When biologists want to talk about life on a global scale, they use the term biosphere.
 

Biosphere All life on Earth and all parts of the Earth in which life exists, including land, water, and the atmosphere The biosphere contains every organism, from bacteria living underground to giant trees in rain forests, whales in polar seas, mold spores drifting through the air—and, of course, humans.  The biosphere extends from about 8 kilometers above Earth’s surface to as far as 11 kilometers below the surface of the ocean.

The Science of Ecology
 

Organisms in the biosphere interact with each other and with their surroundings, or environment.  The study of these interactions is called ecology. Ecology The scientific study of interactions among organisms and between organisms and their physical environment.

The root of the word ecology is the Greek word oikos, which means “house.” So, ecology is the study of nature’s “houses” and the organisms that live in those houses. Interactions within the biosphere produce a web of interdependence between organisms and the environments in which they live.  Organisms respond to their environments and can also change their environments, producing an ever-changing, or dynamic, biosphere.

Ecology and Economics

The Greek word oikos is also the root of the word economics.  Economics is concerned with human “houses” and human interactions based on money or trade.  Interactions among nature’s “houses” are based on energy and nutrients.  As their common root implies, human economics and ecology are linked.  Humans live within the biosphere and depend on ecological processes to provide such essentials as food and drinkable water that can be bought and sold or traded.

Levels of Organization

Ecologists ask many questions about organisms and their environments.  Some ecologists focus on the ecology of individual organisms.  Others try to understand how interactions among organisms (including humans) influence our global environment.  Ecological studies may focus on levels of organization that include those shown in Figure 3–1.
 

Individual Organism A species is a group of similar organisms that can breed and produce fertile offspring.		Population A population is a group of individuals that belong to the same species and live in the same area.
Community An assemblage of different populations that live together in a defined area is called a community.		Ecosystem All the organisms that live in a place, together with their physical environment, is known as an ecosystem.
Biome A biome is a group of ecosystems that share similar climates and typical organisms.		Earth Our entire planet, with all its organisms and physical environments, is known as the biosphere.

What is ecology?
 

REVIEW & DO NOW Answer the following questions:
What is the biosphere? What is ecology?	Name and define the six levels of organization from the individual to the entire planet.

Biotic and Abiotic Factors
What are biotic and abiotic factors?

Ecologists use the word environment to refer to all conditions, or factors, surrounding an organism.  Environmental conditions include biotic factors and abiotic factors, as shown below.

Biotic Factors

The biological influences on organisms are called biotic factors.

Biotic Factor
Any part of the environment which is alive or that comes from a living thing with which an organism might interact

Biotic factors relating to a bullfrog, for example, might include algae it eats as a tadpole, insects it eats as an adult, herons that eat bullfrogs, and other species that compete with bullfrogs for food or space.

Abiotic Factors

Physical components of an ecosystem are called abiotic factors.

Abiotic Factor
Any nonliving part of the environment, such as sunlight, heat, precipitation, humidity, wind or water currents, and soil type

For example, a bullfrog could be affected by abiotic factors such as water availability, temperature, and humidity.

Biotic and Abiotic Factors Together

The difference between biotic and abiotic factors may seem to be clear and simple.  But if you think carefully, you will realize that many physical factors can be strongly influenced by the activities of organisms.  Bullfrogs hang out, for example, in soft “muck” along the shores of ponds.  You might think that this muck is strictly part of the physical environment, because it contains nonliving particles of sand and mud.  But typical pond muck also contains leaf mold and other decomposing plant material produced by trees and other plants around the pond.  That material is decomposing because it serves as “food” for bacteria and fungi that live in the muck.

Taking a slightly wider view, the “abiotic” conditions around that mucky shoreline are strongly influenced by living organisms.  A leafy canopy of trees and shrubs often shade the pond’s shoreline from direct sun and protect it from strong winds.  In this way, organisms living around the pond strongly affect the amount of sunlight the shoreline receives and the range of temperatures it experiences.  A forest around a pond also affects the humidity of air close to the ground.  The roots of trees and other plants determine how much soil is held in place and how much washes into the pond.  Even certain chemical conditions in the soil around the pond are affected by living organisms.  If most trees nearby are pines, their decomposing needles make the soil acidic.  If the trees nearby are oaks, the soil will be more alkaline.  This kind of dynamic mix of biotic and abiotic factors shapes every environment.

What are biotic and abiotic factors?
 

REVIEW & DO NOW Answer the following questions:
What is the environment? What are biotic factors? Give an example of a biotic factor.	What are abiotic factors? Give an example of an abiotic factor.

The Major Biomes
What abiotic and biotic factors characterize biomes?

Latitude and the heat transported by winds are two factors that affect global climate.  States like Oregon, Montana, and Vermont have different climates and biological communities, even though those states are at similar latitudes and are all affected by prevailing winds that blow from west to east.  Why? The reason is because other factors, among them an area’s proximity to an ocean or mountain range, can influence climate.

Regional Climates

Oregon, for example, borders the Pacific Ocean.  Cold ocean currents that flow from north to south have the effect of making summers in the region cool relative to other places at the same latitude.  Similarly, moist air carried by winds traveling west to east is pushed upward when it hits the Rocky Mountains.  This air expands and cools, causing the moisture in the air to condense and form clouds.  The clouds drop rain or snow, mainly on the upwind side of the mountains—the side that faces the winds, as seen below.  West and east Oregon, then, have very different regional climates, and different climates mean different plant and animal communities.

Defining Biomes

Ecologists classify Earth’s terrestrial ecosystems into at least ten different groups of regional climate communities called biomes.

• Biomes are described in terms of abiotic factors like climate and soil type, and biotic factors like plant and animal life.

The distribution of major biomes is shown below.  Note  that even within a defined biome, there is often considerable variation among plant and animal communities.  These variations can be caused by differences in exposure, elevation, or local soil conditions.  Local conditions also can change over time because of human activity or because of the community interactions described in this chapter and the next.

Earth's Major Biomes
 

Tropical Rain Forest

Tropical rain forests are home to more species than all other biomes combined.  As the name suggests, rain forests get a lot of rain—at least 2 meters of it a year! Tall trees form a dense, leafy covering called a canopy from 50 to 80 meters above the forest floor.  In the shade below the canopy, shorter trees and vines form a layer called the understory.  Organic matter on the forest floor is recycled and reused so quickly that the soil in most tropical rain forests is not very rich in nutrients.

• Abiotic factors Hot and wet year-round; thin, nutrient-poor soils subject to erosion • Biotic factors Plant life: Understory plants compete for sunlight, so most have large leaves that maximize capture of limited light.  Tall trees growing in poor shallow soil often have buttress roots for support.  Epiphytic plants grow on the branches of tall plants as opposed to soil.  This allows epiphytes to take advantage of available sunlight while obtaining nutrients through their host. Animal life: Animals are active all year.  Many animals use camouflage to hide from predators; some can change color to match their surroundings.  Animals that live in the canopy have adaptations for climbing, jumping, and/or flight.

 

Tropical Dry Forest

Tropical dry forests grow in areas where rainy seasons alternate with dry seasons.  In most places, a period of rain is followed by a prolonged period of drought. • Abiotic factors Warm year-round; alternating wet and dry seasons; rich soils subject to erosion

• Biotic factors Plant life: Adaptations to survive the dry season include seasonal loss of leaves.  A plant that sheds its leaves during a particular season is called deciduous.  Some plants also have an extra thick waxy layer on their leaves to reduce water loss, or store water in their tissues. Animal life: Many animals reduce their need for water by entering long periods of inactivity called estivation.  Estivation is similar to hibernation, but typically takes place during a dry season.  Other animals, including many birds and primates, move to areas where water is available during the dry season.

 

Tropical Grassland

The Savanna or Shrubland This biome receives more seasonal rainfall than deserts but less than tropical dry forests.  Grassy areas are spotted with isolated trees and small groves of trees and shrubs.  Compacted soils, fairly frequent fires, and the action of large animals—for example, rhinoceroses and elephants—prevent some areas from turning into dry forest.

• Abiotic factors Warm; seasonal rainfall; compact soils; frequent fires set by lightning • Biotic factors Plant life: Plant adaptations are similar to those in the tropical dry forest, including waxy leaf coverings and seasonal leaf loss.  Some grasses have a high silica content that makes them less appetizing to grazing herbivores.  Also, unlike most plants, grasses grow from their bases, not their tips, so they can continue to grow after being grazed. Animal life: Many animals migrate during the dry season in search of water.  Some smaller animals burrow and remain dormant during the dry season.

 

Desert

Deserts have less than 25 centimeters of precipitation annually, but otherwise vary greatly, depending on elevation and latitude.  Many deserts undergo extreme daily temperature changes, alternating between hot and cold. • Abiotic factors Low precipitation; variable temperatures; soils rich in minerals but poor in organic material

• Biotic factors Plant life: Many plants, including cacti, store water in their tissues, and minimize leaf surface area to cut down on water loss.  Cactus spines are actually modified leaves.  Many desert plants employ special forms of photosynthesis that enable them to open their leaf pores only at night, allowing them to conserve moisture on hot, dry days. Animal life: Many desert animals get the water they need from the food they eat.  To avoid the hottest parts of the day, many are nocturnal—active only at night.  Large or elongated ears and other extremities are often supplied with many blood vessels close to the surface.  These help the animal lose body heat and regulate body temperature.

 

Temperate Grassland

Plains and prairies, underlain by fertile soils, once covered vast areas of the midwestern and central United States.  Periodic fires and heavy grazing by herbivores maintained plant communities dominated by grasses.  Today, most have been converted for agriculture because their soil is so rich in nutrients and is ideal for growing crops.

• Abiotic factors Warm to hot summers; cold winters; mode rate seasonal precipitation; fertile soils; occasional fires • Biotic factors Plant life: Grassland plants—especially grasses, which grow from their base—are resistant to grazing and fire.  Dispersal of seeds by wind is common in this open environment.  The root structure and growth habit of native grassland plants helps establish and retain deep, rich, fertile topsoil. Animal life: Because temperate grasslands are such open, exposed environments, predation is a constant threat for smaller animals.  Camouflage and burrowing are two common protective adaptations.

 

Temperate Woodland In open woodlands, large areas of grasses and wildflowers such as poppies are interspersed with oak and other trees.  Communities that are more shrubland than forest are known as chaparral.  Dense low plants that contain flammable oils make fire a constant threat. • Abiotic factors Hot dry summers; cool moist winters; thin, nutrient-poor soils; periodic fires

• Biotic factors Plant life: Plants in this biome have adapted to drought.  Woody chaparral plants have tough waxy leaves that resist water loss.  Fire resistance is also important, although the seeds of some plants need fire to germinate. Animal life: Animals tend to be browsers—meaning they eat varied diets of grasses, leaves, shrubs, and other vegetation.  In exposed shrubland, camouflage is common.

 

Temperate Forest

Temperate forests are mostly made up of deciduous and evergreen coniferous trees.  Coniferous trees, or conifers, produce seed-bearing cones, and most have leaves shaped like needles, which are coated in a waxy substance that helps reduce water loss.  These forests have cold winters.  In autumn, deciduous trees shed their leaves.  In the spring, small plants burst from the ground and flower.

Fertile soils are often rich in humus, a material formed from decaying leaves and other organic matter. • Abiotic factors Cold to moderate winters; warm summers; year-round precipitation; fertile soils • Biotic factors Plant life: Deciduous trees drop their leaves and go into a state of dormancy in winter.  Conifers have needlelike leaves that minimize water loss in dry winter air. Animal life: Animals must cope with changing weather.  Some hibernate; others migrate to warmer climates.  Animals that do not hibernate or migrate may be camouflaged to escape predation in the winter when bare trees leave them more exposed.

 

Northwestern Coniferous Forest

Mild moist air from the Pacific Ocean influenced by the Rocky Mountains provides abundant rainfall to this biome.  The forest includes a variety of conifers, from giant redwoods to spruce, fir, and hemlock, along with flowering trees and shrubs such as dogwood and rhododendron.  Moss often covers tree trunks and the forest floor.  Because of its lush vegetation, the northwestern coniferous forest is sometimes called a “temperate rain forest.”

• Abiotic factors Mild temperatures; abundant precipitation in fall, winter, and spring; cool dry summers; rocky acidic soils • Biotic factors Plant life: Because of seasonal temperature variation, there is less diversity in this biome than in tropical rain forests.  However, ample water and nutrients support lush, dense plant growth.  Adaptations that enable plants to obtain sunlight are common.  Trees here are among the world’s tallest. Animal life: Camouflage helps insects and ground-dwelling mammals avoid predation.  Many animals are browsers—they eat a varied diet—an advantage in an environment where vegetation changes seasonally.

 

Boreal Forest

Dense forests of coniferous evergreens along the northern edge of the temperate zone are called boreal forests, or taiga.  Winters are bitterly cold, but summers are mild and long enough to allow the ground to thaw.  The word boreal comes from the Greek word for “north,” reflecting the fact that boreal forests occur mostly in the northern part of the Northern Hemisphere.

• Abiotic factors Long cold winters; short mild summers; moderate precipitation; high humidity; acidic, nutrient-poor soils • Biotic factors Plant life: Conifers are well suited to the boreal-forest environment.  Their conical shape sheds snow, and their wax-covered needlelike leaves prevent excess water loss.  In addition, the dark green color of most conifers absorbs heat energy. Animal life: Staying warm is the major challenge for animals.  Most have small extremities and extra insulation in the form of fat or downy feathers.  Some migrate to warmer areas in winter.

 

Tundra

The tundra is characterized by permafrost, a layer of permanently frozen subsoil.  During the short cool summer, the ground thaws to a depth of a few centimeters and becomes soggy.  In winter, the top layer of soil freezes again.  This cycle of thawing and freezing, which rips and crushes plant roots, is one reason that tundra plants are small and stunted.  Cold temperatures, high winds, a short growing season, and humus-poor soils also limit plant height.

• Abiotic factors Strong winds; low precipitation; short and soggy summers; long, cold, dark winters; poorly developed soils; permafrost • Biotic factors Plant life: By hugging the ground, mosses and other low-growing plants avoid damage from frequent strong winds.  Seed dispersal by wind is common.  Many plants have adapted to growth in poor soil.  Legumes, for example, have nitrogen-fixing bacteria on their roots. Animal life: Many animals migrate to avoid long harsh winters.  Animals that live in the tundra year-round display adaptations, among them natural antifreeze, small extremities that limit heat loss, and a varied diet.

Other Land Areas Not Easily Classified

Some land areas do not fall neatly into one of the major biomes.

• Because they are not easily defined in terms of a typical community of plants and animals, mountain ranges and polar ice caps are not usually classified into biomes.

Mountain Ranges Mountain ranges exist on all continents and in many biomes.  On mountains, conditions vary with elevation.  From river valley to summit, temperature, precipitation, exposure to wind, and soil types all change, and so do organisms.  If you climb the Rocky Mountains in Colorado, for example, you begin in a grassland.

You then pass through pine woodland and then a forest of spruce and other conifers.  Thickets of aspen and willow trees grow along streambeds in protected valleys.  Higher up, soils are thin.  Strong winds buffet open fields of wildflowers and stunted vegetation resembling tundra.  Glaciers are found at the peaks of many ranges.

Polar Ice Caps

Polar regions border the tundra and are cold year-round.  Plants are few, though some algae grow on snow and ice.  Where rocks and ground are exposed seasonally, mosses and lichens may grow.  Marine mammals, insects, and mites are the typical animals.  In the north, where polar bears live, the Arctic Ocean is covered with sea ice, although more and more ice is melting each summer.

In the south, the continent of Antarctica, inhabited by many species of penguins, is covered by ice nearly 5 kilometers thick in places.

What abiotic and biotic factors characterize biomes?
 

REVIEW & DO NOW Answer the following questions:
List and distinguish Earth's ten major biomes.	Why are mountain ranges and polar ice caps not classified as biomes?

Ecological Methods
What methods are used in ecological studies?

Some ecologists, like the one in Figure 3–3, use measuring tools to assess changes in plant and wildlife communities.  Others use DNA studies to identify bacteria in marsh mud.  Still others use data gathered by satellites to track ocean surface temperatures.

Regardless of their tools, modern ecologists use three methods in their work: observation, experimentation, and modeling.  Each of these approaches relies on scientific methodology to guide inquiry.

Observation

Observation is often the first step in asking ecological questions.  Some observations are simple: Which species live here?  How many individuals of each species are there? Other observations are more complex: How does an animal protect its young from predators?  These types of questions may form the first step in designing experiments and models.
 

Experimentation Experiments can be used to test hypotheses.  An ecologist may, for example, set up an artificial environment in a laboratory or greenhouse to see how growing plants react to different conditions of temperature, lighting, or carbon dioxide concentration.  Other experiments carefully alter conditions in selected parts of natural ecosystems.

Modeling

Many ecological events, such as effects of global warming on ecosystems, occur over such long periods of time or over such large distances that they are difficult to study directly.  Ecologists make models to help them understand these phenomena.  Many ecological models consist of mathematical formulas based on data collected through observation and experimentation.  Further observations by ecologists can be used to test predictions based on those models.

What methods are used in ecological studies?
 

REVIEW & DO NOW Answer the following questions:
What are three of the methods used by ecologists to study life on Earth?