Ecology

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Ecology

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The study of the interactions between organisms and their environment. The environment encompasses all that is external to the organism and is necessary for its existence.

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Abiotic Environment

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One of the two components of an organism's environment; the physical environment. It includes climate, temperature, availability of light and water, and the local topology.

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Biotic Environment

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One of the two components of an organism's environment; the living environment. It includes all living things that directly or indirectly influence the life of the organism including the relationships that exist between organisms.

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Organism

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The individual unit of an ecological system, but the organism itself is composed of smaller units. It contains many organ systems that are made up of organs. Organs are formed from tissues, tissues from cells, cells from many different molecules, molecules from atoms, and atoms from sub-atomic particles.

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Population

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A group of organisms of the same species living together in a given location. Examples include dandelions on a lawn, flies in a barn, minnows of a certain species in a pond, and lions in a grassland area. Environmental factors such as nutrients, water, and sunlight limitations aid in maintaining populations at relatively constant levels.

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Communities

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Consist of populations of different plants and animal species interacting with each other in a given environment. Examples: A lawn contains dandelions, grasses, mushrooms, earthworms, nematodes, and bacteria; A pond contains dragonflies, algae, minnows, insect larvae, etc...; A forest contains moss, pine, bacteria, lichens, ferns, deer, chipmunks, spiders, etc...; The sea contains fish, whales, plankton, etc...

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Biotic Community

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Includes only the populations from all five kingdoms, monerans, protists, plants, fungi and animals, all depending upon each other for survival.

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Species

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Any group of similar organisms that are capable of reproducing fertile offspring.

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Ecosystem

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AKA ecological community. Encompasses the interaction between living biotic communities and the nonliving environment. In studying this, biologists emphasize the effects of the biotic community on the environment and the environment on the community. Examples of communities are the same as an ecosystem.

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Biosphere

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Includes all portions of the planet that support life - the atmosphere, the lithosphere (rock and soil surface), and the hydrosphere (the oceans). It is a relatively thin zone extending a few feet beneath the earth's surface, several miles down into the deepest sea, and several miles high into the atmosphere.

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Physical Environment

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1. Water - the major component of the internal environment of all living things. It may be readily available, or the organism may possess adaptations for storage and conservation of water. 2. Temperature - must be maintained at an optimal level. Protoplasm is destroyed at temperatures below O degrees C and at high temperatures. 3. Sunlight - the ultimate source of energy for all organisms. Green plants must compete for sunlight in forests and have adapted to capture as much sunlight as possible by growing broad leaves, branching, growing to greater height, or producing vines. 4. Oxygen supply - this poses no problem for terrestrial life since the air contains around 20% oxygen. Aquatic plants and animals utilize the small amount of oxygen dissolved in water. Pollution can significantly lower oxygen content in water and threaten aquatic life. 5. Substratum (soil or rock) - determines the nature of plant and animal life in the soil. Soil is affected by: acidity (pH) - rhododendrons and pines are more suited fo

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Photic Zone

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In water, this is the top layer through which light can penetrate and is where all aquatic photosynthetic activity takes place.

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Aphotic Zone

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Only animal life and other heterotrophic life exists here.

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The Niche

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Defines the functional role of an organism in its ecosystem. It is distinct from the habitat, which is the physical place where an organism lives. It describes what the organism eats, where and how it obtains food, what climactic factors it can tolerate and which are optimal, the nature of its parasites and predators, where and how it reproduces, etc...The concept of it embodies every aspect of an organism's existence. No two species can ever occupy the same niche - if so, competition will exist among the same limited resources. However, many organisms in the same niche can exist, but they must be of the same species. A niche is so specific that a species can be identified by the one it occupies.

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Niche Competition Outcomes

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1. One species may be competitively superior to the other and drive the second to extinction. 2. One species may be competitively superior in some regions and the other may be superior in other regions, under different environmental conditions. This would result in the elimination of one species in some places and other in other places. 3. The two species may rapidly evolve in divergent directions under the strong selection pressure resulting from intense competition. Thus, the two species would rapidly evolve greater differences in their niches.

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Autotrophs

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Organisms that manufacture their own food. The green plants utilize the energy of the sun to manufacture food. Chemosynthetic bacteria obtain energy from the oxidation of inorganic sulfur, iron, and nitrogen compounds.

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Heterotrophs

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Organisms that are unable to synthesize their own food and must depend upon autotrophs or other heterotrophs in the ecosystem to obtain food and energy.

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Herbivores

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Animals that consume only plants or plant food. The toughness of cellulose-containing plant tissues has led to the development of structures for crushing and grinding that can extract plant fluids. They have long digestive tracts that provide greater surface area and time for digestion, but they cannot digest much of the food they consume. Symbiotic bacteria capable of digesting cellulose inhabit the digestive tracts of herbivores and allow the breakdown and utilization of cellulose. They are more adept in defense than carnivores because they are often prey. Cows and horses have hoofs instead of toes for faster movement on the grassland. They have incisors adapted for cutting and molars for grinding their food.

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Carnivores

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Animals that only eat other animals. In general, they possess pointed teeth and fang-like canine teeth for tearing flesh. They have shorter digestive tracts due to the easier digestibility of animal food.

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Omnivores

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Animals that eat both plants and animals.

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Interspecific Interactions

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Relations in a community among different species. An integrated system of species that are dependent upon one another for survival. The major types include symbiosis, predation, saprophytism, and scavenging.

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Symbiosis

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A type of interspecific interaction. Symbionts live together in an intimate, often permanent association that may or may not be beneficial to both participants. Some relationships are obligatory - one or both organisms cannot survive without the other. These relationships are classified according to the benefits they symbionts receive. The types of these relationships include commensalism, mutualism, and parasitism.

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Commensalism

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One organism is benefited by the association and the other is not affected. The host neither discourages nor fosters the relationship. Examples: Remora and shark - the remora (sharksucker) attaches itself by a holdfast device to the underside of a shark. The remora obtains the food the shark excretes, wide geographic dispersal, and protection from enemies. The shark is totally indifferent to the association; Barnacle and whale - the banacle is a sessile crustacean which attaches to the whale and obtains wider feeding opportunities through the migrations of the whale.

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Mutualism

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A symbiotic relationship by which both organisms benefit. Examples: Tick bird and rhinoceros - the bird receives food in the form of ticks on the skin of the rhino. The rhino has its ticks removed and is warned of danger by the rapid departure of the bird; Lichen - intimate association between a fungus and an algae. The green algae produces food for itself and the fungus by photosynthesis. The meshes of fungal threads support the algae and conserve rain water. The fungus also provides CO2 and nitrogenous wastes for the algae, all of which are needed for photosynthesis and protein synthesis; Nitrogen-fixing bacteria and legumes; Protozoa and termites; Intestinal bacteria and humans.

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Parasitism

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A parasite benefits at the expense of the host. It exists when competition for food is most intense. Few autotrophs (green plants) exist as parasites (mistletoe is an exception). This symbiotic relationship flourishes among organisms such as bacteria, fungi, and animals. Some parasites cling to the exterior surface of the host (ectoparasites) using suckers or clamps. They may bore through the skin and suck out blood and nutrients. Leeches, ticks, and sea lampreys employ these techniques. Other parasites (endoparasites) live within the host and must pass through defenses such as skin, digestive juices, antibodies, and WBCs. It is advantageous and efficient. The parasite lives with a minimum expenditure of energy and may even have parasites of their own. Examples: Virus and host cell - all viruses are parasites. They contain nucleic acids surrounded by a protein coat and are nonfunctional outside the host. Upon entry of the viral nucleic acid into the host, the virus takes over the host cell functions and redi

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Predation

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Predators are free-living organisms that feed on other living organisms. This includes both carnivores and herbivores. The predator may severely limit the numbers or distribution of the prey and the prey may become extinct. In contrast, the predatory may only slightly affect the prey because the predatory is scarce or commonly utilizes another food source. The predatory usually aids in controlling the numbers of the prey, but not so as to endanger its existence. Predator-prey relationships evolve towards a balance in which the predator is a regulatory influence on the prey, but not a threat to its survival. Examples include the hawk, lion, humans, and Venus flytrap.

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Saprophytism

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Saprophytes include those protists and fungi that decompose (digest) dead organic matter externally and absorb the nutrients; they constitute a vital link in the cycling of material within the ecosystem. Examples include mold, mushrooms, bacteria of decay, and slime molds.

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Scavengers

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Animals that consume dead animals. They require no adaptations for hunting and killing their prey. Decomposers such as the bacteria of decay may be considered scavengers. Examples include the vulture and hyena. The snapping turtle is an organism which may be considered both a scavenger and predator.

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Intraspecific Interactions

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Relations in a community among the same species. Member of the same species compete, but must also cooperate. Intraspecific cooperation may be extensive (formation of societies in animal species) or may be nearly nonexistent. These types of interactions/relationships are influenced by both disruptive and cohesive forces. Competition is the chief disruptive force. Cohesive fores include reproduction and protection from predators and destructive weather.

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Osmoregulation

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An interaction between organisms and their environment. Animals have developed many adaptations for maintaining their internal osmolarity and conserving water. Examples: saltwater fish live in a hyperosmotic environment which causes them to lose water and take in salt. They are constantly in danger of dehydration and must compensate by constant drinking and active excretion of salt across their gills; Freshwater fish live in a hypoosmotic environment which causes intake of excess water and excessive salt loss. These fish correct this condition by seldom drinking, absorbing salts through the gills, and excreting dilute urine; Insects excrete solid uric acid crystals to conserve water; Desert animals possess adaptations for avoiding desiccation (drying up). The camel can tolerate a wide range of body temperatures and possesses fat layers in regions that are exposed to solar radiation; The horned toad has thick scaly skin which prevents water loss. Other desert animals burrow in the sand during the day and sear

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Thermoregulation

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Cellular respiration only transfers a fraction of the energy derived from the oxidation of carbohydrates into the high-energy bonds of ATP. Roughly 60% of the total energy is given off as heat. The vast majority of animals and plants are cold-blooded or poikilothermic, and most of their heat energy escapes to the environment. The body temperature of poikilotherms is very close to that of their surroundings. Since an organism's metabolism is closely tied to its body temperature, the activity of poikilothermic animals is radically affected by environmental temperature changes. As the temperature rises, these organisms become more active. As temperatures fall, they become sluggish and lethargic. Some animals (mammals and birds) are warm-blooded or homeothermic. They have evolved physical mechanisms that allow them to make use of the heat produced as a consequence of respiration. Physical adaptations like fat, hair, and feathers retard heat loss. Homeotherms maintain constant body temperatures that are higher th

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Energy Flow

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The complex pathways involved in the transfer of energy through the living components of the ecosystem (biotic community) can be mapped in the form of a food chain or food web.

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Food Chain

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Energy from the sun enters living systems through the photosynthetic production of glucose by green plants. Within the food chain, energy is transferred from the original sources in green plants through a series of organisms with repeated stages of consumption and finally decomposition. Thus, there are producers, primary consumers, secondary consumers, and decomposers.

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Producers

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The autotrophic green plants and chemosynthetic bacteria are the producers. They utilize the energy of the sun and simple raw materials (CO2, water, minerals) to manufacture carbohydrates, proteins, and lipids. The radiant energy of the sun is captured and stored in the C-H bond. They always form the initial step in any food chain. The wheat plant is a typical producer.

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Primary Consumers

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Animals that consume green plants (herbivores). Examples include the cow, grasshopper, and elephant.

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Secondary Consumers

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Animals that consume the primary consumers (carnivores). These include frogs, tigers, and dragonflies.

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Tertiary Consumers

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Animals that feed on secondary consumers.

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Decomposers

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Include saprophytic organisms and organisms of decay, which include bacteria and fungi. The producers and consumers concentrate and organize materials of the environment into complex living substances. Living things give off wastes during their lifetime and eventually die. Bacteria and fungi decompose the organic wastes and dead tissues to simpler compounds such as nitrates and phosphates that are returned to the environment to be used again by living organisms. These processes are demonstrated in food webs and material cycles (nitrogen, carbon, and water).

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Food Web

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The food chain is not a simple linear chain, but an intricate web. Almost every species is consumed by one or more other species, some of which are on different food chain levels. The result is a series of branches and cross-branches among all the food chains of a community to form a web. The greater the number of pathways in a community food web, the more stable the community (e.g. owls eat rabbits). If rabbits died off because of disease, there would be more vegetation available to mice. Mice would thrive and provide substitute food for owls. Meanwhile, the decimated rabbit population would have a better chance of recovering while owls concentrated their predation on mice.

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Food Pyramids

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Without a constant input of energy from the sun, an ecosystem would soon run down. As food is transferred from one level of the food chain to the next, a transfer of energy occurs. According to the second law of thermodynamics, every energy transfer involves a loss of energy. In addition to the energy lost in the transfer, each level of the food chain utilizes some of the energy it obtains from the food for its own metabolism (i.e. to support life functions), and loses some additional energy in the form of heat. A pyramid of energy is thus a fundamental property of all ecosystems at all levels.

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Pyramids of Energy

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Each member of a food chain utilizes some of the energy it obtains from its food for its own metabolism (life functions) and loses some addition energy in the form of heat. Since this means a loss of energy at each feeding level, the producer organism at the base of the pyramid contains the greatest amount of energy. Less energy is available for the primary consumer and even less for secondary and tertiary consumers. The smallest amount of available energy is thus at the top of the pyramid.

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Pyramid of Mass

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Since organisms at the upper levels of the food chain derive their food energy from organisms at lower levels, and since energy is lost from one level to the next, each level can support a successively smaller biomass. Three hundred pounds of foliage (producer) may support 125 lbs of insects. This may support 50 lbs of insectivorous hens who in turn will be just the right amount to sustain 25 lbs of hawks.

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Pyramid of Numbers

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Consumer organisms that are higher in the food chain are usually larger and heavier than those further down. Since the lower organisms have a greater total mass, there must be a greater number of lower level organisms (A large bass eats tiny minnows, but eats many of them). With the greatest number of organisms at the base (producer level) and the smallest number at the top (final consumer level) we have a pyramid of numbers.

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Material Cycles

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Material is cycled and recycled between organisms and their environments, passing from inorganic forms to organic forms and then back to the inorganic forms. Many of these cycles are accomplished largely through the action of scavengers and decomposers (saprophytes such as bacteria and fungi).

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Nitrogen Cycle

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Nitrogen is an essential component of amino acids and nucleic acids, which are the building blocks for all living things. Since there is a finite amount of nitrogen on the earth, it is important that it be recovered and reused. 1. Elemental nitrogen is chemically inert and cannot be used by most organisms. Lightning and nitrogen-fixing bacteria in the roots of legumes change the nitrogen to the usable, soluble nitrates. 2. The nitrates are absorbed by plants and are used to synthesize nucleic acids and plant proteins. 3. Animals eat the plants and synthesize specific animal proteins from the plant proteins. Both plants and animals give off wastes and eventually die. 4. The nitrogen locked up in the wastes and dead tissues is released by the action of the bacteria of decay which convert the proteins into ammonia. 5. Two fates await the ammonia (NH3). Some is nitrified to nitrites by chemosynthetic bacteria and then to usable nitrates by nitrifying bacteria. The rest is denitrified. This means the ammonia is b

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Carbon Cycle

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1. Gaseous CO2 enters the living world when plants use it to produce glucose via photosynthesis. 2. The carbon atoms in CO2 are bonded to hydrogen and other carbon atoms. 3. The plant uses the glucose to make starch, proteins and fat. 4. Animals eat plants and use the digested nutrients to form carbohydrates, fats, and proteins characteristic of the species. A part of these organic compounds is used as fuel in respiration in plants and animals. 5. The metabolically produced CO2 is released into the air. The rest of the organic carbon remains locked within an organism until its death (except for wastes given off), at which time decay processes by bacteria return the CO2 to the air.

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Conditions for Stability in an Ecosystem

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An ecosystem is self-sustaining and therefore will be stable if there is a relatively stable physical environment (abiotic factors) and a relatively stable biotic community. A stable ecosystem requires a constant energy source and a living system incorporating this energy into organic compounds. Cycling of materials between the living system and its environment is critical.

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The Climax Community

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The stable, living (biotic) part of the ecosystem in which populations exist in balance with each other and with the environment. The type of climax community depends upon all the abiotic factors: rainfall, soil conditions, temperature, shade etc... A climax community persists until a major climactic or geological change disturbs the abiotic factors or a major biotic change (such as disease, mutations, etc...) affects the populations. Once the equilibrium is upset, new climax conditions are produced and new communities will be established in the ecosystem.

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Ecological Succession

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The orderly process by which one biotic community replaces or succeeds another until a climax community is established. Each community stage (sere) in an ecological succession is identified by a dominant species - the one that exerts control over the other species that are present. Thus, in a grassland community, grass is the dominant species. Changes occur because each community that establishes itself changes the environment, making it more unfavorable for itself and more favorable for the community that is to succeed it. Successive communities are composed of populations that are able to exist under the new conditions. Finally, a stage arises in which a population alters the environment in such a way that the original conditions giving rise to that population are recreated. Replacement stops and a climax community (an ecological steady-state) is established. This climax community is permanent in the ecosystem unless the abiotic factors are drastically altered by climactic or geologic upheavals. If this ha

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Terrestrial Biomes

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The evolutionary origin of plants and animals can be traced to the seas. In order to survive on land, these organisms had to develop adaptations to face an environment with a relative lack of water, relative lack of food and supporting medium, varying temperature (as compared to the oceans), and varying composition of the soil as compared to the definite salt composition in the oceans. Each geographic region is inhabited by a distinct community called a biome existing in the major climate areas. Land biomes are characterized and named according to the climax vegetation of the region. The climax vegeation is the vegetation that becomes dominant and stable after years of evolution. Since plants are important food producers, they determine the nature of the inhabiting animal population, and thus the climax vegetation determines the climax animal population. Types of terrestrial biomes include desert, grassland, tropical rain forest, temperate deciduous forest, temperate coniferous forest, taiga, tundra, and pol

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Desert Biome

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Deserts receive less than ten inches of rain each year; the rain is concentrated within a few heavy cloudbursts. The growing season in the desert is restricted to those days after rainfalls. Generally, small plants and animals inhabit the desert. Most desert plants conserve water actively (cactus, sagebrush, mesquite). Desert animals live in burrows (insects and lizards). Few birds and mammals are found here except those that have developed adaptations for maintaining constant body temperatures. Examples include the Sahara in Africa and the Gobi in Asia.

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Grassland Biome

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Grasslands are characterized by a low rainfall (10-30 inches per year), although they receive much more than desert biomes. They provide no shelter for herbivorous mammals (bison, antelope, cattle, zebra) from carnivorous predators. Animals that do inhabit the grasslands have developed long legs and many are hoofed. Examples include the prairies east of the Rockies, the Steppes of the Ukraine, and the Pampas of Argentina.

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Tropical Rain Forest Biome

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Rain forests are jungles characterized by high temperatures and torrential rains. The climax community includes a dense growth of vegetation which does not shed its leaves. Vegetation such as vines, epiphytes (plants growing on other plants), and animals such as monkeys, lizards, snakes, and birds inhabit rain forests. Trees grow closely together; sunlight hardly reaches the forest floor. The floor is inhabited by saprophytes living off dead organic matter. Tropical rain forests are found in Central Africa, Central America, the Amazon basin, and SE Asia.

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Temperate Deciduous Forest Biome

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Have cold winters, warm summers, and a moderate rainfall. Trees such as beech, maple, oaks, and willows shed their leaves during the cold winter months. Animals include deer, fox, woodchuck, and squirrel. These biomes are found in the NE and CE United States and in Central Europe.

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Temperate Coniferous Forest Biome

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These forests are cold, dry, and inhabited by fir, pine, and spruce trees. Much of the vegetation has evolved for water conservation such as needle-shaped leaves. These forests are found in the extreme Northern part of the US and in Southern Canada.

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Taiga Biome

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These biomes receive less rainfall than the temperate forests, have long cold winters, and are inhabited by a single coniferous tree: the spruce. The forest floors contain moss and lichens (fungi and algae). The primary animal inhabitant is the moose, but the black bear, wolf, and some birds are also found there. They exist in the extreme northern parts of Canada and Russia.

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Tundra Biome

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A treeless, frozen plain found between the taiga lands and the Northern ice-sheets. There is only a very short summer and a very short growing season during when the ground becomes wet and marshy. Lichens, moss, polar bears, musk oxen, and arctic hens inhabit here.

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Polar Region

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A frozen area with no vegetation and terrestrial animals. Animals that do inhabit these regions generally live near the polar oceans.

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Terrestrial Biome and Altitude

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The nature of these regions are determined by temperatures and rainfall. The base of a mountain would resemble the biome of a temperate deciduous area. As one ascends the mountain, one would pass a coniferous-like biome, then taiga-like, tundra-like, and polar-like biomes.

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Aquatic Biomes

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More than 70% of earth's surface is covered by water. 90% of the earth's food and oxygen production (photosynthesis) takes place in water. Plants have little controlling influence in communities of this biome compared to their role in terrestrial biomes. These biomes are the most stable ecosystems; the conditions affecting temperature, amount of available oxygen and CO2, and the amount of suspended or dissolved materials are stable over very large areas and show little tendency to change, so aquatic food webs and communities are balanced. There are two types of major aquatic biomes: marine and fresh water.

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Marine Biomes

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The oceans connect to form one continuous body of water that controls the earth's temperature by absorbing solar heat. Water has the distinctive property of being able to absorb or utilize large amounts of heat without undergoing a great temperature change. These biomes contain a relatively constant amount of nutrient materials and dissolved salts. There are 5 distinct zones in which these biomes exist: intertidal, littoral, pelagic, photic, and aphotic zones.

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Intertidal Zone

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The region exposed at low tides that undergoes variations in temperature and periods of dryness. Populations in these zones include algae, sponges, clams, snails, sea urchins, starfish, and crabs.

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Littoral Zone

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The region on the continental shelf that contains ocean area with depths up to 600 ft and extends several hundred miles from the shores. Populations in littoral zone regions include algae, crabs, crustacea, and many different fish species.

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Pelagic Zone

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Typical of the open seas and can be divided into photic and aphotic zones.

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Photic Zone

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The sunlit layer of the open sea extending to a depth of 250-600 ft. It contains plankton; passively drifting masses of microscopic photosynthetic and heterotrophic organisms, and nekton; active swimmers such as fish, sharks, or whales which feed on plankton and smaller fish. The main autotroph is the diatom, an algae.

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Aphotic Zone

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The region beneath the photic zone that receives no sunlight. There is no photosynthesis in this zone and only heterotrophs exist here. Deep-sea organisms in this zone have adaptations enabling them to survive in very cold water, with high pressures, and complete darkness. The zone contains nekton and benthos (the crawling and sessile organisms). Some are scavengers and some predators. The habitat of this zone is fiercely competitive.

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Freshwater Biomes

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These biomes include rivers, lakes, ponds, and marshes - the links between the oceans and land. Rivers are the routes by which ancient marine organisms reached land and evolved terrestrial adaptations. Many forms failed to adapt to land and developed adaptations for fresh water. Others developed special adaptations suitable for both land and fresh water. As in marine biomes, factors affecting life in these biomes include temperature, transparency (illumination due to suspended mud particles), depth of water, available CO2 and oxygen, and most importantly, the salt concentration.

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Marine vs. Freshwater Biomes

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These biomes differ in three basic ways: 1. Freshwater is hypotonic, creating a diffusion gradient that results in the passage of water into the cell. Fresh-water organisms have homeostatic mechanisms to maintain water balance by the regular removal of the excess water. These include the contractile vacuoles of protozoa and excretory systems of fish. Plant cells have rigid cell walls and thus build up cell pressure (cell turgor) as water flows in. This pressure counteracts the gradient pressure, stops the influx of water, and establishes a water balance. 2. In rivers and streams, strong swift currents exist, and thus fish that have developed strong muscles, and plants with root-like hold-fasts have survived and were selected for. 3. Fresh water biomes, except very large lakes, are affected by variations in climate and weather. Temperature of fresh water bodies varies considerably; they may freeze or dry up, and mud from their floors may be stirred up by storms.