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Ecology : the study of the interactions of living organisms with one another and with their environment.
Habitat : the place where a particular population of a species lives.
Community : the many species that live together in a particular habitat.
Ecosystem : a community and all the physical aspects of its habitat (soil, water and weather).
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Ecosystems have no real defined boundaries
Biodiversity : the number of species living within an ecosystem.
Ecosystems are constantly changing.
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Succession : the regular progression of species replacement.
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Primary succession : occurs on land where nothing has grown before
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Secondary succession : occurs in areas where there has been previous growth (abandoned fields or forest clearings)
Competition between species governs succession.
Path of Energy Through an Ecosystem
The sun is the original source of energy on earth.
Life exists because plants are able to capture energy from the sun and convert it to food in the process of photosynthesis.
The amount of food a photosynthetic organism can produce is called its primary productivity .
The overall strength of an ecosystem is a factor of its primary productivity.
 producers are the organisms in an ecosystem that first capture the sun’s energy.
The most common producers are plants, algae and some bacteria. These are the original sources of food in an ecosystem.
 consumers obtain the energy needed to stay alive by eating the producers.
Trophic level : classification of organisms within an ecosystem. Trophic level is determined by the organism’s source of energy
 producers occupy the lowest trophic level
 herbivores (plant eaters) occupy the second trophic level. Herbivores can be classified as primary consumers.

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Carnivores (meat eaters) occupy the third trophic level. Carnivores eat the primary consumers. They are called secondary consumers .
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Omnivores (plant and meat eaters) occupy the highest trophic level. Carnivores that consume other carnivores are also placed at this level. These are called tertiary consumers.
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Every ecosystem must include another class of consumers called detritivores or decomposers.
They receive their energy from dead or decaying matter. They put nutrients back into an ecosystem that can then be reused by other organisms.
Food Chain vs. Food Web
Food chain : path of energy through the trophic levels of an ecosystem
Food web : the complicated interconnected path of energy created because animals feed at several trophic levels the number of organisms decreases from one trophic level to the next highest trophic level because energy is lost to the environment as heat.
 biomass : the dry weight of tissue and other organic matter present in an ecosystem.
This is used to assess the amount of energy present in an ecosystem.
CYCLES WITHIN ECOSYSTEMS
Water Cycle
Process is driven by the sun.
 water vapor in the atmosphere condenses and falls to the earth as rain or snow.
 a portion of this water seeps into the soil and exists as ground water .
 remaining water travels to lakes, rivers and oceans as runoff. Water contained in lakes, rivers, and oceans is heated by the sun. It evaporates and renters the atmosphere and the cycle starts again.
 the amount of vegetation in a region affects the amount of water that evaporates into the atmosphere. As vegetation decreases, rainfall in the area will also decrease.
Carbon cycle
Carbon cycles between the nonliving environment and living organisms.
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Carbon dioxide is removed from air by plants and converted to glucose in photosynthesis.
 glucose is broken down in the process of cellular respiration. Carbon dioxide is given off as a waste product in cellular respiration.
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Carbon dioxide is also returned to the atmosphere when substances are burned.
(wood and fossil fuels)
Nitrogen cycle

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Organisms contain a large amount of nitrogen because both protein and DNA contain nitrogen. Even though the atmosphere is 78% nitrogen gas, most organisms cannot obtain nitrogen from the air. Only a few species of bacteria can remove nitrogen from the air.
The process of removing nitrogen from air is called nitrogen fixation .
The process of nitrogen fixation occurs in soil. It is an anaerobic process, which means it cannot occur if oxygen is present.
The bacteria capable of nitrogen fixation live on the roots of very few plants (legumes and alders)
There are four stages of the nitrogen cycle:
 assimilation : enzymes break the bonds holding the nitrogen atoms together in nitrogen gas. The free nitrogen atoms then bind with hydrogen atoms to form ammonia. The ammonia spreads through the soil and plants absorb it through their roots. The ammonia is then used by the plant to make amino acids which are then strung into proteins. Animals who eat the plants use the amino acids to form their own proteins.
 ammonification : animals excrete nitrogen from their bodies as urine. Other bacteria in soil change the urine to ammonia. These same bacteria convert nitrogen in dead plants and animals to ammonia. This ammonia then goes through assimilation.
 nitrification : other bacteria in the soil convert ammonia to nitrate ions. Some plants are able to assimilate nitrate as well as ammonia.
 denitrification : still other bacteria in the soil react with any nitrate ions that have not been assimilated. They convert the nitrate ions back to nitrogen gas and release the nitrogen gas into the atmosphere.
The growth of plants in an ecosystem is limited by the amount of nitrogen in the soil. This is why we use fertilizer.
The Phosphorous cycle
Phosphate ions are essential parts of both DNA and the energy molecule ATP. Phosphate ions are found in rocks and soil bound to calcium. Plants absorb phosphate through their roots and use it to build DNA and ATP. Animals must eat plants to obtain their phosphate.
Phosphate is returned to the soil when plants and animals die and decay.
High levels of phosphate ions in freshwater will stimulate the growth of algae. The increased numbers of algae will extract all the oxygen from the water leaving none for the fish. The fish suffocate and die.

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Coevolution : back and forth evolutionary adjustments between interacting members of an ecosystem
Predation : occurs when one species feeds on another
Parasitism : occurs when one organism lives in or off another organism. Parasites typically do not kill their prey (called a host) since the host is their food source, but parasites do not benefit the host in any way. Ex. Fleas and ticks
In coevolution, the prey develops some way to elude avoid or fight off its predator. In response, the predator will develop countermeasures. Ex. Plants develop thorns or spines or they give off irritating oils (poison ivy). Some animals have develop immunity to the oils.
Competition : when two species use the same resources like food, nesting areas, water etc.
Symbiosis :when two or more species live together in close, long term association.
 There are two types of symbiosis: o Mutualism : where both participating species benefit o Commensalism : one species benefits the other , but it itself is neither harmed nor helped.
Niche : the functional role of a species in an ecosystem.
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Niches are defined by how they affect energy flow within the ecosystem. Ex.
The niche occupied by a deer is that of an herbivore.
The total niche an organism is potentially able to occupy within an ecosystem
(the entire range of conditions it can tolerate) is called its fundamental niche . o The part of the fundamental niche that a species actually occupies is called its realized niche .
Climate and its effect on ecosystems.
The sun heats the atmosphere and creates air currents. It also heats the ocean and creates ocean currents. The location of these currents influences the weather on the land masses close to them.
Biomes
Marine Biomes
Shallow ocean water : located closest to the shore. Inhabited by a large number of species.
Open sea : extends from the end of the continental shelf to the beginning of the abyss.
Contains a mass of diverse microscopic organisms called plankton . Algae and bacteria are classified as plankton. Plankton is the main food source for many species of fish in the deep ocean.

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Deep sea : begins at a depth of about 1000 ft. No light penetrates to this zone of the ocean.
Water is very cold. Producers at this level do not use light to make food, instead they use chemicals found in the ocean to make their food. This process is called chemosynthesis .
This area is also known as the abyss .
Terrestrial Biomes
Tropical rain forest :
 Rainfall 80-180 in. per year
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Contains at least half of all known species on earth
Soil is thin and infertile
Located at or near the equator
Savannah : dry tropical grassland
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Located between tropical rain forest and desert biomes
Annual rainfall 30-60 in.
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Seasonal droughts occur
Found mainly in Africa
Desert
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Annual precipitation is less than 10 in.
Sparse vegetation
 Found in the interior of continents
Temperate grassland
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Also called prairie
Rich, fertile soil
Temperate deciduous forest
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Mild climates and plentiful rain
Grow in areas with warm summers and cold winters
Annual rainfall 30-100 in. and occurs throughout the year
Found in much of the eastern United States
Taiga : great coniferous forests of the Northwest and Alaska
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Found in cold, wet climates.
Long, cold winters
Most precipitation falls in summer months
Tundra : cold plains of the far north
 Few trees
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Annual rainfall less than 10 in.
Most water is frozen