ecosystems: interactions, energy and dynamics. ecosystem an open system (including the community of...
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Ecosystems: Interactions, Energy and Dynamics
Ecosystem• An open system (including the
community of living things and their non-living environment) through which energy flows
Energy flows throughout an ecosystem• Energy is transferred between
organisms (chemical energy)– Organic matter (food)
• At each step, some energy is lost as heat
Input into Ecosystem
• Solar radiation is the main input into all ecosystems
• Captured by photosynthetic organisms
Input into an Ecosystem
• Atmosphere filters most wavelengths of the EMS
• Optical “window” can get through the atmosphere(UVvisibleIR)
http://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
UV radiation• UVA (315-399 nm)
– Ozone layer cannot absorb– Ages skin
• UVB (280-314 nm)– Ozone layer can partially absorb– Damages DNA (forms DNA crosslinks),
can result in cell death or mutations– Causes sunburns– Ages skin– Stimulates vitamin D production
• UVC (100-279 nm)– Ozone layer completely absorbs
http://www.epa.gov/sunwise/doc/uvradiation.html
Activity: UV-sensitive yeast
• Yeast with a mutation in enzyme in UV damage repair pathway
https://www.phys.ksu.edu/gene/photos/solaruv.html
Results from Increased UV exposure• Increased susceptibility to disease, death– Disrupt development of very young
organisms (eggs, larva)– Dangerous during reproductive age (pass
mutations on to future generations)• Impairs photosynthesis and/or changes
flowering time of some plants• Disrupts organisms to different extent– Shift species composition of ecosystems
http://earthobservatory.nasa.gov/Features/UVB/uvb_radiation2.php
Causes of Increased UV exposure• Depletion of the ozone layer– Hole in ozone layer in the Antactic decreased
phytoplankton in surface water.• Huge impact on ocean food chains, carbon cycle (ocean
carbon storage)
• Loss of shade or protection from UV light– Loss of shade trees/ thick forests– Water bodies (shallower or clearer water cannot
filter as much UV)
Input into an Ecosystem
http://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
Absorbed vs Reflected Sunlight• Sunlight contains a range of visible
light wavelengths– What color is sunlight?
• If an object reflects a certain wavelength of visible light, it will look that color to your eye
• What if an object absorbs all visible wavelengths of light?
• What if an object reflects all visible wavelengths of light?
Activity: Calculating the Energy Flowing Through an Ecosystem
1. Measure the amount of incident (incoming) solar radiation.
Photosynthetic organisms
• Chlorophyll: family of pigments that absorb energy from specific wavelengths of light
Photosynthesis
• Photo: conversion of light energy into chemical energy (ATP)– Energy from light feeds into an electron transport
chain (in membranes of chloroplasts)• Synthesis: assembly of organic compounds– Carbon fixation: fixing carbon into organic
molecules
Photosynthesis2012 Pearson Education, Inc.
Energy traveling through the Ecosystem
• Solar radiation enters the ecosystem
• Photosynthetic organisms convert light into chemical energy (organic matter)
Activity: Calculating the Energy Flowing Through an Ecosystem
2. Complete an Ecosystem Energy Budget
Pyramid of Energy
• At each step, energy available to the organism in the next level drops off.
Pyramid of Energy
Grass
Mouse
Hawk
1 10 100 1000 10000 100000 1000000 10000000
Energy output (log scale)
Energy Output x 100 (kcal/m2/year)
Activity: Food Chains and Webs• Producers: Autotrophs– Organisms that can synthesize their own organic matter from
inorganic sources (CO2)– Photoautotrophs
• Use light as an energy source• Photosynthetic plants, algae
• Consumers: Heterotrophs– Organisms that require a supply of organic matter from their
environment– Chemoheterotrophs
• Use organic (or inorganic) compounds as an energy source
– Wide range of animals• Herbivores, carnivores, omnivores
– Primary consumers, secondary consumers, tertiary consumers, etc
Food Chains and Webs
• Decomposers: Saprophytes• Consume dead/decaying matter, convert it to inorganic substances
• Important for recycling key nutrients through the ecosystem• Bacteria, fungi
Food Chains and Webs
http://www.britannica.com
Searching for Food Sources (Foraging)
• Need to locate appropriate food sources, which may be difficult.
• Foraging Strategies– Specialist foragers (only one type of food source)• (ex) Giant panda
– Generalist foragers (multiple types of food sources)• (ex) human, raccoon
All food sources are not equal
• Size of food source• Nutritional value• Abundance of the food source• Energy used/inherent risk in
obtaining the food
Activity: Foraging
Ecological Succession
• Gradual changes in an ecosystem where populations succeed each other
• Usually plant-driven or plant-dominated, animal populations change in response
Ecological Succession
• Primary Succession– Colonization of bare ground • Sand dunes, volcano flows, mud flats, glacial till
• Secondary Succession– Replacement of a community after a disturbance• Disturbance may be natural or caused by humans• Abandoned fields, areas after a fire
Stages of Succession
• Recognizable stages, may be overlap or skip a stage, each can last variable time period
1. Pioneer stage– First colonizers
• Terrestrial: pioneer plants• Aquatic: plankton
2. Seral stages (may be more than one)– Each point in continuum has characteristic community of
species
3. Climax stage– Mature, self-sustaining stage
Ecological Succession
www.epa.gov/ecopage/upland/oak/oak94/proceedings/platt1.gif
Primary vs Secondary Succession
http://csls-text2.c.u-tokyo.ac.jp/inactive/12_03.html
Primary Succession
Example: Primary Succession on Mt. Hood in Oregon
• http://science.halleyhosting.com/sci/ibbio/ecology/notes/succ/primary.htm
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