A brief hiatus……

My apologies dear SIWG members and followers of this blog for the brief hiatus in blog posts. As you can imagine with the opening of borders with the advent of the COVID vaccines, there has been a race to catch up fieldwork and sample collections. As a result, the contributions from researchers have slowed to a halt.

In addition, I will be moving from ICArEHB in Portugal (☹) to a new position in Berlin at the DAI (😊) as their new archaeozoologist. This has meant that I have been focused on finishing academic and personal projects before my family and I move to Berlin in December. I am very sad to be leaving Portugal, but we have built an amazing new isotope preparation lab and I will continue to be providing support to the ICArEHB family in stable isotopes and archaeozoology. But I am also very excited to start at the DAI, and looking forward to building new projects with colleagues in Germany and across the world.

To kick start the new ‘term/semester’, I have been thinking of blog posts about open access databases (IsoArch, ISOBANK and Neotoma), following on from Suzanna Pilaar-Birch’s workshop with the Neotoma database, and discussing the merits of each and which one you should choose; to ensuring good standards of reporting methods and results for transparency. However, I thought I would start the to start with a discussion about landscape reconstruction.

Last week, I published together with my colleagues from Kiel and Belgrade, a paper about the livestock management and land-use during the late Vinča period in Serbia at the incredible sites of Vinča-Belo brdo and Stubline. This study is a part of a large sampling program of bones and teeth from domesticate and wild animals from the two sites. Our first paper concerned the stable isotope results from bone collagen. In this paper, we found a large variability in δ13C/δ15N results in cattle from Vinča-Belo brdo in comparison form cattle from Stubline, who may have been pastured in forested/wetland areas. While sheep and pigs appeared to have been fed similar diets possibly being kept within the settlements. Wild animals, mainly deer and wild pigs, ranged wide habits including forests (figure of results).

The results from stable carbon and nitrogen isotopic analysis of bone collagen samples from Vinča-Belo brdo.
The results from stable carbon and nitrogen isotopic analysis of bone collagen samples from Stubline.

The recently published paper in PLOS-ONE focused on the results from the sequential sampling of bioapatite from cattle, sheep/goat, pig, and deer teeth. Sequential sampling allows an examination of individual life histories, via δ18O/δ13C. The oxygen isotope provides a seasonal framework to examine variation in plant δ13C foliar values. Carbon isotopes can detect different plant types e.g. C3 plants which a predominant plant type found in Serbia. The carbon isotopes of C3 plants are particularly sensitive to changes in their growing conditions 1. Our results echoed the results from the bone collagen analysis but also provided more clarity about the types of pasture that different species may have used and highlighted potential differences in management practices for sheep and cattle.

The variation seen in cattle bone collagen prevailed in the bioapatite samples, with little similarity between individuals (see here). Some individuals were grazed with open environments while others may have been kept for parts of the year in forested/waterlogged environments. Whereas sheep appeared to be managed very similar at both sites with little variation between individuals (see here). What is intriguing is the variation in δ13C from   ̶ 8‰ to   ̶ 14‰, with the depleted values occurring during winter.

We proposed that this variation was in part by plants growing under high temperatures during summer, perhaps within halophyte communities within relic river channels, when one considers the dynamic fluvial landscape of the Danube. During winter, herds may have been kept within the settlements and fed on collected fodder, such as leafy hay from riverine forest environments. Overall, it supports a uniform herding strategy in contrast with that of cattle.

Pasture reconstruction based on study results. The base images were made available on the ‘Nature scenes with fields’ https://www.vecteezy.com/vector-art/605564-nature-scenes-with-fields-and-mountians licensed to REG. The animal silhouettes are available under CC 4.0 from ArcheoZoo.org.

This is one interpretation of the results, and another group of researchers may interpret the data differently, for example Balasse et al. 20172. Balasse et al. (including myself) studied the material from Popină Borduşani along with other Late Neolithic/Eneolithic sites from the Danubian corridor in Romania. Again, bone collagen and enamel bioapatite wild and domesticated animals were analysed providing a multi-faceted view of animal management. Similar enriched carbon isotope values were interpreted as potential the consumption of C4 plants growing as weeds near the settlement.

These studies highlight differences in pasture use and management that may occur in similar environments. To increase our understanding of past herding practices, future studies need carry out comprehensive sampling and analytical programs of wild and domesticated animals from well preserved archaeological sites, where both bone collagen and enamel bioapatite ared analysed. This would allow for greater resolution of past husbandry practices as well as the landscape in which these herds lived and died.

To move forward to create better interpretive frameworks, we need to build detailed databases of carbon and nitrogen, as well as other isotopes, from ecological studies and analysis of local reference material much in the way is crucial for Strontium isotopes studies. We may never be able to say definitively sheep X lived off a diet of turnips in the winter and rich clover meadows during summer. But we can move to increasing the resolution of past herding strategies via improved sampling and multi-isotopic approaches.

1             Tieszen, L. T. Natural variations in the carbon isotope values of plants: Implications for Archaeology, Ecology and Paleoecology. Journal of Archaeological Science 18, 227-248 (1991).

2             Balasse, M. et al. Investigating the scale of herding in Chalcolithic pastoral communities settled along the Danube River in the 5th millennium BC: A case study at Borduşani-Popină and Hârşova-tell (Romania). Quat. Int. 436, 29-40, doi:10.1016/j.quaint.2015.07.030 (2017).

Gray wolves survived Ice Age extinction event by changing their diets – which may help them cope with ongoing climate change

Zoe Landry @zoey_landry

Master’s student in Biology at Carleton University, soon to be PhD student at the University of Ottawa and member of the SAiVE Lab

Climate change is arguably one of the biggest issues that the Earth is currently facing. Ecosystems all over the world are being affected in different ways, with northern ecosystems being some of the most severely impacted. The Canadian Arctic is currently warming at nearly double the rate of the global average, which is drastically altering the Arctic environment. The effects of climate change will be felt long past our lifetimes, but how exactly climate change will impact northern species, some of which are not found anywhere else in the world, is unknown.

            An unparalleled tool for investigating the long-term responses of species to climate change is, fortunately, available in the form of the fossil record. In the Yukon Territory of Canada, there is a diverse array of fossils from the last Ice Age that provide an excellent opportunity to study the effects of climate change on ancient animals. The end of the Ice Age is characterized by a global shift in climate, with warming temperatures and melting glaciers, culminating in an extinction event where about 70% of large mammal genera died out in North America – similar to what we are seeing in the Canadian Arctic today. One of the most abundant fossil animals found in the Yukon is the gray wolf (Canis lupus), which to this day still calls the Yukon home. Ancient wolves managed to survive the extinction event at the end of the Ice Age, but how did they do so, when so many other species did not? Could wolves have changed aspects of their ecology, such as their diets, over time to cope with environmental changes?

Zoe Landry, lead author of the study, holds a 40,000-year-old gray wolf skull from the Yukon. Credit: Danielle Fraser, © Canadian Museum of Nature.

My colleagues and I set out to investigate these questions, using a combination of two different methods: dental microwear and stable isotope analyses in a recent paper. We studied both Ice Age and recent (circa 1960s) gray wolf specimens from the Canadian Museum of Nature, in Ottawa, Ontario, and the Beringia Interpretive Center (Yukon Government), in Whitehorse, Yukon. By comparing the dietary ecology of modern and ancient wolves, we can better understand how wolves responded to past climatic disturbances, and how they may respond at present and in the future.

Zoe Landry and Danielle Fraser prepare for sampling.

Dental microwear analysis

            Dental microwear analysis involves observing microscopic wear patterns on the surface of animal teeth. Through observations of these patterns, we can make inferences about the types of food an animal ate during the last few days to weeks prior to its life. There are two main types of dental wear: pits and scratches. Pits are small, circular features that are caused by an animal consuming hard food – in the case of carnivores, pits indicate that the animal was eating bones. Scratches are long, linear features that are generated when the teeth of carnivores slide against each other to slice meat from prey.

Our dental microwear analysis revealed very similar wear patterns between both the Ice Age wolves and the recent wolves, which indicated that both groups primarily consumed flesh. This is especially interesting, as previous studies had suggested that during the Ice Age, wolves were scavengers that fed on the remains of animals that other carnivores had killed. We can conclude that gray wolves have maintained their status as competitive hunters over thousands of years, and that actively taking down prey is an important aspect of wolf ecology that is unlikely to change even as their habitat does.

Top: Taking moulds of teeth; Bottom: SEM of tooth surface. Credit: Danielle Fraser

Stable isotope analysis

Stable isotope analyses were performed at the University of California, Merced, by Dr. Sora Kim and Dr. Robin B. Trayler. We analyzed the δ13C and δ15N values from both bone carbonates and collagen. There were minimal changes in the δ13C values between the two groups, which suggest that wolves have remained generalist predators that hunted a variety of large herbivores. There was a very clear difference in δ15N values between the Ice Age and recent wolves, which we determined to be driven by a change in the main prey species that the wolves were hunting.

Zoe sampling material for stable isotope analysis. Credit: Danielle Fraser

Based on diet modelling, we discovered that the primary prey of wolves during the Ice Age were horses (Equus sp.), with moderate contributions from other herbivores, such as caribou (Rangifer tarandus) and muskox (Ovibos moschatus). Obviously, there are not huge herds of wild horses in the Yukon today, as they were one of the species that went extinct in North America at the end of the Ice Age. Instead, gray wolves that inhabit the modern Yukon rely mainly on hunting caribou and moose (Alces alces) to fulfill their dietary needs. This shift from a diet composed largely of horse to one of caribou and moose indicate that the survival of wolves is not fixed on a single prey species. Rather, gray wolves are able to shift their diets from one species to another, and are capable of surviving significant climatic and environmental changes, provided that they have access to a sufficiently large population of large-bodied herbivores.

Implications for wolf conservation

            Our study revealed that gray wolves from the Yukon were able to survive the threat of extinction at the end of the Ice Age by changing their diets to target different prey species, and are very adaptable predators. The key to modern wolf survival is the survival of their current prey species, caribou and moose. Conservation efforts should focus on preserving these large herbivores, and ensuring that their populations remain healthy and at stable sizes as the Arctic environment changes. The continued survival of grey wolves in the Yukon is directly linked to these animals, which further demonstrates the important role of caribou and moose in the Canadian Arctic.

We acknowledge that the institutions at which this research took place are located on the traditional and unceded territories of the Algonquin, Anishnaabeg People, the Yokuts and Miwuk People, the Taa’an Kwächän and Kwanlin Dün People. We are grateful to the placer gold mining community and the Tr’ond¨ek Hw¨ech’in First Nation for their continued support and partnership with our research in the Klondike goldfields region; and the Vuntut Gwitchin First Nation for their collaboration with research in the Old Crow region. This research was funded by: Canadian Museum of Nature Research Activity Grant, and Natural Sciences and Engineering Research Council of Canada Discovery Grant (RGPIN-2018-05305), awarded to my supervisor, Dr. Danielle Fraser; and by funds of the Yukon Palaeontology Program of the Yukon Department of Tourism and Culture, contributed by Dr. Grant Zazula.

Forest pasturing and foddering: stable isotope prespectives

The use of forests for pasturing and fodder resources remains globally an important, preventing over-grazing and providing complementary fodder in times of poor pasture. Traditionally, forests in Europe were a rich source of collected forage (leafy hay) in the form of branches and leaves. At the same time, herd animals can have a negative impact on forests, where grazing is unchecked. The first herders of Central and Northern Europe experienced a landscape ‘Bristling with forests and foul swamps’ as described by Tacitus in 98AD [1]. The impact of animals on forests has been a focus of archaeologists for over 40 years. For example, Iversen [2] highlighted the importance of cattle in the expansion of the initial Neolithic settlements in his landam theory. The elm decline was initial contributed to increased use of leafy hay as animal forage.

How can we study forest pasture and foddering via stable carbon isotopes?

The canopy effect is where plants growing under dense forest canopies will exhibit depleted δ13C values. This is due to a combination of carbon -13 depletion of atmospheric CO2 under the canopy caused by CO2 respired by decaying organic matter and low light intensity at the forest floor decreasing photosynthesis efficiency. Consequently, animals browsing and grazing under heavy forest canopies or being fed leafy hay from these environments will exhibit low carbon isotope values in their tissues. Using this principal, researchers such as Dorothee Drucker and Rhiannon Stevens have explored the use of forests by wild ruminants past and present.

Schematic of the Canopy effect on δ13C values of plants growing under different canopy densities and its relationship to different ruminant tissues (cone collagen/enamel bioapatite)

A cautionary note

The issue of equifinality can arise with the interpretation of stable isotopic values because different growing environments can produce similar effects on the stable isotopic ratios of plants. These continue up the food chain. For example, waterlogged environments can have a similar impact on δ13C values of plant communities as a dense forest canopy. Lynch and colleagues interpreted depleted δ13C values observed in British aurochs as a reflection of animals feeding on plants from waterlogged environments. Whereas, a similar study by Noe-Nygaard and colleagues of Scandinavian aurochs suggested these animals were forest dwellers. This is why it is key prior to the interpretation of stable isotopic results that robust interpretative frameworks using paleoenvironmental are created for testing hypotheses.

Independent methods for determining forest foddering

Compound-specific stable nitrogen isotope analysis of collagen amino acids provides an independent means for identifying consumption of woody plants, such as leafy hay. Developed by researchers at University of Bristol, direct evidence of the plant composition of animal fodder (woody/herbaceous) can be uncovered using the dietary β values based on δ15N CSIA of amino acids from incremental samples of dentine from cattle molars. These values represent the Δ15NGlx-Phe values of the plants at the base of the food web, using a known trophic offset of −4.0‰ between cattle and their diet. The dietary β values are then be compared with established ranges of Δ15NGlx-Phe values expected for herbaceous (−5.4±2.1‰) and woody plants (−9.3±1.6‰), based on modern references. Combining incremental analysis of enamel bioapatite and CSIA-AA of dentine of the same tooth provides a powerful method to identify forest pasturing and seasonal use of leafy-hay.

Look out for upcoming papers by myself and colleagues from University of Bristol, and European institutions from Hungary, Poland, France and Germany, discussing the role of forests in LBK cattle husbandry uncovered during the NeoMilk project (ERC-advance awarded to Prof. Richard Evershed).

References

1. Bogucki, P., 1988. Forest farmers and stockholders. Early agriculture and its consequences in North-Central Europe. Cambridge: Cambridge press.

2. Iversen, J., 1969. The influence of prehistoric man on vegetation, in The Neolithisation of Denmark: 150 years of debate., A. Fischer and K. Kristiansen, Editors. Sheffield Archaeological Monographs: Sheffield. p. 105-16.