- 11)

Phosphorus Cycle: (Campbell: Fig 49- 12)

Bio-Accumulation or Bio-Magnification: (Campbell: Fig 49- 16)

Carbon Dioxide Cycle: (Campbell: Fig 49- 17)