Chapter 55 Ecosystems

Energy Flow Energy flows through an ecosystem, while matter is recycled Law of conservation of mass – matter cannot be created or destroyed Two main processes occur in an ecosystem to transform energy and recycle matter: Photosynthesis: H2O + CO2 + Light energy  Glucose + O2 Cell respiration: Glucose + O2  H2O + CO2 + Energy (ATP)

Relationships Trophic levels - feeding relationships between organisms and an organisms position in that feeding relationship

Relationships Food chain – linear trophic level feeding pathway Food webs - interconnected feeding relationship in a community

Primary producers – trophic level that supports all others; autotrophs Convert light energy to chemical energy (glucose) Primary consumers – herbivores that eat primary producers Secondary consumers – carnivores that eat herbivores Tertiary consumers – carnivores that eat other carnivores Least amount of biomass Decomposers/Detritivores – special consumers that derive nutrition from non-living organic matter These organisms recycle the matter back to the soil for new primary producers to grow Ex: fungi, earthworms, bacteria, slugs, dung flies

Prior Knowledge: Know how to construct a food chain or web from a given list of organisms including correct direction of arrows connecting organisms Know how to label the trophic levels. Organisms may be included in more than one trophic level. Know the % energy transfer from one trophic level to the next and a reason why

Energy Flow NPP = GPP – Rs Primary productivity: amount of energy from light converted to chemical energy (organic molecules) by autotrophs Gross (GPP): total primary productivity energy in an ecosystem Net (NPP): represents the energy in the producer that is available to consumers (stored chemical energy) Gross primary productivity minus the energy used by the primary producer for respiration (Rs) NPP = GPP – Rs

Different ecosystem’s contribution to the Earth’s NPP

Factors affecting Primary Production in Aquatic Ecosystems Light limitation Depth of light penetration (photic zone) Increase in silt or sediment from deforestation up river

Factors affecting Primary Production in Aquatic Ecosystems Nutrient limitation – the element that must be added for production to increase Most often the limiting nutrient is nitrogen or phosphorous in marine ecosystems Areas of upwelling of nutrients in the ocean correspond to growth of phytoplankton and high primary production Nitrogen pollution can cause huge increases in algae in aquatic environments which can lead to eutrophication and a depletion of oxygen

Factors affecting Primary Production in Terrestrial Ecosystems Temperature and moisture are the main factors controlling primary production However just like in aquatic ecosystems, limiting nutrients such as nitrogen and phosphorous in the soil can affect primary production

Energy Flow Biomass: primary productivity reflected as total dry mass of all organic material (g/m²) Secondary productivity: amount of chemical energy in consumer’s food that is converted to new biomass How much energy from food contributes to the organism’s growth Most of the energy is lost as heat or released as waste for detritivores to breakdown

Trophic efficiency: % of energy transferred from one trophic level to the next (5-20%) In other words, 90% of the energy available at one trophic level is NOT transferred to the next Energy pyramid: loss of energy with each transfer in a food chain and is arranged in tiers Biomass pyramid: each tier represents the total dry mass for that trophic level (can be inverted) Numbers pyramid: each tier represents the number of individuals in that trophic level (can be inverted) Energy Flow

Chemical Cycling Biogeochemical cycles: the various nutrient circuits, which involve both abiotic and biotic components of an ecosystem Water, Carbon, Nitrogen, Phosphorus

Water Cycle Biological Importance: Key Processes: Essential for all organisms Availability influences the rates of ecosystem processes such as primary productivity and decomposition Key Processes: Evaporation and transpiration from plants, condensation of water vapor, precipitation, run-off into surface and groundwater

Carbon Cycle Biological Importance: Key Processes: Forms the framework of organic molecules essential for all life Key Processes: Photosynthesis removes CO2 from atmosphere, cellular respiration adds CO2, burning fossil fuels and wood adds CO2, volcanoes add CO2

Nitrogen Cycle Biological Importance: Key Processes: Part of amino acids, proteins, and nucleic acids and is often a limiting plant nutrient Key Processes: Nitrogen fixation by certain bacteria in legume plant roots converts N2 gas to a form plants can use, lightning and volcanic activity fix nitrogen naturally, humans add fertilizer (nitrogen) to soil, other bacteria convert nitrogen again in the soil (nitrites and nitrates), denitrification by certain bacteria converts nitrate to N2 gas, human also release large amounts of nitrogen oxides into the atmosphere

Phosphorous Cycle Biological Importance: Key Processes: Required for nucleic acids, phospholipids, and ATP as well as mineral component of bones and teeth Key Processes: Weathering of rocks adds PO4 to soil, gets into groundwater, P taken up by producers which are eaten by consumers, decomposition of biomass or excretion by consumers adds P back to soil or water

Human Impact Biomagnification: trophic process in which retained substances become more concentrated at higher levels DDT Video