Download Patchiness of the Biosphere - Platteville Public Schools

Objectives
Describe the five levels of ecological study.
Explain how the patchiness of the biosphere creates different
habitats.
Identify key abiotic factors.
Key Terms
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.
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