Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 54 Ecosystems

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecosystems and Physical Laws The laws of physics and chemistry apply to ecosystems – Particularly in regard to the flow of energy Energy is conserved – But degraded to heat during ecosystem processes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophic Relationships Energy and nutrients pass from primary producers (autotrophs) – To primary consumers (herbivores) and then to secondary consumers (carnivores)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Decomposition – Connects all trophic levels

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Detritivores, mainly bacteria and fungi, recycle essential chemical elements – By decomposing organic material and returning elements to inorganic reservoirs Figure 54.3

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 54.2: 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecosystem Energy Budgets The extent of photosynthetic production – Sets the spending limit for the energy budget of the entire ecosystem

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Net primary production (NPP) – Is equal to GPP minus the energy used by the primary producers for respiration Only NPP – Is available to consumers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nutrient Limitation More than light, nutrients limit primary production – Both in different geographic regions of the ocean and in lakes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A limiting nutrient is the element that must be added – In order for production to increase in a particular area Nitrogen and phosphorous – Are typically the nutrients that most often limit marine production

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In some areas, sewage runoff – Has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes Figure 54.7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 geographic scale

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 54.3: Energy transfer between trophic levels is usually less than 20% efficient 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophic Efficiency and Ecological Pyramids Trophic efficiency – Is the percentage of production transferred from one trophic level to the next – Usually ranges from 5% to 20%

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyramids of Production This loss of energy with each transfer in a food chain – Can be represented by a pyramid of net production Figure Tertiary consumers Secondary consumers Primary consumers Primary producers 1,000,000 J of sunlight 10 J 100 J 1,000 J 10,000 J

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The dynamics of energy flow through ecosystems – Have important implications for the human population Eating meat – Is a relatively inefficient way of tapping photosynthetic production

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Worldwide agriculture could successfully feed many more people – If humans all fed more efficiently, eating only plant material Figure Trophic level Secondary consumers Primary consumers Primary producers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The green world hypothesis proposes several factors that keep herbivores in check – Plants have defenses against herbivores – Nutrients, not energy supply, usually limit herbivores – Abiotic factors limit herbivores – Intraspecific competition can limit herbivore numbers – Interspecific interactions check herbivore densities

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 54.4: 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A General Model of Chemical Cycling Gaseous forms of carbon, oxygen, sulfur, and nitrogen – Occur in the atmosphere and cycle globally Less mobile elements, including phosphorous, potassium, and calcium – Cycle on a more local level

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water moves in a global cycle – Driven by solar energy The carbon cycle – Reflects the reciprocal processes of photosynthesis and cellular respiration

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most of the nitrogen cycling in natural ecosystems – Involves local cycles between organisms and soil or water The phosphorus cycle – Is relatively localized

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Decomposition and Nutrient Cycling Rates Decomposers (detritivores) play a key role – In the general pattern of chemical cycling Figure Consumers Producers Nutrients available to producers Abiotic reservoir Geologic processes Decomposers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 54.5: 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nutrient Enrichment In addition to transporting nutrients from one location to another – Humans have added entirely new materials, some of them toxins, to ecosystems

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Contamination of Aquatic Ecosystems The critical load for a nutrient – Is the amount of that nutrient that can be absorbed by plants in an ecosystem without damaging it

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When excess nutrients are added to an ecosystem, the critical load is exceeded – And the remaining nutrients can contaminate groundwater and freshwater and marine ecosystems

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sewage runoff contaminates freshwater ecosystems – Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acid Precipitation Combustion of fossil fuels – Is the main cause of acid precipitation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings North American and European ecosystems downwind from industrial regions – Have been damaged by rain and snow containing nitric and sulfuric acid Figure Europe North America

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings By the year 2000 – The entire contiguous United States was affected by acid precipitation Figure Field pH  – – – – – – – – – –4.4  4.3

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 they become more concentrated in successive trophic levels of a food web

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In biological magnification – Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower Figure Concentration of PCBs Herring gull eggs 124 ppm Zooplankton ppm Phytoplankton ppm Lake trout 4.83 ppm Smelt 1.04 ppm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Atmospheric Carbon Dioxide One pressing problem caused by human activities – Is the rising level of atmospheric carbon dioxide

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rising Atmospheric CO 2 Due to the increased burning of fossil fuels and other human activities – The concentration of atmospheric CO 2 has been steadily increasing Figure CO 2 concentration (ppm)  0.15  0.30  0.45 Temperature variation (  C) Temperature CO 2 Year

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Greenhouse Effect and Global Warming The greenhouse effect is caused by atmospheric CO 2 – But is necessary to keep the surface of the Earth at a habitable temperature

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Increased levels of atmospheric CO 2 are magnifying the greenhouse effect – Which could cause global warming and significant climatic change

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Satellite studies of the atmosphere – Suggest that the ozone layer has been gradually thinning since 1975 Figure Ozone layer thickness (Dobson units) Year (Average for the month of October)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The destruction of atmospheric ozone – Probably results from chlorine-releasing pollutants produced by human activity Figure Chlorine from CFCs interacts with ozone (O 3 ), forming chlorine monoxide (ClO) and oxygen (O 2 ). Two ClO molecules react, forming chlorine peroxide (Cl 2 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. Sunlight ChlorineO3O3 O2O2 ClO Cl 2 O 2 O2O2 Chlorine atoms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Scientists first described an “ozone hole” – Over Antarctica in 1985; it has increased in size as ozone depletion has increased Figure 54.28a, b (a) October 1979 (b) October 2000