ENERGY PATTERNS OF ENERGY FLOW IN ECOSYSTEMS WHAT

ENERGY PATTERNS OF ENERGY FLOW IN ECOSYSTEMS

WHAT IS AN ECOSYSTEM? • Biological community plus all abiotic factors affecting the community • “Ecosystem” first proposed by Arthur Tansley • Boundaries not fixed • Energy flows • Cycle nutrients

LAWS OF THERMODYNAMICS • 1 st LAW: Energy cannot be created or destroyed but may be transformed from one form to another • 2 nd LAW: When energy is converted from one form to another, energy is lost as heat

ENERGY SOURCES IN BIOSPHERE • Sunlight energy – driving force – Energy distribution and carbon dioxide in atmosphere shape ecosystems and biosphere • Biosphere energy and CO 2 shape world climate and weather

ECOSYSTEM ENERGETICS: A THERMODYNAMICS VIEW • Model– characterization of observations by set of equation which express observation in nature

CHARLES ELTON & FOOD WEBS • 1920 s, Charles Elton and others proposed: – Organisms living in the same place not only have similar tolerances of physical factors, but – Feeding relationships link these organisms into a single functional entity • Food web http: //www. history. vt. edu/Barrow/Hist 3144/readings/ecology/index. html

http: //www. nature. ca/ukaliq/images/a 196_fwb_e. jpg

OLD FIELD FOOD WEB

Feeding relationships of the snowshoe hare-dominated food web in the boreal forest of northwestern Canada Dominant species in yellow

ALFRED J. LOTKA AND THERMODYNAMIC CONCEPT • Alfred J. Lotka – Ecosystem as an energytransforming machine – Set of equations representing exchanges of matter and energy among components – Characterize transfer of body mass using series of equations describing how system works

LINDEMAN’S SYNTHESIS • 1942 – Raymond Lindeman brought Lotka’s ideas of the ecosystem as an energy-transforming machine to the attention of ecologists • Incorporated: – Lotka’s thermodynamic concepts – Elton’s food web concept – Tansley’s ecosystem concept http: //www. cedarcreek. umn. edu/people/photo/Lindeman. Raymond 1942. jpg

LINDEMAN’S FOUNDATIONS OF ECOSYSTEM ECOLOGY • Ecosystem is fundamental unity of ecology • Within an ecosystem, energy passes through many steps or links in a food chain • Each link in the food chain is a trophic level (feeding level)

Cedar Bog Lake in Minnesota…site of Raymond Lindemen’s classic research paper in 1942: "The Trophic-Dynamic Concept in Ecology“. Ecology 23: 399 -418

ODUM’S ENERGY FLUX MODEL • Recognized the utility of energy and masses of elements as common “currencies” in comparative analysis of ecosystem structure and function http: //www. researchmagazine. uga. edu/summer 2002/odum. htm Eugene Odum

ODUM EXTENDED HIS MODELS TO INCORPORATE NUTRIENT CYCLING • Fluxes of energy and materials are closely linked in ecosystem function • But: – Energy enters ecosystems as light and is degraded into heat – Nutrients cycle indefinitely, converted from inorganic to organic forms and back again • Studies of nutrient cycling provides index of energy fluxes

Single trophic level Example food chain Odum’s “universal” model of energy flow, which can be applied to any organism

Energy dissipated as heat SUN Producers Consumers Detritus + Decomposers Inorganic nutrients Import Energy Flow Nutrient pool Nutrient Cycling Export

WHAT DO WE KNOW SO FAR? • • Ecosystems Biotic and abiotic components Energy and nutrients Energy transformed from one form to another When energy is transformed, energy is lost Sunlight is ultimate source of energy Food webs link organisms by trophic level

AUTOTROPHS - PRODUCERS • Photoautotrophs - Sunlight energy, Green plants • Chemoautotrophs - Chemical energy, certain bacteria • Primary producers – capture energy from sunlight • Transform sunlight energy to chemical energy – Sugars, starch, ATP http: //www. scienceclarified. com/images/uesc_01_img 0028. jpg http: //141. 150. 157. 117: 8080/prok. PUB/figures/normal/p 323 -006. jpg

PRIMARY PRODUCTION • Producers capture energy of light • Transform sunlight energy into energy of chemical bonds in carbohydrates • 6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2 – For each g of C assimilated, 39 kj energy stored • Gross primary production = total energy assimilated by primary producers • Net primary producion = energy accumulated (in stored form) by primary producers • GPP – NPP = Respiration – Energy consumed by producers for maintenance and biosynthesis

Energy lost and unavailable to consumers Partitioning gross primary productivity into respiration and net primary productivity GPP NPP

NUTRIENTS STIMULATE PRIMARY PRODUCTION • Terrestrial production may be nutrient limited – N most common limiting element • Aquatic systems often strongly nutrient-limited – Open ocean – Addition of nutrients may stimulate unwanted production

Effects of fertilization with N & P on primary production in a salt marsh dominated Carex subspathecea in southern Hudson Bay, Canada.

AQUATIC ECOSYSTEMS RESPONSIVE TO PHOSPHORUS 1975 http: //www. umanitoba. ca/institutes/fisheries/eutro. html 1994

Slow-moving coastal plain stream choked with algal bloom caused by nitrogen and phosphorus from upstream farmland. http: //wps. prenhall. com/wps/media/objects/57/58641/51_8089 ic. gif

GLOBAL PRIMARY PRODUCTION • Correlates with annual precipitation (when light not limiting) • Note relationship among tundra, deserts, and tropics – Oceans – nutrient poor • CO 2 Source of carbon – Follows 1 st Law of Energy

Grams carbon/m 2/yr for globe, as calculated from satellite imagery. Oceans = 46%, land = 54%

PRIMARY PRODUCTION VARIES AMONG ECOSYSTEMS • Maximum under favorable conditions – Intense sunlight – Warm temperatures – Abundant precipitation – Nutrients

NPP vs. Temperature + Precipitation

HETEROTROPHS - CONSUMERS • • • Get energy from external sources “Animals” Primary consumers Secondary consumers Tertiary consumers – Carnivores • Decomposers – Detritivores – Eat dead organic matter

Tertiary consumers Secondary consumers Primary producers Decomposers

Tertiary consumers Secondary consumers Primary producers Decomposers

ECOLOGICAL PYRAMIDS • Trophic levels placed in order • Reflects: – Numbers of organisms at each level – Biomass of each level – Energy at each level

ECOLOGICAL PYRAMIDS • Elton observed predators tended to be larger and less numerous than their prey - described as the ‘pyramid’ of numbers or biomass • Elton hypothesized that this occurred because predators have to be larger than prey

PYRAMID OF NUMBERS # CONSUMERS=TOP CARNIVORES # CONSUMERS # HERBIVORES # PRIMARY PRODUCERS # DECOMPOSERS

PYRAMID OF BIOMASS kg CONSUMERS=TOP CARNIVORES kg CONSUMERS k. G DECOMPOSERS kg HERBIVORES kg PRIMARY PRODUCERS

PYRAMID OF ENERGY k. J CONSUMERS=TOP CARNIVORES k. J CONSUMERS k. J DECOMPOSERS k. J HERBIVORES k. J PRIMARY PRODUCERS

NUMBERS PYRAMID

NUMBERS PYRAMID http: //www. bbc. co. uk/schools/gcsebitesize/img/bi 01010. gif

BIOMASS PYRAMID

BIOMASS PYRAMID

BIOMASS AND (NUMBERS) PYRAMID

ENERGY PYRAMID

Heat is lost as energy flows through food chain

Energy pyramids can never be inverted, but biomass pyramids can be inverted when lower trophic levels are dominated by palatable and small organisms that turnover rapidly

What % of energy is available to the next tropic level?

ENERGY TRANSFER EFFICIENCY • 10% Efficient between trophic levels • What happens to other 90% – How is it dispersed? – Is it lost? – Account for it

ENERGY BUDGET

Energy Budget – energy flow & distribution through ecosystem

ONLY 5% TO 20% OF ENERGY PASSES BETWEEN TROPHIC LEVELS • Energy reaching each trophic level depends on: – Net primary production (base of food chain) – Efficiencies of transfers between trophic levels • Plants use 15 -70% of light energy assimilated for maintenance • Herbivores and carnivores expend more energy on maintenance than plants: - Production of each trophic level is only 5 -20% of level below it.

ECOLOGICAL EFFICIENCY • Ecological Efficiency – Percentage of energy transferred from one trophic level to the next: – Range of 5 -20% typical – Must understand the utilization of energy within a trophic level Not all food components can be assimilated - Undigested fibrous material from elephant dung

FUNDAMENTAL ENERGY RELATIONSHIPS • Components of an animal’s energy budget are related by: • Assimilated Energy = Ingested Energy – Egested Energy • Production = Assimilated Energy – (Respiration. Excretion)

ASSIMILATION EFFICIENCY • Assimilation Efficiency = Assimilation/Ingestion • Function of Food Quality: – SEEDS: 80% – YOUNG VEGETATION: 60 -70% – PLANT FOODS OF GRAZERS, BROWSERS: 30 -40% – DECAYING WOOD: 15% – ANIMAL FOODS: 60 -90%

NET PRODUCTION EFFICIENCY • Net production efficiency = production/assimilation • depends on metabolic activity: – birds: <1% – small mammals: <6% – sedentary ectotherms: as much as 75% • Gross production efficiency = assimilation efficiency x net production efficiency – = production/ingestion, ranges from below 1% (birds and mammals) to >30% (aquatic animals). High rate of metabolism results in low production efficiencies

DETRITUS FOOD CHAINS • Ecosystems support two parallel food chains: – herbivore-based (relatively large animals feed on leaves, fruits, seeds) – detritus-based (microorganisms and small animals consume dead remains of plants and indigestible excreta of herbivores) – herbivores consume: • 1. 5 -2. 5% of net primary production in temperate forests • 12% in old-field habitats • 60 -99% in plankton communities

What limits the length of the food chain?

Do aquatic or terrestrial ecosystems have more trophic levels? What factor contributes most to variation in food chain length among these ecosystems?

SOME GENERAL RULES • Assimilation efficiency increases at higher trophic levels. • GPP and NPP efficiencies decrease at higher trophic levels. • Ecological efficiency ~ 10%. • ~ 1% of NPP ends up as production on the third trophic level – the energy pyramid narrows quickly. • To increase human food supplies means eating lower on the food chain!

Food energy available to the human population depends on their trophic level.