Técnicas e Instrumentos de Recolección de Datos

1.5.1

Goals of the dissertation

There is a growing body of work using isotopic compositions of megafauna to understand the ecology of the mammoth steppe. The majority of work on collagen in the mammoth steppe has focused on single sampling of bone or adult teeth. Bone provides a time- averaged signal of the last several years of an animal’s life (Balasse et al., 1999; Koch et al., 1994).

Teeth and tusk, by comparison, provide a “snapshot” view of an animal’s life, as the collagen in teeth and tusk is deposited once and not remodelled over an animal’s lifetime (Koch et al., 1994; Metcalfe et al., 2010). Measuring the isotopic composition of an adult tooth or tusk is also commonly used to assess the isotopic composition of the adult diet of the animal, in the same manner that bone collagen is used (e.g. Mann et al., 2013;

Metcalfe et al., 2013; Szpak et al., 2010). This approach, however, is made more

powerful by taking multiple samples, typically of smaller size, from an individual tusk or tooth to investigate seasonal or yearly changes. This approach is invaluable for

investigating signals that are not generated year-round – for example, weaning happens once in an animal’s lifetime, pregnancy occurs seasonally for species such as caribou (Finstad and Kielland, 2011) and many dietary resources are population-limiting

seasonally rather than year-round (Adamczewski et al., 1988; Heggberget et al., 2002). In situations such as these, isotopic compositions can reveal dietary switching over time (Peterson and Fry, 1987). One study has examined the differences in the isotopic

composition of woolly mammoth teeth formed at different ages to assess the timing of nursing and weaning (Metcalfe et al., 2010), and another studied serially sampled increments of a juvenile mammoth’s tusk to assess age of weaning (Rountrey et al., 2007). Moving beyond collagen as the tissue examined, still other studies have serially sampled woolly mammoth hair (Iacumin et al., 2006, 2005), horse tooth enamel

(Bellissimo, 2013) and tusk enamel of woolly mammoths (Fox et al., 2007) to investigate seasonal changes in the species.

There remain, however, a number of unresolved questions concerning the ecology of the mammoth steppe:

(1) Extensions of the serial sampling approach to other tissues, such as antler, and to other species should allow more exploration of seasonal changes within the mammoth steppe.

(2) Isotopic work to date on the mammoth steppe has focused on bulk tissue isotopic analysis. While the isotopic compositions of both carbonate and phosphate components of bioapatite from mammoth steppe animals are now routinely measured and interpreted (e.g. Bellissimo, 2013; Fox et al., 2007), only bulk protein from keratin and collagen has been analysed for these animals. Individual amino acid analysis, by comparison, has proven invaluable for elucidating an individual’s trophic level and the major components of their diet in a number of modern (e.g. Hannides et al., 2009; Miller et al., 2012; Popp et al., 2007;

Sherwood et al., 2011) and archeological studies (e.g. Fogel and Tuross, 2003; Naito et al., 2010; Styring et al., 2010). This method has the potential to provide insight into the diet of several species from the mammoth steppe, and to better resolve their ecology. For example, its application to woolly mammoth collagen could resolve the “woolly mammoth conundrum”. It could also help to better resolve the diet of a variety of herbivores, using the 15N of source amino acids (McCarthy et al., 2007; McClelland and Montoya, 2002; Popp et al., 2007) and linear discriminant analysis classification of amino acid δ13C (Larsen et al., 2013, 2012, 2009).

(3) While there have been numerous studies of bulk collagen isotopic compositions of megaherbivores from the mammoth steppe (e.g. Bocherens et al., 2011, 1994; Drucker et al., 2003a, b; Fizet et al., 1995; Fox-Dobbs et al., 2008; Iacumin et al., 2010; Mann et al., 2013; Metcalfe, 2011; Metcalfe et al., 2013; Raghavan et al., 2014; Stevens et al., 2009; Szpak et al., 2010), reviews that integrate and explain the metadata arising from these studies are few (Bocherens, 2015, 2003). Several studies investigate multiple species, time periods or sites across the mammoth steppe. However, no single study has simultaneously examined the changes in published δ13CBulk and 15NBulk for all megaherbivore species among different

sites and time periods. As well, overlaps in the isotopic composition of species, such as those observed for the 15N of horse and mammoth in Germany and Ukraine (Bocherens, 2015), have not been quantified using models of isotopic niche. Mathematical tools such as SIBER (Jackson et al., 2011; Parnell et al., 2010) are being increasingly used in ecological work to provide insight into niche size and the degree of niche overlap between species, and thus the way that different species use and share resources (Layman et al., 2012). These tools could help to understand ecological patterns and changes over time, and between geographic areas.

To understand the mammoth steppe, the ecology of the species that inhabited it must be understood on both the individual and population levels. This thesis will accomplish this through applications of ecological techniques that have not been previously used in the mammoth steppe:

(1) I examine seasonal changes and individual animal responses through changes in the isotopic composition over the length of an antler and comparison between this tissue and bone.

(2) I use amino acid δ13C and 15N to separate dietary and metabolic isotopic signals, allowing me to better understand and classify herbivore and carnivore diets. (3) I use SIBER analyses to understand the resource use of animal populations and

Using these techniques, I am able to assess the typical megafaunal ecology of the

mammoth steppe, as well as to assess ecological responses to climatic and anthropogenic changes over time and between geographic locations.

1.5.2

Organization of the dissertation

This thesis is composed of four distinct research chapters (Chapters 2 through 5), each of which is prepared as a stand-alone article for publication, plus this introduction (Chapter 1) and some broader conclusions (Chapter 6). Supplementary tables and figures for Chapters 2-5 are contained in the appendices.

Chapter 1 provides a general introduction to the mammoth steppe, carbon and nitrogen isotopic systematics of plants and animals, and a review of relevant previous isotopic investigations, with a focus on animal collagen.

Chapter 2 examines the carbon and nitrogen isotopic compositions of collagen from elk, moose and caribou antler and bone. As these tissues that have different growth periods, their isotopic compositions can provide a seasonal signal (antler) and an annual signal (bone). We serially sampled antler to investigate the changes in its isotopic composition over a single season, and compared antler isotopic compositions with those of bone to determine seasonal ecological differences as well as differences through the Late Pleistocene and Holocene. We establish that the isotopic compositions of antlers cannot be directly compared to those of bone when reconstructing a species’ diet, and that each tissue provides a distinct set of ecological information concerning that species.

Chapter 3 examines the characteristic but anomalously high woolly mammoth bulk collagen 15N using a source (phenylalanine) and trophic (glutamate) amino acid. Using this approach, we established that the woolly mammoth ate a distinct diet or lived in a distinct habitat within the mammoth steppe. In some cases, this habitat may have been shared with horse. Understanding that the woolly mammoth’s high 15

NBulk arose from a

dietary or habitat source provides insight into the ecology of a keystone herbivore of the mammoth steppe, which provides a starting point to investigate the rest of the megafaunal species.

Chapter 4 further investigates the isotopic compositions of amino acids in mammoth steppe herbivores and carnivores. The 15N of 8 amino acids are used to establish the trophic position of a variety of megaherbivores and megacarnivores, and to establish that there likely were differences in the plant types consumed by certain species or

individuals. These differences are further evaluated using the δ13C of 9 amino acids. We use LDA of the δ13C for 7 of these amino acids to classify the diets of each herbivore individual, and of the herbivores consumed by the carnivores. Differences in δ13CBulk and

15

NBulk are linked to differences in diet, such as the consumption of aquatic plants by the

giant beaver and decayed plants by horse and woolly mammoth.

Chapter 5 integrates data for δ13CBulk and 15NBulk of megaherbivores from numerous sites

across the mammoth steppe. Using SIBER (Jackson et al., 2011), isotopic niche spaces were defined for each herbivore at each site for four time periods (pre-LGM, LGM, post- LGM and Holocene). Species are shown to have had consistent niche positions and niche overlaps across the mammoth steppe before the LGM. These niches were disrupted during the LGM, and were not re-established post-LGM. This analysis suggests that a major ecosystem shift occurred during the LGM that weakened the ecosystem’s stability as a whole, and made it more susceptible to changes from other climatic or anthropogenic effects.

Chapter 6 summarizes the previous chapters and discusses the implications of these new data for our understanding of the mammoth steppe as a whole.