Niche
One of the most important ideas associated with ecosystems is the niche concept. A niche refers to the role of a species in its ecosystem. It includes all the ways species’ members interact with the abiotic and biotic components of the ecosystem.
Two important aspects of a species’ niche include the food it eats and how it obtains the food. Figure below shows pictures of birds that occupy different niches. The various species eat different types of food and obtain the food in different ways. Notice how each species has evolved a beak that suits it for these aspects of its niche.
Figure 15.3
Each of these 11 species of birds has a distinctive beak that suits it for its particular niche. For example, the long slender beak of the Nectarivore allows it to sip nectar from flowers, and the short sturdy beak of the Granivore allows it to crush hard, tough grains.
Habitat
Another aspect of a species’ niche is its habitat. A species’ habitat is the physical environment to which it has become adapted and in which it can survive. A habitat is generally described in terms of abiotic factors, such as the average amount of sunlight received each day, the range of annual temperatures, and average yearly rainfall. These and other factors in a habitat determine many of the traits of the organisms that can survive there.
Consider a habitat with very low temperatures. Mammals that live in the habitat must have insulation to help them stay warm. Otherwise, their body temperature will drop to a level that is too low for survival. Species that live in these habitats have evolved fur, blubber, and other traits that provide insulation in order for them to survive in the cold.
Human destruction of habitats is the major factor causing other species to decrease and become endangered or go extinct. Small habitats can support only small populations of organisms. Small populations are more susceptible to being wiped out by catastrophic events from which a large population could bounce back. Habitat destruction caused the extinction of the dusky seaside sparrow shown in Figure below. Many other bird species are currently declining worldwide. More than 1,200 species face extinction during the next century due mostly to habitat loss and climate change.
Figure 15.4
The dusky seaside sparrow, which used to live in marshy areas of southern Florida, was declared extinct in 1990.
Competitive Exclusion Principle
A given habitat may contain many different species, each occupying a different niche. However, two different species cannot occupy the same niche in the same geographic area for very long. This is known as the competitive exclusion principle. It is another basic principle of ecology. If two species were to occupy the same niche, they would compete with one another for the same food and other resources in the environment. Eventually, one species would outcompete and replace the other.
Humans often introduce new species into areas where their niches are already occupied by native species. This may occur intentionally or by accident. Consider the example of kudzu. Kudzu is a Japanese vine that was introduced intentionally to the southeastern United States in the 1870s to help control soil erosion. The southeastern United States turned out to be a perfect habitat for kudzu, because it has no natural enemies there. As a result, kudzu was able to outcompete native species of vines and take over their niches. The extent to which kudzu has invaded some habitats in the southeastern United States is shown in Figure below.
Figure 15.5
Kudzu covers the trees in this habitat near Atlanta, Georgia, in the southeastern United States. Native species of vines cannot compete with kudzus thriving growth and lack of natural enemies.
Methods of Ecology
Ecology is more holistic, or all-encompassing, than some other fields of biology. Ecologists study both biotic and abiotic factors and how they interact. Therefore, ecologists often use methods and data from other areas of science, such as geology, geography, climatology, chemistry, and physics. In addition, researchers in ecology are more likely than researchers in some other sciences to use field studies to collect data.
Field Studies
Ecological research often includes field studies because ecologists generally are interested in the natural world. Field studies involve the collection of data in real-world settings, rather than in controlled laboratory settings. The general aim of field studies is to collect observations in wild populations without impacting the environment or its organisms in any way.
Ecologists commonly undertake field studies to determine the numbers of organisms of particular species in a given geographic area. Such studies are useful for a variety of purposes. For example, the data might help an ecologist decide whether a given species is in danger of extinction.
Sampling
In field studies, it usually is not possible to investigate all the organisms in an area. Therefore, some type of sampling scheme is generally necessary. For example, assume an ecologist wants to find the number of insects of a particular species in a given area. There may be thousands of members of the species in the area. So, for practical reasons, the ecologist might count only a sample of the insects. In order to select the sample, the ecologist could divide the entire area into a grid of one-meter-square test plots. Then the ecologist might systematically select every tenth (or other numbered) test plot and count all the insects in the plot.
Statistical Analysis
Like other scientists, ecologists may use two different types of statistical analysis to interpret the data they collect: descriptive statistics and inferential statistics. Descriptive statistics are used to describe data. For example, the ecologist studying insects might calculate the mean number of insects per test plot and find that it is 24. This descriptive statistic summarizes the counts from all the test plots in a single number. Other descriptive statistics, such as the range, describe variation in data. The range is the difference between the highest and lowest values in a sample. In the same example, if the numbers of insects per test plot ranged from 2 to 102, the range would be 100.
Scientists often want to make inferences about a population based on data from a sample. For example, the ecologist counting insects might want to estimate the number of insects in the entire area based on data for the test plots sampled. Drawing inferences about a population from a sample requires the use of inferential statistics. Inferential statistics can be used to determine the chances that a sample truly represents the population from which it was drawn. It tells the investigator how much confidence can be placed in inferences about the population that are based on the sample.
Modeling
Ecologists, like other scientists, often use models to help understand complex phenomena. Ecological systems are often modeled using computer simulations. Computer simulations can incorporate many different variables and their interactions. This is one reason they are useful for modeling ecological systems. Computer simulations are also working models, so they can show what may happen in a system over time. Simulations can be used to refine models, test hypotheses, and make predictions. For example, simulations of global warming have been used to make predictions about future climates.
Lesson Summary
Ecology is the scientific study of living things and their relationships with the environment. Levels of organization in ecology include the biosphere, population, community, and ecosystem.
An ecosystem is a natural unit consisting of all the living organisms in an area functioning together with all the non-living physical factors of the environment. Each species has a unique role in an ecosystem, called its niche. The physical environment where a species lives is its habitat.
Ecologists use field studies and sampling schemes to gather data in natural environments. Like other scientists, ecologists use statistics to describe and make inferences from data. They also use computer simulations to model complex phenomena.
Review Questions
Define abiotic and biotic components of the environment.
What does the biosphere consist of?
How do ecologists define an ecosystem?
What does the competitive exclusion principle state?
Assume an ecologist is studying interactions among different species in an ecosystem. What level of organization should the ecologist study? Why?
Why are field studies and computer simulations important methods of investigation in ecology?
Compare and contrast the ecosystem concepts of niche and habitat.
Further Reading / Supplemental Links
Desonie, Dana, Biosphere: Ecosystems and Biodiversity Loss. Chelsea House Publications, 2007.
Novacek, Michael, Terra: Our 100-Million-Year-Old Ecosystem and the Threats That Now Put It at Risk. Farrar, Straus, and Giroux, 2007.
http://estrellamountain.edu/faculty/farabee/biobk/BioBookcommecosys.html
http://estrellamountain.edu/faculty/farabee/biobk/BioBookpopecol.html
http://green.nationalgeographic.com/environment/global-warming/gw-overview.html
http://www.science.doe.gov/ober/CCRD/model.html
http://interactive2.usgs.gov/learningweb/explorer/topic_eco.htm
http://www.dmoz.org/Science/Biology/Ecology/
http://www.enviroliteracy.org/category.php/3.html
http://www.sciencedaily.com/news/earth_climate/ecosystems/
http://www.soinc.org/events/ecology/index.htm
http://www.topix.net/science/ecology
http://en.wikipedia.org
Vocabulary
abiotic components
The non-living physical aspects of the environment; includes sunlight, soil, temperature, wind, water, and air; also known as abiotic factors.
biosphere
The areas of Earth where all organisms live; extends from about 11,000 meters below sea level to 15,000 meters above sea level.
biotic components
The living organisms in the environment; also known as biotic factors.
community
Populations of different species that live in the same area and interact with one another.
competitive exclusion principle
States that two different species cannot occupy the same niche in the same geographic area for very long.
descriptive statistics
Statistical analysis used to describe data.
ecology
The scientific study of the interactions of living things with each other and their relationships with the environment.
ecosystem
A natural unit consisting of all the living organisms in an area functioning together with all the nonliving physical factors of the environment.
field studies
Studies that involve the collection of data in real-world settings, rather than in controlled laboratory settings; allows observations of wild populations without impacting the environment or its organisms in any way.
habitat
The physical environment to which an organism has become adapted and in which it can survive.
inferential statistics
Statistical analysis that draws inferences about a population from a sample; used to determine the chances that a sample truly represents the population from which it was drawn.
niche
The role of a species in its ecosystem; includes all the ways species’ members interact with the abiotic and biotic components of the ecosystem.
organism
A life form consisting of one or more cells.
population
Organisms of the same species that live in the same area and interact with one another.
range
Statistic used to describe the difference between the highest and lowest values in a sample.
Points to Consider
An ecosystem needs continuous inputs of energy in order for its organisms to survive. In most ecosystems, this energy comes from sunlight.
Which organisms in an ecosystem capture the energy from sunlight? How do they transform the energy so that other organisms in the ecosystem can use it? Why is the energy that enters an ecosystem eventually used up?
Lesson 15.2: Flow of Energy
Lesson Objectives
Describe how autotrophs use energy to produce organic molecules.
Identify different types of consumers, and give examples of each type.
Explain how decomposers resupply elements to producers.
Describe food chains and food webs, and explain how energy is transferred between their trophic levels.
Introduction
Energy enters most ecosystems from sunlight. However, some ecosystems, such as hydrothermal vent ecosystems at the bottom of the ocean, receive no sunlight and obtain energy instead from chemical compounds. Energy is used by some organisms in the ecosystem to make food. These organisms are called primary producers, or autotrophs, which include small plants, algae, photosynthetic prokaryotes and chemosynthetic prokaryotes. From primary producers, energy eventually is transferred to all the other organisms in the ecosystem through consumers or decomposers known as heterotrophs.
Producers
Producers are organisms that produce organic compounds from energy and simple inorganic molecules. Producers are also called autotrophs, which literally means “self nutrition.” This is because producers synthesize food for themselves. They take energy and materials from the abiotic environment and use them to make organic molecules. Autotrophs are a vital part of all ecosystems. The stability of the producers is vital to the survival of every ecosystem; without this stability an ecosystem may not thrive; in fact, the ecosystem may collapse. The organic molecules the producers make are needed by all the organisms in the ecosystem. There are two basic types of autotrophs: photoautotrophs and chemoautotrophs. They differ in the type of energy they use to synthesize food.
Photoautotrophs
Photoautotrophs are organisms that use energy from sunlight to make food by photosynthesis. As you may recall from the Photosynthesis Chapter, photosynthesis is the process by which carbon dioxide and water are converted to glucose and oxygen, using sunlight for energy. Glucose, a carbohydrate, is an organic compound that can be used by autotrophs and other organisms for energy. As shown in Figure below, photoautotrophs include plants, algae, and certain bacteria.
Figure 15.6
Different types of photoautotrophs are important in different types of ecosystems. Each type of photoautotroph pictured here is an important producer in some ecosystem.
Plants are the most important photoautotrophs in land-based, or terrestrial, ecosystems. There is great variation in the plant kingdom. Plants include organisms as different as trees, grasses, mosses, and ferns. Nonetheless, all plants are eukaryotes that contain chloroplasts, the cellular “machinery” needed for photosynthesis.
Algae are photoautotrophs found in most ecosystems, but they generally are more important in water-based, or aquatic, ecosystems. Like plants, algae are eukaryotes that contain chloroplasts for photosynthesis. Algae include single-celled eukaryotes, such as diatoms, as well as multicellular eukaryotes, such as seaweed.
Photoautotrophic bacteria, called cyanobacteria, are also important producers in aquatic ecosystems. Cyanobacteria were formerly called blue-green algae, but they are now classified as bacteria. Other photosynthetic bacteria, including purple photosynthetic bacteria, are producers in terrestrial as well as aquatic ecosystems.
Both cyanobacteria and algae make up phytoplankton. Phytoplankton refers to all the tiny photoautotrophs found on or near the surface of a body of water. Phytoplankton usually is the primary producer in aquatic ecosystems.
Chemoautotrophs
In some places where life is found on Earth, there is not enough light to provide energy for photosynthesis. In these places, producers called chemoautotrophs use the energy stored in chemical compounds to make organic molecules by chemosynthesis. Chemosynthesis is the process by which carbon dioxide and water are converted to carbohydrates. Instead of using energy from sunlight, chemoautotrophs use energy from the oxidation of inorganic c
ompounds, such as hydrogen sulfide (H2S). Oxidation is an energy-releasing chemical reaction in which a molecule, atom, or ion loses electrons.
Chemoautotrophs include bacteria called nitrifying bacteria, which you will read more about in Lesson 3. Nitrifying bacteria live underground in soil. They oxidize nitrogen-containing compounds and change them to a form that plants can use.
Chemoautotrophs also include archaea. Archaea are a domain of microorganisms that resemble bacteria. Most archaea live in extreme environments, such as around hydrothermal vents in the deep ocean. Hot water containing hydrogen sulfide and other toxic substances escapes from the ocean floor at these vents, creating a hostile environment for most organisms. Near the vents, archaea cover the sea floor or live in or on the bodies of other organisms, such as tube worms. In these ecosystems, archaea use the toxic chemicals released from the vents to produce organic compounds. The organic compounds can then be used by other organisms, including tube worms. Archaea are able to sustain thriving communities, like the one shown in Figure below, even in these hostile environments.
Figure 15.7
Red tube worms, each containing millions of archaea microorganisms, grow in a cluster around a hydrothermal vent in the deep ocean floor. Archaea produce food for themselves (and for the tube worms) by chemosynthesis.
CK-12 Biology I - Honors Page 66