The Princeton Guide to Ecology

By Simon A. Levin | Go to book overview

III.6
Top-Down and Bottom-Up
Regulation of Communities
E. T. Borer and D. S. Gruner
OUTLINE
1. What are “top-down” and “bottom-up” processes?
2. A history of converging views
3. A few system vignettes
4. Theory: Seeking generality
5. Moving beyond vignettes: Empirical generality and tests of theory
6. Where do we go from here?

In this chapter we briefly trace the historical debate and outline the theoretical and empirical evidence for factors controlling the biomass of predators, herbivores, and plants within and among ecosystems.


GLOSSARY

autotroph. Organisms that make their own food by synthesizing organic compounds from inorganic chemicals, usually via photosynthesis (e.g., algae, vascular plants).

biomass. The total mass of living biological material.

consumer. See heterotroph.

food web. Network of feeding relationships among organisms in a local community.

heterotroph. Organisms that must consume organic compounds as food for growth (e.g., animals, most bacteria, and fungi).

primary producer. See autotroph.

trophic. From Greek, “food,” this term refers to feeding of one species on another, as in “trophic interactions” or “trophic links.”

trophic level. Feeding position in a food chain: autotrophs form the basal trophic level, herbivores represent the second trophic level, and so on.


1. WHAT ARE “TOP-DOWN” AND “BOTTOM-UP”
PROCESSES?

Humans are dramatically altering the global budgets of elemental nutrients that limit the growth and biomass of autotrophs, or primary producers. Through activities such as fossil fuel combustion and application of agricultural fertilizers, global pools of nitrogen and phosphorus have doubled and quintupled, respectively, relative to preindustrial levels. The impacts of these nutrient fertility bonanzas are most obvious in surface waters of lakes and coasts. Nutrient eutrophication often causes rapid and explosive blooms of algae and microorganisms and equally rapid death, decomposition, and ecosystem-wide oxygen starvation, or hypoxia. The Gulf of Mexico hypoxic “dead zone” at the mouth of the Mississippi River annually swells over areas exceeding 18,000 km2, larger than the U.S. state of Connecticut. Nutrient eutrophication is a jarring example of a bottom-up process, resource supply, that can dramatically alter autotrophs and the food webs that rely on them for energy and nutrition.

Concurrently, humans are changing the role and composition of consumers in food webs via species removals and additions. Habitat loss and degradation and selective hunting and fishing deplete consumers disproportionately from food webs; many top predators such as tigers, wild dogs, wolves, and sharks have been hunted to near ecological extinction. At the same time, humans are adding consumers to food webs for endpoints such as conservation, recreation, and agriculture as well as accidentally introducing invasive consumer species. In a dramatic example, the brown tree snake (Boiga irregularis), a nocturnal predator, was accidentally introduced to Guam after World War II. This single species has eaten its way through

-296-

Notes for this page

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items

Items saved from this book

This book has been saved
Highlights (0)
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

Citations (0)
Some of your citations are legacy items.

Any citation created before July 30, 2012 will labeled as a “Cited page.” New citations will be saved as cited passages, pages or articles.

We also added the ability to view new citations from your projects or the book or article where you created them.

Notes (0)
Bookmarks (0)

You have no saved items from this book

Project items include:
  • Saved book/article
  • Highlights
  • Quotes/citations
  • Notes
  • Bookmarks
Notes
Cite this page

Cited page

Style
Citations are available only to our active members.
Buy instant access to cite pages or passages in MLA, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited page

Bookmark this page
The Princeton Guide to Ecology
Table of contents

Table of contents

Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this book

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Help
Full screen
/ 810

matching results for page

    Questia reader help

    How to highlight and cite specific passages

    1. Click or tap the first word you want to select.
    2. Click or tap the last word you want to select, and you’ll see everything in between get selected.
    3. You’ll then get a menu of options like creating a highlight or a citation from that passage of text.

    OK, got it!

    Cited passage

    Style
    Citations are available only to our active members.
    Buy instant access to cite pages or passages in MLA, APA and Chicago citation styles.

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

    1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

    Cited passage

    Thanks for trying Questia!

    Please continue trying out our research tools, but please note, full functionality is available only to our active members.

    Your work will be lost once you leave this Web page.

    Buy instant access to save your work.

    Already a member? Log in now.

    Author Advanced search

    Oops!

    An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.