Ecosystems Chapter 54

Ecosystem involves all abiotic and biotic factors in area. Trophic levels - groups in which organisms are placed according to eating patterns. Ecosystems - involve nutrient cycles.

Autotrophs - self-feeders (usually photosynthesize) -primary producers They use light to make sugars, other chemicals necessary for life.

Heterotrophs - rely on organisms for food. Herbivores – eat primary producers (primary consumers) Carnivores - eat primary consumers (secondary consumers) Tertiary consumers - eat secondary consumers.

Detritivores - decomposers - break down detritus (dead organic matter left after organism dies) Organic matter must be recycled in ecosystem. Biggest decomposers - fungi and prokaryotes (secrete enzymes to break down dead material)

Primary production - amount of light that can be converted to energy in a given time. All contributes to energy budget in an area (determines how much energy available to ecosystem)

Gross primary productivity - amount of light energy converted to chemical energy. Net primary productivity - gross productivity minus amount of energy used by primary producers for respiration (amount of energy left over)

Primary production - expressed in terms of biomass (amount of vegetation added to ecosystem per unit area per unit time) Each ecosystem different amount of biomass.

Oceans - amount of light to hit ocean floor contributes biomass. Light can only go to certain level; primary productivity of area may be lower in deeper oceans.

Primary Productivity Map

Nutrients also contribute to biomass in aquatic areas. Nitrogen - plant growth (can be limited in water) Water pollution adds nutrients to water (eutrophication) Shifts organisms living in water and is a negative impact of humans.

Eutrophication of lake

Land areas - temperature and water availability also determines primary productivity. Minerals in soil can affect production as well.

Efficiency between trophic levels is at best 20%. Transfer from one level to next is only 20% of energy from level before.

Biomass pyramids show transformations between trophic levels. Differ dramatically between ecosystems.

Nutrient cycling involves abiotic and biotic factors (biogeochemical cycling) Water cycling physical cycle and not chemical; not considered biogeochemical cycle, but still essential to ecosystem.

Carbon cycle is a biogeochemical cycle.

Nitrogen enters an ecosystem in 2 ways. Added to soil in usable form. Can also enter through nitrogen fixation - prokaryotes convert nitrogen into usable organic compounds like amino acids.

Product of nitrogen fixation is ammonia. Ammonia picks up H + in soil to become ammonium (ammonification) Plants can use this nitrogen. Aerobic bacteria can turn ammonium into a nitrate (nitrification)

Nitrates - used by plants. In final step, other bacteria use oxygen from nitrates and release N 2 back into atmosphere (denitrification)

Phosphorus occurs only in phosphate - plants absorb and use to make organic nutrients. Does not come from atmosphere. Recycling of phosphorus is usually confined to specific areas.

Rate of decomposition determines rate of chemical cycling. Tundra - decomposition can take years; rain forest - decomposition takes much less time.

Humans affect rate of chemical cycling due to habits. Farmers - disturb crop areas by removing nutrients in soil. Humans - add fertilizers to soil which disrupt chemical balances. Chemicals can enter water, disrupting animals that live there.

Burning of fossil fuels - major contributors to nutrients in atmosphere. Sulfur and nitrogen placed into atmosphere change into acid precipitation.

Acid precipitation

Acid precipitation can alter pH of soil and alter the vegetation that lives there.

Poisonous materials also added to our soils and water. Further up food chain, more organism is affected by chemicals. DDT (a pesticide) damaged birds and fish when it met with water.

Amount of carbon dioxide in atmosphere has been rising for decades. Carbon dioxide helps to keep in heat that would normally escape atmosphere (greenhouse effect)

Ozone layer is thinning as a result of fossil fuels. Ozone protects humans from UV rays.