Ecosystems and Physical Laws Ecologists view ecosystems as transformers of energy and processors of matter Laws of physics and chemistry apply to ecosystems, particularly energy flow Energy is conserved but degraded to heat during ecosystem processes

Trophic Relationships Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores) Energy flows through an ecosystem, entering as light and exiting as heat Nutrients cycle within an ecosystem

Microorganisms and other detritivores Tertiary consumers Secondary consumers Detritus Primary consumers Sun Primary producers Heat Key Chemical cycling Energy flow

Decomposition Decomposition connects all trophic levels Detritivores, mainly bacteria and fungi, recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs

Physical and chemical factors limit primary production in ecosystems Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems Only a small fraction of solar energy actually strikes photosynthetic organisms

Gross and Net Primary Production Total primary production is known as the ecosystem’s gross primary production (GPP) Net primary production (NPP) is GPP minus energy used by primary producers for respiration Only NPP is available to consumers Ecosystems vary greatly in net primary production and contribution to the total NPP on Earth Overall, terrestrial ecosystems contribute about two-thirds of global NPP and marine ecosystems contribute about one-third

Open ocean Continental shelf Upwelling zones Extreme desert, rock, sand, ice Swamp and marsh Lake and stream Desert and semidesert scrub Tropical rain forest Temperate deciduous forest Temperate evergreen forest Tropical seasonal forest Savanna Cultivated land Estuary Algal beds and reefs Boreal forest (taiga) Temperate grassland Woodland and shrubland Tundra Freshwater (on continents) Terrestrial Marine Key Percentage of Earth’s surface area Average net primary production (g/m 2 /yr) ,500 2,0001,500 1, Percentage of Earth’s net primary production , , , ,600 1,200 1,300 2,

Light Limitation Depth of light penetration affects primary production in the photic zone of an ocean or lake

Nutrient Limitation More than light, nutrients limit primary production in geographic regions of the ocean and in lakes A limiting nutrient is the element that must be added for production to increase in an area Nitrogen and phosphorous are typically the nutrients that most often limit marine production Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth in an area of the ocean

Atlantic Ocean Shinnecock Bay Moriches Bay Long Island Coast of Long Island, New York Great South Bay Phytoplankton Inorganic phosphorus Great South Bay Moriches Bay Shinnecock Bay Station number Phytoplankton biomass and phosphorus concentration Phytoplankton (millions of cells/mL) Inorganic phosphorus (µm atoms/L) Ammonium enriched Station number Phytoplankton (millions of cells per mL) Starting algal density Phytoplankton response to nutrient enrichment Phosphate enriched Unenriched control

The addition of large amounts of nutrients to lakes has a wide range of ecological impacts In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species

Primary Production in Terrestrial and Wetland Ecosystems In terrestrial and wetland ecosystems, climatic factors such as temperature and moisture affect primary production on a large scale Actual evapotranspiration can represent the contrast between wet and dry climates Actual evapotranspiration is the water annually transpired by plants and evaporated from a landscape It is related to net primary production

Control August 1980 July June Live, above-ground biomass (g dry wt/m 2 ) N + P N only P only

Energy transfer between trophic levels is usually less than 20% efficient Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time When a caterpillar feeds on a leaf, only about one- sixth of the leaf’s energy is used for secondary production An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration

Growth (new biomass) Cellular respiration Feces 100 J 33 J 67 J 200 J Plant material eaten by caterpillar

Trophic Efficiency and Ecological Pyramids Trophic efficiency is the percentage of production transferred from one trophic level to the next It usually ranges from 5% to 20% A pyramid of net production represents the loss of energy with each transfer in a food chain

1,000,000 J of sunlight 10,000 J 1,000 J 100 J 10 J Tertiary consumers Secondary consumers Primary consumers Primary producers

Trophic level Dry weight (g/m 2 ) Tertiary consumers Secondary consumers Primary consumers Primary producers Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida.

Trophic level Dry weight (g/m 2 ) Primary consumers (zooplankton) Primary producers (phytoplankton) 21 4 In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton) supports a larger standing crop of primary consumers (zooplankton).

Trophic level Number of individual organisms Tertiary consumers Secondary consumers Primary consumers Primary producers 3 354, ,624 5,842,424

The green world hypothesis proposes several factors that keep herbivores in check: – Plant defenses – Limited availability of essential nutrients – Abiotic factors – Intraspecific competition – Interspecific interactions

A General Model of Chemical Cycling Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level A model of nutrient cycling includes main reservoirs of elements and processes that transfer elements between reservoirs All elements cycle between organic and inorganic reservoirs

Fossilization Reservoir a Reservoir b Reservoir c Reservoir d Organic materials available as nutrients Organic materials unavailable as nutrients Inorganic materials available as nutrients Inorganic materials unavailable as nutrients Living organisms, detritus Coal, oil, peat Atmosphere, soil, water Minerals in rocks Assimilation, photosynthesis Burning of fossil fuels Weathering, erosion Formation of sedimentary rock Respiration, decomposition, excretion

Biogeochemical Cycles In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors: 1. Each chemical’s biological importance 2. Forms in which each chemical is available or used by organisms 3. Major reservoirs for each chemical 4. Key processes driving movement of each chemical through its cycle

Transport over land Precipitation over land Evaporation from ocean Precipitation over ocean Net movement of water vapor by wind Solar energy Evapotranspiration from land Runoff and groundwater Percolation through soil

Cellular respiration Burning of fossil fuels and wood Carbon compounds in water Photosynthesis Primary consumers Higher-level consumers Detritus Decomposition CO 2 in atmosphere

Assimilation N 2 in atmosphere Decomposers Nitrifying bacteria Nitrifying bacteria Nitrogen-fixing soil bacteria Denitrifying bacteria Nitrification Ammonification Nitrogen-fixing bacteria in root nodules of legumes NO 3 – NO 2 – NH 4 + NH 3

Sedimentation Plants Rain Runoff Weathering of rocks Geologic uplift Soil Leaching Decomposition Plant uptake of PO 4 3– Consumption

Decomposition and Nutrient Cycling Rates Decomposers (detritivores) play a key role in the general pattern of chemical cycling Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition

Concrete dams and weirs built across streams at the bottom of watersheds enabled researchers to monitor the outflow of water and nutrients from the ecosystem. One watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling. The concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed. Deforested Control Completion of tree cutting Nitrate concentration in runoff (mg/L)

Agriculture and Nitrogen Cycling Agriculture removes nutrients from ecosystems that would ordinarily be cycled back into the soil Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

Contamination of Aquatic Ecosystems Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem When excess nutrients are added to an ecosystem, the critical load is exceeded Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems

Acid Precipitation Combustion of fossil fuels is the main cause of acid precipitation North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid

Field pH  – – – – – – – – – –4.4 <

Toxins in the Environment Humans release many toxic chemicals, including synthetics previously unknown to nature In some cases, harmful substances persist for long periods in an ecosystem One reason toxins are harmful is that they become more concentrated in successive trophic levels In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower

Zooplankton ppm Phytoplankton ppm Lake trout 4.83 ppm Smelt 1.04 ppm Herring gull eggs 124 ppm Concentration of PCBs

Chlorine atoms O3O3 Chlorine Cl 2 O 2 CIO O2O2 O2O2 Chlorine from CFCs interacts with ozone (O 3 ), forming chlorine monoxide (CIO) and oxygen (O 2 ). Sunlight causes Cl 2 O 2 to break down into O 2 and free chlorine atoms. The chlorine atoms can begin the cycle again. Two CIO molecules react, forming chlorine peroxide (Cl 2 O 2 ). Sunlight

Animations and Videos Chapter Quiz Questions – 1 Chapter Quiz Questions – 2 An Idealized Energy Pyramid Energy Flow and The Water Cycle The Global Hydrological Cycle The Carbon Cycle The Global Carbon Cycle Nitrogen Cycle The Global Nitrogen Cycle

Animations and Videos Phosphorus Cycle Sulfur Cycle Nitrogen Fixation Animation