LAB 12 ECOLOGY OBJECTIVES: Describe the interrelationships between producers, consumers, decomposers, and abiotic components of a forest ecosystem. Study the diagram of a biomass pyramid, and explain the decrease in biomass at each trophic level. Describe the flow of energy through a community. INTRODUCTION: read text 31.1 Life on earth is maintained in a delicate balance by ecological interrelationships. All organisms, including humans, are subject to the ecological principles that govern the relationships of organisms with their environment. Ecology is the study of interactions between organisms and their environment, including both biotic (living) and abiotic (nonliving) components. It is primarily concerned with the study of populations, communities, and ecosystems. Early studies of ecology were purely descriptive studies of the species of organisms present and a description of their physical environment. Later on, ecology was studied as functional units which emphasized organisms interacting among themselves and with their physical environment. An ecosystem is an ecological unit which consists of both the community and the abiotic components of a defined area. Soil, air, water, and temperature are examples of abiotic components. Since the primary interactions involve the flow of energy, and ecosystem can be viewed as interacting populations of organisms through which energy passes. In most ecosystems, the primary source of energy is sunlight (there are a few exceptions to this statement), the energy of which is trapped in food molecules produced by photosynthesis by organisms having chlorophyll. Such organisms, mostly plants and some protists and bacteria, are referred to as producers. All other organisms must get their energy by feeding on producers or their remains, or on other organisms which feed on producers. Organisms which feed directly on the producers are known as primary consumers. Organisms which feed on primary consumers are known as secondary consumers, and so forth. In the end, the dead remains of all of these organisms are decomposed for energy by such decomposer organisms as bacteria or fungi. These 4 groups of organisms are referred to as the trophic (feeding) levels of the ecosystem. Animals within each of these trophic levels are also described as herbivores (plant-eating), carnivores (meat-eating), and omnivores (eating both plant and animals). The chemicals making up the bodies of organisms can then be recycled, but the energy is finally lost from the ecosystem in the form of unusable heat energy. Thus energy does not cycle in an ecosystem but makes a one- way trip though it. Usually, the total amount of biomass (total mass of the living organisms in a trophic level) is reduced with each successive trophic level because of inefficiency of energy transfer and heat loss at each exchange. Therefore, one would expect the biomass of producers in an ecosystem to be greater than the biomass of primary consumers, and the biomass of primary consumers to be greater than the biomass of secondary consumers. Chemical energy of organic nutrients flows through the community from producers to consumers to st decomposers. The transfer of energy follows the laws of thermodynamics. The 1 law of thermodynamics states nd that energy is neither created nor destroyed but only changed in form. The 2 law of thermodynamics states that usable energy is reduced with each energy transfer. The quantitative relationships of producers and consumers based on energy flow may be depicted in an ecological pyramid. The 3 types of ecological pyramids are (1) a pyramid of numbers, (2) a pyramid of biomass (dry weight), and (3) a pyramid of calories (energy). Generally each pyramid shows a decrease in quantity from the base (producers) to the apex (top carnivore). In unique situations, pyramids of numbers and biomass may be inverted, but the pyramid of calories never is inverted. In general, only about 10% of the energy in one trophic level (layer in the pyramid) is transferred to the next trophic level. The remaining 90% is respired or unassimilated in the process. Thus, herbivores contain about 10% of the calories in the plants consumed. Primary carnivores are reduced to 1% of the energy stored in producers. Figure one. Top Flow of energy Carnivore CARNIVORE – 2o consumers HERBIVORES – 1o consumers PRODUCERS / AUTOTROPHS ECOLOGICAL INTERACTIONS: * read table 31.1 Symbiotic Relationship - 2 or more species of organisms live together, and at least one gains benefit. Commensalism – benefits one species and neither hurts or helps the other. Mutualism – both species benefit Parasitism – one species benefits, the other is harmed. Many examples of interactions between species occur in the eastern forests. For example: o Lichens, which are examples of mutualism between an alga and a fungus where both organisms benefit from the association. o parasitic plants, such as mistletoe o The symbiotic relationship between nitrogen-fixing bacteria and legumes. Nitrogen is an indispensable part of amino acids and proteins. Plants are able to use inorganic nitrogen in the form of nitrates, but they depend on certain bacteria to convert organic debris into this usable form. The most common pathway is the conversion of organic nitrogen first into ammonia, then into nitrites (NO 2-) and finally into nitrates (NO3) that can be used by plants. Certain bacteria are able to fix (convert) atmospheric nitrogen into organic nitrogen. Rhizobium is a nitrogen-fixing bacterium found in nodules on the roots of legumes (e.g. bean, peas, alfalfa). The bacteria and plants live in a mutualistic symbiosis because both organisms benefit from the association. PLANT SUCCESSION: Succession refers to the process of replacement of one group of species by another group of species. Usually the first group of plants will change the environment so that it is less suitable for themselves and more suitable for another group of species. This cycle is repeated many times in a given area over a long period of time. Succession, called primary succession, can start with areas of bare rock or open water. Over time the rock develops soil and the open water areas will fill in. Different plant groups will then occupy these areas in a succession until a final stable plant community called a climax community is developed which will maintain itself. More common examples of succession, called secondary succession, begin on areas that already have soil but vegetation has been removed by agricultural uses or by fire. In the first case (called ‘old field’ succession) an agricultural field is abandoned and soon grows up in weeds and grasses. The grasses become invaded by trees such as cedar and pine and an evergreen forest develops. This forest eventually gives way to a hardwood forest in most areas. LAB QUESTIONS: 1. Write the term or name the trophic levels described below: uses sunlight energy to make its own food molecules by photosynthesis: provides energy and organic nutrients for all members of the community. breaks down dead organic material so chemical elements can be recycled animals that feed directly on plants animals that feed on other animals. members of a species that live together (& interbreed) in an area. consists of both the community and the abiotic components of a defined area. Animals feeding on both plants and animals. Animal group not preyed upon by other animals. Ultimate source of energy for the earth. 2.The 3 layers in most forest ecosystems are the , , and . 3. The end of plant succession is a community which maintains itself with no further changes. 4. List the different stages in ‘old field’ plant succession. 5. Describe the main difference between primary and secondary succession. 6. Explain why only about 10% of the energy stored in one trophic level is transferred to the next higher level. 7. In dry years, the biomass of producers is significantly decreased. What would be the effect on a rodent population? A hawk population? 8. Which of the following simplified food chains would support a larger human population – A or B (circle one)? A. Cereal (grain/carbs) & legumes (protein) beef human B. Cereal (grain/carbs) & legumes (protein) human Explain your answer. 9. Categorize the organisms found in a marine food web (text - fig 29-4b), according to their ecological roles. ECOLOGICAL ROLE MARINE ORGANISM (name) Producers = Primary consumers = Secondary Consumers = Tertiary cconsumers = 10. On a sheet of paper, draw a food web of the following organisms (if you aren’t sure where an organisms fits into the web, ask your instructor). It might be helpful to divide them into their trophic categories (i.e. producer, primary consumer, etc.) before you begin drawing. a. earthworm d. beetle g. meadow vole j. deer m. fox b. millipede e. toad h. white-footed mouse k. oak trees n. coyote c. pill bug f. shrew i. raccoon l. forbs/ grasses Now you should explore the components of your own ecosystem here in Southeastern Ohio, and discover different ecological interactions occurring in the natural world around you. Take a walk in the woods or think about observations you’ve made in the past – how many names of the living things around you do you know? Can you place them in their trophic categories? The Forest Ecosystem Eastern North America, including Southeastern Ohio, is part of the deciduous hardwood forest. In this part of Ohio the dominant forest type is Oak – Hickory. o Name the most prominent producers in the forest ecosystem. The producers in the forest exist in several horizontal layers. The canopy of the forest is defined as consisting of those trees whose crowns are at the top forming a continuous layer of the forest. o What were the major canopy trees in your ecosystem? The understory is composed of those plants whose diameters measured 5 cm at the height of 4.5 ft above ground level and whose crowns are below the top layer of the forest. o List the major understory trees that occur? The shrub & ground layers are composed of those tree seedlings and saplings less than 5 cm in diameter. Shrubs and herbaceaous plants would also be in the layer. o List several plants that you would see in this shrub & ground layer. o Name some of the primary consumers (herbivores) that you would expect to find in the forest ecosystem. o Name some of the secondary consumers (carnivores). Examine a fallen tree. It’s being decomposed by bacteria and fungi (the decomposer trophic level). o What effect should this decay process have on the mineral content of the soil? o What would happen if this ‘ecosystem service’ wasn’t provided by the decomposers?
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