Chapter 3 Notes
Sept 24, 2013
Chapter 3: Environmental Systems & Ecosystem Ecology
Earth's systems include cycles that shape the landscapes around us & guide the flow of key chemical
elements & compounds that support life & regulate climate.
Cycles: Flows of elements, compounds, and energy from reservoir to reservoir through the Earth’s
Systems are networks of relationships
A system is a network of relationships among parts, elements, or components that interact w/ &
influence one another through the exchange of energy, matter, or info.
Systems receive inputs of energy, matter or info, process these inputs & produce outputs.
Open Systems: systems that receive inputs of both energy & matter & produce outputs of both.
Closed Systems: systems that receive inputs of both energy & matter & produce outputs of energy
but not matter. Matter cycles among the various parts of the system but doesn't leave or enter the
Energy inputs to Earth's env systems include: solar radiation, heat released by geo-thermal activity,
organismal metabolism & human activities such as fossil fuel combustion.
Info inputs can come in the form of sensory cues from visual, chemical, magnetic or thermal signals.
Inputs of matter occur when chemicals or physical material moves among systems, such as when
seeds are dispersed long distances or migratory animals deposit waste far from where they consumed
Feedbacks are common in env systems
Feedback Loop: a circular process in which a system's output serves as input to that same system.
Negative feedback loop: a feedback cycle in which output of 1 type acts as input that moves the
system in the opposite direction. The input & output essentially neutralize each other's effects,
stabilizing the system. Ex: N.F regulates our body temp. If we get too hot, our sweat glands pump out
moisture that evaporates to cool us down or move to a shady place. If we get too cold, we shiver,
creating heat, or move to the sunlight. N.F loops enhance stability.
Positive feedback loop: A feedback cycle in which output of one type acts as input that moves the
system in the same direction. The input and output drive the system further toward one extreme or
another. Ex: Climactic warming leading to the melting of ice, which exposes underlying darker
surfaces. Darker surfaces absorb more sunlight, causing further warming → more melting. P.F are
common in natural systems that have been altered by human impact.
Dynamic Equilibrium: The state reached when processes within a system are moving in opposing
directions at equivalent rates so that their effects balance out.
Homeostasis is a state of balance
Processes is D.E can contribute to homeostasis.
Homeostasis: the tendency of a system to maintain constant or stable internal conditions.
Resistance: is a property of homeostatic systems → strength of the system's tendency to remain
Resilience: measure of how readily the system will return to its original state once it has been
Homeostatic systems are often said to be in a stable or steady state.
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Chapter 3 Notes
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Steady State: A state of dynamic equilibrium or balance in which there is no net change in the
system. In a reservoir at steady state, inputs are equal to outputs.
A whole may be more than the sum of its parts
Emergent properties: characteristic that are not evident in the individual components of a system.
Env systems may be perceived in various ways
Earth's components are divided into broad structural systems
1) Geosphere: The physical Earth, distinct from the organisms that inhabit it. The rock & sediment
beneath our feet, in the planet's uppermost layers.
2)Atmosphere: The thin layer of gases surrounding planet Earth.
3)Hydrosphere: Earth’s water—salt or fresh, liquid, ice, or vapour—that resides in surface bodies,
underground, and in the atmosphere.
4)Cryosphere: The temporarily & everlasting frozen parts of the hydrosphere, including snow, sea
ice, lake & river ice, glaciers & ice caps & sheets.
5)Biosphere: The sum total of all the planet’s living organisms and the abiotic portions of the
environment with which they interact
6)Anthroposphere (anthrosphere/technosphere): The built, manufactured, industrialized, and
domesticated aspects of the world.
Ecosystem: All organisms and nonliving entities that occur and interact in a particular area at the
same time; a grouping of communities of organisms.
Ecosystems are systems of interacting biotic & abiotic components.
Ecosystem ecology: the study of energy & nutrient flows among living & nonliving components of
systems. Energy flows through ecosystems. Arrives as radiation from the Sun, powers the sytem &
exists in the form of heat. Matter is generally recycled within ecosystems.
Energy is converted to biomass
Biomass: Biological material; comprises living and recently deceased organic matter.
Gross Primary Production: The energy that results when autotrophs convert solar energy (sunlight)
to energy of chemical bonds in sugars through photosynthesis. Autotrophs use a portion of this
production to power their own metabolism, which involves oxidizing organic compounds by cellular
respiration. Also called GPP.
Net Primary Production: The energy or biomass that remains in an ecosystem after autotrophs have
metabolized enough for their own maintenance through cellular respiration. Net primary production is
the energy or biomass available for consumption by heterotrophs. Also called NPP.
NPP equals GPP minus respiration (NPP=GPP- respiration by autotrophs).
Secondary Production: The total biomass that heterotrophs generate by consuming autotrophs.
Ecosystems vary in the rate at which plants covert energy to biomass.
Productivity: The rate at which plants convert solar energy (sunlight) to biomass. Ecosystems whose
plants convert solar energy to biomass rapidly are said to have high productivity.
Tropical forests, coral reefs, algal beds have the highest NPP. Deserts, tundra & open ocean tend to
have the lowest NPP.
Nutrient availability limits productivity
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Chapter 3 Notes
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Nutrient: An element or compound that organisms consume & require for survival.
Macronutrients: Elements/compounds that organisms require in relatively large amounts. Include:
nitrogen, carbon, phosphorus.
Micronutrients: Nutrients needed in small amounts.
Nutrients stimulate production by autotrophs.
Limiting Factor: A physical, chemical, or biological characteristic of the environment that restrains
When nutrients such as nitrogen & phosphorus are added to a system, producers show the greatest
response to whichever nutrient has been in shortest supply. Phosphorus tends to be limiting in
freshwater systems & nitrogen in marine systems.
Marine hypoxic zones result primarily from excess nitrogen, whereas freshwater ponds tend to suffer
eutrophication when they contain too much phosphorus.
Ecosystems are integrated spatially
Sometimes the entire biosphere is viewed as a single all-encompassing ecosystem. But term is most
often used to refer systems of moderate geographic extent that are somewhat self-contained.
Adjacent ecosystems often share components & interact extensively.
Areas where ecosystems meet often consist of transitional zones called ecotones, in which elements
of each ecosystem mix.
Landscape ecologists study geographic patterns
Landscape ecology: scientists study how landscape structure affects the abundance, distribution &
interaction of organisms. This approach is useful for scientists, citizens, policy-makers in planning for
sustainable regional development.
Remote sensing and GIS are important tools
Remote sensing technologies: collect info about a target object from a distance. They are improving
our ability to take a landscape perspective on complex ecosystems.
Geographic Info System (GIS): a common tool that makes use of remotely sensed data. Consists of
computer software that takes multiple types of spatially referenced data & combines them on a
common set of geographic coordinates.
Models help scientists understand complex systems
Model: a simplified representation of a complex natural process, designed to help us understand how
the process occurs & to make predictions.
Ecosystems provide vital services
When Earth's ecosystems function normally & undisturbed, they provide goods & services that we
could not survive w/o.
Ecological processes form the soil that nourishes our crops, purify the water we drink & the air that
we breathe, store & stabilize supplies of water that we use, pollinate the food plants we eat, etc.
The negative feedback cycles that are typical of ecosystems regulate & stabilize the climate & help to
dampen the impacts of the disturbances we create in natural systems.
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Chapter 3 Notes
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The cycling of nutrients is one of the most important & fundamental of the ecosystem services that
support life on this planet. Chemical elements/compounds that we need - carbon, nitrogen,
phosphorus, water - move through the env in complex, global biogeochemical cycles.
Nutrients & other materials move in biogeochemical cycles
Nutrients move through ecosystems in nutrient cycles or biogeochemical cycles.
Biogeochemical Cycle: The comprehensive set of cyclical pathways by which the materials that are
crucial for life and biological processes move through the environment, changing from organic to
inorganic form and moving from biotic to abiotic reservoirs.
In these cycles, materials travel through the atmosphere, hydropshere & geosphere & from one
organism to another in dynamic equilibrium. After we die, the nutrients in our bodies will spread
widely through the physical env, eventually being incorporated by an untold # of organisms in the
Reservoir: A location where materials in a cycle remain for a period of time, before moving to
another reservoir. Also called a pool.
Residence Time: The average amount of time a material in a cycle remains in a given pool or
reservoir before moving to another reservoir.
Flux: The movement of materials (or energy) among pools or reservoirs in a cycle. Fluxes are rates,
so they are stated in terms of mass or volume of material moving b/w reservoirs per unit of time. The