Ecosystems Chapter 55 AP Biology

Objectives…I can… Describe the flow of energy in an ecosystem. Explain how decomposition connects all trophic levels in an ecosystem. Define gross and net primary production. Distinguish among pyramids of net production, of biomass, and of numbers. Describe the water cycle, the nitrogen cycle, the carbon cycle, and the phosphorous cycle.

Objectives…I can… Describe how agricultural practices can interfere with nitrogen cycling. Describe the causes and consequences of acid precipitation. Explain why toxic compounds have a greater effect on top level carnivores. Describe how increased carbon dioxide in the atmosphere could affect the Earth. Describe the causes and consequences of ozone depletion.

Overview: Ecosystems, Energy, and Matter An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact.

Ecosystems can range from a microcosm, such as an aquarium to a large area such as a lake or forest. Figure 54.1

Energy flows through ecosystems, while matter cycles within them. Regardless of an ecosystem’s size its dynamics involve two main processes: energy flow and chemical cycling. Energy flows through ecosystems, while matter cycles within them.

Energy flows through an ecosystem entering as light and exiting as heat. Figure 54.2 Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow

Trophic Relationships Primary producers – autotrophs (make their own food) ex: plants Heterotrophs – consumers (eat other organisms) ex: animals, fungi Primary consumers – herbivores (eat plants) Secondary consumers – carnivores (eat primary consumers) Tertiary consumers – carnivores (eat secondary consumers) Omnivores – eat producers and other consumers

Also called decomposers Detritivores - mainly bacteria and fungi, recycle essential chemical elements Also called decomposers Figure 54.3

Primary Productivity Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period. It is the photosynthetic output of an ecosystem’s producers. Physical and chemical factors limit primary production in ecosystems.

Gross and Net Primary Production Total primary production in an ecosystem is known as that ecosystem’s gross primary production (GPP). Not all of this production is stored as organic material in the growing plants. Net primary production (NPP) is equal to GPP minus the energy used by the primary producers for respiration (to make energy for their own life processes). Only NPP is available to consumers.

CFU 1. True or False – Matter flows through an ecosystem, where as energy is recycled. 2. What are three terms that most photosynthetic organisms are known by? 3. Why are detritovores necessary in any ecosystem. 4. What is the difference between gross and net primary productivity?

Different ecosystems vary considerably in their net primary production. Lake and stream Open ocean Continental shelf Estuary Algal beds and reefs Upwelling zones Extreme desert, rock, sand, ice Desert and semidesert scrub Tropical rain forest Savanna Cultivated land Boreal forest (taiga) Temperate grassland Tundra Tropical seasonal forest Temperate deciduous forest Temperate evergreen forest Swamp and marsh Woodland and shrubland 10 20 30 40 50 60 500 1,000 1,500 2,000 2,500 5 15 25 Percentage of Earth’s net primary production Key Marine Freshwater (on continents) Terrestrial 5.2 0.3 0.1 4.7 3.5 3.3 2.9 2.7 2.4 1.8 1.7 1.6 1.5 1.3 1.0 0.4 125 360 3.0 90 2,200 900 600 800 700 140 1,600 1,200 1,300 250 5.6 1.2 0.9 0.04 22 7.9 9.1 9.6 5.4 0.6 7.1 4.9 3.8 2.3 65.0 24.4 Figure 54.4a–c Percentage of Earth’s surface area (a) Average net primary production (g/m2/yr) (b) (c)

Secondary Production The secondary production of an ecosystem is the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given period of time. Energy transfer between trophic levels is usually around 10% efficient. (Rule of Ten – only 10% of the energy is “passed on” to the next level)

Pyramids of Production This loss of energy with each transfer in a food chain can be represented by a pyramid of net production. Figure 54.11 Tertiary consumers Secondary Primary producers 1,000,000 J of sunlight 10 J 100 J 1,000 J 10,000 J

Most biomass pyramids show a sharp decrease at successively higher trophic levels. Figure 54.12a (a) 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/m2) Primary producers Tertiary consumers Secondary consumers Primary consumers 1.5 11 37 809

Number of individual organisms Pyramids of Numbers A pyramid of numbers represents the number of individual organisms in each trophic level. Figure 54.13 Trophic level Number of individual organisms Primary producers Tertiary consumers Secondary consumers Primary consumers 3 354,904 708,624 5,842,424

Laws of Thermodynamics and Ecosystems First Law of Thermodynamics – energy cannot be created or destroyed, it can be transformed   Second Law of Thermodynamics – in each energy transformation some energy is lost (usually as heat)

CFU 1. What happens to the amount of biomass as you move up an ecological pyramid? 2. Describe the efficiency of the energy transfer between trophic levels. 3. How does the Second Law of Thermodynamics apply to an ecological pyramid?

Biogeochemical Cycles Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem. Life on Earth depends on the recycling of essential chemical elements. Nutrient circuits that cycle matter through an ecosystem involve both biotic and abiotic components and are often called biogeochemical cycles.

Biogeochemical Cycles Figure 54.17 Transport over land Solar energy Net movement of water vapor by wind Precipitation over ocean Evaporation from ocean Evapotranspiration from land Percolation through soil Runoff and groundwater CO2 in atmosphere Photosynthesis Cellular respiration Burning of fossil fuels and wood Higher-level consumers Primary Detritus Carbon compounds in water Decomposition THE WATER CYCLE THE CARBON CYCLE

Water moves in a global cycle driven by solar energy. The carbon cycle reflects the reciprocal processes of photosynthesis and cellular respiration.

THE NITROGEN CYCLE THE PHOSPHORUS CYCLE Figure 54.17 N2 in atmosphere Denitrifying bacteria Nitrifying Nitrification Nitrogen-fixing soil bacteria bacteria in root nodules of legumes Decomposers Ammonification Assimilation NH3 NH4+ NO3 NO2  Rain Plants Consumption Decomposition Geologic uplift Weathering of rocks Runoff Sedimentation Plant uptake of PO43 Soil Leaching THE NITROGEN CYCLE THE PHOSPHORUS CYCLE

Chemical Cycles in Ecosystems Chart

Nitrogen Cycle Nitrogen Fixation – (assimilation) – bacteria on the roots of legumes (Ex: bean plants) fix atmospheric nitrogen as ammonium -Also can also be done by lightning and UV radiation Nitrification – (assimilation) – done by nitrifying bacteria, ammonium becomes nitrite

Nitrogen Cycle Denitrification – (release) - done by denitrifying bacteria, nitrogen is released back to the atmosphere Ammonification – bacteria convert organic compounds back to ammonium

As the human population has grown in size The human population is disrupting chemical cycles throughout the biosphere. As the human population has grown in size our activities have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world.

Agriculture and Nitrogen Cycling Agriculture constantly removes nutrients from ecosystems that would ordinarily be cycled back into the soil. Figure 54.20

Nitrogen is the main nutrient lost through agriculture thus, agriculture has a great impact on the nitrogen cycle. Industrially produced fertilizer is typically used to replace lost nitrogen but the effects on an ecosystem can be harmful.

Sewage and fertilizer runoff contaminates freshwater ecosystems causing eutrophication, excessive algal growth, which can cause significant harm to these ecosystems.

Acid Precipitation Combustion of fossil fuels is the main cause of acid precipitation. Figure 54.21 4.6 4.3 4.1 Europe North America

By the year 2000 the entire contiguous United States was affected by acid precipitation.

Toxins in the Environment Humans release an immense variety of toxic chemicals including thousands of synthetics previously unknown to nature. One of the reasons such toxins are so harmful is that some toxins become more concentrated in successive trophic levels of a food web. This is called biological magnification.

In biological magnification toxins concentrate at higher trophic levels because at these levels biomass tends to be lower. Figure 54.23 Concentration of PCBs Herring gull eggs 124 ppm Zooplankton 0.123 ppm Phytoplankton 0.025 ppm Lake trout 4.83 ppm Smelt 1.04 ppm

Rising Atmospheric CO2 Due to the increased burning of fossil fuels and other human activities the concentration of atmospheric CO2 has been steadily increasing. Figure 54.24 CO2 concentration (ppm) 390 380 370 360 350 340 330 320 310 300 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 1.05 0.90 0.75 0.60 0.45 0.30 0.15 0.15  0.30  0.45 Temperature variation (C) Temperature CO2 Year

The Greenhouse Effect and Global Warming The greenhouse effect is caused by atmospheric CO2 trapping heat in the atmosphere. It is necessary to keep the surface of the Earth at a habitable temperature. - Increased levels of atmospheric CO2 are magnifying the greenhouse effect which could cause global warming and significant climatic change.

Depletion of Atmospheric Ozone Life on Earth is protected from the damaging effects of UV radiation by a protective layer or ozone molecules present in the atmosphere.

Satellite studies of the atmosphere suggest that the ozone layer has been gradually thinning since 1975 Figure 54.26 Ozone layer thickness (Dobson units) Year (Average for the month of October) 350 300 250 200 150 100 50 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

The destruction of atmospheric ozone probably results from chlorine-releasing pollutants (chloroflourocarbons) produced by human activity (arosal spray cans, freon use) Figure 54.27 1 2 3 Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (ClO) and oxygen (O2). Two ClO molecules react, forming chlorine peroxide (Cl2O2). Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again. Sunlight Chlorine O3 O2 ClO Cl2O2 Chlorine atoms

Scientists first described an “ozone hole” over Antarctica in 1985; 1987 –Montreal Protocol – limited use of CFC’s worldwide Good News! It is showing signs of recovery at this time.

What can you do to help preserve the Earth’s ecosystems?