BIOL 4120 Principles of Ecology Lecture 18 Ecosystem
BIOL 4120: Principles of Ecology Lecture 18: Ecosystem Ecology (Energy in the Ecosystem) Dafeng Hui Office: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu
Ecosystem Definition: 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 outputs Open 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) 18. 1 Ecosystem function obeys thermodynamic principles 18. 2 Primary production provides energy to the ecosystem 18. 3 Many factors influence primary production 18. 4 Primary production varies among ecosystems 18. 5 Only 5%– 20% of assimilated energy passes between trophic levels 18. 6 Energy moves through ecosystems at different rates 18. 7 Ecosystem energetics summarizes the movement of energy populations
18. 1 Ecosystem function obeys thermodynamic principles History of Ecosystem Ecology Alfred J. Lotka, 1925 Energy transformation and thermodynamic principles Raymond Lindeman, 1942 Pyramid of energy (left) Eugene Odum, University of Georgia, 1953 Fundamentals 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 energy flow First law of thermodynamics: Energy is neither created nor destroyed. Second law of thermodynamics When 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 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 photosynthesis Net primary productivity (NPP): rate of energy as storage as organic matter after respiration NPP=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: Li. Cor, 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 among 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 1. Great transport of nutrient from bottom to top 2. Nutrient from terrestrial ecosystems High productivity is along coastal regions
Recap: Energy in ecosystems 1 st and 2 nd law of thermodynamics Primary production provides energy to the ecosystem Many factors influence primary production Primary production varies among ecosystems
18. 5 Only 5%– 20% of assimilated energy passes 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 young Secondary 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 consumer A: 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 quantified 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 food chains Food chain is a flow of energy Feeding relationships within a food chain are defined in terms of trophic or consumer level 1 st level: Autotrophs or primary producer 2 nd level: herbivores (1 st level consumers) Higher level: carnivores (2 nd 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 trophic 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 NPP HANPPWestern Europe/south central Asia = 70 percent HANPPSouth America = 6 percent
18. 8 Energy move through different ecosystems 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 pools Residence time (years): litter accumulation (g m-2) =-------------------------rate of litter fall (g m-2 yr-1) Forests: Tropic: 1 -2 yrs Temperate (southeastern US): 4 -16 yrs Mountain and boreal forests: more than 100 yrs
Net 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
Relationship of Secondary production and primary production Secondary production depends on primary production for energy Sam Mc. Naughton (Syracuse Uni. ) 69 studies for terrestrial ecosystems (from Arctic tundra to tropical forests)
Similar relationship in lake ecosystems 43 lakes+12 reservoirs Tropic to Arctic
Energy flow through trophic levels can be quantified Energy flow within a single trophic compartment Consumption efficiency: In/Pn-1 Ecological efficiency (food chain efficiency): Pn-1/Pn 14/200=7%
- Slides: 39
