Carnivorous Pitcher Plants Play Host To Complex Food Web

Brett Smith for – Your Universe Online

At first glance, pitcher plants appear to be simple carnivorous plants that entrap and digest hapless insects that fall into them. However, a closer look reveals a complex food web of fly larvae, rotifers, midge larvae, and bacteria that exist within the plants´ pitcher.

According to a new study by Harvard University, the predator-prey interactions among pitcher plant inhabitants provide an ideal model for understanding food webs on a larger scale.

“It´s shocking, the complex world you can find inside one little pitcher plant,” said Harvard´s Ben Baiser, the lead author of the new study, which appeared in the journal Oikos.

The organisms found within a pitcher plant´s leaves play a key role in the plant´s ability to extract nutrients. After an insect drowns in the pitcher, midge larvae feed on the carcass and break it down to smaller pieces. Bacteria eat the smaller pieces, rotifers eat the bacteria, and the pitcher plant benefits by absorbing the rotifers´ waste, according to the scientists.

The entire web can shift in seconds and can change drastically with the addition or removal of a single organism, the authors said.

According to study co-author Aaron Ellison, a senior ecologist at the university´s Harvard Forest department, the predators and prey within the plants provide a unique opportunity to study food webs in general.

“With pitcher plants, you can hold the whole food web in your hand,” he said in a statement. “The vast number of pitcher plants in one bog provide endless opportunities for detailed experiments on how food webs work, not only in pitcher plants, but also in bigger ecosystems that are harder to manipulate, like ponds, lakes, or oceans.”

To investigate the food webs found within pitcher plants, the Harvard researchers investigated food webs inside 60 different pitcher plants from British Columbia, Quebec City, and Georgia. The team was able to identify 35 different types of organisms inside; not including the various different bacteria species.

Baiser said, “We wanted to know: how did we get different food webs in individual pitchers from the same species pool? What caused these food webs to form the way they did?”

Ecologists have outlined the various factors that comprise any food web and the Harvard researchers used these standards when analyzing the various species interactions found inside their pitcher plants.

“Say you´ve got a bunch of lakes,” Baiser said. “And you´ve got a big bucket holding all the species that can live in those lakes. When you dump out the bucket, which creatures end up in which lake? What matters more: the size of the lake, or the fact that predator species X is there, too? Or is it random? Those models help us tease those factors apart.”

According to the Harvard scientists, the predator-prey interactions found within pitcher plants are highly structured and not a series of random events.

“You take out one species, and that affects everything else,” Baiser explained.

In their conclusion, the researchers noted that their approach to analyzing the pitcher plant food webs could be applied to “any well-resolved food web for which data are available from multiple locations.”