Salamanders can be a proxyindicator for climate change. Changes in salamanders have been linked to climate changes during ancient times, and in a very recent study, salamanders in the US Appalachians seem to have changed in relation to anthropogenic global warming. In fact, the changes observed in these Appalachian salamanders is quite large, very rapid, and thus, alarming. I’m going to describe this study in some detail, and as a bonus for sticking with me on this, I’ll throw in some entertaining Climate Science Denialism near the end. As an additional bonus prize, you’ll get a nice new shiny Internet Meme to print out and attach to your refrigerator.
Salamanders (Order Caudata) are ectothermic, meaning that they get most of their heat from the environment in which they live. There are over 650 species of them and for the most part they are temperate, with none living in Africa and not too many species in Central or South America. The greatest diversity is in the United States. They are opportunistic predators.
Salamanders are diverse in their life histories and behavior. There are species that live all their time in water, and some that spend some of their life cycle in water and some on land, and some that actually never live in the water. Of the former some only shift to land living under certain conditions. Most salamanders are small, but there is an American species that grows to about 75 cm and a Chinese salamander that is abut 1.8 meters long and eats Pandas. OK, I’m only kidding about it eating Pandas. But it is that big. And, of course, people of the region eat them so they are nearly extinct.
There is a paper just out, “Widespread rapid reductions in body size of adult salamanders in response to climate change,” by Nicholas Caruso, Michael Sears, Dean Adams, and Karen Lips, that looks at 20th century changes in body size of 15 species of Plethodon salamanders from the 1950s to the present. This study has a lot of very interesting features (other than the findings). First, it incorporates a huge collection of data (and salamanders) made by a now emeritus researcher, Richard Highton, who had an interest in the beasts and collected piles of information on them. I love it when these old collections are a) usable and b) used. In this case, only a small percentage of the 140,000 salamanders Highton collected (that we know of) were part of the study.
(I would like to pause for a moment and say that I feel much better now. When I was a kid, my friend Kirk and I would collect salamanders and put them in a bait bucket, and put the bait bucket under the cabin. In these hot and dry conditions up in the Adirondack park in August, the salamanders would mummify and become tiny toys we would play with. Until I read this paper I felt partly responsible for the decline of the salamanders. Now, I realize that our small contribution to this was, well, small. But I digress….)
Second, the huge amount of data collected by Highton was supplemented by additional data. This helps anchor the data to current conditions and methods, and, frankly, it probably helps anchor the researchers to the old data as well.
Third, and I think this is the most important part, the researchers did not simply observe changes in key variables over time but they developed a sophisticated model of the biology underlying the data. Here’s the thing. If you observe change in some variable across time, space, or conditions you can speculate about the process underlying the change. But unless you have a sensible biological model to explain (and in some cases develop) the links, you’ve got bupkis. Here, the researchers looked at several possible underlying causal variables and were able to narrow down the list of suspects to two, which, in turn, are affected by climate change (and vary across elevation as well, which is nice because prior studies have shown elevation to be a key factor in recent changes in salamander biogeography).
This study looked at salamanders in West Virginia, Virginia, North Carolina, and Tennessee. The source of the samples is complex and involved multiple sampling efforts combining, as mentioned, the old samples taken by Highton and newer samples. I’ll let you read the original paper if you really want all those details. The key measurement of the salamanders was the SVL, which as you know means Snout-Vent-Length. Also recorded were temperature, humidity, elevation, and all sorts of other variables about the study sites.
Here is the key result in pictures:
As you can see, salamander length goes down over time. Each plot (the stats were all done in R) shows a different species over time, and generally the length goes down. Massive statistical analyses on these data, looking for underlying variables, resulted in this cool little graph showing that warmer-drier conditions were primarily responsible for the changes.
The aforementioned statistical model helps explain how and why the changes occur. It actually turns out to be very simple. As ectomorphs, salamanders get more active when it is warmer. Heat them up and their metabolic rate goes up, so they burn more energy. As you know, life is all about the partitioning of energy into three major categories: Reproduction, maintenance, and growth. The increased metabolic rate cuts into the maintenance part of that system, so the others may be reduced. I’d like to know if reproduction is diminished, but clearly, growth is affected. The science behind the following graph is complex (again, read the original if you want to bask in the formulae) but the meaning is pretty clear.
For different regions (where temperature, humidity, elevation, etc may vary) the models incorporating climate change and slamanderness of the salamanders show a modest uptick in activity, or virtually no change, happening along side a significant upward trend in energy expenditure. Temperature matters when it comes to size.
Now here’s the bonus climate science denialism controversy I promised you. Anthony Watts, on his blog Watts Up With That, mentioned this study and then made fun of it. He and his readers derided this excellent piece of science by pointing and laughing at two things. First, the scientists studying the salamanders used OMG COMPUTER MODELS. All climate science denialists know that all computer models are wrong. That is not true of course. Also, the modeling done in the salamander study was different … it was physiological modeling not climate modeling, and it was an excellent piece of work. Essentially, the salamander modeling took reasoning based on long established biology and expanded on it mathematically, then took that and used various techniques to test the mathematical modeling for validity. The second Wattsian complaint about the study is that some other study in the past showed that salamanders GREW, not SHURNK when it got warmer.
And yes, there is in fact a study from a few years ago that looked at fossil salamanders from the last 3,000 years, and showed an increase in body size with warming conditions. But comparing these studies is absurd. This would be like comparing a study of how big lions grow depending on how many antelopes there are from year to year with a different study on the evolution of lions across time as their body size changed. But worse, because these are species living in different regions. So it would be like studying size changes in African lions over decades in Amboseli with long term evolutionary trends in saber tooth cats in Mongolia, and assuming that you are looking at the same thing.
I suppose if one rejects science as does Watts, one would be more comfortable with the creationist idea that there are not really different species of animals, but rather, “kinds” of animals. In this way, one could think of all salamanders as just a “kind.” I suppose.
There are a lot of reasons the studies seem to show opposite patterns. In Yellowstone, that particular species of salamander can get larger if they change from a water based life history strategy to a land based one. In that region warm conditions may increase food supplies in terrestrial areas but not aquatic areas. Water based salamanders can evolve to be larger if their water bases become smaller and shallower, increasing predation and thus selecting for larger body size.
The main difference between the studies is the temporal resolution. The study reported here covers decades of phenotypic change within the range of norm of reaction (i.e., probably not mostly genetic) while the Yellowstone study is over evolutionary time. But there are other differences. Mike Sears, one of the authors of the Appalachian salamander paper, told me this:
Ambystomid salamanders [Yellowstone] require water for reproduction. Some adults live in terrestrial environments, but their larvae all require water. Plethodon salamanders [Appalachian], on the other hand are terrestrial for all life stages. Plethodon salamanders are lungless. They depend on their skin for oxygen exchange, meaning that they are limited to cooler, wetter habitats in terrestrial environments. Because their habitats are predicted to get drier and warmer, this lifestyle imposes some immediate stress (e.g., dry out and you can’t breathe). In fact, if these animals lose too much water over the course of an evening, they retreat from activity.
Most importantly, regardless of the differences between these two species, climate change biologists would not expect all species to respond similarly, within or among species. For instance, ectothermic animals from the Tropics might be expected to be negatively affected by increasing temperatures, whereas temperate species might benefit from them. For that matter, animals with large species ranges might be expected to respond differently to warming climates across their ranges, benefitting some populations while harming others. In fact, for species that are negatively impacted by warming climates, declining body size has been observed and should be expected given basic physiological principles.
Here’s the thing. Anthony Watts and his friends in the Climate Science Denialism gaggle love themselves them cherries. And, this is an example. Using just the titles of articles and not understanding the underlying science behind them, one can pretend to find contradictions that aren’t really there. Also, this is easy to get; it does not take much effort to misconstrue the meanings of a bunch of journal article titles. An active climate science denier can probably do several over a weekend. This expedience then allows the denier to blend the cherries into a nice Gish Gallop. Just look at Anthony Watt’s blog; the cherries flow there like the effluence of a hippopotamus with diarrhea. Who ate a lot of metaphorical cherries.
Anyway, back to the salamanders. There are many cases of well established biologically understood links between climate and physiology. And that is nice because it allows us to observe climate change in the past. But as this article on salamanders (and the Yellowstone paper as well) points out these systems have an important additional implication: Climate change is going to change more than just climate. From the paper:
Regardless of whether the effect is genetic or environmental, the degree of body size reduction we documented in Plethodon was both large and rapid. For the six species displaying significant trends, body size reduced by an average of nearly 8% across the time period examined. When standardized for within-population variation, this corresponds to approximately a 1% body size reduction per generation in these species. This magnitude of change is on par with some of the largest phenotypic changes observed in contemporary populations. Thus, these changes represent some of the fastest responses to environmental perturbations ever recorded and lend support to the observation that phenotypic responses, particularly those related to anthropogenic disturbance, are both more rapid and more extreme than those observed in natural contexts or over longer time periods. The rapidity and the widespread extent of these changes across so many species in a biodiversity hotspot may signal rapid adaptation to novel environmental conditions.
And now, for your patience, your refrigerator magnet:
For another writeup see Climate change makes salamanders shrink, scientists say: A warmer and drier climate is likely causing wild salamanders in North America to shrink, say scientists by Cudeshna Chowdhury.
Caruso, N., Sears, M., Adams, D., and Lips, K. 2014. Widespread rapid reductions in body size of adult salamanders in response to climate change. Global Change Biology. DOI: 10.1111/gcb.12550
Bruzgul J. E., Long W. & Hadly E. A. 2005. Temporal response of the tiger salamander (Ambystoma tigrinum) to 3,000 years of climatic variation. BMC Ecol., 5. 7 (2005).