BIO150Y Optimal Information Foraging  

How and Why to Cite your Sources

Building upon the research of others...

Why cite?


When you quote a source - or even when you summarize or paraphrase information found in books, articles or web pages - you must acknowledge the original author.

By properly citing your references you:
  • demonstrate your work has a factual basis
  • assist readers in locating references for their own use

However, if you use someone else's words or ideas without crediting them, you are committing a type of theft called plagiarism. Read How Not to Plagiarize.

It can be difficult to figure out what needs to be credited. Use this rule: If you knew a piece of information before you started doing research, generally you do not need to credit it. You also do not need to cite well-known facts, such as dates, which can be found in many encyclopedias. All other information such as quotations, statistics, and ideas should always be cited in your papers.

How to cite?

Citations are located:
  • in the body of the text

  • at the end of the work in a bibliography or as footnotes, depending on the citation style

Many different styles exist such as:
  • MLA (Modern Language Association)

  • APA (American Psychiatric Association)

  • Vancouver

  • many journals have their own citation style that authors must follow

Regardless of the style used, every source mentioned in the text must be fully cited in the bibliography or footnotes. The examples below demonstrate the style that is required of BIO150 students, as mentioned in the BIO150 lab manual.

  • Citations within the text must include the author(s) and date of publication.

  • You can incorporate the reference at the end of the sentence or as part of the sentence.

  • If the author is not known, use the abbreviation Anon. instead of a name.

  • If there are three or more authors of a work, cite the primary author (whose name appears first) folowed by the Latin expression et al.

Citing Web sites

Citing within the text

The zebra mussel, Dreissena polymorpha, is a recent invader found throughout the Great Lakes (Association for Biodiversity Information, 2001).

Reference list

Association for Biodiversity Information. 2001. Zebra mussel. Web site: NatureServe, Arlington, Virginia. URL: Article read on May 1, 2002.

The author appears first (in this example the author is an institution), followed by the publication date and title of the page. This is followed by the title of the Web site containing the page, its location, and URL. The author and publication date can usually be found at the bottom of a page where the copyright information is located. Note that you must include the date you accessed the page since Web pages can change quite often.

Citing journal articles

Citing within the text

Ricciardi and Rasmussen (1998) argue that biologists should devote more effort to predicting which freshwater species may become invaders of the Great Lakes region.

Reference list

A journal article citation contains: the authors (all of them), publication year, article title, journal title in italics, volume number, and the pages on which the article appears. For example:

Ricciardi, A., and J. B. Rasmussen. 1998. Predicting the identity and impact of future biological invaders: A priority for aquatic resource management. Canadian Journal of Fisheries and Aquatic Sciences, 55: 1759-1765.

Citing books and encyclopedia articles

Citing within the text

When you incorporate a direct quotation from your source, your citation should also include the page number:

According to Williamson (1996: 143) freshwater pests like zebra mussels are particularly difficult to control.

If there are three or more authors of a work, cite the primary author (whose name appears first) followed by the Latin expression et al.

After the St. Lawrence Seaway was opened in 1959, the risk of non-indigenous species invading the Great Lakes increased significantly (Leach et al., 1999).

When citing an encyclopaedia article, or a chapter in an edited book, use the author of the article or chapter, not the editor of the book itself:

Before the nineteenth century, zebra mussels were only found in the Black, Caspian, and Azov seas (Schloesser, 1995).

If the author is not known, use the abbreviation Anon. instead of a name:

The Great Lakes are connected to each other by a series of straits and canals (Anon., 1994).

Reference list


This is the basic citation format for print resources:

Williamson, M. 1996. Biological Invasions. Chapman & Hall, London. 244 pages.

All print citations must include author, date, title, publisher information, and page numbers. The following examples demonstrate some variations on this format.

Chapter in an edited book

List the authors of the chapter first, followed by the publication date, chapter title, book title, book editors, publisher information, and number of pages. For example:

Leach, J. H., E. L. Mills, and M. R. Dochoda. 1999. Non-indigenous species in the Great Lakes: Ecosystem impacts, binational policies, and management. Chapter 7, in Great Lakes Fisheries Policy and Management: A Binational Perspective (W. W. Taylor and C. P. Ferreri, editors). Michigan State University Press, East Lansing, Michigan. 551 pages.

Encyclopaedia article (print):

Include the article author, year of publication, and title, as well as the page numbers on which the article appears, the encyclopaedia name, volume number, and publisher information. For example:

Schloesser, D. W. 1995. Introduced species, zebra mussels in North America. Pages 337-356, in Encyclopedia of Environmental Biology (Vol. 2). Academic Press, San Diego.

If the author is not known, use Anon. instead. For example:

Anon. 1994. Great Lakes. Page 484, in The Cambridge Encyclopedia. 2nd ed. Cambridge University Press, Cambridge, England.

Encyclopaedia article (electronic):

This is similar to citing a print article, except that you must include the URL and date accessed. Also, you do not need to italicize the name of the encyclopaedia. For example:

Sheath, R. G. 2001. Biogeography of freshwater algae. Encyclopedia of Life Sciences. Retrieved April 22, 2002 from Encyclopedia of Life Sciences on the World Wide Web:

If the author is not known, substitute Anon. for the author name. For example:

Anon. 2002. Ecology. Encyclopaedia Britannica. Retrieved May 20, 2002 from Britannica Online database on the World Wide Web:

More info

For more information on citing and citation styles, visit the following sites:


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