Notes on the Web - Unit Two- Part 4
Ecosystem Ecology
Bruce G. Stewart
General Objectives and Study Guide
Your objectives for these Notes on the Web and associated readings and exercises are:
To define ecology and the related levels of biological organization that are within its scope;
Related Textbook Readings:
For General Biology (BIO 1114) Class only: Johnson and Losos (2008 Chapter 37
For General Zoology (Z00 1114) Class only : Hickman, et al. (2006) Chapter 37 and 38.
Energy Flow and Cycling of Material Resources
Two necessities of life, energy and nutrients can be used to emphasize the interdependence of all species. Energy, as we have learned, is a necessary requirement for all living things. How do you obtain the energy to run your body? What other organisms do you depend on? Some examples might be obvious to you: a largemouth bass filet, a beefsteak, a piece of wheat bread, juice from a fruit. However, it is not this simple. We also depend on the food sources of our prey. Where do cattle get their energy? From grasses? Where do the grasses obtain their energy?
Where does a largemouth bass obtain its energy? From species of minnows? Where do the minnows obtain their energy? From aquatic invertebrates? Where do aquatic invertebrates obtain their energy? From green algae? Where do the green algae obtain their energy?
Ultimately, all the energy needed by organisms comes from the Sun. However, not all organisms can trap this energy directly. Through the pathways of food webs, energy is transferred stepwise to other organisms. These pathways can be outlined to help us understand energy flow. An important concept here is that energy is not recyclable. It must continually enter the food web by way of the photosynthesizers. Ecologically, these organisms are called primary producers. Primary producers are also called autotrophs (which mean "self feeding"). Primary producers use part of the energy they convert for maintenance, part is lost as heat, and part is incorporated into their body structure. Organisms that cannot photosynthesize are called heterotrophs (which means "different feeding") or consumers. First level consumers called herbivores eat the body structure of primary producers. Herbivores use metabolism to convert part of the energy for maintenance, part of the energy is lost as heat, and part is stored within their own body structures. This process continues through the food web. Each higher level consumer (carnivores) obtains its energy from what is left in the body structures of its prey. Some organisms (called omnivores) feed on both primary producers and consumers. Others (called decomposers) feed on dead organic matter like body remains and excreted waste. Through these various pathways, energy is available for organisms to do the work of living. However, only about 10% of the energy taken in by an organism can be passed on to the next level because so much is lost as heat or used in maintenance. This is why big fierce animals are rare!
Nutrient Cycles
Nutrients, unlike energy, cycle in the biotic (living) and abiotic (non-living) world. You can think of nutrients like bricks of a house. A house can be built of bricks when a bricklayer uses his energy to do work. Once the house is built, the energy used to build the house is gone for good. However, with more input of energy, the house could be torn down and the bricks used to build another house. The bricks, like nutrients, are not lost.
Nutrients like carbon, nitrogen, and so on are used and reused in an ecosystem. The pathways they follow through the biotic and abiotic parts of an ecosystem are called nutrient cycles. Food webs are a part of nutrient cycles, but there are other abiotic parts, too.
Most existing forms of life depend directly or indirectly on one another for their existence. While energy flow and nutrient cycling emphasize the interdependence of living things, there are countless other important interactions. Now consider the way we humans fit into this big picture.
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Teach your children what we have taught our children-- that the earth is our mother Whatever befalls the earth befalls the sons and daughters of the earth. If men spit upon the ground they spit upon themselves. This we know. The earth does not belong to us; we belong to the earth This we know. All things are connected like the blood which unites one family. All things are connected. Whatever befalls the earth befalls the sons and daughters of the earth. We did not weave the web of life; We are merely a strand in it. Whatever we do to the web, we do to ourselves.... CHIEF SEATTLE |
Textbook Study Reminder
Study your related textbook readings thoroughly. The brief notes above are only meant as an introduction and do not cover the objectives comprehensively, but your textbooks do an excellent job of this... with beautiful illustrations! Check the general objectives above to make sure that you have covered all of the topics in the textbook readings.
The "Self Test" and other questions will be helpful for general biology students, although many more detailed questions will be included in the lecture exam. Similarly, study questions in the zoology textbook will be helpful review for general zoology students, but again, they are not comprehensive.
As with all materials throughout the semester, you will have opportunities to ask questions or ask that any relevant material from your assignments be discussed in class and/or in threaded discussions on Internet.
© 2005, 2007 Bruce G. Stewart
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