The Most Popular Life Style on Earth

One of the main challenges to understanding how food webs behave is drawing the web in the first place. Ecologists need to observe which species are eating which. In some cases, a single species of prey may be the main source of food for a predator; other predators may prefer to liven up their diet with many species. But a perfect picture of a food web would be too difficult to assemble and too difficult to analyze. So ecologists have had to decide how much detail they can live without. Until the 1990s, they universally agreed that parasites could be ignored. Parasites seemed like little more than hangers-on, with no significant effect on the food web of their hosts.

Then, in 1997, two Canadian biologists, David Marcogliese and David Cone, published a paper titled “A Plea for Parasites.” (2) Parasites, they argued, might well play a pivotal role in food webs. Some of them were deadly, thus controlling populations of predators and prey alike. Others didn’t kill their hosts but lived inside them, feeding on their food and diverting energy that might produce more hosts. And many parasites needed to live in more than one species of host throughout their life cycle"in other words, they moved through the food web. To say parasites didn’t matter to food webs seemed absurd.

Marcogliese and Cone knew it wouldn’t be easy to rectify the problem. Parasites may be the most successful life form on Earth, but scientists know relatively little about them because they’re so hard to study. Documenting parasites requires years of dissections, of careful study with microscopes, of experiments. “It’s an enormous amount of work,” Marcogliese says.