Climate change will create a toxic brew for herbivores

A WARMER world might be a poisoned one. A compilation of studies suggests that as temperatures rise, herbivorous mammals will suffer greater effects from the toxins they eat, with animals living in dry regions at particular risk.

Mammals can maintain a constant body temperature and so are thought to be less vulnerable to temperature changes than cold-blooded animals like reptiles. But Denise Dearing at the University of Utah in Salt Lake City has found evidence that mammals feel the heat in subtle ways.

Plants produce toxins to defend themselves against animals that eat them. In response, herbivores limit the amount of toxins they eat, often by eating a wide range of plants.

That strategy may need some adjusting as climate change pushes temperatures up. Dearing found a number of lab studies scattered through the scientific literature showing that animals kept at higher temperatures become less able to process toxins (Journal of Comparative Physiology B, DOI: 10.1007/s00360-012-0670-y).

In one study in mice, raising the temperature from 26 ?C to 36 ?C made them more vulnerable to caffeine: they died after receiving just one-fifth of the normal lethal dose. Meanwhile, in the wild, white-throated woodrats often eat juniper, which is toxic, but they eat less of it in summer even though the juniper is readily available.

Mammals use their livers to process toxins, and Dearing thinks their ability to do so may slow down in the heat. The effect could also apply higher up the food chain - predators often have to deal with toxins produced by their prey, such as scorpion venom.

Nathalie Pettorelli at the Institute of Zoology in London says herbivores in dry regions, such as the Arabian oryx, have a limited range of plants to choose from, so if one becomes too toxic they may have little else to eat. Herbivores in lush forests should still have a wide range of options.

And just to make things a little more interesting, there is also evidence that plants produce more toxins as temperatures creep up. If that is the case, herbivores face a double whammy.

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