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