ABSTRACT
We are immersed in life. We breathe it in, we walk on it, we touch it. Each footstep on a fertile lawn or forest mat will send tremors to trillions of bacteria, millions of algae, fungi, and protozoa, and hundreds of insects and worms. The skin on our bodies, when viewed microscopically, is a teaming matrix of tiny caverns filled with bacteria, viruses, and mites. So dense are the unseen life forms on our
bodies that they form an almost complete shell about each of us. Every breath draws in untold numbers of fungal spores, bacteria, viruses and other microbes. Life abounds most everywhere inhabited by humans. Life thrives on the nutrients in soil and water, the oxygen and carbon dioxide in the air, and on the sunlight that ultimately powers most life. In those areas of earth where nutrients are depleted, oxygen is rare, sunlight is extinguished, or moisture is diminished, life becomes reduced or absent. Conditions for most life are found in a layer about the globe that extends from approximately five miles in the atmosphere (where some microbial spores and insects may be found) to five miles below the ocean’s surface, where some unusual life forms adapted to darkness and high pressure survive. This theoretical “layer of life” is called a biosphere because life is thought not to exist outside this area. Most life occurs in a much narrower layer extending from about a 600foot depth in the ocean where sunlight is able to penetrate, to the summer snow line of high mountain peaks where a thin layer of soil supports plant life such as lichens and mosses. Within this biosphere, the forms and quantities of life vary dramatically. Surface-or land-based life may be categorized into major regions known as biomes. Biomes are based on the dominant types of vegetation that are strongly correlated
OBJECTIVES FOR THIS CHAPTER
A student reading this chapter will be able to:
1. Discuss and define the concepts of biosphere and climate
2. List and explain the factors influencing climate
3. Define the term biome; list the major global biomes, and discuss their primary features
4. Describe the flow of energy through ecosystems
5. Describe and explain the various trophic levels
6. List and explain the various nutrient cycles including the carbon, nitrogen, and phosphorous cycles
7. Define the term
succession
, explain the mechanisms of succession, and discuss the types of human intervention that interfere with succession
with regional climate patterns. We will explore the various types of biomes in short order, but first let us look at the driving force of these regional differences — the climate.
