By Dr. Becker
Rising global temperatures are complicating survival for countless species worldwide, but one of the hardest hit may be ectotherms, or animals that depend on external sources of body heat. Unlike humans, which regulate their own body temperatures, ectotherms, such as lizards, are cold-blooded animals that must control their body temperature by moving in or out of the sun or shade (although even then they can only influence their body temperature within limits).
Previous research has suggested that by 2080, 20 percent of lizard species may go extinct, in large part due to rising temperatures.1 This, in turn, could have repercussions on the animals that eat lizards (including birds and snakes) as well as insects, which may increase in population without lizards around to control their numbers.
An unforeseen consequence of climate change may be related to lizards' gut microbiome. As it's become increasingly clear that animals depend on their microbial communities to thrive, recent research showing rising temperatures' effects on lizards' gut microbiome raises alarming red flags.
Small Temperature Increases Lead to Major Changes in Lizards' Microbiome
Researchers from the University of Exeter in the U.K. conducted a study to determine what effect temperature increases of 2 degrees C and 3 degrees C (3.6 degrees F and 5.4 degrees F) would have on lizards' gut-microbial diversity.2 This rise in temperature mirrors what has been predicted to occur in southern Europe by 2080.3 After spending time living in local temperatures, intermediate temps (2 degrees C higher than local temps) or warm temps (3 degrees C above local temps), the lizards' gut microbes were tested.
A 34 percent decrease in microbial diversity was noted among the lizards living in the warm conditions. "We found that 2 to 3 degrees C warmer climates cause a 34 percent loss of populations' microbiota diversity, with possible negative consequences for host survival," the researchers noted.
Although it's unknown if the same effect would be seen in wild lizards, and what consequences the reduced microbial diversity will cause, the results point to a need for further research on the way climate change may influence microbiomes. Kevin Kohl, Ph.D., microbial ecologist and animal physiologist at Vanderbilt University, told The Scientist:4
"Environmental temperature is known to be so important to the biology of ectotherms … Separately, we know that microbes are important to the biology of all animals … This work does a great job integrating these two ideas and demonstrating the complex interactions that could be taking place out in nature — interactions that could change under patterns of climate change."
Distribution of Shade-Providing Plants and Rocks May Also Influence Lizard Survival
Lizards depend on access to shade to cool off on hot days, but some predictions on lizard survival — including the one that 20 percent may go extinct in the coming decades — were based on assumptions that lizards always have access to shade when they need it.
In reality, research published in the Proceedings of the National Academy of Sciences found that lizards fare better at keeping their body temperatures in the optimal range when they have access to plentiful small patches of shade.5 Clemson University biologist Michael Sears, Ph.D., who led the study, told NPR:6
"It's sort of like, if you were out jogging, and there was only one tree and it was a long way to the next one, and it was a hot day — that's a bad environment … But if there were a bunch of trees along the way providing little bits of shade, you'd feel a lot better … Everything in between, all bets are kind of off now, because what our study suggests is that how bushes are placed in an environment might really impact the lizards just as much as the temperature itself."
Many Species Are Already Stressed by Rising Temperatures
It's been suggested that ectotherms living in already-warm climates may face the greatest consequences of rising temperatures, while those living in cooler climates may actually benefit from warming temperatures.7 A study conducted in 2009 suggested that tropical forest lizards, which are intolerant of warm temperatures, were already showing stressful body temperatures during the summer months several decades ago.
"Simulations suggest that warming will not only further depress their physiological performance in summer, but will also enable warm-adapted, open-habitat competitors and predators to invade forests," the researchers suggested. "Forest lizards are key components of tropical ecosystems, but appear vulnerable to the cascading physiological and ecological effects of climate warming, even though rates of tropical warming may be relatively low."8
Other species have also been affected by climate change. A team of researchers from four U.S. universities concluded, for instance, that climate change is behind the smaller size of certain salamanders in the Appalachian Mountain region of the U.S.9 Six species of salamanders have decreased in size from 2 percent to 18 percent since the 1950s.
Aside from certain ectotherms, warm-blooded animals like polar bears are also feeling the stress. There are only an estimated 22,000 to 25,000 polar bears left worldwide, and one-third of these may be in "imminent danger" within the next 10 years, according to a government report released as part of the U.S. Fish and Wildlife Service's recovery plan for the polar bear.10 As temperatures rise, the sea that ice polar bears depend on to hunt is disappearing, leaving them without a steady food source.
Individual Changes May Help
Actions to curb global warming must be taken on a global scale, however, making small changes, like consuming products like pasture-fed beef, free-range poultry and wild salmon rather than CAFO (concentrated animal feeding operations) meats (for you and your pets) may help. CAFOs (and genetically engineered crops) play a significant role in greenhouse gas emissions, as they release more greenhouse gases into the atmosphere than the entire global transportation industry.
The conversion of croplands to grasslands significantly reduces annual greenhouse gas emissions, as do simple natural farming methods, like composting, which you can do in your own backyard. By supporting small, local farmers raising animals on pasture, and composting their waste, as well as composting your own kitchen scraps at home, you can help make a difference in climate change and possibly help protect the survival of lizards, salamanders and other species at risk.