Chapter 54 – Ecosystems

TJ Biology Olympiad

Cassandra Xia

Trophic structure – feeding systems

Divided into trophic levels- based on main source of nutrition

Primary Producers—autotrophs

-photoautotrophs

  • plants
  • phytoplankton (algae and bacteria)
  • multicellular algae and aquatic plants

-chemoautotrophic bacteria which oxidizes H2S

Primary Consumers—herbivores

-eat plants or algae

-Opportunistic – supplement diet with heterotrophic material if available (e.g. with eggs and hatchlings)

Secondary consumers

-carnivores that eat herbivores

Tertiary consumers

-carnivores that eat carnivores

Detritivores

-eat detritus (non-living organic material = feces, fallen leaves, dead organisms)

Gross primary productivity- the amount of light energy converted to chemical energy (organic compounds) by autotrophs of an ecosystem during a time period; the rate at which light energy is converted to chemical energy in an ecosystem

-not all stored as organic material because some used in cell respiration

-measured in g/m2/yr of dry weight or J/m2/yr

Net primary productivity- what is stored as organic material

-NPP = GPP – Respiration

-Available to consumers in the ecosystem

-NPP:GPP ratio smaller for large producers which have to support large stem and root systems

More on primary productivity

-Open ocean has low NPP by area, but contributes a lot to Earth’s NPP due to huge surface area

-Estuaries and reefs have high NPP by area, but contributes little to Earth’s NPP due to small suface area

-Tropical rain forest have high NPP by area, and contributes a lot to Earth’s NPP yay

-Limiting nutrient- the thing that must be added in order for production to increase in a particular area

  • usually nitrogen or phosphorus
  • sometimes light

Secondary Productivity- the rate at which an ecosystem’s consumers convert the chemical energy of the food they eat into their own new biomass

-Energy in a consumer is lost in:

  • Cell respiration
  • Feces
  • Growth (available energy for the next level)

-Carnivores are slightly more efficient at converting energy into biomass because meat is easier to digest. BUT animals unlike plants use up a lot of energy running around and stuff, so if all humans were to go vegetarian there would be enough food for everyone to eat

Ecological efficiency- percentage of energy transferred from one trophic level to the next (varies from 5% to 20% but use the “10% rule”)

Ecological pyramids

-Mostly all bottom-heavy

-Types:

  • Productivity pyramid
  • Pyramid of numbers
  • Biomass pyramid
  • Turnover time = Standing crop biomass (kg/m2) / Productivity (kg/m2/day)

Water Cycle

-Evaporation over the ocean, evapotranspiration over land

-Clouds rain over ocean and land

-Runoff and groundwater return to ocean (percolation through soil)

Carbon Cycle

-Photosynthesis and respiration have opposing effects on CO2 levels

-Because of the burning of locked away carbon in the form of fossil fuels, CO2 levels steadily increasing and contributing to the Greenhouse Effect

-CO2 levels have seasonal fluctuation:

  • Lowest during summer
  • Highest during winter
  • Why?

-In the ocean, it is more complicated:

  • The ocean has reactions between limestone(CaCO3), water, and CO2
  • H2O + CO2 <=> H2CO3

H2CO3 + CaCO3 <=> Ca(HCO3)2 <=> Ca2+

+ 2HCO3-

2HCO3- <=> 2H+ + 2CO32-

  • As CO2 is used for photosynthesis in marine environments, the first equation shifts to the left.
  • Some aquatic autotrophs can use HCO3-
  • The amount of carbon in the ocean is 50 times that in the atmosphere, the ocean may be an important carbon sink as carbon dioxide levels increase

Phosphorous Cycle

-Organisms need phosphorus for

  • Nucleic acids
  • Phospholipids
  • ATP
  • Bones & teeth

-Weathering of rocks adds phosphate to the soil

-Plants absorb phosphorus in the inorganic form of phosphate (PO43-)

-Consumers get it by eating plants

-Decomposers return it to the soil

-Also, phosphorus leaches into the water table, draining into the sea

-There it becomes incorporated into sedimentary rocks that may be part of a terrestrial ecosystem later in time

-Phosphates in the form of sewage and runoff fertilizer causes eutrophication in aquatic systems

Nitrogen Cycle- this is probably the most quizzed thing on the whole exam. A question on the nitrogen cycle is practically guaranteed. It is worth learning.

-Nitrogen is needed to build amino acids and therefore proteins.

-Nitrogen is the most abundant element in the Earth’s atmosphere, but it cannot be used by most organisms if it is in the form N2

-N2 is converted into more usable forms in three main ways

  • By nitrogen fixation- free-living soil bacteria, cyanobateria, and bacteria in root nodules of legumes converts N2 to NH3
  • Atmospheric deposition (lightning)- converts to NH4+ or NO3- which dissolves in rain and gets added to the soil
  • Industrial production of fertilizer

-Most soil is slightly acidic so NH3 produced by nitrogen fixation picks up an H+ and becomes NH4+

-Plants can absorb NH4+ but they can also absorb NO3-

-Nitrification by nitrifying bacteria converts NH4+ to NO3-

-Animals get their nitrogen by eating plants

-Cycle part:

  • Denitrification- denitrifying bacteria convert NO3- back to N2
  • Ammonification- bacterial and fungal decomposers convert organic nitrogen in plants and animals to NH4+

Decomposition rates depend on:

  • Temperature
  • Availability of H2O and O2
  • Soil chemistry
  • Fires

Long Term Ecological Research (LTER) at Hubbard Brook

-Forestlogged and herbicide sprayed

-Water runoff increased

-Ca2+ x 4 loss, K+ x 15 loss, NO3- x 60 loss

Environmental Hazards

Agriculture and Nitrogen Cycling

-Move nutrients from one area to another

-Nutrients lost through shipping agriculture and erosion

-Fertilizers must be added for “free period” (no need to add nutrients)

Toxins

-Many cannot be degraded by microorganisms

-Some compoundsmay be converted to toxins
e.g. Hg CH3—Hg
insoluble soluble, accumulates in tissues of fish and humans

-Chlorinated hydrocarbons (DDT and PCBs) are indicated in endrocrine disruption

-Undergo biological magnification- increased concentrations of toxins in successive trophic levels of a food web caused by eating toxins concentrated in the tissues of lower level organisms

  • DDT and DDE (product of partial breakdown) interfere with calcium deposition in egg shells of eagles, pelicans, and ospreys

Accelerated Eutrophication of Lakes

-Cultural eutrophication is eutrophication caused by humans. Sources of it include

  • Sewage
  • Factory wastes
  • Runoff of animal waste
  • Fertilizers

-Algae blooms

-Some algae die

-Decomposing bacteria use up O2

Carbon Dioxide and the Greenhouse Effect

-Greenhouse effect: gases absorb reradiate infrared radiation back at the earth, increasing temperature (without it, earth’s surface temperature would be -18° C)

-More CO2is being released by burning fossil fuels and is contributing to global warming

  • Melt polar ice
  • Alter precipitation patterns (central US drier)

-With more CO2, plants become more productive but the higher levels favorC3 plants (like wheat + soy) over C4 plants (like corn) causing C3 plants to spread into areas originally covered by C4 plants

Depletion of Atmospheric Ozone

-Chlorofluorocarbons (refrigerants) is a catalyst in the reaction O3→ O2

-Cold temperature over Antarctica facilitate reactions