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Community. All the organisms of all the species inhabiting an area. Plant communities apparently determined by chance occurrence of species with similar requirements. Unclear in animal communities. The properties and structure of a community are defined by its species composition and the interactions between the species. Interspecific Interactions Competition: -/Predation (includes herbivory and parasitism): +/Mutualism: +/+ (obligatory or facultative= facilitation) Commensalism: +/0 Key in shaping communities: competition, predation and mutualism. Species interactions involved in determining trophic structure, dominant and keystone species, and community control. All affect community structure. Trophic structure. Feeding relationships between organisms. Food chain, trophic levels and food web. Food webs have few trophic levels: energetic and dynamic stability hypotheses. Dominant species. Control in community due to abundance. Keystone species. Control in community due to ecological role. Community organization. Bottom-up model. Changes in community structure controlled by bottom trophic levels (competition and available food). Top-down model. Changes in community structure controlled by upper trophic levels (predation). Communities are dynamic, constantly changing, due to disturbance. Humans are the greatest agents of disturbance. Ecological succession- Transitions in species composition over ecological time. Primary succession- It begins in a virtually lifeless area where soil has yet not formed. Secondary succession- Occurs where an existing community has been cleared by some disturbance that leaves the soil intact. Question from February 22nd 1- Wouldn’t ash and other material be nutrient-rich and counted as soil, therefore making it secondary succession? Chapter 54 Ecosystem Ecology Organismal ecology coping Population ecology limiting factors Community ecology interspecific interactions and diversity Ecosystem ecology energy flow and chemical cycling Landscape ecology effects on interactions at lower levels Biosphere ecology global effects Ecosystem Ecology Ecosystem. All the organisms living in a community AND the abiotic factors with which they interact. The most inclusive ecosystem is the biosphere or whole-Earth ecosystem. PaleoProject NASA page 1198 ECOSYSTEM DYNAMICS 1- Energy flows through ecosystems. 2- Matter cycles within ecosystems. (DECOMPOSERS) All trophic levels are connected by decomposition. Without decomposition life on Earth would stop. Tertiary consumers, etc. 1st Law of Thermodynamics Energy is conserved, it can only be transformed. 2nd Law of Thermodynamics. Energy transformation is inefficient, some lost as heat. PHOTO, chemo Elements are not lost, but move through trophic levels and ecosystems. Fig. 54.1 pages 1199-1200 ENERGY FLOW Primary Production. Light energy converted to chemical energy (organic compounds) by an ecosystem’s autotrophs in a given period of time (1% converted). Sets Ecosystem’s Energy Budget. Energy per unit area per unit time (J/m2/ yr) OR Biomass (dry weight) of organic molecule per unit area per unit time (gC/m2/ yr). pages 1200-1201 Fig. 54.3 Gross Primary Production (GPP) = Total Primary Production (amount of light energy converted to chemical energy per unit time) Some used as fuel for cellular respiration, then: Net Primary Production (NPP) = GPP – R (as little as 25% of GP in forests) Only NPP is available to consumers. Ocean: 46%; Land: 54% pages 1200-1201 Fig. 54.4 Fig. 54.5 pages 1201-1205 Nutrition addition experiment Fig. 54.9 Secondary Production Amount of chemical energy in consumer’s food converted to new chemical energy in a given period of time. At individual level: Detritivores Production efficiency= fraction of food energy that is not used for respiration. Heat Fig. 54.10 page 1206 PE= 1-3% PE= 10% PE= 40% Trophic Efficiency Percentage of production transferred from one trophic level to the next. Values are 5-20% depending on ecosystem. Thus, 80-95% of energy is lost; loss is multiplied in each trophic level, forming a pyramid. ~10% Idealized pyramid of net production ~10% ~10% ~1% Fig. 54.11 page 1206 Consequence of trophic efficiencies: total dry weight of all organisms (standing crop) diminishes with each successive trophic level. (pyramid of biomass). Some aquatic ecosystems have inverted pyramids. Fig. 54.12 Predators usually larger than prey, so limited biomass in upper thropic levels formed by a small number of large individuals (pyramid of numbers). pages 1206-1208 Fig. 54.13 Herbivores consume a small percentage of the plant biomass (globally, <17% of the annual plant production). The green world hypothesis Several factors keep herbivores in check: -Plant defenses: toxins, spines, mutualistic invertebrates, etc. -Not all essential nutrients plenty available: organic nitrogen. -Abiotic factors limit herbivores. -Intraspecific competition: density-dependence. -Interspecific interactions: predation, parasitism and diseases. page 1208 Life on Earth depends on the recycling of essential chemical elements. General model of nutrient cycling Biological and geological processes move nutrients in the ecosystem. pages 1208-1209 Fig. 54.15 Water cycle is driven globally by solar energy. + pages 1210 + Fig. 54.16 The Carbon cycle is defined by the reciprocal processes of photosynthesis and cellular respiration. + balanced pages 1210 Fig. 54.17 Nitrogen enters ecosystem by atmospheric deposition and nitrogen fixation by prokaryotes. MOST of nitrogen cycling involves local processes between organisms and soil or water. pages 1210-1211 Fig. 54.18 Generalized scheme of biogeochemical cycles Decomposition rates determine the rates of nutrient cycling. pages 1212-1213 Fig. 54.20 Nutrient cycling is strongly regulated by vegetation. When plants are not present, nutrients are lost from the system. Fig. 54.21 pages 1213-1214 Ohio reservoir Gizzard shad Ecologists are recognizing the need of understanding how landscapes (comprise different ecosystems) and food webs interact. Bioscience 2005