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Levels of Ecology*

Miranda Dudzik

Based on The Scope of Ecology� by

OpenStax

This work is produced by OpenStax-CNX and licensed under the

Creative Commons Attribution License 3.0�

Abstract

By the end of this section, you will be able to:

• De�ne ecology and the four levels of ecological research• Describe examples of the ways in which ecology requires the integration of di�erent scienti�c disci-

plines• Distinguish between abiotic and biotic components of the environment• Recognize the relationship between abiotic and biotic components of the environment

Ecology is the study of the interactions of living organisms with their environment. One core goal ofecology is to understand the distribution and abundance of living things in the physical environment. At-tainment of this goal requires the integration of scienti�c disciplines inside and outside of biology, such asbiochemistry, physiology, evolution, biodiversity, molecular biology, geology, and climatology. Some ecologi-cal research also applies aspects of chemistry and physics, and it frequently uses mathematical models.

*Version 1.1: Oct 13, 2013 10:14 pm -0500�http://cnx.org/content/m44856/1.3/�http://creativecommons.org/licenses/by/3.0/

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Climate change can alter where organisms live, which can sometimes directly a�ect human health.Watch the PBS video �Feeling the E�ects of Climate Change�1 in which researchers discover apathogenic organism living far outside of its normal range.

1 Levels of Ecological Study

When a discipline such as biology is studied, it is often helpful to subdivide it into smaller, related areas. Forinstance, cell biologists interested in cell signaling need to understand the chemistry of the signal molecules(which are usually proteins) as well as the result of cell signaling. Ecologists interested in the factors thatin�uence the survival of an endangered species might use mathematical models to predict how current con-servation e�orts a�ect endangered organisms. To produce a sound set of management options, a conservationbiologist needs to collect accurate data, including current population size, factors a�ecting reproduction (likephysiology and behavior), habitat requirements (such as plants and soils), and potential human in�uences on

1http://openstaxcollege.org/l/climate_health

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the endangered population and its habitat (which might be derived through studies in sociology and urbanecology). Within the discipline of ecology, researchers work at four speci�c levels, sometimes discretely andsometimes with overlap: organism, population, community, and ecosystem (Figure 1).

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Figure 1: Ecologists study within several biological levels of organization. (credit �organisms�: modi�-cation of work by "Crystl"/Flickr; credit �ecosystems�: modi�cation of work by Tom Carlisle, US Fishand Wildlife Service Headquarters; credit �biosphere�: NASA)

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2 Organismal Ecology

Researchers studying ecology at the organismal level are interested in the adaptations that enable individualsto live in speci�c habitats. These adaptations can be morphological, physiological, and behavioral. Forinstance, the Karner blue butter�y (Lycaeides melissa samuelis) (Figure 2) is considered a specialist becausethe females preferentially oviposit (that is, lay eggs) on wild lupine. This preferential adaptation means thatthe Karner blue butter�y is highly dependent on the presence of wild lupine plants for its continued survival.

Figure 2: The Karner blue butter�y (Lycaeides melissa samuelis) is a rare butter�y that lives only inopen areas with few trees or shrubs, such as pine barrens and oak savannas. It can only lay its eggs onlupine plants. (credit: modi�cation of work by J & K Hollingsworth, USFWS)

After hatching, the larval caterpillars emerge and spend four to six weeks feeding solely on wild lupine(Figure 3). The caterpillars pupate (undergo metamorphosis) and emerge as butter�ies after about fourweeks. The adult butter�ies feed on the nectar of �owers of wild lupine and other plant species. A researcherinterested in studying Karner blue butter�ies at the organismal level might, in addition to asking questionsabout egg laying, ask questions about the butter�ies' preferred temperature (a physiological question) or thebehavior of the caterpillars when they are at di�erent larval stages (a behavioral question).

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Figure 3: The wild lupine (Lupinus perennis) is the host plant for the Karner blue butter�y.http://cnx.org/content/m47774/1.1/

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3 Population Ecology

A population is a group of interbreeding organisms that are members of the same species living in the samearea at the same time. A population is identi�ed, in part, by where it lives, and its area of population mayhave natural or arti�cial boundaries: natural boundaries might be rivers, mountains, or deserts, while exam-ples of arti�cial boundaries include mowed grass, manmade structures, or roads. The study of populationecology focuses on the number of individuals in an area and how and why population size changes over time.Population ecologists are particularly interested in counting the Karner blue butter�y, for example, becauseit is classi�ed as federally endangered. However, the distribution and density of this species is highly in�u-enced by the distribution and abundance of wild lupine. Researchers might ask questions about the factorsleading to the decline of wild lupine and how these a�ect Karner blue butter�ies. For example, ecologistsknow that wild lupine thrives in open areas where trees and shrubs are largely absent. In natural settings,intermittent wild�res regularly remove trees and shrubs, helping to maintain the open areas that wild lupinerequires. Mathematical models can be used to understand how wild�re suppression by humans has led tothe decline of this important plant for the Karner blue butter�y.

4 Community Ecology

A biological community consists of the di�erent species within an area, typically a three-dimensional space,and the interactions within and among these species. Community ecologists are interested in the processesdriving these interactions and their consequences. Questions about interactions between members of thesame species often focus on competition a limited resource. Ecologists also study interactions that happenbetween di�erent species. Examples of these types of interactions include predation, parasitism, herbivory,competition, and pollination. These interactions can have regulating e�ects on population sizes and canimpact ecological and evolutionary processes a�ecting diversity.

For example, Karner blue butter�y larvae form mutualistic relationships with ants. Mutualism is a formof a long-term relationship that has coevolved between two species and from which each species bene�ts.For mutualism to exist between individual organisms, each species must receive some bene�t from the otheras a consequence of the relationship. Researchers have shown that there is an increase in the probabilityof survival when Karner blue butter�y larvae (caterpillars) are tended by ants. This might be because thelarvae spend less time in each life stage when tended by ants, which provides an advantage for the larvae.Meanwhile, the Karner blue butter�y larvae secrete a carbohydrate-rich substance that is an importantenergy source for the ants. Both the Karner blue larvae and the ants bene�t from their interaction.

5 Ecosystem Ecology

Ecosystem ecology is an extension of organismal, population, and community ecology. The ecosystem iscomposed of all the biotic components (living things) in an area along with the abiotic components (non-living things) of that area. Some of the abiotic components include air, water, and soil. Ecosystem biologistsask questions about how nutrients and energy are stored and how they move among organisms and thesurrounding atmosphere, soil, and water.

The Karner blue butter�ies and the wild lupine live in an oak-pine barren habitat. This habitat ischaracterized by natural disturbance and nutrient-poor soils that are low in nitrogen. The availability ofnutrients is an important factor in the distribution of the plants that live in this habitat. Researchersinterested in ecosystem ecology could ask questions about the importance of limited resources and themovement of resources, such as nutrients, though the biotic and abiotic portions of the ecosystem.

: Ecologist

A career in ecology contributes to many facets of human society. Understanding ecological issuescan help society meet the basic human needs of food, shelter, and health care. Ecologists canconduct their research in the laboratory and outside in natural environments (Figure 4). Thesenatural environments can be as close to home as the stream running through your campus or

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as far away as the hydrothermal vents at the bottom of the Paci�c Ocean. Ecologists managenatural resources such as white-tailed deer populations (Odocoileus virginianus) for hunting oraspen (Populus spp.) timber stands for paper production. Ecologists also work as educators whoteach children and adults at various institutions including universities, high schools, museums, andnature centers. Ecologists may also work in advisory positions assisting local, state, and federalpolicymakers to develop laws that are ecologically sound, or they may develop those policies andlegislation themselves. To become an ecologist requires an undergraduate degree, usually in anatural science. The undergraduate degree is often followed by specialized training or an advanceddegree, depending on the area of ecology selected. Ecologists should also have a broad backgroundin the physical sciences, as well as a sound foundation in mathematics and statistics.

Figure 4: This landscape ecologist is releasing a black-footed ferret into its native habitat as part of astudy. (credit: USFWS Mountain Prairie Region, NPS)

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Visit this site2 to see Stephen Wing, a marine ecologist from the University of Otago, discuss therole of an ecologist and the types of issues ecologists explore.

6 Section Summary

Ecology is the study of the interactions of living things with their environment. Ecologists ask questionsacross four levels of biological organization�organismal, population, community, and ecosystem. At theorganismal level, ecologists study individual organisms and how they interact with their environments. Atthe population and community levels, ecologists explore, respectively, how a population of organisms changesover time and the ways in which that population interacts with other species in the community. Ecologistsstudying an ecosystem examine the living species (the biotic components) of the ecosystem as well as thenonliving portions (the abiotic components), such as air, water, and soil, of the environment.

2http://openstaxcollege.org/l/ecologist_role

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7 Review Questions

Exercise 1 (Solution on p. 11.)

Which of the following is a biotic factor?

a. windb. disease-causing microbec. temperatured. soil particle size

Exercise 2 (Solution on p. 11.)

The study of nutrient cycling though the environment is an example of which of the following?

a. organismal ecologyb. population ecologyc. community ecologyd. ecosystem ecology

8 Free Response

Exercise 3 (Solution on p. 11.)

Ecologists often collaborate with other researchers interested in ecological questions. Describe thelevels of ecology that would be easier for collaboration because of the similarities of questions asked.What levels of ecology might be more di�cult for collaboration?

Exercise 4 (Solution on p. 11.)

The population is an important unit in ecology as well as other biological sciences. How is apopulation de�ned, and what are the strengths and weaknesses of this de�nition? Are there somespecies that at certain times or places are not in populations?

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Solutions to Exercises in this Module

to Exercise (p. 10)Bto Exercise (p. 10)Dto Exercise (p. 10)Ecologists working in organismal or population ecology might ask similar questions about how the bioticand abiotic conditions a�ect particular organisms and, thus, might �nd collaboration to be mutually bene-�cial. Levels of ecology such as community ecology or ecosystem ecology might pose greater challenges forcollaboration because these areas are very broad and may include many di�erent environmental components.to Exercise (p. 10)It is bene�cial to consider a population to be all of the individuals living in the same area at the same timebecause it allows the ecologist to identify and study all of the abiotic and biotic factors that may a�ect themembers of the population. However, this de�nition of a population could be considered a drawback if itprohibits the ecologist from studying a population's individuals that may be transitory, but still in�uential.Some species with members that have a wide geographic range might not be considered to be a population,but could still have many of the qualities of a population.

Glossary

De�nition 4: abioticnonliving components of the environment

De�nition 4: bioticliving components of the environment

De�nition 4: conspeci�csindividuals that are members of the same species

De�nition 4: ecologystudy of interaction between living things and their environment

De�nition 4: heterospeci�csindividuals that are members of di�erent species

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