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A new study shows climate change may be doing real harm to the lower end of the food chain.

Woodrats struggle to survive on their usual diet under warmer temperatures, indicates the University of Utah study published online Jan. 13 in the British journal Proceedings of the Royal Society B.

The insight shows that mammals may be more affected by global warming than previously thought, senior author Denise Dearing said in a statement.

The takeaway from Dearing's research is that animals — and potentially birds — won't be able to eat as many plants as they do now, the biology professor said, so they will need to find cooler places to live or go extinct.

"In terms of climate changes," said biology doctoral student Patrice Kurnath, "this study suggests that plant-eating animals all over the world may have problems dealing with their preferred food sources."

Poison played a key role in the research.

The rodents in the study have a diet full of plants with safe levels of toxins that their livers can handle. Not each species has such a poisonous diet, but more than two of every five kinds of mammal is an herbivore and likely eats some kind of plant toxins. The list includes rabbits, deer, moose, elk, sheep, horses and cows.

In their experiments, researchers observed about 45 woodrats. Some of the rodents lived at 82-84 degrees Fahrenheit and others as low as 70-72.

At the warm temperature, woodrats ate less food overall. They tolerated less of the toxic plant ingredient creosote resin — only two-thirds as much — as rodents at the cool temperature. 

Researchers also paid attention as the mercury rose. They found a "tipping point" where the mammals stopped being able to tolerate the toxins at 77 degrees.

The team believes liver processing of toxins may be reduced at warmer temperatures because more energy is needed to regulate body temperature.

The research was funded by the National Science Foundation, American Society of Mammalogists and the Society for Integrative and Comparative Biology.

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