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THE ECOSYSTEM Agriscience 381 Wildlife and Recreation Management # 8984-A TEKS: (c)(3)(A) Introduction Ecology is the study of the relationship between living organisms and their environment. Environment is an organism’s immediate surroundings. An ecosystem is made up of levels containing groups of organisms. Ecological levels are as follows. Individuals Populations Communities Ecosystems Biomes Biosphere Individual organisms of a single species make up a population. Populations of more than one species makes up a community. Communities make up an ecosystem. Ecosystems make up a biome and biomes make up the biosphere. Earth is made up of living organisms and inert substances. It is the result of millions of years of evolution or change that is continuous. The Earth is a series of different ecosystems. Each ecosystem has its own parameters for life. These parameters include temperature, pH, and rainfall. All species of plants and animals fit into ecosystems to which they have adapted. Sometimes those parameters change. When that happens, plants must adapt or die; animals must adapt, move, or die. Early in the development of Earth, all water was fresh, including the oceans. Over millions of years, water moved mineral salts through soil, down streams and rivers, and eventually to the oceans’ waters. As the water evaporated back into the hydrological cycle, the oceans’ freshwater became brackish water and then eventually saltwater. Photo by M. Jasek People are part of the ecosystem. People are the only species that can upset the balance in an ecosystem. What appears to be a stable ecosystem, in fact, can be easily upset by over-exploitation of resources. There is a misconception that humans will one day destroy the Earth. In reality, people may destroy the parameters needed for survival. If the human population became extinct, the Earth would heal itself and life without the human element would continue. Ecosystem A biotic community is a group of plants and animals that share the same area and environment. In this community, plants and animals are interdependent. Here biotic and abiotic components are constantly interacting. Biotic components are all living organisms, from the smallest microbe to the largest animal. Photo by E. B. Forsythe courtesy of U. S. Fish and Wildlife Service. Abiotic components are non-living elements that include soil nutrients, water, air, and temperature. Photo by Lynn Betts courtesy of USDA Natural Resources Conservation Service. An ecosystem can be as large as a forest or ocean or as small as a river bank or tree cavity. Each component in an ecosystem relies on others within the system for sustaining life. A simple example of interdependency is as follows: Herbivores eat plants. Carnivores eat herbivores. Both generate waste products that feed microbes, bacteria, and insects. This helps feed the plants that herbivores eat. Biomes Biomes are large areas with a distinct combination of plants and animals. These areas are influenced largely by latitude, soil, temperature, and rainfall. The number of biomes may vary depending on how they are divided. Biomes can be present on land or in water. Aquatic biomes have their own set of characteristics. On land, there are six major biomes in the United States. Terrestrial Biomes The six major biomes in the United States are classified as tropical, temperate forests, grasslands and savannas, tundra, taiga, and desert. Tropical Only Hawaii and a few U. S. Pacific Islands have this biome. These biomes are commonly found along either side of the equator. Photo by M. Jasek. Tropical forests and tropical grasslands are part of this biome. Tropical forests are in areas with more than 90 inches of rainfall annually. Tropical grasslands occur in areas with low rainfall. Photo by M. Jasek. Temperate Forests Temperate forests are located in the southern United States, mainly east of the Mississippi Delta. Photo by John & Karen Hollingsworth courtesy of U. S. Fish and Wildlife Service. This area has high value conifers that are gradually being replaced by hardwoods. Plant life in this biome yields a variety of acorns, cones, berries, and fruits. Photo by M. Jasek. Grasslands and Savannas This biome has low rainfall and occupies the plains of the western United States northward into Canada. Photo by M. Jasek. Vegetation consists mainly of grasses and forbs. In the U. S., only grasslands exist. Photo by M. Jasek Browsing animals, predators, and small mammals, along with reptiles and birds, make up the animal life in this biome. Savannas do not exist in the North American continent. In savannas, soil fertility is lower than in grasslands. Savannas are common in Brazil, Africa, Australia, and India. Tundra This biome is located in the Artic area or at high elevations. Biomes at high elevation are alpine tundra. The low temperatures and permanently frozen ground (permafrost) of Alaska is common to this biome. Certain varieties of grasses and shrubs, lichens and mosses grow in this area. Photo by M. Jasek. Tiaga (Boreal Forests) Taiga areas are not as cold as tundra. Conifers will grow in taiga. Also called boreal forests, trees can support heavy quantities of snow and low temperatures. Photo by Laura Kennedy courtesy of U. S. Fish and Wildlife Service. Desert In the United States, the desert biome is located in the western USA. Little or no rainfall is characteristic of desert biomes in states like Nevada, Arizona, and California. Photo by David McMahan courtesy of U. S. Fish and Wildlife Service. Temperature extremes from daytime highs to extremely cold nights are common. Photo by John and Karen Hollingsworth courtesy of U. S. Fish and Wildlife Service. Aquatic Biomes Water freshness is a measure of the amount of salt in the water. The four levels of freshness are: fresh, brackish, salt, and brine. Fresh water has less than five parts per thousand (ppt.) salt. Brackish water ranges from 6 to 15 ppt. Salt water ranges from 16 to 30 ppt. Brine is any water with more than 30 ppt. of salt. The only area in the United States with this level of salt (brine) is the Great Salt Lake in Utah. This level does not support enough life to consider it a biome. There are four aquatic biomes: • Lakes and ponds, • Streams, • Oceans and seas, and • Wetlands and estuaries. Animals and plants have adjusted to the varying levels of freshness in each of the biomes. Photo by Eric Engbretson courtesy of U. S. Fish and Wildlife Service. Lakes and Ponds Inland lakes and ponds are usually freshwater. Those along the coast may contain brackish or salt waters. Some lakes and ponds are fed by a watershed or rainfall. Others are fed by melting snow and ice or by groundwater. Photo by Craig Rieben courtesy of U. S. Fish and Wildlife Service. The temperature of water is determined by its water source and by the surrounding climate. Water also has temperature variations within it, some as much as 10 to 15 degrees within as little depth as two or three feet. These temperature levels are called thermoclines. Life in an aquatic biome ranges from microscopic organisms to large fish. Microscopic organisms include phytoplankton, zooplankton, algae, insects, and small crustaceans. Larger vegetation includes lily pads, reeds, exposed tree roots, and trees. Photo courtesy of U. S. Fish and Wildlife Service. Dead trees that fall into lakes and ponds provide a source of shelter for aquatic species. Artificial structures can be added for additional shelter. Swamps are part of this aquatic biome. Swamps are usually shallow and more cluttered with vegetation. Photo by Ned Trovillion courtesy of U. S. Fish and Wildlife Service. Streams Streams range in size from creeks to rivers. Photo by J. Schmidt courtesy of U. S. Fish and Wildlife Service. They are fresh, flowing water moving from higher elevation to lower elevation. The steeper the change in elevation, the faster the water travels. Photo by Ed Austin & herb Jones courtesy of Yellowstone Park, National Park Service, DOI. As water travels faster, fewer plants grow in the water. Rocks, coves, and holes are sometimes the only shelter for fish. Oceans and Seas Oceans and seas are the largest bodies of water. These are normally saltwater bodies. Along coastlines, water may become brackish when mixed with freshwater. During heavy rainfall, coastal waters may even become fresh. Many marine species require saltwater to reproduce, but can grow in fresh, brackish waters or salt waters. Photo by Gary Stolz courtesy of U. S. Fish and Wildlife Service. Wetlands and Estuaries Wetlands can be either fresh or salt waters. They can occur near any water source. Land exposed to water cover for a long period allows water-tolerant plants to establish. This attracts certain types of wildlife, such as beaver, nutria, and waterfowl. Swamp and marsh vegetations grow in wetlands. Swamp is made up of larger vegetation, such as trees. Photo by John & Karen Hollingsworth courtesy of U. S. Fish and Wildlife Service. Marshes are wet, grassy, low-lying areas. Photo by George Gentry courtesy of U. S. Fish and Wildlife Service. Estuaries are tidal areas, where the ocean and land meet. More than 90 percent of all species in the oceans depend on estuaries during some phase of their life cycle. Photo courtesy of U. S. Fish and Wildlife Service. Ecological Niche Each organism in an ecosystem performs a specific function called a niche. This is its job in relation to the other organisms in the ecosystem. In some cases, different species will complement each other and are dependent on each other. Lichens are the result of two organisms, a fungus and an algae, living in a symbiotic relationship. Photo by M. Jasek. Regardless of the function, they all work to keep the system in balance. A coyote hunting mice represents a predator-prey relationship. Photo by J. Schmidt courtesy of Yellowstone Park, National Park System, DOI. Food Webs A food web is the relationship of all animals in a community and the organisms they eat. Plants are producers or autotrophs. Animals are consumers or heterotrophs. A basic law of physics is that matter can be changed from one form to another; it can neither be created nor destroyed by ordinary physical and chemical changes. Nutrients move from plant to animal to animal to soil to plant. This is the basis for a successful ecosystem. Illustration: Christine Stetter Plants take nutrients from the soil and energy from the sun to produce glucose, which is used for growth and reproduction. Herbivores consume a variety of plants. Photo by J. Schmidt courtesy of Yellowstone Park, National Park Service, DOI. Omnivores feed on both plants and animals. Photo by John Nickles courtesy of U. S. Fish and Wildlife Service. Carnivores feed on other animals. Photo by J. R. Douglass courtesy of Yellowstone Park, National Park Service, DOI. The way that these organisms interact closely resembles a spider web and is referred to as a food web. A food chain is a single pathway within a food web. However, seldom does an organism feed on just one other organism. A food pyramid illustrates the feeding hierarchy of the food chain or food web. The pyramid directly corresponds to the amount of food (energy) available at each level. As movement occurs up the pyramid, the population of species declines. At the bottom of the pyramid are plants. An energy pyramid shows the amount of energy that is passed from one level to the next. Some of the energy at each level is used by the organism and some is given off as heat. Only about 10% is passed on to the next level. In the perfect ecosystem, the plant population exceeds the population of herbivores that feed on the plants. At the next level, the population of all herbivores is greater than the population of all omnivores in that ecosystem. The smallest population of species is the carnivores. Any change in population at any level in this pyramid upsets the whole scheme. For example, if the predator population was reduced by hunting due to them preying on domestic animals, the wild rabbit population could outgrow the food supply of grasses on which it feeds. Another important part of the food web, yet much less noticeable, is the decomposer. Decomposers are small organisms that break down complex organisms into inorganic substances. The more important of these substances are water, carbon, nitrogen, phosphorus, calcium, and sulfur. In this form, the plants (producers) can continue the nutrient cycle in the food chain. ALL RIGHTS RESERVED Reproduction or redistribution of all, or part, of this presentation without written permission is prohibited. Instructional Materials Service Texas A&M University 2588 TAMUS College Station, Texas 77843-2588 http://www-ims.tamu.edu 2006