Download
1 / 37
370 likes | 382 Views
Learn about ecology, the study of organisms' relationships with their environments. Explore biotic and abiotic factors, trophic levels in food chains, and the flow of energy through ecosystems.
E N D
Chapter 15 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.
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
Biotic and Abiotic Environmental Factors • 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
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)
Levels of Organization in Ecology • 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
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.
The Food Chain • 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 • 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
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
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.
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.
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.
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
The Carbon Cycle • 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 Hydrologic Cycle • 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 Nitrogen Cycle • 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.
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. • Animal get phosphorus from plants. • Decomposers release phosphorus from dead organisms back into the soil.
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
Agriculture and the Nitrogen Cycle • 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
Converting Ecosystems to Human Use • 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 • 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.
