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Dynamics of Ecosystems Chapter 54-55 Biology Raven and Johnson 7th Ed 1 Mimicry • • Batesian mimicry – Palatable insects resemble brightly colored, distasteful species. Mullerian mimicry – Unrelated protected species resemble one another. predators learn more quickly 2 Mimicry • • Batesian mimicry – Palatable insects resemble brightly colored, distasteful species. Mullerian mimicry – Unrelated protected species resemble one another. predators learn more quickly 3 Coevolution and Symbiosis • Coevolution involves long-term mutual evolutionary character adjustments of two or more species. – predator-prey interactions – symbiotic relationships two or more kinds of organisms live together in permanent relationships commensalism, mutualism, and parasitism 4 Interactions Among Ecological Processes • Keystone species – Species that have a particularly strong effect on community composition. top predators 5 Succession • Succession is the process of ecosystems changing from a simple to a more complex structure. – primary succession - occurs in bare or open areas eutrophication of oligotrophic lakes Lichens first, then mosses, then larger plants. – secondary succession - occurs following only when soil is already present 6 Carbon Cycle CO2 is formed in many ways, but only photosynthesis can break it down. 7 The Nitrogen Cycle • • Relatively few types of organisms can fix nitrogen into forms that can be used for biological processes. Nitrogen fixation: N2+ 3H2 2NH3 – Only symbiotic bacteria fix enough nitrogen to be of major significance in nitrogen production. – ammonification – denitrification 8 Nitrogen Cycle 9 The Phosphorus Cycle • Phosphates weather from soils into water, enter plants and animals, and are redeposited in the soil when plants and animals decompose. – Millions of tons are added to agricultural land annually to increase crop production. Superphosphate- can cause oligotrophication of water sources by “choking”. 10 Phosphorus Cycle 11 Trophic Levels • • Autotrophs - capture light energy and manufacture own chemical energy – primary producers Heterotrophs - must obtain organic molecules that have been synthesized by autotrophs – consumers 12 Trophic Levels – – – – Primary consumers - herbivores Secondary consumers - organisms that feed on herbivores Decomposers - break down complex organic material into simpler compounds Detritivores - live on refuse of an ecosystem 13 Trophic Levels 14 Trophic Levels • • Trophic level refers to the feeding level of an organism. – Organisms from each trophic level constitute a food chain. Interconnected food chains constitute a food web. On average, 10% of the organic matter (energy) transfers from one trophic level to the next. 15 Primary Productivity • • Primary productivity refers to the amount of organic matter produced from solar energy in a given area during a given period of time. – Gross primary productivity is the total organic matter produced. – Net primary productivity is the amount of organic matter produced that is available to heterotrophs. Secondary productivity - rate of production by heterotrophs 16 The Energy in Food Chains • Due to the Second Law of Thermodynamics, food chains are generally limited to three or four steps (trophic levels). – A community’s productivity is ultimately determined by the amount of sunlight it receives. – In northern climates, net primary productivity often increases as the growing season lengthens. 17 18