For lizards roaming a warming world, shade is vital

How animals cope with climate change is about more than just rising temperatures – shade is a huge factor too.

Now a new study adds another layer of complexity.

When nutting out how animals will deal with global warming, biologists must not only take the total amount of shaded area into account, but how the shady patches are distributed.

Michael Sears, a biologist at Clemson University in South Carolina, and colleagues created a computer model to track lizards’ movement between sun and shade – and then compared it with real life lizards.

The work, published in the Proceedings of the National Academy of Sciences, calls for more refined modelling to predict how animals might respond to warming temperatures, and shines a light on lizard biology, too.

Lizards are often used as models because they rely on changes in environmental temperature, such as sun or shade, to regulate their own body heat.

As Sears points out, they’re “like little thermostats running round”.

The researchers’ aim was to show that simply recording temperature change doesn’t make for accurate modelling – the energy spent by animals to regulate their body temperatures also depends on the ease of access to cooler areas.

So the team developed an algorithm to model digital lizards in warming environments.

To test different patterns of sun and shade, they created three different environments: one in which shade was provided in a single large area, one with four smaller areas of shade and a third with 16 patches of shade.

The model showed that as lizards moved around in search of food, they needed less energy to regulate body temperature if they moved into the occasional cool patch.

More specifically, lizards were estimated to experience 9% more variation in body temperature in the environment with just one large clump of shade. 

Later, the team tested their computer model by recreating the simulation with real lizards in 20-square-metre custom-built environments, with shade patterns that echoed the computer simulation.

The body temperature of each lizard was monitored over two days using a tiny implanted thermometer and, sure enough, lizards in environments with one giant shade experienced 12% more body temperature variance than those with four patches of shade, and 10% more than those with 16 patches.

On a broader level, this study suggests that the existing models for climate change effects on animals could be inaccurate, explains Mike Angilletta from Arizona State University and co-author of the study.

“The real fear is that previous research has underestimated the risk of extinction,” he says.

“Most models assume that an animal can be anywhere in its environment at any time, which doesn’t account for how much energy an animal spends to regulate its temperature. 

“Animals have to move and search for shade, which makes cooling down more difficult when patches of shade are far apart.”