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.

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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.

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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

Learning from guano: In search of a paleo-seabird proxy

By Jessica Conroy (University of Illinois Urbana-Champaign, USA)

Take a vacation to the Galápagos Islands and you’re bound to see some of the archipelago’s most colorful denizens perched on guano-splashed basalt rocks, or a sweet ball of puffy white feathers sitting patiently in her nest, waiting for breakfast.

Seabirds like the red-footed and blue-footed booby are some of the unique inhabitants of the Galápagos. Apart from being photogenic, they are impressive animals, with amazing hunting abilities, sometimes flying over 100 km away from their nesting sites in search of food.

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A Genovesa red-footed booby. Credit: Jonathan Overpeck

Seabirds are also harbingers of the large changes sweeping the world ocean. A study of long-term seabird populations shows many species are declining.  Recent research also points to longer-term changes in some seabird populations relative to the last several millennia, likely related to recent human exploitation of the marine ecosystem.

Natural climate and ocean variability can also affect seabird populations. In the tropical Pacific, many species of seabirds suffer the effects of interannual El Niño events, which influences the abundance of seabird prey by altering ocean properties such as temperature and nutrient availability. In the Galápagos, blue-footed booby populations are decreasing, perhaps due to shifts in climate that operate over decades.

It is important to define the natural baseline of these varying populations. In order to place recent changes in a long-term context, scientists must establish the range of natural ups and downs in seabird populations prior to recent changes. But unfortunately, there are very little long-term seabird population data.

Lake sediments have long offered a way to tell us something about past environments– how much it rained, or variations in past temperatures. But, in the right setting, could lake sediments tell us something about seabirds? We thought one such lake may have an interesting story to tell.

Genovesa Island is a small, uninhabited island in the northeastern part of the Galápagos. With no surface water, it is not a tempting site for human settlement; Darwin did not even make it here. But, it is home to thousands of red-footed boobies and lesser numbers of great frigatebirds. According to the only estimate of the island’s bird population in the scientific literature, it is home to the largest colony of red-footed boobies in the world. The birds nest across the island, including the steep crater walls at the center of the island, which shelter a very inaccessible (to humans) crater lake.

The Genovesa seabirds produce large quantities of guano. The crater is streaked in white, and the air has an acrid smell. Some of this guano makes it into the lake, either directly, or by washing in during rainy periods. We hypothesized that there would be a geochemical signal of this guano archived in the lake sediments. One candidate for a paleo-guano proxy was the stable isotopic composition of nitrogen in lake organic matter. The heavier, less abundant stable isotope of nitrogen, 15N, is preferentially sequestered in organisms, with animals higher on the food web containing more 15N relative to 14N. As seabirds sit high on the food web, they, and their guano, have a distinctly high 15N/14N ratio—much higher than the 15N/14N values related to other processes and organisms that are typically found in lake sediments.

We measured 15N/14N in organic matter in Genovesa lake sediments and guano samples. The data, expressed in delta notation, d15N, where the 15N/14N ratio is normalized to the ratio of 15N/14N in air, showed high values in both guano samples and in the sediments, supporting a geochemical signature of seabird presence in the sediment. Although pretty cool, this result has been observed before, in arctic seabird ponds. The most interesting aspect of our study was the variability in d15N values over time.

We found that higher d15N values, which we interpreted as indicating increased seabird activity on Genovesa, coincided with decadal changes in the counts of anchovies and sardines in the eastern Pacific. With more of these fish in the region, d15N was higher, suggesting more seabird activity on the island.  An abrupt increase in d15N also occurred around 1830 AD, right when ocean sediment cores off the coast of Peru and Chile showed increased ocean productivity and nutrients. Another abrupt shift occurred in the mid 1960s. Thus, seabird activity has been highly variable at Genovesa over the last 400 years, increasing and decreasing in concert with decadal and abrupt changes in the ocean environment.

What do these results imply about the seabirds living on Genovesa? They seem to be doing ok, at least in context of last 400 years. Although this year’s monster El Niño event may have a negative impact on seabirds elsewhere in the Galápagos, past observations and our guano proxy suggest Genovesa seabirds don’t seem to feel El Niño events the same way.  But a recent  increase in decade-to-decade ups and downs in the d15N guano proxy record suggests that perhaps Genovesa seabirds are becoming more sensitive to regional ocean and climate changes on the decadal timescale. Or, there may have been a strengthening of climate change on the decadal timescale in this region during the 20th century. We hope to extend our lake sediment record deeper into the past and explore more potential guano indicators in order to find out.

About the author:

Jessica Conroy is an assistant professor in the Departments of Geology and Plant Biology at the University of Illinois Urbana-Champaign.

A response to Mike Hulme’s “Climate and its changes: a cultural appraisal”

By Werner Krauss, University of Hamburg, Germany

A cultural appraisal of climate and its changes is more than only adding social sciences and humanities to climate research; it fundamentally changes the concept of climate change and, as a consequence, the nature of climate politics. For a long time, culture has been considered as the object of analysis for social sciences as their contribution to successfully implementing science-based climate policies. But Mike Hulme (2015) reminds us in a friendly fashion that climate is more than the statistics of average weather or a system of interconnected spheres and global thresholds. For him, climate is first and foremost an idea that helps to stabilise the relationships between cultures and weather, with climate change as the latest step in the cultural evolution of this idea. His approach fundamentally differs from the conception of global climate politics framed by planetary boundaries and aiming at stabilising climate at 2-or less degrees above preindustrial levels; his cultural appraisal suggests an alternative to the regime of experts and the fantasies about the magic of big data and technological solutions.

The anthropologist Melissa Leach once coined in an interview with the Guardian (2007) the drastic term “bullshit research”. She conducted ethnographic research in hot spots of environmental and climate change in Africa, and there the reality she encountered differed profoundly from scientific scenarios. Explaining the causes of drought, of migration or conflict as a result of climate change was more often than not plain wrong; the causes were complex, the scientific attributions were prematurely drawn from model calculations and not based on empirical evidence. Together with James Fairhead, in their book Misreading Landscapes (1996), they documented how scientists and environmentalists had interpreted desertification in the savannah as a result of deforestation by the indigenous population; in reality, it was indigenous people who had planted the existing trees to fight desertification. This case is not unique, and in many case studies, ethnographers find complex realities instead of simple and mono-dimensional explanations like water- or climate-wars.

While Mike Hulme’s article focuses on making a general argument for introducing culture into the debate about a changing climate, there remains the question of what a no-bullshit research agenda might look like. I doubt that “culture” is an appropriate entity for research; while it makes sense to say that “other cultures” have differing concepts of the culture-weather nexus from our “modern” ones, it is impossible to single out specific cultures as consistent and autonomous, even less to delineate a geographical space identical with cultures (even though in climate research, outdated conceptions like culture areas or climate determinism come to life again). But how to conduct climate research and avoid the pitfalls of current top-down conceptions?

In his article, Mike Hulme introduces the concept of landscape to illustrate the “dyad of climate-culture”. Landscapes are far more than visual or aesthetic representations, nor are they static formations frozen in time and space. Instead, they are social practices and designate the process of making space. They are the result of the interaction of nature, culture and history, but also of symbols, perceptions and imaginaries; or, in the terms of Latour’s actor-network-theory, they are networks animated by human and non-human interactions. It is here where we can observe and critically analyse the transition from land- into climate-scapes, with climate politics as one of the main drivers. Landscapes are political assemblies where matters of concern are decided, such as questions concerning property, access to land or weather-related issues like coastal protection or the transition of former rural areas into emerging energy landscapes. To manage landscapes successfully needs the consent of those who inhabit, shape and administer them; only then, climate change indeed means the “re-negotiation of cultural relationships between humans and their changing weather”, and climate change finally becomes an emergent form of life (Callison 2014).

Thus, Mike Hulme indeed offers an approach to climate change that profoundly differs from the current science-based understanding. There is more to his cultural appraisal than simply adding social sciences and humanities to climate science; the question is about differing ideas of governance, of democracy and about power relations, inside science and in the relation between science, politics and society. Conflicts and frictions are unavoidable where expert regimes rub with societies and cultures; instead of dreaming the impossible dream of stabilizing climate, a cultural appraisal of climate offers insight into the potential of specific landscapes to deal with changing climates.

About the author:

Werner Krauss is currently a fellow at the Cluster of Excellence “CliSAP” (Integrated Climate System Analysis and Prediction), University of Hamburg, project “Understanding science in interaction” (USI). As a cultural anthropologist, his main focus of research is on human-environment relationships, the anthropology of landscapes and heritage, and climate change. He is an editor of the climate blog Die Klimazwiebel.

References:

Callison, Candis (2014) How Climate Change Comes to Matter: the Communal Life of Facts. Duke University Press.

Fairhead, J. and M. Leach (1996) Misreading the African Landscape: Society and Ecology in a Forest-Savanna Mosaic. Cambridge University Press.

The Guardian (2007) Melissa Leach: The Village Voice. http://www.theguardian.com/education/2007/jul/17/highereducationprofile.academicexperts (accessed 07/17/2015).

Hulme, Mike (2015) Climate and its changes: a cultural appraisalGeo: Geography and Environment, doi: 10.1002/geo2.5