Energy Flow Through and Ecosystem

Energy in living systems Food chains, webs and pyramids, ultimately show energy flow Obey the laws of thermodynamics Obey systems laws – input, transfer, transformation, output

Thermodynamics Review Universal laws that govern all energy changes in the universe, from nuclear reactions to the buzzing of a bee. a)The 1 st law: Energy can be transferred and transformed but not created or destroyed -Energy flow in the biological world is unidirectional: –Sun energy enters system and replaces energy lost from heat –Energy at one trophic level is always less than the previous level

Thermodynamics Review (b) The 2 nd law: Energy transformations proceed spontaneously to convert matter from a more ordered, less stable form, to a less ordered, more stable form -Energy lost as heat from each level -Energy at one level less than previous because of these losses

Energy Flow in Communities Energy unlike matter does not recycle through a community it flows Energy comes from the sun Converted by autotrophs into glucose

Energy Flow in Communities Amount of Light energy converted into chemical energy by autotrophs in a given time period - Gross Primary Production GPP The amount to pass on to consumers after plants have used their share - Net Primary Production NPP NPP = GPP - R

The Source of All energy on Earth is the …

Figure 3-10 Page 52 Energy emitted from sun (Kcal/cm 2 /min) Wavelength (micrometers) Visible Light is The usable Energy

What is the sun? 72% hydrogen, 28% helium Temp and pressure high so H nuclei fuse to form He releasing energy Fusion energy radiated as electromagnetic energy Earth receives 1 billionth of the suns Energy Most reflected away or absorbed by atmospheric chemicals

Energy to Earth 30% solar energy reflected back into space by atmosphere, clouds, ice 20% absorbed by clouds & atmosphere 50% remaining –Warms troposphere and land –Evaporates and cycles water –Generates wind

Energy to Earth < 0.1% captured by producers for photosynthesis Energy eventually transformed to heat and trapped by atmosphere “Natural Greenhouse Effect” Eventually reradiated into space

So if sunlight in = sunlight + heat out What state is the system in? Stable Equilibrium

Summary of solar radiation pathways Incident radiation comes in, it is then… –Lost by reflection (ice caps) and absorption (soil, water bodies) –Converted from light to chemical energy (photosynthesis in producers) –Lost as chemical energy decreases through trophic levels –Through an ecosystem completely converted from light energy into heat –Reradiated as heat back to the atmosphere

Energy Flow II Energy measured in joules or kilojoules per unit area per unit time Energy conversion never 100% efficient Some energy lost as heat Of visible light reaching producers, only 1% is converted to chemical energy Other levels are 10% efficient – only assimilate %10 of energy from previous level

Figure 54.1 An overview of ecosystem dynamics

Energy Flow and Food webs Biomass = the total dry weight of all organisms in one trophic level Usable energy degraded with each transfer –Loss as heat, waste, metabolism

Energy Flow and Food webs % transferred = ecological efficiency  ranges from 5-20% More trophic levels = less energy available at high levels

If that loss happens at every trophic level think about how much energy is lost. Makes the lower trophic levels most efficient in terms of overall energy available in the system

Energy Flow through Producers Producers convert light energy into chemical energy of organic molecules Energy lost as cell respiration in producers then as heat elsewhere When consumers eat producers energy passes on to them In death organic matter passes to saprophytes & detritivores

Energy Flow through Consumers Obtain energy by eating producers or other consumers Energy transfer never above 20% efficient, usually between 10 – 20%

Energy Flow through Consumers Food ingested has multiple fates 1.Large portion used in cell respiration for meeting energy requirements (LOSS) 2.Smaller portion is assimilated used for growth, repair, reproduction 3.Smallest portion, undigested material excreted as waste (LOSS)

Figure Energy partitioning within a link of the food chain

Energy flow through Decomposers Some food is not digested by consumers so lost as feces to detritivores & saprophytes Energy eventually released by process of cell respiration or lost as heat

Construct and analyze energy flow diagrams for energy movement through ecosystems Trophic level boxes are storages – biomass per area (g m -2 ) Energy Flow in arrows – rate of energy transfer (g m -2 day -1 )

Energy values in KJ m -2 y -1 Often the size of the boxes and arrows is proportional to their amount