Overview: Cool Ecosystem Chapter 55 • An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with Ecosystems and Restoration which they interact Ecology • Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest • Ecosystems’ dynamics involve two main processes: energy flow and chemical cycling • Energy flows through ecosystems while matter cycles within them Concept 55.1: Physical laws govern energy Conservation of Energy flow and chemical cycling in ecosystems • Laws of physics and chemistry apply to • Ecologists study the transformations of energy ecosystems, particularly energy flow and matter within their system • The first law of thermodynamics states that energy cannot be created or destroyed, only transformed • Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat Conservation of Mass • The second law of thermodynamics states that • The law of conservation of mass states that every exchange of energy increases the entropy of matter cannot be created or destroyed the universe • Chemical elements are continually recycled within • In an ecosystem, energy conversions are not ecosystems completely efficient, and some energy is always • In a forest ecosystem, most nutrients enter as dust lost as heat or solutes in rain and are carried away in water • Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products Energy, Mass, and Trophic Levels • Autotrophs build molecules themselves using • Energy and nutrients pass from primary photosynthesis or chemosynthesis as an energy producers (autotrophs) to primary consumers source (herbivores) to secondary consumers • Heterotrophs depend on the biosynthetic output of (carnivores) to tertiary consumers (carnivores other organisms that feed on other carnivores) Figure 55.4 Sun Key Chemical cycling • Detritivores, or decomposers , are consumers Heat Energy flow that derive their energy from detritus , nonliving Primary producers organic matter • Prokaryotes and fungi are important detritivores Primary Detritus • Decomposition connects all trophic levels consumers Secondary and Microorganisms and other tertiary consumers detritivores Concept 55.2: Energy and other limiting Ecosystem Energy Budgets factors control primary production in • The extent of photosynthetic production sets the ecosystems spending limit for an ecosystem’s energy budget • In most ecosystems, primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period • In a few ecosystems, chemoautotrophs are the primary producers The Global Energy Budget Gross and Net Production • The amount of solar radiation reaching the Earth’s • Total primary production is known as the surface limits photosynthetic output of ecosystems ecosystem’s gross primary production (GPP) • Only a small fraction of solar energy actually • GPP is measured as the conversion of chemical strikes photosynthetic organisms, and even less is energy from photosynthesis per unit time of a usable wavelength • Net primary production (NPP) is GPP minus energy used by primary producers for respiration • NPP is expressed as − Energy per unit area per unit time (J/m 2⋅yr), or − Biomass added per unit area per unit time (g/m 2⋅yr) Figure 55.5 TECHNIQUE 80 Snow • NPP is the amount of new biomass added in a Clouds given time period 60 • Only NPP is available to consumers Vegetation • Standing crop is the total biomass of 40 photosynthetic autotrophs at a given time Soil Percentreflectance • Ecosystems vary greatly in NPP and contribution 20 to the total NPP on Earth Liquid water 0 400 600 800 1,000 1,200 Visible Near-infrared Wavelength (nm) Figure 55.6 Net primary production • Tropical rain forests, estuaries, and coral reefs are (kg carbon/m 2....yr) among the most productive ecosystems per unit 3 area • Marine ecosystems are relatively unproductive per 2 unit area, but contribute much to global net primary production because of their volume 1 0 Figure 55.7 • Net ecosystem production (NEP) is a measure Float surfaces of the total biomass accumulation during a given for 6–12 hours period to transmit data to satellite. • NEP is gross primary production minus the total respiration of all organisms (producers and Total cycle time: Float descends 10 days consumers) in an ecosystem to 1,000 m and “parks.” O2 concentration is • NEP is estimated by comparing the net flux of CO 2 recorded as float ascends. and O 2 in an ecosystem, two molecules connected by photosynthesis Drift time: 9 days • The release of O 2 by a system is an indication that it is also storing CO 2 Primary Production in Aquatic Ecosystems Light Limitation • In marine and freshwater ecosystems, both light • Depth of light penetration affects primary and nutrients control primary production production in the photic zone of an ocean or lake Figure 55.8 RESULTS Nutrient Limitation 30 Ammonium enriched • More than light, nutrients limit primary production 24 Phosphate in geographic regions of the ocean and in lakes enriched • A limiting nutrient is the element that must be Unenriched added for production to increase in an area 18 control • Nitrogen and phosphorous are typically the nutrients that most often limit marine production 12 • Nutrient enrichment experiments confirmed that Phytoplankton density nitrogen was limiting phytoplankton growth off (millionsofcells per mL) 6 the shore of Long Island, New York 0 ABCGD E F Collection site • Experiments in the Sargasso Sea in the subtropical Atlantic Ocean showed that iron limited primary production • Upwelling of nutrient-rich waters in parts of the oceans contributes to regions of high primary production • The addition of large amounts of nutrients to lakes has a wide range of ecological impacts Primary Production in Terrestrial Ecosystems • In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of • In terrestrial ecosystems, temperature and most fish species moisture affect primary production on a large • In lakes, phosphorus limits cyanobacterial growth scale more often than nitrogen • Primary production increases with moisture • This has led to the use of phosphate-free detergents Nutrient Limitations and Adaptations That Reduce Them • Actual evapotranspiration is the water transpired by plants and evaporated from a landscape • On a more local scale, a soil nutrient is often the • It is affected by precipitation, temperature, and limiting factor in primary production solar energy • In terrestrial ecosystems, nitrogen is the most • It is related to net primary production common limiting nutrient • Phosphorus can also be a limiting nutrient, especially in older soils Concept 55.3: Energy transfer between trophic levels is typically only 10% efficient • Various adaptations help plants access limiting nutrients from soil • Secondary production of an ecosystem is the – Some plants form mutualisms with nitrogen-fixing amount of chemical energy in food converted to bacteria new biomass during a given period of time – Many plants form mutualisms with mycorrhizal fungi; these fungi supply plants with phosphorus and other limiting elements – Roots have root hairs to increase surface area – Many plants release enzymes that increase the availability of limiting nutrients Figure 55.10 Production Efficiency • When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for Plant material secondary production eaten by caterpillar • An organism’s production efficiency is the 200 J fraction of energy stored in food that is not used for respiration Production Net secondary production × 100% 67 J Cellular = 100 J respiration efficiency Assimilation of primary production Feces 33 J Not assimilated Growth (new biomass; Assimilated secondary production) Trophic Efficiency and Ecological Pyramids • Birds and mammals have efficiencies in the • Trophic efficiency is the percentage of range of 1 −3% because of the high cost of production transferred from one trophic level to the endothermy next • Fishes have production efficiencies of around • It is usually about 10%, with a range of 5% to 20% 10% • Trophic efficiency is multiplied over the length of a • Insects and microorganisms have efficiencies of food chain 40% or more • Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer • A pyramid of net production represents the loss of • In a biomass pyramid, each tier represents the dry energy with each transfer in a food chain weight of all organisms in one trophic level • Most biomass pyramids show a sharp decrease at successively higher trophic levels Figure 55.12 Trophic level Dry mass (g/m 2) Tertiary consumers 1.5 Secondary consumers 11 • Certain aquatic ecosystems have inverted Primary consumers 37 Primary producers 809 biomass pyramids: producers (phytoplankton) are consumed so quickly that they are outweighed by (a) Most ecosystems (data from a Florida bog) primary consumers • Turnover time is a ratio of the standing crop biomass to production Trophic level Dry mass (g/m 2) Primary consumers (zooplankton) 21 Primary producers (phytoplankton) 4 (b) Some aquatic ecosystems (data from the English Channel) Concept 55.4: Biological and geochemical processes cycle nutrients and water in • Dynamics of energy flow in ecosystems have important implications for the human population ecosystems • Eating meat is a relatively inefficient way of • Life depends on recycling chemical