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Extreme seasonal changes in Amazon river levels threaten forest conservation by indigenous people

  • The Amazon has experienced intense floods and droughts for the past 10 years, a likely effect of climate change.
  • Surveys taken of animals between 2009 and 2015 showed terrestrial mammal populations dropped by 95 percent during intense floods, whereas aquatic animals suffered dramatic declines during an extreme drought.
  • Scientists fear these seasonal extremes will drive the Cocama people of Peru out of the forest, depriving it of its primary conservationists.

Rivers in the Amazon are cycling between increasingly severe states of flood and drought, as predicted by climate change models, and the results are directly impacting local wildlife and the indigenous people who protect the forest, a new study shows.

The study, published online recently in the journal Conservation Biology, looked at seven years of population data on mammals, birds, fish and reptiles from the river bottom to the forest canopy in the Pacaya-Samiria National Reserve of Peru, and examined which groups thrived and which suffered from ever more extreme wet and dry seasons. For many, it didn’t look good.

“We watched the animal populations in the yearly analysis, and we were seeing them crash in front of our eyes!” said lead author Richard Bodmer, a conservation biologist from the University of Kent in the U.K. But the crashes seemed to follow a cyclic pattern.

1. Populations of red-bellied piranhas (Pygocentrus nattereri) dramatically decreased in the Peruvian Amazon during the 2010 drought. Photo from Pixabay.
1. Map showing the location of the Pacaya-Samiria National Reserve in Peru (background) and a view of the Samiria River (foreground). Map from Google Maps; photo by Mark Goble, Flickr.

Populations of aquatic animals like red-bellied piranhas (Pygocentrus nattereri) and pink river dolphins (Inia geoffrensis), for example, dried up during the Amazon’s record-breaking drought in 2010 to just half of the population densities that scientists saw the year before. But in the five subsequent years between 2011 and 2015, when extreme floods raised water levels to twice their usual heights, those river populations bounced back.

On the other hand, land-based mammal populations, whose numbers had stayed steady during the drought, sank by 95 percent during the five years of intense flooding. Mammals such as black agoutis (Dasyprocta fuliginosa) and white-lipped peccaries (Tayassu pecari) drowned in the historically high floods of 2012 and 2015, Bodmer said.

These opposing population ebbs and flows could disrupt the entire rainforest ecosystem, “leading to the extinction of key plant and animal species,” Whaldener Endo, a conservation biologist with the National Research Centre for Carnivore Conservation in Brazil, said in an email. Endo was not part of the study.

1. A home and crop field of indigenous river dwellers submerged by extreme floods in 2009 in the Juruá region of Brazil. Many people left their forest homes for urban areas. Photo courtesy of Whaldener Endo.

For Bodmer, who trains and works with the indigenous Cocama people to establish community-based conservation programs, though, the consequences could be more immediate.

If years of intense, uninterrupted flooding are followed by years of extreme drought, the study warned, no animal populations will recover — the numbers will just remain low. And that’s bad news for the indigenous people who depend on them.

“The people look at the forests as a grocery shop,” Bodmer said. “They are conserving those intact forests because that’s their livelihood.”

1. A group of Cocama children in the Pacaya-Samiria region of Peru. People like the Cocama make up an essential part of conservation efforts in the Amazon. Photo courtesy of Richard Bodmer and FundAmazonia.

The indigenous communities are used to the seasonal cycles, so they alter their food sources according to when they’re easiest to catch: land-based bushmeat in the wet season, fish in the dry season. But if all their animal resources collapsed following persistent periods of intensifying flood and drought, it would leave them with little to sustain themselves.

That’s a real problem, Endo concurred. In the Juruá region of Brazil where he works, people along the river farm for a living. When the floods rose to record levels, he said, fields were submerged, homes were flooded, and some residents left the forests for the cities. “They don’t have other options to move their communities to more suitable areas in the forest,” Endo said, since they already live at the highest elevations along the river.

“That’s where the danger lies in this type of seasonal intensification,” Bodmer said. If the indigenous people can’t find the motives for conservation because there are fewer animals available for them to use, then “they might just give it up. And if they give it up, the Amazon won’t be conserved because they’re the ones who are doing it right now.”

As he talked, Bodmer watched from his covered launch on the Samiria River as rare pink river dolphins leaped from the water.

“We don’t know what this next year’s going to bring,” he said. “But the river is already quite high for this time of year in November.”

2. A pink river dolphin (Inia geoffrensis) leaps from the Samiria River in northeastern Peru. These dolphins, along with scores of fish and crocodilians, suffered from an intense drought in 2010, but most recovered during extreme floods between 2011 and 2015. Photo courtesy of Richard Bodmer and FundAmazonia.

Citation

 

Bodmer, Richard et al. (2017). Major Shifts in Amazon Wildlife Populations from Recent Climatic Intensification. Conservation Biology. https://doi.org/10.1111/cobi.12993.

 

Jeremy Rehm (@jrehm_sci) is a graduate student in the Science Communication Program at the University of California, Santa Cruz. Other Mongabay stories by UCSC students can be found here.