Download Objectives • Describe the five levels of ecological study. • Explain

Objectives
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Describe the five levels of ecological study.
Explain how the patchiness of the biosphere creates different habitats.
Identify key abiotic factors.
Key Terms
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ecology
biotic factor
abiotic factor
population
community
ecosystem
biosphere
habitat
Millions of species live in Earth's diverse environments, which range from
scorching deserts to bubbling deep-sea vents, from lush rain forests to your
school's grounds. This section introduces the study of how living things interact
with these varied environments.
The Study of Ecology
The scientific study of the interactions among organisms and between
organisms and their environments is called ecology. Ecologists, scientists who
conduct research in ecology, test their hypotheses outdoors in the field as well
as in the laboratory. Ecologists also use computer models to understand these
complex interactions. Understanding ecology helps people make decisions
about environmental issues, such as how best to manage forests, rivers, and
other natural resources.
An organism's environment consists of other organisms as well as nonliving
factors. The prokaryotes, protists, animals, fungi, and plants in the environment
are called biotic factors. The nonliving physical and chemical conditions are
called abiotic factors. Ecologists study the relationships among biotic and
abiotic factors at five increasingly broad levels: organisms, populations,
communities, ecosystems, and the biosphere.
Individual Organisms The smallest unit of ecological study is the individual
organism. A blue sweetlip fish is one example of an organism in a coral reef
environment. Other examples of organisms in a coral environment include
other fish, sponges, and the small coral animals that make up the reef.
Ecologists ask questions about the adaptations that enable organisms to meet
the challenges posed by their environments. For example, how are the reef
organisms affected by the changing sunlight levels to which they are exposed?
Populations A population is a group of individual organisms of the same
species living in a particular area. A group of sweetlip fish in the reef
environment is an example of a population. In contrast, all the fish living
around a reef do not form a single population because they represent more than
one species. Ecologists often ask questions about factors that affect the size and
growth of a population. For instance, what factors limit the number of sweetlip
fish living around a reef?
Communities The coral reef is home to a collection of living things including
fish, coral animals, microscopic algae, and all other organisms living in and
around the reef. All of the organisms inhabiting a particular area make up a
community. Ecologists investigate interactions among the organisms in a
community. For example, how do different species of algae-eating fish compete
for food? How might a disease that strikes coral animals affect the other species
in the community?
Ecosystems An ecosystem includes the abiotic factors and the biotic factors in
an area. A coral reef ecosystem includes the reef's many species and its
nonliving conditions, such as the water temperature and amount of sunlight.
Questions at the ecosystem level may relate to the flow of energy and
chemicals. For example, how does nitrogen move within the reef ecosystem?
Biosphere The broadest level of ecological study is the biosphere. The
biosphere is the sum of all Earth's ecosystems. You can picture the biosphere as
the "envelope" of air, land, and water that supports and includes all life on
Earth: the atmosphere to an altitude of several kilometers; the land to a depth of
about 2 kilometers; lakes and streams; and the oceans to a depth of several
kilometers. Questions at the biosphere level involve global issues, such as
investigating the effects of climate change on living things.
Aside from energy, which enters the biosphere as sunlight and exits as heat, the
biosphere is essentially a closed system. This means that the chemicals in the
biosphere's living and nonliving things mostly come from within the system—
they are not supplied from the outside. (One exception is the occasional
meteorite that adds material to Earth.) You'll read more about how the
biosphere's raw materials are recycled in Chapter 36.
Patchiness of the Biosphere
The biosphere is not spread out uniformly around the planet. Looking at Earth
from a space shuttle, you would see that the biosphere is "patchy"—like a quilt
of different environments, including land and oceans, lakes and ice. Zoom in
closer to observe just one continent, and you would see an uneven distribution
of ecosystems such as deserts, grasslands, forests, and rivers. A still smaller
area, such as a wilderness, may contain patches of woods, fresh water, and
marshes. All these environmental variations are due mainly to differences in
abiotic factors such as temperature, soil type, and the availability of water and
light.
This patchiness creates a number of different habitats, or specific environments
in which organisms live. Each habitat has characteristic abiotic and biotic
factors. For example, a wilderness may include several habitats: patches of
forest, marshy areas, and a river. The forest patches are home to trees and
certain species of birds and animals. The marshy land areas provide a habitat
for many species of prokaryotes, fungi, and insects that live in and on top of the
wet soil. And within the river habitat is a surface "microhabitat" that supports
floating plankton and swimming animals, while the deeper water is a separate
microhabitat, with different light and temperature conditions and a different
community of organisms.
Key Abiotic Factors
The organisms that inhabit forests are adapted to the characteristic physical
conditions of forest habitats. These abiotic factors include sunlight, water,
temperature, soil, and wind.
Sunlight The sun provides light and warmth and is the energy source for almost
all ecosystems on Earth. Sunlight powers photosynthesis by plants, the main
producers in most terrestrial (land) ecosystems. Within a forest, much less
sunlight reaches the forest floor than reaches the tops of the tall trees. This
varying amount of sunlight creates different microhabitats. In aquatic (water)
environments, sunlight provides energy for photosynthetic producers such as
algae. The fact that sunlight only penetrates a short distance into a body of
water affects where algae live within a lake or ocean.
Water Water is essential to all life on Earth. All organisms contain water—in
fact, you consist of nearly 70 percent water! Among its many important
properties, water can dissolve gases such as oxygen and solutes such as salt, as
you read in Chapter 4. Terrestrial organisms have adaptations that keep them
from losing too much water and drying out. For example, some plants such as
pine trees have needle-shaped leaves with a waxy coating. These leaves
minimize the amount of water that evaporates into the air. Aquatic organisms
also must balance their water uptake and water loss. Otherwise, their cells may
burst or shrivel due to osmosis (Chapter 6 describes this process).
Temperature Most life exists within a fairly narrow range of temperatures, from
about 0°C to about 50°C. Few organisms can maintain an active metabolism
below 0°C for long, and most organisms' enzymes are denatured (they lose
their shape and stop working) above 50°C. However, extraordinary adaptations
enable certain species to live at extreme temperatures. Some species of
prokaryotes, for example, can thrive in hot springs as hot as 80°C and around
deep-sea vents, which are even hotter.
Soil Soil is the product of abiotic forces (such as ice, rain, and wind) and the
actions of living things (such as microorganisms, plants, and earthworms) on
the rocks and minerals of Earth's crust. The structure and chemical makeup of
soil and rock in an area affect the types of plants that grow there. For example,
areas with a certain type of dry, nutrient-poor soil are often dominated by little
bluestem grasses. These grasses have extensive roots that obtain scarce
moisture in the soil. Their long, narrow leaves roll up in hot, dry weather,
reducing water loss. In aquatic environments as well, the characteristics of the
underlying sand or rock affect the types of plants and algae that can grow. This
in turn influences the other organisms found there.
Wind Wind can affect the distribution and the activities of organisms in several
ways. Wind moves clouds and rain over Earth's surface. Wind also stirs up
water in ponds, lakes, and streams, creating currents that in turn bring up
nutrients from the bottom. Many land plants depend on wind to help disperse
their pollen and seeds.
Severe Disturbances Major natural disturbances that affect ecosystems include
fires, hurricanes, tornadoes, drought, floods, and volcanic eruptions. Some
disturbances, such as volcanic eruptions, are so infrequent that organisms have
not acquired evolutionary adaptations to them. Other disturbances, such as
fires, occur frequently in some communities. Many organisms in such
communities have adapted to these disturbances. For example, in dry
scrublands where fires are common, many plants can regrow from their roots
after a brush fire destroys their aboveground parts.
Concept Check 34.1
1. Draw a diagram showing the relationship among the five levels of ecological
study.
2. Describe what is meant by the "patchiness" of the environment.
3. Explain the importance of sunlight as an abiotic factor in terrestrial
ecosystems.
4. Define biotic and abiotic factors and give an example of each for a particular
ecosystem.
5. Explain why it is more accurate to define the biosphere as the global
ecosystem than as the global community.
Copyright © 2006 by Pearson Education, Inc., publishing as Pearson Prentice
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