What Happens When the Food Chain is Interrupted?

Food chains or food webs are the feeding interactions of organisms in a community and can be used to illustrate the effects on the ecosystem of the absence or scarcity of a member organism. Each organism in a food web plays an important role within that web, and changes in the number of a single species can cause a dramatic chain reaction that can spread throughout the web. The Center for Conservation and Biodiversity (CBC) at the American Museum of Natural History stated that "The health of all species on Earth is largely determined by the complex linkages and interactions among organisms and the systems in which they live."

Food Web Terminology

• The CBC says the term "food chain," defined as "a simple feeding interaction," is no longer preferred by scientists. The new term for the complex feeding patterns of species in a biologically diverse community is "food web." Community ecologists, the scientists who research food webs and related subjects, use the adjective "trophic" to describe feeding relationships. For example, there is a trophic interaction between foxes, robins and earthworms because robins consume earthworms and foxes consume robins and their eggs. Community ecologists pay particular attention to an ecosystem's "keystone species." The keystone species, often a predator, has a significant impact on the food web, even in low numbers in the community, because it controls species that would otherwise consume too much of a vital resource, such as trees and other plant life. For example, the reintroduction of wolves into Yellowstone National Park resulted in the restoration of songbird habitat, according to the organization Keystone Conservation. Songbirds now abound in the park because wolves have reduced the number of elk, which had over-browsed willow and cottonwood trees.

Disappearance of a Species

• To illustrate what happens when there is a disruption in a food chain or web, the CBC charted a forest kelp ecosystem with and without sea otters to show the adverse effects of the absence of that predator. Sea otters, a very hungry keystone species, consume sea urchins, which have a significant impact in an ecosystem because of the massive quantities of kelp and invertebrate skeletons they consume. Therefore, anything that significantly effects the sea urchin population directly impacts the entire kelp forest community. When sea otters are present, the sea urchin population is kept in check and the kelp forest community prospers. Unfortunately, killer whales have begun consuming sea otters because sea lions, their preferred prey, are in decline. The resultant decrease in sea otter populations in some Alaskan waters has led to barren, kelp-depleted ecosystems dominated by swollen populations of sea urchins.

Cascading Extinctions

• Writing for the journal "Animal Ecology," ecologists Anna Eklof and Bo Ebenman state that "The loss of a species from an ecological community can trigger a cascade of secondary extinctions." The researchers found that simple communities are more vulnerable to species loss than complex communities. The most common cause of secondary cascading extinctions is a "direct bottom-up effect" in which consumers die off because there is nothing left for them to eat. An example reported by National Geographic News states that a climate change promoted forest growth that killed off lower-lying plant species by blocking the sunlight. Mammoths that depended on the plants for food became extinct as a result.

Early Warning Signals

• A series of experiments conducted by a team of researchers led by S.R. Carpenter demonstrated that statistical methods can be applied to identify early signals that ecosystems may be undergoing catastrophic changes. For example, statisticians can record the rate of return of a species from an event that deceases or increases its numbers and determine whether there is a significant slowing or speeding of that rate over time.

  According to the study, which was published in 2011 in the journal "Science," the team's findings are important because the disruption of an ecological community could eventually lead to large-scale adverse effects on vital resources such as water, fish, forests and grazing lands.