Featured Research

from universities, journals, and other organizations

Food Chain Length Depends On Size Of Pond

Date:
July 11, 2000
Source:
Cornell University
Summary:
Surveying aquatic life from the Great Lakes to small ponds, ecologists at Cornell University and the Institute of Ecosystem Studies (IES) have found that food-chain length -- the number of mouths food passes through on the way to the top predators -- is determined by the size of an ecosystem, not by the amount of available food energy.

ITHACA, N.Y. -- Surveying aquatic life from the Great Lakes to small ponds, ecologists at Cornell University and the Institute of Ecosystem Studies (IES) have found that food-chain length -- the number of mouths food passes through on the way to the top predators -- is determined by the size of an ecosystem, not by the amount of available food energy.

The finding, which is reported in the June 29 issue of the journal Nature, should help resolve one of the oldest questions in ecological science: How long are food chains and what determines their length?

But the systematic accounting of food-chain links and lengths also serves as a warning: The so-called top predators -- such as eagles, falcons and most of the fish that anglers catch to eat -- are more likely to accumulate high concentrations of mercury, PCBs and other contaminants when they live in large ecosystems. And that puts humans, the ultimate predators, at risk.

"If your neighbor comes home with two fish -- a 10-pound trout from Lake Erie and the same size fish from a smaller lake -- ask for the fish from the small lake. Your risk of consuming bioaccumulated contaminants is probably lower with the trout from the smaller lake," said David M. Post in a prepublication interview.

A graduate student of ecology at Cornell and IES, Post is one of three authors (together with Michael L. Pace, aquatic ecologist at IES in Millbrook, N.Y., and Nelson G. Hairston Jr., professor of ecology and evolutionary biology at Cornell) of the report titled "Ecosystem size determines food-chain length in lakes." Their results show that larger lakes have longer food chains than smaller lakes. The same principle may apply to food chains in terrestrial ecosystems, such as large forests and smaller forest fragments, Post observed.

"The standard, textbook explanation for 70 years has been that food-chain length is determined by energy availability," Post said. "Our results show that it is not energy availability that constrains food-chain length, but rather something else related to the size of the ecosystem. We do not know what that something is just yet, but it's clearly not the amount of energy."

The study was conducted in large lakes (Erie and Ontario), medium-sized lakes (such as Champlain, between Vermont and New York, and some of the larger Finger Lakes in western New York) as well as small lakes and several ponds near Madison, Wis., and West Point, N.Y. Researchers studied aquatic food chains that begin with green photosynthetic algae and culminate in large fish like walleye, lake trout, northern pike and largemouth bass. Between the bottom and the top are dozens and perhaps hundreds -- depending on the size of the ecosystem -- of intermediary organisms, such as tiny invertebrates, little fish and medium-sized fish.

Because the researchers couldn't hold their breath long enough to follow food chains from the bottom to the top and count the mouths along the way, they essentially counted backward from the top. In tissue samples of fish in each lake and pond, the researchers measured the ratio of the stable isotopes of nitrogen, a common constituent of all organisms.

Most of the nitrogen in the world is nitrogen-14, but a small percentage is the heavier nitrogen-15. As nitrogen moves up the food chain, more nitrogen-15 than nitrogen-14 accumulates in the tissue of animals at higher "trophic positions." By knowing the ratio of nitrogen-15 to nitrogen-14 of fish at the top of the food chain, compared with the ratio of nitrogen-15 to nitrogen-14 for organisms at the bottom, Post and his colleagues could measure the length of the food chains.

In ecological terms, the researchers were trying to determine the trophic position of various organisms in the food chains, Post explained: "A vegetarian and a cow occupy roughly the same trophic position and would have the same amount of nitrogen-15 in their tissue when they're both eating the same plants; a carnivore who eats the cow that ate the plants is at a higher trophic position and would have more nitrogen-15 in his tissue than the vegetarian or the cow," he said.

What the researchers at Cornell and IES found surprised them because it showed that productivity and energy availability are less important to food-chain length than the size of the ecosystem: Small, nutrient-rich and highly productive lakes have shorter food chains than do the larger, low-productivity, crystal-clear lakes. And big lakes have longer food chains than smaller lakes with the same productivity levels. The 10-pound fish from the large lake is feeding at a higher trophic position than a 10-pound fish from the small lake.

The finding helps explain why a large forest will support greater diversity of life forms than will a forest fragment. But it probably won't change strategies for sport fishing, Post says. "You are still more likely to catch a big fish in a nutrient-rich, productive lake simply because there are more fish to catch. Just be aware," says the Cornell ecologist, "that the big fish from the large lake is at the top of a longer food chain and that more contaminants may have accumulated. The old saying, 'You are what you eat,' applies to whatever -- or whomever -- is at the top of the food chain."

Related World Wide Web sites:

-- Institute of Ecosystem Studies: http://www.ecostudies.org/

-- Cornell Ecology and Evolutionary Biology: http://www.es.cornell.edu/


Story Source:

The above story is based on materials provided by Cornell University. Note: Materials may be edited for content and length.


Cite This Page:

Cornell University. "Food Chain Length Depends On Size Of Pond." ScienceDaily. ScienceDaily, 11 July 2000. <www.sciencedaily.com/releases/2000/07/000705060459.htm>.
Cornell University. (2000, July 11). Food Chain Length Depends On Size Of Pond. ScienceDaily. Retrieved July 30, 2014 from www.sciencedaily.com/releases/2000/07/000705060459.htm
Cornell University. "Food Chain Length Depends On Size Of Pond." ScienceDaily. www.sciencedaily.com/releases/2000/07/000705060459.htm (accessed July 30, 2014).

Share This




More Plants & Animals News

Wednesday, July 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Thousands Flocking to German Crop Circle

Raw: Thousands Flocking to German Crop Circle

AP (July 30, 2014) Thousands of people are trekking to a Bavarian farmer's field to check out a mysterious set of crop circles. (July 30) Video provided by AP
Powered by NewsLook.com
Concern Grows Over Worsening Ebola Crisis

Concern Grows Over Worsening Ebola Crisis

AFP (July 30, 2014) Pan-African airline ASKY has suspended all flights to and from the capitals of Liberia and Sierra Leone amid the worsening Ebola health crisis, which has so far caused 672 deaths in Guinea, Liberia and Sierra Leone. Duration: 00:43 Video provided by AFP
Powered by NewsLook.com
At Least 20 Chikungunya Cases in New Jersey

At Least 20 Chikungunya Cases in New Jersey

AP (July 30, 2014) At least 20 New Jersey residents have tested positive for chikungunya, a mosquito-borne virus that has spread through the Caribbean. (July 30) Video provided by AP
Powered by NewsLook.com
Raw: Otters Enjoy Water Slides at Japan Zoo

Raw: Otters Enjoy Water Slides at Japan Zoo

AP (July 30, 2014) River otters were hitting the water slides to beat the summer heatwave on Wednesday at Ichikawa City's Zoological and Botanical Garden. (July 30) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News



      Save/Print:
      Share:

      Free Subscriptions


      Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

      Get Social & Mobile


      Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

      Have Feedback?


      Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
      Mobile: iPhone Android Web
      Follow: Facebook Twitter Google+
      Subscribe: RSS Feeds Email Newsletters
      Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins