Ch. 5 - How Ecosystems Work

3.1 Energy Flows in Ecosystems

• Sunlight is the source of energy for almost all producers in almost all ecosystems.  The provides the energy used by produces to make fook the sun is also the indirect source of energy for nearly all consumers.

Organisms classified on how they obtain their enegy

• Life on Earth could not exisit without producers.  With no producers, consumers and decomposers would run out of food soon and die off, all live would die off without the energy of producers.
• Consumers
  • Herbivores eat only plants, ominvores eat both plants and animals. EX: grasses, trees, ect.
  • Carnivore eats only other consumers. EX: Lions, hawks
  • Ominvore eats both producers and consumers. EX: bears, people
  • Decomposer  breaks down dead organisms in an ecosystem, returning nutrients to the soil or wate 
• In a food web an organism could be both predator and prey.
• More people could be supported by eating only plants than eating both plants and animals. 90 percent of the energy is lost in each step of the food chain, and since plants are the 1st step, humans would recieve more energy and be able to feed more people by eating only plants.
• Energy is lost at each trophic level, organisms at higher trophic levels need more food to suport themselves than do organisms at lower trophic levels.
  • Prodcuers at the bottom of an energy pyramid have 1000 times more energy than a hawk (teriary consumer) at the top of the pyramid
• Each trophic level can support fewer organisms than the level below it.

The Cycling of Materials

3.2  THE CYCLING OF MATERIALS

• Materials in ecosystems are endlessly recycled by natural processes.
• Carbon, water, and nitrogen are three materials essential for life, and each follows a recognizable cycle.

Carbon Cycle

• Plants take in carbon from the atmosphere during photosynthesis; organisms then eat the plants and release the carbon to the atmospere by cellular respiration.
• Producers take in carbon dioxide from the air and use it to make simple sugars during a process called photosynthesis.  Many sugar molecules can then be linked to fom starches, which the plant uses to store energy.  The energy and carbon in the starches are used by the animals that eat the plants.
• Humans add carbon to the atmosphere by burning large amounts fo fossil fuels.  The increasing population also increases carbon dioxide through the process of cellular respiration.  Also by cutting down large amounts of forests are decreasing plants that take out CO₂ out of the atmosphere.  All these activities may contribute to global warming.
• Animals exhale CO₂ into the atmospehre.

Nitrogen Cycle

• The atmosphere is 78% nitrogen
• Lighning fixes some nitrogen with then falls to the Earth
• Nitrogen-fixing bacteria in soil and root nodules (legume plants) produce ammonia
• bacteria convert ammonia into nitrates, which plants can use
• When animals die or deposit urine or dung, the nirogen they obtained from eating plants or other animals is converted by bacteria into ammonia.  
• Some ammonia is abosrbed by the soil, and some is released into the atmosphere as nitrogen gas.

Water Cycle

• The sun drives the water cycle.
•  In the water cycle, evaportation releases water vapor into the air.  The vapor condenses into liquid vapor at cooler temperatures in the atmospehere, the liquid then falls to earth as percipitaiton.

How Ecosystems Change

3.3 How Ecosystems Change

Succession

• The types or grangisms in a community follow a regular pattern of change over time, succession.
• Primary succession occurs on bare rock where nothing has ever grown. 
  •  This involves a sequence or stages that is similar to secondary suceesion and ends in a climax community.
• Secondary succession takes place where other commmunities have lived before.
• Eventually a climax community takes hold and persits until it is distrubed.
• Forest fires are a necessary part of secondary succession i n some areas because certain organisms reproduce only after a forest fire has cccurred, such as the jack pine.
• Periodic forest fires may also prevent larger major fires.
• An example of a pioneer species is Lichens, they can grow on bare rock and gradually break the rock down starting the process of soil formation.

Soil Formation

• Soil formation - water can freeze and thaw in cracks in rocks making the rock to breakdown further.  Dust particles in the air are trapped in the cracks and as the dead remains of the lichens and bacteria buld up, mosses later gain hold, breaking the rock some more.  as the mosses die, they decay and are added tothe growing pile or organic material, fertile soil is now beginning to form, seeds are able to germainate and successon begins.