Vocabulary

ecology interdependence ecological model biosphere ecosystem community population

Word Roots and Origins ecology from the Greek oikos, meaning "house," and logos, meaning "study of"

figure 18-1

All of the different species shown are interconnected in the forest. © An unusually plentiful crop of acorns helps support a large population of deer and mice. © The deer and mice help support a large population of ticks. © Ticks carry the bacterium that causes Lyme disease. They pass on the disease to humans who visit the forest.

All of the different species shown are interconnected in the forest. © An unusually plentiful crop of acorns helps support a large population of deer and mice. © The deer and mice help support a large population of ticks. © Ticks carry the bacterium that causes Lyme disease. They pass on the disease to humans who visit the forest.

Effects of Interdependence

A consequence of interdependence is that any change in the environment can spread through the network of interactions and affect organisms that appear far removed from the change. One example is the interrelationships among species in forests in the eastern United States. Through these relationships, as shown in Figure 18-1, acorn production is connected to the spread of Lyme disease, an infection that can damage the human nervous system.

In most years, oak trees produce few or no acorns. Every few years, however, they produce a huge crop of acorns. The large number of acorns supports larger populations of deer and mice, which feed on acorns. Ticks feed on the blood of animals, so the tick population also increases. The increased number of ticks increases the chance that ticks will bite any humans in the forest. The bite of the deer tick can transmit the bacterium that causes Lyme disease to humans. So, in general, after a season of high acorn production, the cases of Lyme disease increase.

www.scilinks.org Topic: Ecosystems Keyword: HM60466

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