LG 3 Energy Flow and Nutrient Cycling in Ecosystems Food Web Categories Grazing Food Web - Detrital Food Web - Sunlight and Ecosystem Productivity Gross Primary Productivity - Net Primary Productivity - Biomass - Variation in Primary Productivity - Energy Transfer Through Ecosystems Secondary Productivity - Ecological Efficiency - Ecological Pyramids - Biogeochemical Cycles The Hydrologic Cycle - The Carbon Cycle - The Nitrogen Cycle - The Phosphorus Cycle -
Transcript
LG 3Energy Flow and Nutrient Cycling in
EcosystemsFood Web Categories
Grazing Food Web -
Detrital Food Web -
Sunlight and Ecosystem Productivity
Gross Primary Productivity -
Net Primary Productivity -
Biomass -
Variation in Primary Productivity -
Energy Transfer Through Ecosystems
Secondary Productivity -
Ecological Efficiency -
Ecological Pyramids -
Biogeochemical Cycles
The Hydrologic Cycle -
The Carbon Cycle -
The Nitrogen Cycle -
The Phosphorus Cycle -
Ecology
Learning Goal ThreeTrace the flow of energy and the
cycling of nutrients through ecosystems.
Food Web Categories
• Grazing Food Web
Includes the producer, herbivore, and carnivore trophic levels.
• Detrital Food Web
Includes detritivores and decomposers.
Sunlight and Ecosystem Productivity
• Gross Primary ProductivityThe rate at which producers convert solar energy
into chemical energy in an ecosystem• Net Primary Productivity
Chemical energy that remains after producers use energy for their own maintenance.• Biomass
A measure of the dry weight of biological material per unit area or volume of habitat. Used by ecologists to measure primary productivity.
Variation in Primary Productivity• Factors that influence primary
productivitySunlight/Temperature – Areas with most sunlight and fairly constant year round temperatures generally exhibit high primary productivity, like at the equator.Water – Adequate water is also required.Limiting Nutrients – Any element in short supply that is needed by producers, ie., phosphorus, nitrogen, etc.
Energy Transfer Through Ecosystems
• Secondary ProductivityAs energy is transferred from
producers to consumers, some is stored as consumer biomass.• Ecological Efficiency
Ratio of net productivity at one trophic level
to net productivity at the trophic level below it.
Ecological Pyramids
• Pyramid of Energy
A depiction of the available energy at
each trophic level.
Only about 10% of the energy of each trophic level is stored in the tissues of the next level. 90% is generated as
heat from biological processes.
• Pyramid of Biomass
Depicts the progressive reduction in productivity at higher trophic levels.
• Pyramid of Numbers
Depicts the relatively low numbers of organisms at the tip of an ecological pyramid
Biogeochemical Cycles
• Earth is a closed system.
Energy vs Matter
Unlike energy which has a constant cosmic input, Earth is a closed system with respect to matter. Matter is recycled between the Earth and living organisms through a series of biogeochemical cycles.
The Hydrologic Cycle
• Water molecules move from the atmosphere to land, eventually ending up in the ocean where they evaporate back into the atmosphere. Some evaporates from soil and from plants through a process known as transpiration.
The Carbon Cycle
• Carbon enters food webs through the process of photosynthesis as green plants convert atmospheric carbon dioxide into carbohydrates.
• Heterotrophs acquire their carbon compounds by eating plants and/or other consumers.
• Carbon dioxide reenters the atmosphere by the process of respiration from both plants, animals, and other organisms.
The Nitrogen Cycle
• Nitrogen is required by organisms for important biological molecules like nucleic acids and proteins.
• Approximately 70% of the Earth’s atmospheric gases consist of nitrogen but it cannot be used by organisms in this form
• Nitrogen Fixation
Molecular nitrogen (N2 ) is converted into ammonia (NH3 ) by certain types of bacteria. Legumes (beans, alfalfa) contain root nodules that harbor nitrogen-fixing bacteria in a mutualistic relationship.
• AmmonificationSome types of
bacteria and fungi convert organic nitrogen compounds into ammonia as they break down detritus.
• NitrificationOther types of
bacteria convert nitrogen compounds into nitrites and nitrates which are also usable by plants.
• Denitrification
Yet other types of bacteria convert nitrites and nitrates back into atmospheric nitrogen, thus completing the cycle.
The Phosphorus Cycle• The phosphorus cycle is the only
biogeochemical cycle that does not have a gaseous phase
• Phosphorus compounds stored in the Earth’s crust are released into soil through the process of erosion.
• Plants take in phosphate ions and use them to produce DNA and other important molecules.
• Consumers get their phosphorus from what they eat.
• Phosphates are returned to the soil in animal waste products and through the process of decompostion.
