Chapter 15: Ecosystem Dynamics Lecture Outline Enger, E. D., Ross, F. C., & Bailey, D. B. (2012). Concepts in biology (14th ed.). New York: McGraw- Hill. 1 15-1
What is ecology? Ecology is the branch of biology that studies the relationship between organisms and their environments. The environment is anything that affects an organism during its lifetime. Includes living and nonliving components 15-2
Biotic and Abiotic Environmental Factors 15-3 Biotic factors are other living things that affect an organism. Other members of that individual s population Pathogens Food Abiotic factors are physical things that affect an organism. The atmosphere Sunlight Temperature
Biotic and Abiotic Environmental Factors 15-4
The Impact of Environment: Examples Fish in a stream Temperature of the water (abiotic) is affected by the presence of trees (biotic factor). The amount of food in the stream (biotic) The composition of the stream bed affects how fast the stream flows and the oxygen content of the water (abiotic). Plants Minerals in the soil (abiotic) The amount of sunlight or rainfall hitting the plant (abiotic) Predators and pathogens (biotic) 15-5
Levels of Organization in Ecology 15-6 Ecologists study organismal interactions at different levels. Ecologists study How individual organisms interact with their environment How populations of the same species change over time How different species in a community interact How all of the abiotic and biotic components in one geographical area interact as an ecosystem
Levels of Organization in Ecology 15-7
Trophic Levels and Food Chains Organisms fit into different categories based on how they satisfy their energy requirements. The flow of energy through living things on earth begins with the sun. Energy flows through organisms as they use the energy from the sun and as they eat each other. Each stage of energy flow is called a trophic level. The sequence of organisms eating each other is called a food chain. 15-8
Trophic Levels in a Food Chain 15-9
The Food Chain 15-10 First trophic level Producers use the energy from the sun to make their own food. Plants and certain bacteria perform photosynthesis. Second trophic level Consumers obtain energy by eating organic matter. Primary consumers eat the producers directly. Herbivores eat plants. Third trophic level Secondary consumers eat primary consumers. Primary carnivores eat primary consumers. Fourth trophic level Secondary carnivores eat primary carnivores.
Other Components of the Food Chain 15-11 Omnivores Eat both plants and animals Are classified into trophic levels depending on what they are eating Humans are omnivores. Decomposers Obtain their energy by breaking down the organic matter of dead organisms Convert nonliving organic matter into simple inorganic molecules that can be re-used by producers Bacteria, fungi, and other microorganisms
A Summary of Trophic Levels 15-12
Energy Flow through Ecosystems The relationship between each trophic system can be represented by a pyramid. The different levels in the pyramid can represent different things. The amount of energy available at each level The quantity of organisms in each level The mass of organic matter in each level 15-13
Energy and Trophic Levels 15-14
The Pyramid of Energy To understand how energy flows through trophic levels, we must remember the laws of thermodynamics. Energy is neither created nor destroyed. Energy flows through trophic levels. When energy is converted from one form to another, some of it escapes to the surroundings as heat. As energy flows through each successive trophic level, some will be lost as heat. Therefore, the energy in the higher trophic levels is less than the initial energy obtained by primary producers. 90% of the energy in a trophic level is lost as it is transferred to the next trophic level. 15-15
Energy Losses in an Herbivore 15-16
Energy Flow Through an Ecosystem 15-17
The Pyramid of Numbers The energy at each trophic level is difficult to define. Ecologists will simply count the number of organisms classified in each trophic level. When these numbers are generated, a pyramid relationship emerges. There are more primary producers than there are consumers. There are fewer secondary consumers than primary consumers. 15-18
Pyramid of Numbers 15-19
The Pyramid of Biomass Counting the number of organisms may be deceiving because large consumers weigh more than plants. Measuring the mass of organic matter at each trophic level is more informative. Mass is the collective weight of all of the individuals in a given trophic level. The pyramid of biomass shows the 90% loss at each level. 15-20
The Pyramid of Biomass 15-21
The Cycling of Materials in Ecosystems Biogeochemical Cycles The amount of matter making up the earth is relatively constant, even though organisms are constantly using it. Occurs because much of the matter used by organisms is recycled All of the building blocks of organic matter are recycled. Carbon, nitrogen, hydrogen, oxygen, and phosphorus 15-22
The Carbon Cycle 15-23 Inorganic carbon in the atmosphere is captured and converted to organic carbon molecules used by organisms. The carbon is then released back to the abiotic environment. The role of producers: Carbon dioxide gas in the atmosphere provides the carbon with which plants build organic molecules. The role of consumers: Animals eat the organic molecules and release carbon dioxide back into the atmosphere. The role of decomposers: Carbon left in organisms after they die is released by decomposers.
The Carbon Cycle 15-24
The Hydrologic Cycle 15-25 Hydrogen is recycled as water. The water cycle also recycles oxygen. Heat causes water in oceans, lakes, rivers, and soil to evaporate into the atmosphere. Plants absorb water from the soil and release it into the atmosphere via transpiration. Water vapor in the atmosphere condenses into rain or snow. The rain or snow hits the land, some gets absorbed into the soil, and the rest runs off into oceans, lakes, streams, etc.
The Hydrologic Cycle 15-26
The Nitrogen Cycle 15-27 Nitrogen is necessary to build proteins and nucleic acids. Nitrogen gas cannot be utilized by most organisms; it must be converted to nitrates or ammonia. Role of nitrogen fixing bacteria: Nitrogen gas is incorporated into ammonia. Nitrogen-fixing bacteria live in soil and attached to the roots of some plants.
The Nitrogen Cycle Role of producers and consumers: Plants use the ammonia released by these bacteria to make organic molecules. Animals get their nitrogen from plants. Animals release their excess nitrogen as ammonia or urea. Role of decomposers and other soil bacteria: Decomposers break down nitrogen-containing organic molecules to ammonia. Nitrifying bacteria convert ammonia to nitrite, which is converted by other bacteria to nitrate, which can be used by plants. Denitrifying bacteria convert nitrites back into nitrogen gas and release it into the atmosphere. 15-28
The Nitrogen Cycle 15-29
The Phosphorus Cycle Phosphorus is necessary for nucleic acids, bones, teeth, etc. Phosphorus is stored in rocks. Erosion releases phosphorus into water. Plants get phosphorus from the water. Animals get phosphorus from plants. Decomposers release phosphorus from dead organisms back into the soil. 15-30
The Phosphorus Cycle 15-31
Unique Features of the Nitrogen Cycle Most of the difficult chemical conversions are made by bacteria and other microorganisms There are two loops in the cycle The first takes nitrogen gas from the atmosphere by nitrogen-fixing bacteria and then back to the atmosphere by denitrifying bacteria The second uses decomposers to recycle nitrogen compounds directly back to producers 15-32
Agriculture and the Nitrogen Cycle 15-33 In naturally occurring soil, nitrogen is often a limiting factor. To increase yields, farmers: Add inorganic fertilizers may contain nitrate, ammonia, or both Alternate nitrogen producing crops (soybeans) with nitrogen demanding crops (corn) Soybean roots have nitrogen-fixing bacteria symbionts. Grow a nitrogen producing crop and plow it under to allow decomposers to release the ammonia. Spread manure and allow decomposers to release ammonia for plant use.
Human Use of Ecosystems The extent to which humans use an ecosystem is tied to its productivity. Productivity is the rate at which an ecosystem can accumulate new organic matter. Plants are important to productivity. Ecosystems with high productivity are warm and moist with nutrient-rich soil. Rainforests, forests, grasslands Marshes and estuaries Ecosystems with low productivity Deserts, arctic areas, open ocean 15-34
Converting Ecosystems to Human Use 15-35 In the ancient past, humans were simply another consumer. In the recent past, the development of agriculture changed how humans affected ecosystems. Humans manipulate certain ecosystems to increase productivity. These manipulations can be destructive and negatively affect other organisms in the ecosystem. The great plains, agriculture and the loss of buffalo Converting grasslands to grazing lands displaces native species. Over-fishing aquatic ecosystems creates ecological imbalance.
The Energy Pyramid and Human Nutrition 15-36 Human demand for food is so large that humans must occupy several trophic levels to meet the need. Eating at the third trophic level (eating meat) results in a 99% loss of energy. Cows have to eat a lot of grain, then we only get a portion of the energy in the cow meat. Eating at the second trophic level (eating plants) allows for a more efficient transfer of energy. Eating plants means more food for more people. However, plants, particularly grains, do not provide complete nutrition for under-nourished people. Protein is difficult to obtain from grains alone.
Human Pyramids of Biomass 15-37