Revisiting the effects of climate change on salamander body size: the role of natural history collections

Our recent paper, The relationship between climate and adult body size in redback salamanders (Plethodon cinereus), found that salamanders were larger in warmer parts of their range. We also found that that body size increased significantly in places where the climate had become hotter and drier.


Image credit: Brian Gratwicke

Small-bodied lungless salamanders breathe through their skin, and tend to come to forage on the surface in cool, damp conditions associated with spring and fall, which is the best time to find them. They have thrived in the cool, temperate climate of the Appalachian Mountains, making this region a global hotspot for salamander diversity. Because of their preference for cool, damp environments, salamander biologists worry that predictions of warmer climates and more intense rainfall events and longer dry spells in between may be bad news for these distinctive creatures.

Several studies using museum specimens found that salamanders in warmer areas have larger bodies, but one recent study suggested that salamanders were actually shrinking in response to climate change. Subsequent papers have dwelled on the challenges of using museum specimens to draw these types of conclusions, but none re-examined the actual phenomenon of the shrinking salamanders. We designed a new study to revisit the question using museum specimens in a way that accounts for some of the previous limitations.

We selected redback salamanders, which are one of the most abundant vertebrates both by number and biomass in forests in the Eastern United States. One classic study by Thomas Burton and Gene Likens at Hubbard Brook Forest in New Hampshire found densities of about 3,000 salamanders per hectare, mostly redbacks.  This wide-ranging, abundant species is also very well represented in museum collections. About 70,000 redback specimens are held in the Smithsonian’s Museum of Natural History, mostly collected between 1950 and 2000.


A Redback salamander Plethodon cinereus specimen at the Smithsonian Museum of Natural History. Image by Brian Gratwicke

A collection of this size allowed us to pre-emptively select our comparison groups in a way that would eliminate sampling bias, maintain large sample sizes and maximize our power to answer the question.  We corrected our samples for potential sources of sampling bias including seasonal collection bias and potential destructive sampling bias. We found that redback salamander body size actually increased 1.8% in the places that had warmed significantly. Our observations do not really shed any light on whether climate-change is a potential threat to redback salamanders, but there does appear to be a measurable effect on the species.

The nature and culture surrounding natural history collections is changing, and very few redback salamander specimens were lodged after the year 2000, restricting the time period we could analyze. This likely is a product both of the ethics debate surrounding indiscriminate collecting, and the growing popularity of new citizen science tools like iNaturalist which create photographic specimens in publicly accessible databases with critical collection information. We were able to use citizen-science databases like the Maryland Herp Atlas  and iNaturalist to verify that the salamanders are still common in all the counties that have warmed significantly, but body size data were not available. We actively support and participate in these non-destructive efforts, but view them as complimentary to well-curated natural history specimens, rather than a substitute.

Brian Gratwicke is a biologist at the National Zoo’s Smithsonian Conservation Biology Institute in Front Royal, Virginia, USA

Drawing, remembering, knowing: natural history and the ecological imagination

By Meredith Root-Bernstein (Aarhus University)

Geo: Geography and Environment recently published my personal essay about how natural history practices have helped me to think about interdisciplinary research and collaborations.  I emphasize in the essay how developing and sharing habits of observing, interpreting, and considering the human contexts of nature can help form shared understandings as the basis for exchanges about social and natural sciences of the environment.  In that essay, I discuss seeing an espino (Acacia caven) with a liana growing on it in central Chile.  My research involves searching for the key problems and solutions for the conservation of a silvopastoral system (“espinal”) and the surrounding shrub and forest habitats in this mediterranean-climate zone.  The most common species in espinal is the espino (Acacia caven).  Yet, I had never seen an espino with a liana, and I became intrigued by trying to understand the potential ecological and social meanings of this unusual species assemblage.  Here, I expand on that essay with a discussion of a sketch of the liana and the espino.  While looking for something else I came across this drawing I made of the espino and its liana:

Bernstein image

I had forgotten about the sketch, and I have also forgotten the exact circumstances of making it.  I am sure that I didn’t make it in situ, and a few days probably elapsed between seeing the tree and making the drawing. The structure of the trunk is hard to read.  First I thought it suggested that the tree is old and perhaps has ridges or hollows, but this doesn’t match the photograph.  I also couldn’t think of any example of thick, undulating or textured espino trunks.  Something was wrong, either with the drawing, my memory, or my knowledge of espinos.  Then, while walking past some trees here in Denmark with ivy on them, I realized by analogy that I had drawn the vines of the liana descending to the ground.

The liana seems to be partly imaginary.  I remember seeing red stems and green leaves, but I am fairly sure that there were no black drupes at the time and that I only saw images of them by looking up the species on the internet.  The drawing thus knits together memory and imagination to represent the way I was thinking about my observation.

The ambiguity of the sketch forced me to think about the visual and structural patterns that things make, and how those map onto our other kinds of knowledge and memory.   There are really two issues here: one is that the sketch was by nature approximate, hasty, and in this case not based on direct observation but rather memory and its own approximations.  All of these aspects confer an abstract nature on the sketch.  It excludes the inessential and retains only an impression, just enough to reconstruct what was seen.  The second issue though relates to my lack of experience thinking about and observing lianas.  This led to what might be a not-so-clear abstraction of a liana growing up a trunk, and certainly created ambiguity in interpretation.  But the ivy I saw that helped me to understand the sketched pattern of something I had only seen once before—a liana on an espino—taught me about lianas and vines in general.

An important part of natural history is personal memory, the accumulation of implicit and tacit knowledge.  How do we make these memories relevant to interpreting the future as well as the past?  Writing, sketching and showing others are all important means of communication, that emphasize different aspects of nature—the narratives and cycles, the structural patterns, the kinaesthetic and embodied knowledge of where, when and how.

It is well-known that natural history drawings have features that photographs do not: they can represent a general or ideal example of something, facilitating recognition, and they can bring attention to particular features or patterns through emphasis, selectivity and abstraction.

As I mention in the article, I think of natural history as seeking patterns, which can be used to interpret the past, but also potentially the future.  In my drawing, I imagined the visual effect of the liana on the espino in a season when it had fruit. In the Anthropocene, it might be interesting to think more about the natural history of the future.  How will places look, behave and feel under climate change? How will we read the landscape of abandoned infrastructures in the future?  What unexpected species pairing will we find somewhere next year, testimony to some casual event yesterday?  These visions don’t have to be apocalyptic—and they don’t have to be written.   Drawings can often be both more subtle and more complex than words.  They have their own logic of organization and representation.

I recently saw a short article in the ESA Bulletin about how ecologists can avoid midlife crises and burnout.  Going into the field from time to time was one suggestion.  I would also add to that that the practice of natural history, and the attempt to communicate it, if only to oneself later on, can be both enjoyable and meaningful.  It was a pleasant surprise to find this sketch that I had forgotten about, and it brought a new angle to what the liana and the espino taught me about the socioecological interactions of central Chile.

Who knows, practicing a little natural history on your days out might even inspire a new line of research, maybe an interdisciplinary one.  You don’t have to try to be serious and professional about natural history, which might take away the enjoyment of being in nature.  Play is an important way to explore the world, and its not just for children.  Many accomplished scientists, among others, take time to have fun with no clear purpose as a way to think better (see here  and here).  Later on, accumulated memories will certainly make something useful out of what you observe in nature for fun, whether it’s a publishable research project or some extra emotional attachment helping you to find satisfaction and motivation.  Indeed, my paper in GEO: Geography and Environment, and this blog post, were written just for fun and have helped me to recognise how important natural history is for my enjoyment of my job.

Meredith Root-Bernstein is a postdoctoral researcher in the Aarhus University Research on the Anthropocene (AURA) project, based in the Department of Bioscience, Aarhus University, Denmark