Ecosystems: Decomposers and Pop. Size

• Generally microorganisms
• Secrete enzymes onto dead and waste material
• Enzymes break down material
• Molecules are absorbed into the organism
• Once absorbed, molecules are stored to be respired in order to release energy

Nitrogen Fixation

• Nitrogen is highly unreactive so needs to be fixed for plants to utilise it.
• Bacteria such as Rhizobium live within root nodules of bean plants.
• The bacteria supply the plant with fixed nitrogen in exchange for carbon (mutualistic relationship)

Nitrification

• Occurs once chemoautotrophic bacteria absorb ammonium ions.
• These bacteria gain energy from absorbing by oxidising ammonium ions to nitrates or nitrites to nitrates.

Denitrification

• Some bacteria convert nitrates into nitrogen gas.
• Occurs in anaerobic conditions- bacteria use nitrates as a source of oxygen, releasing nitrogen gas nitrous oxide.

Lag phase

• Only a few individuals.
• Still adjusting to a new habitat.
• Rate of reproduction is slow.

Log phase

• Individuals have adapted to habitat.
• Resources are plentiful and competetion is minimal.
• Reproduction exceeds mortality.
• Population size is rapidly increaseing.

Stationary phase

• Population has levelled out.
• This is the carrying capacity.
• The habitat can't maintain a higher population.
• Reproduction and mortality rates are equal.
• Population size remains fairly constant.

Biotic Factors

• Factors that are related to living things such as:
• Competition, both interdependent and intradependent
• Predation

Abiotic Factors

• Factors that are not related to living things:
• Availabity of water or food
• Disease
• Extreme, freak weather

Population of both predator and prey size often follows a pattern similar to:

• Predator population increases
• Demand for prey increases from the predator
• Prey population decreases as a result of predation
• Predator has less prey for food so competition increases
• With increased competition, predator populaton decreases
• As a result of decreased predator population, prey population increases
• With an increase in prey the predator population increases
• The cycle starts again