An inaccessible cave preserved clues to Jamaica’s climatic past in the sedimentary layers of bat guano
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PICTURE: The Jamaican fruit-eating bat (ARTIBEUS JAMAICENSIS) is one of five species that can be found in the distance from its home cave in Jamaica. View More CREDIT: SHERRI AND BROCK FENTON
WASHINGTON – Deep in a Jamaican cave is a treasure trove of bat droppings deposited in successive layers by generations of bats over 4,300 years.
Analogous to past records found in layers of sea mud and Antarctic ice, the guano pile is roughly the size of a tall man (2 meters), largely undisturbed, and contains information about climate changes and the shifting of food sources in the Bats over the millennia according to a new study.
“We study natural archives and reconstruct natural histories, mainly from lake sediments. This is, to our knowledge, the first time scientists have interpreted previous bat diets, ”said Jules Blais, limnologist at the University of Ottawa and author of the new study in the Journal of Geophysical Research: Biogeosciences, AGU’s Journal for Research on the Interactions Between Biological and Geological and chemical processes in the earth’s ecosystems.
Blais and colleagues applied the same techniques used for lake sediment to a guano deposit found in Home Away from Home Cave, Jamaica. A vertical “core” was extracted from the top of the stack to the oldest deposits below, and brought to this the laboratory for biochemical analysis.
According to the researchers, around 5,000 bats from five species currently use the cave as daytime shelter.
“As we see in lake sediments around the world, the guano deposit recorded history in clear layers. It wasn’t all mixed up, ”Blais said. “It is a huge, continuous deposit with radiocarbon dates dating back 4,300 years in the oldest lower strata.”
The new study looked at nutritional biochemical markers called sterols, a family of robust chemicals made by plant and animal cells that are part of the diet that bats and other animals eat. For example, cholesterol is a well-known sterol made by animals. Plants make their own distinctive sterols. These sterol markers enter feces through the digestive system and can be retained for thousands of years.
“This study breaks new ground as a piece of work that shows what can be done with poo,” said Michael Bird, an environmental change researcher at James Cook University in Queensland, Australia who was not involved in the new study was. “They really expanded the toolkit that can be used for guano deposits around the world.”
Past climates, past diets
Like sediment and ice core records, the guano core extracted from the Jamaican cave recorded the chemical signatures of human activities such as nuclear testing and lead gas burning, which, along with radiocarbon dating, helped researchers correlate the history observed in guano with other events in Earth’s climatic history.
Bats pollinate plants, suppress insects, and spread seeds as they forage for food. Changes in bat diet or species representation in response to climate can have reverberant effects on ecosystems and agricultural systems.
“We concluded from our results that the past climate had an impact on the bats. Given the current climate change, we expect changes in how bats interact with the environment, ”said Lauren Gallant, researcher at the University of Ottawa and author of the new study. “That could have consequences for ecosystems.”
The new study compared the relative amounts of plant and animal sterols in the guano core that moved through the guano layers in time to find out how bat species as a group have shifted their exploitation of different food sources in the past.
The research team, which included bat biologists and a local cave expert, also tracked live bats in Belize and tracked their food consumption and excretion to provide a basis for the types of sterols that end up in the feces when bats feed on different food groups.
The new study found that plant sterols, compared to animal sterols, occurred about 1,000 years ago during the Medieval Warm Period (900-1,300 AD), at a time when cores of lake sediments in Central America indicated the climate in America was unusually dry. A similar spike occurred 3,000 years ago, at a time known as the Minoan Warm Period (1350 BC).
“Drier conditions tend to be bad for insects,” Blais said. “We hypothesized that fruit diets were preferred in dry spells.”
The study also found changes in guano’s carbon composition, likely due to the arrival of sugar cane in Jamaica in the 15th century.
“It’s noteworthy that they can find biochemical markers that still hold information 4,000 years later,” Bird said. “Everything collapses quickly in the tropics.”
The approach demonstrated in the new study could be used to extract ecological information from guano deposits around the world, even those that are only a few hundred years old, Bird said.
“Very often there are no lakes and the guano is a good way to get information about the past. It also contains biological information that lakes don’t have. “Said Bird. “There’s a lot more to do and a lot more caves out there.”
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Notes for journalists: This research study is available free of charge for 30 days. Download a PDF copy of the paper here. Neither the newspaper nor this press release are under an embargo.
Paper title: “A 4,300-year history of diet changes in a bat colony identified from a tropical guano deposit.”
Authors:
- Lauren Gallant (University of Ottawa, Canada)
- MB Fenton (University of Western Ontario, Canada)
- Chris Grooms (Queens University, Canada)
- Wieslaw Bogdanowicz (Museum and Zoological Institute, Poland)
- RS Stewart (Jamaican Caves Organization, Ewarton, Jamaica)
- Elizabeth Clare (Queen Mary University of London, United Kingdom)
- John Smol (Queens University, Canada)
- Jules Blais, corresponding author (University of Ottawa, Canada)
From EurekAlert!
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