BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 18: Ecosystem Lecture 18: Ecosystem Ecology (Energy in the Ecology (Energy in the

Ecosystem)Ecosystem)

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

EcosystemDefinition: biotic community and abiotic environment functioning as a

system. Includes organism-complex and whole complex of physical factors.

Forest Ecosystem Forest is a system composed of autotrophy, heterotrophy, and abiotic

environment, each component processing and exchanging energy and matter.

Inputs: exchanges from the surrounding environment into the ecosystem

Outputs: exchange from inside ecosystem to the surrounding environment

Closed ecosystem: an ecosystem with no inputs and outputsOpen ecosystem: an ecosystem with inputs and outputs

Ecosystem ecology: exchanges of energy and matter between ecosystem and environment and among components within the ecosystem (energy flow and nutrient cycling).

Outline (Chapter 22)Outline (Chapter 22)

18.1 Ecosystem function obeys thermodynamic 18.1 Ecosystem function obeys thermodynamic principles principles

18.2 Primary production provides energy to the 18.2 Primary production provides energy to the ecosystem ecosystem

18.3 Many factors influence primary production18.3 Many factors influence primary production18.4 Primary production varies among ecosystems18.4 Primary production varies among ecosystems18.5 Only 5%– 20% of assimilated energy passes 18.5 Only 5%– 20% of assimilated energy passes

between trophic levelsbetween trophic levels18.6 Energy moves through ecosystems at different 18.6 Energy moves through ecosystems at different

ratesrates18.7 Ecosystem energetics summarizes the movement 18.7 Ecosystem energetics summarizes the movement

of energy populationsof energy populations

18.1 Ecosystem function obeys 18.1 Ecosystem function obeys thermodynamic principles thermodynamic principles

History of Ecosystem Ecology

Alfred J. Lotka, 1925Energy transformation and thermodynamic principles

Raymond Lindeman, 1942Pyramid of energy (left)

Eugene Odum, University of Georgia, 1953Fundamentals of Ecology

E. P. Odum developed a “ universal” model of energy flow through ecosystems. The energy ingested by organisms at each trophic level is reduced by respiration and excretion, so that less energy is available for consumption by the next trophic level.

Laws of thermodynamics govern Laws of thermodynamics govern energy flowenergy flow

First law of thermodynamics:Energy is neither created nor destroyed.

Second law of thermodynamicsWhen energy is transferred or transformed, part of the energy assumes a form that cannot pass on any further.

As energy is transferred from one organism to another in the form of food, a portion is stored as energy in living tissue, whereas a large part of that energy is dissipated as heat.

18.2 Primary production provides 18.2 Primary production provides energy to the ecosystem energy to the ecosystem

Flow of energy through a terrestrial ecosystem starts with the harnessing of sunlight by autotrophs.

Rate at which light energy is converted by photosynthesis to organic components is referred to as primary productivity.

Gross primary productivity (GPP): Total rate of photosynthesisNet primary productivity (NPP): rate of energy as storage as organic matter after respirationNPP=GPP-R

Productivity is the rate at which organic matter is created by photosynthesis (g m-2 yr-1)

Standing crop biomass: amount of accumulated organic matter in an area at a given time

Biomass is expressed as g organic matter per square meter (g m-2)

How to measure?

Terrestrial ecosystem:1. Flux based

Measure photosynthesis (equipment: LiCor, Eddy flux method)

net photosynthesis

2. Biomass based estimation Change in standing crop biomass (SCB) over a given time interval

NPP=delta SCB +loss of biomass due to death of plant + loss due to consumption. (see Hui & Jackson 2006 for grasslands)

18.4 Primary production varies 18.4 Primary production varies among ecosystemsamong ecosystems

Patterns of productivity reflect global patterns of temperature and precipitation. High NPP in equatorial zone and coastal region.

Geographic variation in primary productivity of world’s oceans

High productivity is along coastal regions

1. Great transport of nutrient from bottom to top

2. Nutrient from terrestrial ecosystems

Recap: Energy in ecosystemsRecap: Energy in ecosystems

11stst and 2 and 2ndnd law of thermodynamics law of thermodynamics

Primary production provides energy to the ecosystem Primary production provides energy to the ecosystem

Many factors influence primary productionMany factors influence primary production

Primary production varies among ecosystemsPrimary production varies among ecosystems

18.5 Only 5%– 20% of assimilated energy 18.5 Only 5%– 20% of assimilated energy passes between trophic levelspasses between trophic levels

Net primary production is the energy available to the heterotrophic component of the ecosystem

Either herbivores or decomposers eventually consume all plant productivity, but often it is not all used within the same ecosystem.

Secondary production: net energy of production of consumers•Energy stored in plant material, once consumed, some passes through the body as waste products. •Of the energy assimilated, part is used as heat for metabolism (respiration) and maintenance – capturing or harvesting food etc, and lost as heat.•Energy left over from maintenance and respiration goes into production, including growth of new tissues and production of youngSecondary productivity: secondary production per unit of time

Energy use is a complex process. Not all consumers have the same efficiency

A simple model of energy flow through consumer

I: food ingested by a consumerA: a portion is assimilated across the gut wall, convert nutrient to body biomass (digestion, absorption)E: remainder is expelled from the body as waste products (egested energy). animal excrete small portion as nitrogen-containing compounds (as ammonia, urea, uric acid) (excreted energy) R: of the energy assimilated, part is used for respiration (respired energy)P: remainder goes to production (new growth and reproduction)

Based on these data, we can calculate:Assimilation efficiency A/I, ratio of assimilation to ingestion measure the efficiency with which consumer extracts energy from food Secondary consumers: 60-90%

Production efficiency P/A, ratio of production to assimilation measure the efficiency with which the consumer incorporates assimilated energy into secondary production. Homoeothermic: low, 1 % (birds) -6% (small mammals) Poikilotherimic: high, as much as 75%.

Production efficiency varies mainly according to taxonomic class

Endotherms have low P/A

Invertebrates have high P/A

Vertebrates: ectotherms have intermediate

Energy flow through trophic levels can be Energy flow through trophic levels can be quantifiedquantified

Energy flow within a single trophic compartment

Consumption efficiency:

In/Pn-1

Ecological efficiency (food chain efficiency):

Pn-1/Pn

14/200=7%

18.6 Ecosystems have two major 18.6 Ecosystems have two major food chainsfood chains

Food chain is a flow of energy

Feeding relationships within a food chain are defined in terms of trophic or consumer level1st level: Autotrophs or primary producer2nd level: herbivores (1st level consumers)Higher level: carnivores (2nd level consumers)

Some consumers occupy more than one trophic level: omnivores.

Within any ecosystem, there are two major food chains

Difference

1. Source of energy for herbivores

2. Energy flow direction

3. interconnected

18.7 Energy decreases in each successive 18.7 Energy decreases in each successive trophic leveltrophic level

Energy pyramid

M. Imhoff and L. Bounoua (NASA’s Goddard Space Flight Center) used satellite-derived data to estimate the human appropriation of terrestrial NPP (HANPP)

Mean annual HANPP = 24.2 Pg (1 Pg = 1015 g) = 20 percent of terrestrial annual NPPHANPPWestern Europe/south central Asia = 70 percentHANPPSouth America = 6 percent

18.8 Energy move through different 18.8 Energy move through different ecosystems at different ratesecosystems at different rates

Ecological efficiency: determine how much energy assimilated by plants reach high level of tropic levels.

Another feature of energy transfer is the rate of energy transfer (how fast or how long energy stays in one tropic level)

Residence time (years): energy stored in biomass (g m-2) =--------------------------------------------------- net productivity (g m-2 yr-1)

Also called biomass accumulation ratio

Tropic: =42 kg m-2/ 1.8 kg m-2 yr-1 = 23 yrs

Residence time for litter poolsResidence time for litter pools

Residence time (years): litter accumulation (g m-2) =--------------------------------------------------- rate of litter fall (g m-2 yr-1)

Forests:

Tropic: 1-2 yrsTemperate (southeastern US): 4-16 yrsMountain and boreal forests: more than 100 yrs

Net Ecosystem ProductivityNet Ecosystem Productivity

NEP: a measure of net carbon accumulation

NEP = NPP – Soil heterotrophic respiration = GPP – Plant Respiration – Soil heterotrophic respiration = GPP – Aboveground Plant Respiration – Soil Respiration

NEP: 1%– 2% of the total gross primary production (~2 billion tons)

Fossil fuel burning: 8 billion tons of carbon

The End

Secondary production depends on primary production for energy

Sam McNaughton (Syracuse Uni.)

69 studies for terrestrial ecosystems (from Arctic tundra to tropical forests)

Relationship of Secondary production and primary production

Similar relationship in lake ecosystems

43 lakes+12 reservoirs

Tropic to Arctic

Energy flow through trophic levels can be Energy flow through trophic levels can be quantifiedquantified

Energy flow within a single trophic compartment

Consumption efficiency:

In/Pn-1

Ecological efficiency (food chain efficiency):

Pn-1/Pn

14/200=7%