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\nAn ecosystem consists of a community of living organisms interacting with each other and the environment.\n The source of energy that fuels most ecosystems is the Sun. Plants use the Sun's energy to produce food in\n a process called photosynthesis. Organisms that use energy from the Sun or energy stored in chemical\n compounds to produce their own nutrients are called autotrophs. They are also called producers because\n most other organisms depend on autotrophs for nutrients and energy. Heterotrophic organisms that cannot\n make their own food may obtain nutrients by eating other organisms. A heterotroph that feeds only on\n plants is called an herbivore. Herbivores are also called first order heterotrophs. Carnivores that feed\n on herbivores are called second order heterotrophs. Carnivores that feed on other carnivores are called\n third order heterotrophs. A food chain is a simple model of how energy and matter move through an\n ecosystem.
\nEach level of production and consumption in a food chain is a trophic level. The autotrophs form the\n first trophic level, first order heterotrophs (herbivores) constitute the second trophic level, second\n order heterotrophs the third trophic level, and third order heterotrophs are layered on top.
\nIn the pyramid of energy, the energy moves in only one direction and decreases at each succeeding trophic\n level. The total energy transfer from one trophic level to the next is, in general, only about ten percent\n or less. This is called the energy conversion efficiency. Organisms fail to capture and eat all the food\n available at the trophic level below them. The food consumers ingest is used to metabolize and build body\n tissues. Some food is given off as waste. The energy lost at each trophic level enters the environment as\n heat.
\nA pyramid of biomass expresses the weight of living material at each trophic level. Biomass is calculated\n by finding the average weight of each species at that trophic level and multiplying the weight by the\n estimated number of organisms in each population. In terrestrial ecosystems, biomass decreases as the\n trophic level increases. In contrast to terrestrial ecosystems, freshwater and marine ecosystems have less\n primary producer biomass than biomass present at higher trophic levels, leading to an inverted biomass\n pyramid. This is because algae and phytoplankton have a shorter lifespan, are more edible than terrestrial\n plants, and are more rapidly grazed. Their biomass does not accumulate.
\nIn this exploration, you will study and analyze five simplified model ecosystems: a deciduous forest, a\n hot desert, a freshwater lake, grassland, and an Antarctic ocean shore. Many more plant and animal species\n would be involved in a real-world ecosystem. The field notes for each model ecosystem present a profile of\n the plant and animal inventory for each ecosystem.
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