Extreme rainfall patterns disrupt rainforest food webs

The extreme rainfall patterns associated with climate change will disrupt food webs in the rainforests of Central and South America, according to a new study from the University of British Columbia.

The research provides new insight into how climate change will impact forest ecosystems across the region, which is known as the Neotropics.

The team replicated future rainfall patterns that have been predicted by climate scientists throughout the Neotropics. 

The experts found that food webs became top-heavy with predators when there were large daily fluctuations in rainfall.

“This has knock-on effects for all parts of the rainforest system, because the larval insects in the bromeliads are destined to become winged adults that then are part of the forest ecosystem around them,” said study co-author Professor Diane Srivastava.

For the investigation, the scientists performed identical experiments in Argentina, Brazil, Columbia, Costa Rica, French Guiana, and Puerto Rico. 

The experiments were focused on bromeliads, large flowering plants that trap water and provide a habitat for many insects. After covering bromeliads with rain shelters, the researchers were able to replicate 30 different rainfall patterns by watering them on strict schedules.

“This is the first study, to my knowledge, where we have a replicated study of how precipitation patterns affect an entire food web in multiple sites,” said Professor Srivastava. “Every day we’d run around with a watering can with a list of how much water each bromeliad should get on each day. We had a customized rainfall schedule for each bromeliad in every field site.”

While the extreme rainfall patterns resulted in top-heavy food webs, more consistent rainfall produced the opposite outcome. The researchers found that when similar amounts of rainwater was available to the plants each day, the larval communities consisted of fewer predators and more prey.

“We were actually expecting to see the opposite pattern,” said Professor Srivastava. “We often think of predators being the most sensitive to environmental change, but we got the opposite result.” 

“One reason may be that, when the water level in the bromeliad went down during drier days, there was less aquatic habitat, so the prey was condensed into a small amount of water together with their predators. This can really benefit predators and disadvantage prey.”

The findings can be applied to other rainfall-dependent aquatic ecosystems, said Srivastava. “In any small pond or lake which is primarily determined by rainfall, we can expect to see a similar effect.”

“We should be concerned about these findings, because we’ve shown that these extreme perturbations in rainfall really do affect the flow of energy through the food web.”

The study is published in the journal Nature Communications.