Ecosystems And Energy Flow

Ecosystems • Ecosystems are composed of all the communities and their associated physical environments, including the physical, chemical, and biological processes. – Ecosystems may sustain themselves entirely through photosynthetic activity, energy flow through food chains, and nutrient recycling.

Ecosystems • Abiotic components: non-living chemical and physical factors – Temperature, light, nutrients, water

• Biotic components: all living organisms – Interactions among organisms

Biotic Components of Ecosystems

Trophic relationships among organisms determine energy flow and chemical cycling in an ecosystem • Interlocking food webs determine the flow of energy through the different ecosystem levels. – Food web made up of interlinking food chains.

Ecosystem structure vs. processes • The structure is the food chain or web (trophic system) • Processes = energy production and energy consumption • Production is the rate of incorporation of energy and materials into the body of organisms • Consumption (Assimilation) is the metabolic use of organic materials for growth and reproduction

The Food Web

Primary Producers • Plants, algae, and many species of bacteria • Photoautotrophs, chemoautotrophs • Limnetic zone of lakes: algae & bacteria • Littoral zone of fresh and marine ecosystems: multicellular algae & aquatic plants • Terrestrial ecosystems: plants

Primary and HigherOrder Consumers

• Are opportunistic feeders • They consume autotrophs, but also heterotrophs • Primary consumers feed on producers. – Secondary consumers feed on primary consumers, and / or producers. – Detritivores are consumers that break down organisms into smaller pieces which are then available to decomposers

Decomposers • Living organisms eventually die • Recycled, decomposed and returned to the abiotic environment • Decomposers break down organic material to forms that are released back into the ecosystem for reassimilation by other organisms. • Decomposers: bacteria and fungi • Decomposition interconnects all trophic levels

• Detritivores consume dead organic matter • Decomposers also consume dead organic matter, but decompose it into plant nutrients

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Trophic levels • Producers • 1° Consumers • Detritivores • 2° Consumers • 3° Consumers • Decomposers

• Autotrophs • Heterotrophs – Herbivores •Detritivores – Omnivores – Carnivores – Decomposers

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The Food Web

The trophic relationships among organisms is often complex.

Energy Flow in Ecosystems

• Primary Productivity • Secondary Productivity • The flow of energy through the food webs

Energy Flow in Food Webs • First law of thermodynamics – energy cannot be created or destroyed, only transformed – Can thus construct energy budgets for food webs that trace energy flow from green plants to tertiary consumers (and if needed beyond) • Second law of thermodynamics – energy conversions are not 100% efficient and that, in any transfer process, some energy is lost

Energy Flow in Food Webs • Can compare the efficiency of energy transfer through trophic levels in different types of food webs • Two measures of the efficiency of consumers as energy transformers – Production efficiency – Trophic-level transfer efficiency

Primary Productivity • Defined as the amount of light energy that is converted to chemical energy (organic compounds) by the autotrophs • Global energy budget: only 1-2% of solar radiation is used by photosynthetic organisms • Yet they produce 170 million tons of organic material (biomass) per year

51% of solar energy is absorbed at the Earth’s surface.

nly 1-2% of solar radiation is used by photosynthetic organism

Primary Productivity • Influences on primary production – Water • In terrestrial systems, linear relationship with annual precipitation

– Temperatures • transpiration rate can predict aboveground primary

Primary Productivity • Influences on primary production – Nutrients (nitrogen and phosphorus) • Can be limiting factor • Liebig’s law of the minimum – species biomass or abundance is limited by the

Primary productivity varies • Highest in tropical rainforests • Decreases progressively toward the poles • May cause the polar-equatorial gradient of species richness • Greatest marine production occurs on coral reefs where temperature is high and light is not limiting

Net Primary Production in Ecosystems

Energy production in ecosystems • Gross primary productivity (GPP) = plant production or carbon fixed during photosynthesis • R = energy lost in plant cellular respiration • Net primary productivity = GPP- R – Amount of energy available to primary consumers – Measured in calories – Use dry weight (mainly carbon compounds)

Productivity and Efficiency • Assimilation: – the total energy consumed as biomass that has accumulated over a given time span. The amount an organism consumes.

• Net productivity: – the amount of chemical energy of the food they eat converted into their own new biomass

• Production Efficiency: The percentage of energy assimilated by an organism that becomes incorporated into new

Energy flow through a food web (a)Energy lost as heat in a single trophic level (b)Energy lost in the conversion between one trophic level and the next

Production efficiency = net productivity/ assimilation x 100

• Production efficiency – Percentage of energy assimilated by an organism that becomes incorporated into new biomass – Invertebrates average 10-40% – Example: A caterpillar consumes 1000 J of energy • 320 J lost to cellular respiration Production • 500 J lost as feces efficiency =growth and development • 180 J used for

[180 J/ 1000 J] x 100 = 18%

• Production efficiency – Vertebrates have lower production efficiencies • Fish (ectotherms) around 10% • Birds and mammals (endotherms) 1-2%

Production efficiency = [16J/ 1000J] x 100= 1.6%

Trophic level transfer efficiency

– Amount of energy at one trophic level that is acquired by the trophic level above and incorporated into biomass – Examines energy flow between trophic levels, not just individual species – Averages around 10% with much variation • Some marine food chains exceed 30% – Low for 2 reasons • Many organisms cannot digest all of their prey • Much assimilated energy lost as heat – Limits number of trophic levels in a food

Energy flow through a food web (a)Energy lost as heat in a single trophic level (b)Energy lost in the conversion between one trophic level and the next

Example in a freshwater lake: 100 g/m2 phytoplankton, trophic level n-1 14 g/m2 of zooplankton trophic level n Trophic level transfer efficiency = [14 g/m2 of zooplankton / 100 g/m2 phytoplankton] x 100 = 14%

Pyramid of Numbers • Number of individuals decreases at each trophic level • Trophic-level transfer efficiencies expressed as an Eltonian pyramid • Elton’s analysis of trophic levels in a pond

• Holds up for many ecosystems • Grasslands and marshes • What about forests?

Inverted Pyramids • Inverted pyramids – single producer supports hundreds of herbivores and thousands of predators – Oak tree supports beetles, caterpillars, and their predators • Still makes sense when using a pyramid of biomass

• In forests, insects out number plants • But the biomass of the plant community is still greater than the total biomass of insects and vertebrates

Inverted Pyramids • Can still occur even in pyramid of biomass – Small phytoplankton standing crop supports higher biomass of zooplankton by processing large amounts of energy – Use pyramid of energy • The amount of free energy produced by the phytoplankton is greater than the zooplankton • More “bang for your buck”

• The production efficiency of zooplankton is

• The laws of thermodynamics ensure that the highest amounts of free energy are found at the lowest trophic levels

Biomagnification • The tendency for certain chemical elements to accumulate or build up in food chains. • Biomagnification in a Michigan Lake food chain

Biomagnification • Tendency of certain chemicals to accumulate or build up within food chains • Dichlorodiphenyltri chloroethane (DDT) • Interferes with eggshell formation resulting in thin shelled eggs that break • US banned DDT in early 1970s • Still used in other countries

Energy flow in Ecosystems: Water Cycle

• The water cycle is largely a process of evaporation and precipitation – Amount remains relatively stable.

• Some percentage of rainfall percolates down through the soil to the water table, while other water is taken up by plants, or evaporated back into the atmosphere. • Water also evaporates from the soil surface, plants, animals, and the lower atmosphere.

• More than 90% of the water entering a plant passes into leaf air spaces and then evaporates through the stomata into the atmosphere – Usually less than 5% of water escapes through

The Water Cycle

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Energy flow in Ecosystems The Carbon Cycle • Carbon dioxide is the most important gas • Carbon enters plants, etc., as CO2 – Bacteria process carbon in a fashion that allows it to be recycled. – Obtain energy from the molecules, and convert carbohydrates to carbon dioxide as a result of respiration.

• Cellular respiration, combustion, and erosion of limestone return CO2 to the environment – Burning of fossil fuels has significantly increased the amount of carbon dioxide released into the atmosphere.

Carbon cycle

Carbon Sources (availability) • Atmosphere (0.3%) • Biomass of organisms, living or dead • Carbon moves through the food chain through the consumption of organisms

The Carbon Cycle

Carbon Sinks (where carbon is stored)

• Wood, other durable organic material • Coal • Oil • Peat • Marine biomes CaCo3 • Calcium carbonate forms limestone sediments • Geologic uplift exposes the carbon to erosion which returns it to the biotic

Carbon Cycle Summary 1. Photosynthesis removes carbon from the abiotic envirnoment (fixes carbon into organic molecules) 2. Carbon moves through food chain through consumption of one organisms by another 3. Cellular respiration, combustion, and erosion of limestone return carbon to the atmosphere, water and abiotic environment

Seasonal Fluctuations of CO2

• Northern hemisphere

– Lowest in the summer – Higher in the winter – More land, more plants, in the north – More photosynthesis taking Carbon out of the atmosphere – The burning of fossil fuels has greatly

Global Warming • The Greenhouse Effect occurs because certain gases, greenhouse gases, allow sunlight to pass through the atmosphere, but trap the heat radiation given off after the ground absorbs the solar energy. – Carbon Dioxide, Methane, Nitrous oxide, Ozone, CFCs • Act similar to the glass panels on a greenhouse.

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Burning of fossil fuels has significant effects on the content of carbon dioxide in the atmosphere. –

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Releases carbon stored in the fossil fuels.

Deforestation eliminates photosynthesizing organisms that remove carbon dioxide from the

Probable Effects of Global Warming 1. Sea level rise 2. Precipitation patterns will change – – –

Droughts Flooding Changing biomes

3. Range of organisms will change 4. Affect on Agriculture

The Nitrogen Cycle • Nitrogen is crucial for all organisms – Nucleic acids – Proteins – Chlorophyll

• Atmosphere is 78% nitrogen • N2 is very stable and must be broken apart by organisms, combined with other atoms into a usable form

The Nitrogen Cycle 1. Nitrogen fixation 2. Nitrification 3. Assimilation 4. Ammonificatio n 5. Denitrification

The nitrogen cycle

1. Nitrogen Fixation • Conversion of N2 → NH3 – – – –

Combustion volcanic action Lightning Industrial processes (making fertilizer)

• Bacteria – Nitrogenase enzyme – Leghemaglobin binds oxygen – Need an anaerobic environment • Nodules • heterocysts

Anabaena, living. LM.

Anabaena, a gram-negative, oxygenic, photosynthetic, filamentous Cyanobacterium (prokaryote). The larger cells in the filament called heterocysts are involved in nitrogen fixing. SEM X660.

Nitrogen-fixing nodules on Soybean roots (Glycine max), 3-6 mm.

• Nitrification: NH3 → NO3 • Soil bacteria convert in a two step process

• Assimilation: Roots absorb NH3, NH4, or NO3 and incorporate them into nucleic acids and protein • Ammonification: Amino acids and nucleotides are broken down into waste products NH3 or NH4 • Denitrification: the reduction of NO3 to N2 • Denitrifying bacteria return some of the

Human activities have changes the global nitrogen budget 1. Nitrogen fertilizers used in agriculture cause excess nitrogen to enter aquatic biomes • Decline of coastal fisheries • Algal blooms • Oxygen depletion of marine and aquatic environments

Human activities have changes the global nitrogen budget • Combustion of gases converts N2 →N2O • Photochemical smog • Acid rain (nitric acid) • Global warming and ozone depletion

The Phosphorus Cycle • The only cycle that does not have a gaseous state • Inorganic phosphate PO43- is released from rocks and sediments through the action of erosion.

Phosphate Cycle • Soil PO43- is absorbed by plants and incorporated into nucleic acids, phospholipids and ATP • Animals obtain most of their PO43- by consumption of other animals and from water • PO43- is released to the soil again by decomposers

• Dissolved PO43- gets absorbed by algae and Phosphorous Cycle aquatic plants in Aquatic • Cycling by Ecosystems consumption • Decomposers break down waste and returns PO43- to sediments on the seabed • Some returns to terrestrial environment through geologic processes • Some returns to the

Human effects on the natural cycling of phosphorous • Cycling of PO43- from aquatic to terrestrial environments is very slow • Human activities accelerate the longterm loss of PO43- from the terrestrial environment – Mining – Fertilizers and agricultural run-off – Sewage

Abiotic Factors in the Biosphere • Sunlight • Temperature • Water • Wind • Rocks and soil • Periodic disturbance

Abiotic Factors in the Biosphere • Sunlight • Provides energy that drives all ecosystems • Intensity and quality of light determines distribution of organisms • Photoperiod affects development and behavior – Migration, flowering, mating, mood

Solar radiation and latitude •

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Input of Solar Energy Earth’s movement in space

Abiotic Factors in the Biosphere • Temperature • Inability of most organisms to regulate internal temperature • Cells rupture and freeze below O C • Proteins denature above 45 C • Extraordinary adaptations enable some organisms to survive outside of this range.

Abiotic Factors in the Biosphere • Water • Availability varies dramatically among habitats • Adaptations to life on land

Major surface ocean currents determine climate

Ocean Currents

Abiotic Factors in the Biosphere • Wind • Amplifies the effects of temperature • Heat and water loss due to evaporation & transpiration • Can affect the growth form of plants

Wind Effects: Flagging

Abiotic Factors in the Biosphere

• Rocks and Soil Physical structure, pH, mineral composition • Periodic Disturbances

– Fires, hurricanes, volcanic eruptions, tornadoes – Recolonization of disturbed area and succession

• Effect of fire on certain ecosystems – Fire frees the nutrient minerals locked in organic matter, removes plant cover, and increases erosion – Many ecosystems, such as savanna, chaparral, grasslands, and certain forests, contain fireadapted organisms

Climate has a direct effect on the biology of organisms

omponents of Climate

• Temperatur e* • Water* • Light • Wind

• • • • • •

Climate is determined by:

Input of Solar Energy Earth’s movement in space Temperature Water Light Wind