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ECOLOGY QUESTION 1983: L. PETERSON/ECHS Describe the trophic levels in a typical ecosystem. Discuss the flow of energy through the ecosystem, the relationship between the different trophic levels, and the factors that limit the number of trophic levels. STANDARDS:DESCRIPTION AND SYSTEM RELATIONSHIPS: Max. = 8 pointsDefine and/or identify:__ producers__ consumers (herbivores - carnivores - omnivores)__ decomposersIdentification of:__ autotrophs__ heterotropsDefine:__ trophic level__ Complex systemComparisons (Pyramids):__ organism (numbers)__ organism (size)__ organism (biomass)__ inverted, numbers and/or biomass __ Material Cycling__ Description of food chain and/or web ENERGY FLOW IN THE SYSTEM: Max. = 6 points__ source__ process (photosynthesis)__ producers support the system__ energy loss__ quantification of lossUse of Energy:__ heat__ metabolic__ building compounds__amount of energy contained (comparative)Relationship of R:__ Prnet__ Prgross LIMITING FACTORS: (No Max.)__ Energy (2 points)__ Change in Prnet__ Change in Prgross__ Biomass (materials)__ Producer numbers__ Efficiency
ECOLOGY QUESTION 1985: L. PETERSON/ECHS Describe the process of ecological succession from a pioneer community to a climax community. Include in your answer a discussion of species diversity and interactions, accumulation of biomass, and energy flow. STANDARDS:DESCRIPTION__ Definition of Succession__ Differentiation (Primary/Secondary)Examples:__ Pioneer__ Climax__ Sere (two or more examples = 2 points)__ Modification of the environment SPECIES DIVERSITY__ Explanation of increase__ Types of Competition (or Niche)__ Examples__ Change in Population Density__ Description of Food Web__ R-Strategists -> K-Strategists (2 points)__ Change in Symbiotic Relationships (increase toward mutualisms) BIOMASS__ Production increase and explanation (2 points)__ Levels of Organizationm (Autotrophs & Heterotrophs)__ Examples of Producers (etc.)__ Pyramid or Explanation ENERGETICS__ Source (Sun)__ Utilization - Photosynthesis__ Explanation of Decrease (entropy -unused) OR Pyramid + Explanation__ Climax Stability (Dynamic Equilibrium)__ P/R toward 1__ Net Productivity Decrease
ECOLOGY QUESTION 1986: L. PETERSON/ECHS Describe the biogeochemical cycles of carbon and nitrogen. Trace these elements from the point of their release from a decaying animal to their incorporation into a living animal. STANDARDS: The question was divided into two sections for grading, with a maximum number of points of 8 per section. For each maximum assigned, there were more points possible to allow the student several ways to reach the maximum. For the CARBON CYCLE, it was possible to earn points for each of the following statementsor ideas:__ Explanation of the role of green plants as producers__ Mention of herbivores in a way that indicated an understanding of their role __ An indication that carnivores obtained C from herbivores__ Discussion of the role of decomposers in returning C to the atmosphere as CO2__ Mention of CO2 production via respiration of green plants, herbivores or carnivores__ Discussion of the C in oil, natural gas, and coal as originating from the remains of organisms__ Mention of CO2 release to the atmosphere through the burning of fuel or through release of C from limestone.__ Discussion of the existence of dissolved CO2 in the bodies of water on the earth.__ An indication that human activity had a significant impact on the carbon cycle. In the case of the nitrogen cycle, there were 14 possible points from which it was possible for the student to earn the maximum of 8 for that portion of the questions. __ An indication that organic molecules were broken down to amino acids after death__ Discussion of deamination__ Mention of NH4+ as the product of deamination__ Indication that ammonium ion can be converted to nitrate (a second point if there is inclusion of the further oxidation to nitrate)__ Discussion of denitrification__ Mentioning the role of microbes, industry, or lightning in affecting atmosheric nitrogen.__ Understanding that when nitrogen gas is fixed, it is converted to the ammonium ion.__ Indication that nitrate or nitrite or ammonium ions can be taken up by organisms__ Mention of nitrogen loss to living organisms which results from burning or leaching__ Indication that plants use absorbed nitrogen to make proteins__ An understanding of the conversion by animals of plant proteins into animal proteins__ Indication that on death or in excretion organic nitrogen is released into the environment.__ Indication of a significant impact of human activity on the nitrogen cycle.
ECOLOGY QUESTION 1989: L. PETERSON/ECHS Using an example for each, discuss the following ecological concepts. a) Succession b) Energy flow between trophic levels c) Limiting factors d) Carrying capacity STANDARDS:a) SUCCESSION: Max. = 3 points__ Definition: demonstrate process of change in communities through time__ modification of environment/transition of species composition__ Examples: generalized - lake -> marsh -> meadow -> forest specific - lichen -> moss -> herbs -> shrubs -> forest__ Primary - no life/soil -> pioneer organisms/soil development__ Secondary - disturbance -> climax/stable community b) ENERGY FLOW BETWEEN TROPHIC LEVELS: Max. = 3 points__ Examples: grass -> locust -> mouse -> snake grass -> herbivore -> carnivore -> detritivore producer -> 1' consumer -> 2' consumer -> 3' consumer food chain/web - elaboration of trophic levels__ Producers (autotrophs) start energy flow__ Consumers (heterotrophs) acquire energy from primary producers__ Productivity - measure of rate at which energy is converted from radiant to biomass and kinetic energy of action or PG - R = PN __ Efficiency - 10% rule/90% energy loss or pyramid of energy c) LIMITING FACTORS: Max. = 3 points__ Definition: any factor operating to restrict population growthExamples:__ biotic - population density, competition, predation__ abiotic - moisture, temperature, weather/climate, wind, sunlight, soil, topography, geographic location, nutrients__ density-dependent - change birth/death rate as density changes__ density-independent - change birth/death rate regardless of density d) CARRYING CAPACITY: Max. = 3 points__ Definition: number of individuals of a population (species) sustainable by an environment (as long as the environment remains the same)__ Examples: predator/prey; rabbits in Australia; deer on Kaibab; human population; __ Limiting factor(s) determine carrying capacity (competition, waste, predation)__ Population grows -> rate slows -> stabilize (N decreases) or__ Population falls -> growth resumes -> stabilizes (N decreases) or__ dN/dt = rN (K-N/K) with explanation or graph with explanation__ K/r strategies related to carrying capacity
Describe the trophic levels in a typical ecosystem. Discuss the flow of energy through the ecosystem, the relationship between the different trophic levels, and the factors that limit the number of trophic levels.
Trophic levels are the position that an organism occupies in the food chain. Organisms at higher trophic levels prey upon those at lower trophic levels. The bottom level is the source of energy for the higher levels. In the typical ecosystem, plants are the primary producers and therefore are part of the first trophic level. The second level consists of herbivores that consume producers, and this delegates them as primary consumers. The third level consists of carnivores that eat the primary consumers, so these are called secondary consumers.
Energy is not distributed evenly through the ecosystem; lower levels gain more energy than higher ones. Most ecosystems rely on the sun for energy and for the plants (producers) to convert it into energy to be passed along to primary consumers, and from primary consumers to secondary consumers and so on. The producers are autotrophs and photosynthetic organisms that can perform photosynthesis in order to grow. Consumers are heterotrophs and feed on other organisms, be it plant or animal. There is another type of organism that cleans up after the others, and they are called detritivores. Detritivores (or decomposers) use energy from waste or dead organisms, and they complete the cycle by returning nutrients back into the soil or carbon dioxide to the air.
The number of trophic levels is limited by the amount of energy available, which is always set. Trophic levels can include tertiary consumers, quaternary consumers, and so on until there is no longer any more energy available for the biggest and neediest consumers. Energy starts from the resource, which would be the sun in almost all cases. Then plants use the sun and convert it into energy for consumers to use. Which each level of consumer, however, only...