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E.Ecosystem09 - Ecosystems THE REALM OF ECOLOGY Biosphere...

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Ecosystems Biosphere Ecosystem Ecology: Interactions between the species in a given habitat and their physical environment. Community Population Organism THE REALM OF ECOLOGY Biosphere Ecosystems Communities Populations Organisms Factors that Limit Communities Abiotic (nonliving) Limiting Factors – Temperature – Water Soil type – Sunlight – Salinity Wind stress Altitude, depth Biotic (living) Limiting Factors Food source – Competition – Predators Social factors, mates Pathogens, parasites – Vegetation SIMPLE TERRESTRIAL ECOSYSTEM Sun Producer Precipitation Falling leaves and twigs Producers Primary consumer (rabbit) Secondary consumer (fox) Carbon dioxide (rabbit) Oxygen (O 2 ) Water Soil decomposers Soluble mineral nutrients Energy flow and chemical cycling Energy flow is one-way Energy enters ecosystems through photosynthesis or chemosynthesis Some energy is used by producers, some is passed through food chain • All energy eventually dissipates as heat Figure 54.2 Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow
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Chemical materials are re cycle d Actual atoms are constantly rearranged into new molecules Energy needed to form new bonds, but atoms are reused – Carbon cycle – Nitrogen cycle Figure 54.2 Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow Energy flows through the food web Energy from lower trophic levels is transferred to higher trophic levels 5% - 20% of energy consumed is available to next trophic level Energy returns to the physical environment as heat – Remember thermodynamics! Energy is neither created nor destroyed!” Hardwood forest Oak trees, caterpillars, birds Energy pyramid reflects loss of energy at each trophic level Only 1% of solar energy reaching Earth is used by living systems 5% - 20% of energy consumed is available to next trophic level Plant material eaten by caterpillar Cellular respiration Feces 100 J 33 J 200 J 67 J Growth (new biomass) Figure 54.10 Pyramid of net production Energy pyramid reflects loss of energy at each trophic level Endotherms: 1-3% production efficiency Ectothermic vertebrates: ~10% Inverts: as much as 40% – Caterpillar Feeding efficiency = growth/consumed = 17% Production efficiency = growth/assimilated = 33% Plant material eaten by caterpillar Cellular respiration Feces 100 J 33 J 200 J 67 J Growth (new biomass)
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Eating high on the food chain is expensive! Less than 10% passed on to next trophic level Pyramid of net production Most food webs limited to 4–5 steps Energetic hypothesis : – Too little energy passed through steps to support another step Dynamic stability hypothesis : – Even if average 1°-production sufficient, oscillations & deviations in 1°-production cause fluctuations in higher steps below minimum viable population.
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