Ecosystems Chapter 47

Impacts, Issues Bye-Bye, Blue Bayou  Among many effects of global warming, coastal marshes in Louisiana are disappearing under rising water – along with habitat and revenues

47.1 The Nature of Ecosystems  Ecosystem An array of organisms and a physical environment, all interacting through a one-way flow of energy and a cycling of nutrients Sustained by ongoing inputs of energy and nutrients (open system)

Overview of Participants  Primary producers (autotrophs) Obtain energy from nonliving sources (sunlight) Build organic compounds from CO 2 and water  Consumers (heterotrophs) Get energy and carbon from organic sources Carnivores, herbivores, parasites, omnivores

Overview of Participants  Detritivores, such as earthworms and crabs, eat small particles of organic matter (detritus)  Decomposers, such as bacteria and fungi, feed on organic wastes and remains and break them down into inorganic building blocks

Energy and Nutrients  Energy flows one way Producers capture light energy and convert it to bond energy in organic molecules (photosynthesis) Metabolic reactions break bonds (aerobic respiration) and give off heat, which is not recycled  Nutrients are cycled Producers take up inorganic compounds from the environment; decomposers return them

Trophic Structure of Ecosystems  Trophic levels Hierarchy of feeding relationships in which energy is transferred when one organism eats another Each trophic level is a number of transfers away from the system’s original energy input

Food Chain  Food chain A sequence of steps by which some energy captured by primary producers is transferred to organisms at successively higher tropic levels Omnivores feed at several levels  A number of food chains cross-connect with each other as food webs

47.1 Key Concepts Organization of Ecosystems  An ecosystem consists of a community and its physical environment  A one-way flow of energy and a cycling of raw materials among its interacting participants maintain it  It is an open system, with inputs and outputs of energy and nutrients

47.2 The Nature of Food Webs  Food webs Multiple interconnecting food chains, including grazing and detrital food chains  Grazing food chain Energy stored in producers flows to herbivores, which tend to be large animals  Detrital food chain Energy in producers flows to decomposers and detritivores, which tend to be small

Land Versus Aquatic Food Chains  In land ecosystems, most of the energy stored in producers moves through detrital food chains  In aquatic ecosystems, most of the energy in producers flows to grazers rather than detritivores

How Many Transfers?  Cumulative energy losses from energy transfers between trophic levels limits the length of food chains to four or five trophic levels Food chains tend to be shortest in variable habitats, longer in stable habitats Food webs with more carnivores have fewer connections; herbivores have more connections

47.2 Key Concepts Food Webs  Food chains are linear sequences of feeding relationships  Food chains cross-connect as food webs  Most energy that enters a food web returns to the environment, mainly as metabolic heat  Nutrients are recycled within the food web

47.3 Energy Flow Through Ecosystems  Primary producers capture energy and take up nutrients, which move to other trophic levels  Primary production Rate at which producers capture and store energy Gross primary production – amount captured Net primary production – amount used in growth

Ecological Pyramids  A biomass pyramid depicts dry weight of organisms at each trophic level in an ecosystem Largest tier is usually producers For some aquatic systems, pyramid is inverted  An energy pyramid depicts the energy that enters each trophic level in an ecosystem Largest tier is always producers

A Biomass Pyramid  An aquatic ecosystem: Silver Springs, Florida

Ecological Efficiency  Between 5 and 30 percent of energy in tissues of organisms at one trophic level ends up in tissues of those at the next trophic level Some energy is lost as heat Some biomass is not digested  Efficiency of transfers tends to be greatest in aquatic systems (less lignin, more ectotherms)

47.4 Biological Magnification  Biological magnification Some harmful substances, such as DDT, become increasingly concentrated in tissues of organisms as they move up the food chain

DDT and Silent Spring  DDT is a synthetic pesticide used extensively in the 1940s and 1950s; it also killed other organisms such as songbirds and fishes  Biological magnification of DDT in bird top carnivores weakened eggs; populations shrank  Rachel Carson’s book Silent Spring exposed dangers of DDT, prompting its ban in the US

The Mercury Menace  Mercury from coal-burning power plants, mines and industries washes into aquatic habitats  Mercury accumulates in fish top carnivores, and people who eat them  Mercury damages developing human nervous systems; children and women who are pregnant or nursing should avoid eating contaminated fish

Key Concepts Energy and Materials Flow  Ecosystems differ in how much energy their producers capture and how much is stored in each trophic level  Some toxins that enter an ecosystem can become increasingly concentrated as they pass from one trophic level to another

47.5 Biogeochemical Cycles  In a biogeochemical cycle, an essential element moves from nonliving environmental reservoirs, into living organisms, then back to the reservoirs  Elements essential to life (nutrients) include oxygen, hydrogen, carbon, nitrogen, phosphorus

Biogeochemical Cycles  Nutrients move from inorganic reservoirs (rocks, sediments, water, atmosphere) to living systems through primary producers  Photosynthetic organisms take up dissolved ions and carbon dioxide; bacteria fix nitrogen gas

47.6 The Water Cycle  The water cycle moves on a global scale Water moves slowly from the world ocean (the main reservoir) through the atmosphere (by evaporation and transpiration), onto land (by condensation and precipitation), then back to the ocean

Where Water Moves  Watershed An area from which all precipitation drains into a specific waterway  Groundwater Water in soil and aquifers (permeable rock layers that hold water)  Runoff Flows over saturated ground into streams

A Global Water Crisis  Plenty of saltwater, little freshwater Two-thirds of freshwater use sustains agriculture  Salinization Buildup of mineral salts in soil Stunts crop plants and decreases yields  Aquifers are becoming polluted and depleted

Desalinization  Desalinization The removal of salt from seawater to increase freshwater supplies Requires a lot of fossil fuel Used mainly in places with large fuel reserves and small populations

47.7 Carbon Cycle  In the carbon cycle, carbon moves though all food webs, to and from its major reservoirs Earth’s crust: 66 to 100 million gigatons World ocean: 38,000 to 40,000 gigatons Fossil fuel reserves: 4,000 gigatons Detritus in soil: 1,500 to 1,600 gigatons Air: 766 gigatons (mostly as CO 2 ) Biomass: 540 to 610 gigatons

Movements of Carbon  Most of the annual cycling of carbon occurs between the ocean and the atmosphere Some CO 2 in surface waters is converted to bicarbonate (carbon-oxygen cycling) and moved by ocean currents to deep ocean reservoirs  Photosynthesis, aerobic respiration, decomposition, and formation of carbonate sediments all contribute to the carbon cycle

Humans Are Altering the Carbon Cycle  Each year we withdraw 4 to 5 gigatons of fossil fuel from environmental reservoirs; and put 6 gigatons more carbon into the air than can be recycled to ocean reservoirs  Excess CO 2 entering the atmosphere may be a factor in global climate change

47.8 Greenhouse Gases, Global Warming  Greenhouse effect Radiant energy from the sun is absorbed by Earth’s surface and radiated back as heat Gases in the upper atmosphere trap heat like a greenhouse, and radiate it back to Earth Greenhouse gases: carbon dioxide, water, nitrous oxide, methane, chlorofluorocarbons (CFCs)

Atmospheric Observations  Atmospheric CO 2 fluctuates annually with patterns of photosynthesis  Average concentrations of CO 2 and other greenhouse gases are increasing  Human activities – mainly burning of fossil fuels – increase greenhouse gases

Global Warming  Global warming A long-term increase in temperature near Earth’s surface, currently about 1.8°C (3.2°F) per century  Scientists expect far-reaching effects Melting glaciers and rising sea levels Altered global precipitation patterns, droughts and flooding, more intense hurricanes

47.9 Nitrogen Cycle  Gaseous nitrogen (N 2 ) makes up about 80 percent of the lower atmosphere Most organisms can’t use gaseous nitrogen  The nitrogen cycle starts with nitrogen fixation Nitrogen-fixing bacteria convert N 2 in the air to ammonia (NH 3 ), then to ammonium (NH 4 + ) and nitrate (NO 3 - ), which plants easily take up

Other Nitrogen Inputs Into Ecosystems  Ammonification Bacteria and fungi make additional ammonium available to plants when they break down nitrogen-rich wastes and remains  Nitrification Bacteria convert ammonium to nitrite (NO 2 - ), and then to nitrate, which plants easily take up

Losing Nitrogen from Ecosystems  Denitrification Denitrifying bacteria convert nitrate or nitrite to gaseous nitrogen (N 2 ) or nitrogen oxide (NO 2 )  Ammonium, nitrite, and nitrate are also lost from land ecosystems in runoff and by leaching

Disruptions by Human Activities  Deforestation and conversion of grassland to farmland causes nitrogen loss Plant removal increases erosion and leaching  Synthetic ammonium fertilizers increase soil acidity and encourage ion exchange Calcium and magnesium ions are washed away  Burning fossil fuels releases nitrogen oxides Contribute to global warming and acid rain

47.10 The Phosphorus Cycle  Phosphorus cycle A sedimentary cycle that moves phosphorus from its main reservoir (Earth’s crust) through soils and sediments, aquatic habitats, and bodies of living organisms

Phosphate and the Phosphorus Cycle  Phosphorus in rocks is mainly phosphate (PO 4 3- ) Water moves phosphate through ecosystems  Phosphorus is a limiting factor on plant growth Taken up by plants only in ionized form Required for ATP, phospholipids, nucleic acids Depleted when forest is converted to farmland

Eutrophication: Too Many Nutrients  Eutrophication Nutrient enrichment of any ecosystem that is otherwise low in nutrients; often a form of nutrient pollution from agricultural runoff or sewage  Eutrophication of a lake can cause excessive algal growth, oxygen depletion, and fish kills

Eutrophication  Phosphorus is often the limiting factor in aquatic ecosystems

Key Concepts Cycling of Water and Nutrients  The availability of water, carbon, nitrogen, phosphorus, and other substances influences primary productivity  These substances move slowly in global cycles, from environmental reservoirs, into food webs, then back to reservoirs