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| BIO 190: The Class: Chapter 39: Lesson 39 | ||||
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| BIO 190: The Class: Chapter 39: Lesson 39 | ||||
The Biosphere: Spaceship Earth
The biosphere of the earth is made up of the thin layers of land, sea and atmosphere which sustain all life on the planet. It is comprised of three components:
A biome is a biotic unit characterized by a distinctive array of plant life. The terms was used originally by botanists to describe areas have distinctive vegetation, such as tundra, forests and deserts. Zoologists have also come to use this construct, recognizing that while a biome is defined by its dominant array of plants, animals live on plants and so each biome supports certain kinds of animal life.
To further explore earth's biomes,
As you learn about the biotic communities on earth, keep in mind how people have influenced the biomes you are studying, particularly in those areas most heavily populated by people.
The following is a list of the earth's biomes. Be sure you understand the predominant features of each. Return to the MBG Biome Map and the descriptions in your textbook on pages 780-782 for further clarification.
Inland Waters
There are two major divisions of inland water. Lotic habitats are running waterways, such as streams, brooks and rivers. Lentic habitats have less movement and are characterized by fauna which is tolerant of a lower oxygen concentration. The organisms included under the following headings tolerate pond and lake conditions.
Estuaries are transition zones which occur where fresh water flows into the sea. Estuaries have an unstable salinity compared with oceans because of the fresh water flowing into them. Even so, they are rich in nutrients and support a wide variety of fauna.
Oceans
Oceans represent the largest percentage of the earth's biosphere and supports more than 200,000 species of life-protists, plants and animals. Of these species, 98% are benthic, meaning they live on the sea bottom. Only 2% live in the open ocean, and called pelagic species.
Regions of the Oceans
Compared with the terrestrial environment the marine world is rather
uniform. Even so, the ocean can be divided into regions with distinctive
life forms.
Littoral or Intertidal Region: This is the zone where earth and sea meet. Though it is a harsh physical environment, it provides an extremely rich environment which supports a great variety of life forms.
Sublittoral or Subtidal Region: This is the area below the littoral zone which is always submerged. It also supports a great variety of life.
Neritic or Shallow Water Region: This is the zone of shallow water which lies off shore and extends to the continental shelf. This area has a greater productivity of animal life than does the open ocean because it has the benefit of the nutrients dumped into the ocean by rivers and from the upwellings along the edge of the continental shelf. It is in this region that the major fisheries of the world are found.
For more information on this region and fisheries, open the National Marine Fisheries Information Page.
Pelagic or Open Ocean Region: This zone is the largest of the ocean, yet the least productive in terms of biological life. There are exceptions in areas of upwelling or where currents converge because of the availability of nutrients.
The pelagic region is subdivided on the basis of depth. The epipelagic layer is the area from the surface of the ocean to a depth of about 200 meters. Below that is the mesopelagic layer which still receives light and supports a variety of animal life. Below that are the areas of the ocean characterized by constant darkness, very cold temperatures and much pressure. The deep-sea forms found here rely on organic material dropping down from above for sustenance.
Zoogeography
This area of zoology examines how animal life is distributed and the factors which cause this distribution.
Disjunct Distribution: A significant problem for zoogeographers is to explain how very closely related species come to live in widely separated areas of a continent, or the world. The two major causes for a disjunct distribution are disperal and vicariance.
Distribution by Dispersal
The mechanisms which characterize the movements of animals by dispersal
are the emigration of animals from one location and immigration
into a new locality. In short, either by their own power or by natural
forces, animals expand into new locales. An important component of
the explanations of distribution by dispersal is the concept of a center
of origin from which the animals dispersed.
Distribution by Vicariance
This explanation of disjunct distributions states that formerly contiguous
land areas have become disjunct due to physical changes in the environment.
In other words, the disjunct distribution is the result of the separation
of land masses which were previously joined. The prime example
of this phenomenon is continental drift.
Continental Drift
Continental drift is a geological theory which has recently gained
widespread acceptance amongst geologists. The theory posits that
once continuous landmasses later broke into the continents and islands
we see today. The theory of plate tectonics, which proposes that
the earth's crust is made up of rocky plates that shift in position over
time, has found much supporting evidence, which in turn gives credence
to the theory of continental drift.
For further information on Continental Drift theory and plate tectonics, open the two links below from Macquarie University in Australia.
Go on to Assignment 39
or
Go back to Chapter 39
Copyright 1997 Northern Arizona
University Department of Biological
Sciences
ALL RIGHTS RESERVED