| Ecosystems- an overview |
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An ECOSYSTEM is all the living and non living things that interact in a particular area.
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A Brief description of the Delaware Bay as an Ecosystem
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In the Delaware Bay there is water that varies in the amount of salt as you go up toward the Delaware River. There are many things that influence the composition of the water from human uses of the river and the land that surrounds the river and the bay to the amount of rainfall. The lower the rainfall in a given year the saltier the water is. Salty water can travel up the river in years with low rainfall because not much fresh water mixes with it! Saltwater organisms can travel further up river in search of food and breeding grounds.
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There are thousands of organisms that live in and around the bay. Still others only come to the bay at certain times of the year such as migratory birds. The birds stop in the Delaware Bay on their way to breeding grounds in the arctic. Some of these birds fly non-stop from Southern South America before they reach the bay. They stop in the bay for one reason, Horseshoe crab eggs.
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The Horseshoe crab is a very ancient type of organism that is still around today. One of its main breeding grounds in the world is the Delaware Bay. This is another type of organism that lives in and influences they bay. It eats things like clams and mussels among other things.
So the bay must support the clams and mussels in order to support the Horseshoe crab.
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The clams filter microscopic plants and animals called Plankton from the water. Plant-like plankton (phytoplankton) need sunlight, water and dissolved carbon dioxide to make food for themselves through photosynthesis. They need nutrients dissolved in the water as well. The animal-like plankton (zoo-plankton) eat the phytoplankton. So the Bay must support these to support the clams, to support the Horseshoe crabs to support the shore birds. All of the organisms mentioned need oxygen and can only live within a certain range of temperature.
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By now you should get the picture!
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The living parts of an ecosystem are called BIOTIC FACTORS. In the Delaware Bay description above the Biotic Factors in the Bay Ecosystem were the shore birds, the Horseshoe crab, the clams the mussels, and the plankton. All of these organisms have an effect on the others.
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The non-living parts of the ecosystem are called ABIOTIC FACTORS. In the Delaware Bay description above the Abiotic Factors in the Bay Ecosystem were the water, salt, nutrients, sunlight, and gases (like carbon dioxide and oxygen). The temperature of the bay influences the organisms that can live there. Much of the nutrients found in the water dissolve from soil on shore and run-off into the bay, so soil is an Abiotic Factor influencing the Bay Ecosystem.
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An organism must get food, shelter water and other things in order to live, grow and reproduce from the area that it lives in. The place that an organism obtains these things is called its HABITAT.
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An Ecosystem can have many habitats for many different types of organisms. Can you think of at least two different habitats from the brief description above?
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The Bay is home to thousands of different kinds of plankton. There are dozens of different types of shorebirds that visit here. There is one type of horseshoe crab that lives in the Bay. Each of these different types of organisms are called a SPECIES
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A SPECIES is a group of organisms that are similar and can reproduce with each other and produce
offspring that can themselves reproduce.
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All members of a species that lives in a given Ecosystem is called a POPULATION.
All of the populations of organisms that live in an area interact with each other and form a COMMUNITY.
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The smallest level or organization is a single organism, which belongs to a population of other members of its species. The population belongs to a community of different species. The community and abiotic factors together form an ECOSYSTEM.
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A population can be very large or small. Studying populations can be a tricky task! How would you go about sampling the population size of the grass plants that make up the front yard of the school?!! Population density is often used when you can not count each individual of a species. For instance: You counted 60 grass plants in a 10 cm X 10 cm plot. There are 100 of these squares in one square meter so there would be 6000 grass plants in one square meter! (Would YOU want to count them all?!) Now multiply 6000 time the number of square meter in the front yard of the school and you would have a good estimate of the number of grass plants in the yard!
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A population of organisms can not grow forever! It should be obvious that something will limit the size it can grow to. These things are called LIMITING FACTORS. (catchy name, eh?!) Some limiting factors include food, nutrients, space and weather conditions. When a population has reached its maximum that the given Ecosystem can support it has reached its CARRYING CAPAPCITY.
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For instance if a field only has enough grass seeds to feed 30 mice regularly, then when more are born or try to move in, some will starve. The population will maintain its numbers right around 30. If something should change the amount of material that is limiting the population (like more grass grows) then the population will rise. If someone came in with a bulldozer and paved half of the field the population would decline.
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Space and food are the two most common limiting factors and play a tremendous part in ecology of organisms around where the two legged beasties live (us humans that is!) humans have the nasty habit of wiping out habitat for such worthy ventures as shopping malls and the like!
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