Chapter 55 Part 1: Energy transformations in ecosystems

Ecosystems

consists of all organisms living in community + abiotic factors they interact w

What can a single introduced species have dramatic effects on

Both biotic and abiotic components of an ecosystem

Ecosystem size range

small microcosm (ex: space under fallen log) to large area (ex: lake/island)

2 main processes of ecosystem's dynamics

Energy flow and Chemical cycling

How do energy and matter travel in ecosystems?

Energy flows through, Matter cycles within

Concept 55.1

Physical laws govern energy flow and chemical cycling in ecosystems

First law of thermodynamics

Energy can't be created/destroyed, only transformed

Generally, how energy travels through ecosystem

Enters as solar radiation, is conserved, and lost from organisms as heat

Second law thermodynamics

every exchange of energy increases the entropy of the universe

In ecosystems are energy conversions efficient?

Not completely efficient, some energy is always lost as heat

Law of conservation of mass

matter can't be created or destroyed

How often are chemical elements recycled within ecosystems

Continually recycled

How do nutrients travel in forest ecosystems

Nutrients enter as dust/solutes in rain and carried away in water

What does it mean Ecosystems are open systems

Ecosystems absorb energy and mass, release heat and waste products

How do autotrophs work?

Build molecules themselves using photo/chemosynthesis as an energy source

How do heterotrophs work?

Depend on biosynthetic output of other organisms

How does energy move through trophic levels?

Primary producers > primary consumers > secondary consumers > tertiary consumers > quaternary consumers

Primary producers

aka Autotrophs

Primary consumers

aka Herbivores

Secondary consumers

aka Carnivores

Tertiary consumers

aka Carnivores that feed on other carnivores

Decomposers or Detritivores

consumers get their energy from detritus

Detritus

nonliving organic matter

Examples important detritivores

Prokaryotes and fungi

What connects all trophic levels

Decomposition

Concept 55.2

Energy and other limiting factors control primary production in ecosystems

Primary production

amount of light energy converted to chemical energy by autotrophs during given time period

How often are chemoautotrophs the primary producers in ecosystems

In few ecosystems

What sets the spending limit for an ecosystem's energy budget?

The extent of photosynthetic production

What limits the photosynthetic output of ecosystems?

The amount of solar radiation reaching Earth's surface

How much solar energy is actually usable

Only small fraction of solar energy actually strikes photosynthetic organisms > even less is in usable wavelength

Gross Primary Production (GPP)

total primary production of an ecosystem

How is GPP measured

measured as the conversion of chemical energy from photosynthesis per unit time

how NPP calculated

GPP minus energy used by primary producers for respiration

How is NPP expressed

Energy per unit area per unit time (J/m^2(yr)) or

Biomass added per unit area per unit time (g/m^2(yr))

Net Primary Production (NPP)

amount of new biomass added in a given time period

Only what is available to consumers?

NPP

What is the total biomass of photosynthetic autotrophs at a given time?

Standing crops

What does satellite data indicate about NPP

Ecosystems vary greatly in NPP and contribution to the total NPP on Earth

Which ecosystems are most productive ecosystems per unit area?

Tropical rain forests

Estuaries

Coral Reefs

Marine ecosystems

Relatively unproductive per unit area

Contribute a lot to global NPP because of their size

Net Ecosystem Production (NEP)

measure of total biomass accumulation during given period

NEP calculation

GPP minus total respiration of all organisms (producers and consumers) in an ecosystem

How is NEP estimated?

Compare net flux of CO2 and O2 in an ecosystem (2 molecules connected by photosynthesis)

What does the release of O2 by a system indicate?

It's also storing CO2

What controls primary production in marine and freshwater ecosystems?

Light and nutrients

What does depth of light penetration affect?

Primary production in the photic zone of an ocean/lake

What limits primary production more than light?

Nutrient availability

Limiting nutrient

Element that must be added for production to increase in an area

Common limiting nutrients

Nitrogen and Phosphorous

Iron

What contributes to regions of high primary production?

Upwelling of nutrient-rich waters in parts of the ocean

Adding large amounts of nutrients to lakes has _________

A wide range of ecological impacts

What is upwelling?

Caused by temperature differences in water > moves sediments from bottom layers to top > allows organisms at top to use nutrients

Eutrophication

A process by which nutrients, particularly phosphorus and nitrogen, become highly concentrated in a body of water, leading to increased growth of organisms such as algae or cyanobacteria

What caused eutrophication?

Some areas: sewage runoff caused eutrophication of lakes, can > loss of most fish species

What limits cyanobacterial growth

Phosphorous, more than nitrogen

What has this led to?

Use of phosphate-free detergents

What affects primary production of terrestrial ecosystems? on a larger scale

Temperature and moisture

True or False: Primary production increases with moisture

True

Evapotranspiration

water transpired by plants and evaporated from landscape

What affects evapotranspiration

Precipitation, temperature, solar energy

What concept is evapotranspiration related to?

Net primary production (NPP)

On a local scale, what limits primary production?

Soil nutrient

Terrestrial ecosystems most common limiting nutrient

Nitrogen

Another limiting nutrient esp. in older soils

Phosphorus

Various adaptations help plants access limiting nutrients from soil

-Some plants mutualisms with nitrogen-fixing bacteria

-Mutualisms with mycorrhizal fungi (supply plants w P)

-Root hairs increase SA

-Release enzymes increase availability limiting nutrients

Special about legume roots

Root nodules contain nitrogen-fixing bacteria

Concept 55.3

Energy transfer between trophic levels is typically only 10% efficient

Secondary Production

amount of chemical energy in food converted to new biomass during given period of time

Example with caterpillar eating leaf

Only about 1/6 of leaf's energy is used for secondary production

Production Efficiency

fraction of energy stored in food that's not used for respiration

Calculation for production efficiency

(net secondary production x 100%) / assimilation of primary production

Efficiencies of birds and mammals

Range 1-3% bc high cost of endothermy

Efficiency of fish

around 10%

Efficiency of insects and microorganisms

40% or more

Trophic efficiency

percentage of production transferred from one trophic level to the next

about 10% (ranges from 5-20%)

How does tropic efficiency change over length of food chain

Multiplied over length of food chain

How much of chemical energy fixed by photosynthesis reaches tertiary consumer?

About 0.1%

What does a pyramid of net production represent

The loss of energy with each transfer in a food chain

In a biomass pyramid, what does each tier represent

The dry mass of all organisms in one trophic level

What do most biomass pyramids show at successively higher trophic levels?

Sharp decrease

Are aquatic ecosystems more efficient than terrestrial ecosystems?

Yes, they can be

Certain aquatic ecosystems have inverted biomass pyramids

Producers (phytoplankton) are consumed so quickly that they're outweighed by primary consumers

Turnover time

ratio of standing crop biomass to production