Palaeobiodiversity research based on stable isotopes: Correction of the sea spray effect on bone carbonate δ13C and δ18O by Gaussian Mixture Model clustering (original) (raw)
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Science of The Total Environment, 2019
Palaeobiodiversity research based on stable isotope analysis in coastal environments can be severely hampered by the so-called "sea spray" effect. This effect shifts the isotopic signal of terrestrial individuals towards too marine values. It is commonly agreed upon that sea spray influences sulphur stable isotopes. However, we were able to approximate a remarkable sea spray effect also in carbon and oxygen stable isotopes of bone carbonate previously. In the present study we could approximate a minimum sea spray effect of about 13.9% even present in oxygen isotope values of bone phosphate, which was validated by Gaussian Mixture Model (GMM) clustering. This approximated value is by some magnitudes smaller than the minimum sea spray effect approximated for both δ 13 C carb and δ 18 O carb , and quite close to the sea spray detected for δ 34 S coll in a previous study. It may therefore be interpreted as purer minimum sea spray signal compared to the approximation in bone carbonate. Furthermore, detection of sea spray in δ 18 O phos can serve as additional validation of the effect present in bone carbonate, which is more prone to diagenetic alteration compared to bone phosphate. Moreover, the presence of the sea spray effect in both δ 18 O carb and δ 18 O phos demonstrates that sea spray can be taken up by terrestrial mammals
Mammalian stable isotope ecology in a Mesolithic lagoon at Skateholm
2002
were subjected to stable carbon and nitrogen isotope analysis, and terrestrial and marine isotopic end-values for the site were established. The various stages that the Baltic Sea has passed through entail varying salinity, and although the correlation between salinity and 13 C is not strictly linear, there is a close correspondence between increasing salinity and increasing 13 C values. Accordingly we used the 13 C values for marine organisms, in this case grey seals, as indicators of the prevailing Baltic Sea stage. The Skateholm I and II settlements coincided with the early Littorina stage of the Baltic-in other words, marine conditions were brackish but not as saline as later on, during the Littorina maximum. The faunal measurements also provide a valuable background for the interpretation of human stable isotope data.
Paleobiology, 2003
Ecomorphological and biogeochemical (trace element, and carbon, nitrogen, and oxygen isotope ratios) analyses have been used for determining the dietary niches and habitat preferences of large mammals from lower Pleistocene deposits at Venta Micena (Guadix-Baza Basin, Spain). The combination of these two approaches takes advantage of the strengths and overcome the weak- ness of both approaches. The range of δ13Ccollagen values for ungulate species indicates that C3 plants were dominant in the diet of these mammals. δ13Ccollagen values vary among ungulates: perissodactyls have the lowest values and bovids the highest ones, with cervids showing intermediate values. The hypsodonty index measured in lower molar teeth and the relative length of the lower premolar tooth row indicate that the horse, Equus altidens, was a grazing species, whereas the rhino, Stephanorhinus etruscus, was a mixed feeder in open habitats. The similar δ13Ccollagen values shown in both perissodactyls does not reflect differences in feeding behavior with other ungulates, but rather a lower isotope enrichment factor in these monogastric herbivores than in ruminants, owing to their lower metabolic efficiency. The cervids Eucladoceros giulii and Dama sp. show low hypsodonty values, indicating that they were mixed feeders or browsers from forested habitats, an ecomorphologically based conclusion corroborated in the former by its low δ15Ncollagen content (canopy effect). Bovid species (Bovini aff. Leptobos, Soergelia minor, and Hemitragus albus) presumably inhabited open environments, according to their comparatively high hypsodonty and δ15Ncollagen values. Carnivore species (Homotherium latidens, Megantereon whitei, Pachycrocuta brevirostris, Canis falconeri, and Canis etruscus) exhibit higher δ15Ncollagen values than ungulates. These results record the isotopic enrichment expected with an increase in trophic level and are also supported by low bone Sr:Zn ratios. The elevated δ15Ncollagen value for a sample of Mammuthus meridionalis, which came from an individual with unfused epiphyses, confirms that it was a suckling animal. The δ15Ncollagen value of the scimitar-cat H. latidens is well above that obtained for the young individual of Mammuthus, which indicates that juvenile elephants were an important part of its diet. The hippo, Hippopotamus antiquus, yielded unexpectedly high δ15Ncollagen values, which suggest feeding on aquatic, non-N2-fixing plants. The high δ18Ohydroxyl values of bovids Hemitragus and Soergelia and of cervid Dama indicate that these ungulates obtained most of their water requirements from the vegetation. The megaherbivores and Eucladoceros exhibit the lowest δ18Ohydroxyl values, which suggest increased water dependence for them. Paleosynecological analysis was based on the relative abundance of species of large mammals from different ecological categories, determined by feeding behavior and locomotion types. The comparison of the frequencies of such categories in Venta Micena with those found in modern African communities indicates that the composition of the paleocommunity closely resembles those of savannas with tall grass and shrubs. The net above-ground primary productivity estimated for the on-crop biomass of the mammalian species preserved in the fossil assem- blage also yields a figure congruent with that expected for an open environment.
Differentiating aquatic mammal habitat and foraging ecology with stable isotopes in tooth enamel
2001
We analyzed the carbon and oxygen isotope composition of tooth enamel from mammals inhabiting marine and terrestrial ecosystems to determine whether these stable isotopes were robust indicators of foraging and habitat preferences. Consumers were separated into six habitats (offshore, nearshore, kelp beds, estuarine, freshwater, terrestrial). Consumer δ13C values were correlated with the δ13C values of primary producers within each habitat, suggesting that δ13C values of tooth enamel are a viable proxy for foraging zones. Offshore and terrestrial consumer δ13C values were not significantly different, however, indicating that carbon isotope analysis alone is not sufficient to distinguish foraging within these two ecosystems. We propose that oxygen isotopes can be used along with δ13C values to further clarify habitat use. Oxygen isotopes were assessed as an indicator of habitat use. Consumers were grouped into four categories: aquatic-marine, aquatic-estuarine, aquatic-freshwater, and terrestrial. Populations of aquatic taxa had significantly lower standard deviations for δ18O values than those of terrestrial taxa. Mean δ18O values of aquatic taxa were significantly different among groups, but surprisingly, the mean values for freshwater taxa were higher than those for marine taxa. We conclude that variation in δ18O values of mammalian populations is a valid indicator of aquatic habits, but that mean δ18O values should be utilized with caution when trying to discriminate between marine and freshwater habitat use. Together, δ13C and δ18O values serve as valuable tools for identifying foraging and habitat preferences in modern marine and terrestrial ecosystems, and may provide similar information on ancient ecosystems.
Paleobiology, 2003
Ecomorphological and biogeochemical (trace element, and carbon, nitrogen, and oxygen isotope ratios) analyses have been used for determining the dietary niches and habitat preferences of large mammals from lower Pleistocene deposits at Venta Micena (Guadix-Baza Basin, Spain). The combination of these two approaches takes advantage of the strengths and overcome the weakness of both approaches. The range of ␦ 13 C collagen values for ungulate species indicates that C 3 plants were dominant in the diet of these mammals. ␦ 13 C collagen values vary among ungulates: perissodactyls have the lowest values and bovids the highest ones, with cervids showing intermediate values.
Using stable isotope biogeochemistry to study marine mammal ecology
Marine Mammal Science, 2010
Stable isotope analysis (SIA) has emerged as a common tool in ecology and has proven especially useful in the study of animal diet, habitat use, movement, and physiology. SIA has been vigorously applied to the study of marine mammals, because most species live in habitats or undergo large migrations/movements that make them difficult to observe. Our review supplies a complete list of published SIA contributions to marine mammal science and highlights informative case examples in four general research areas: (1) physiology and fractionation, (2) foraging ecology and habitat use, (3) ecotoxicology, and (4) historic ecology and paleoecology. We also provide a condensed background of isotopic nomenclature, highlight several physiological considerations important for accurate interpretation of isotopic data, and identify research areas ripe for future growth. Because it is impossible to conduct controlled laboratory experiments on most marine mammal species, future studies in marine mammal ecology must draw on isotopic data collected from other organisms and be cognizant of key assumptions often made in the application of SIA to the study of animal ecology. The review is designed to be accessible to all audiences, from students unfamiliar with SIA to those who have utilized it in published studies.
Identifying Aquatic Habits Of Herbivorous Mammals Through Stable Isotope Analysis
Palaios, 2008
Large-bodied, semiaquatic herbivorous mammals have been a recurring component of most continental ecosystems throughout the Cenozoic. Identification of these species in the fossil record has largely been based on the morphological similarities with present-day hippopotamids, leading to the designation of this pairing of body type and ecological niche as the hippo ecomorph. These morphological characters, however, may not always be diagnostic of aquatic habits. Here, enamel ␦ 13 C and ␦ 18 O values from living hippopotamuses were examined to define an isotopic signature unique to the hippo ecomorph. Although ␦ 13 C values do not support unique foraging habits for this ecomorph, living and fossil hippopotamids typically have low mean ␦ 18 O values relative to associated ungulates that fit a linear regression (␦ 18 O hippopotamids ؍ 0.96 ؎ 0.09· ␦ 18 O fauna Ϫ 1.67 ؎ 2.97; r 2 ؍ 0.886, p Ͻ 0.001). Modeling of oxygen fluxes in large mammals suggests that high water-turnover rates or increased water loss through feces and urine may explain this relationship. This relationship was then used to assess the aquatic adaptation of four purported hippo ecomorphs from the fossil record: Coryphodon (early Eocene), Moeritherium and Bothriogenys (early Oligocene), and Teleoceras (middle-late Miocene). Only fossil specimens of Moeritherium, Bothriogenys, and large species of Coryphodon had ␦ 18 O values expected for hippo ecomorphs; ␦ 18 O values for Teleoceras and a small species of Coryphodon were not significantly different from those of the associated fauna. These results show that the mean ␦ 18 O value of fossil specimens is an effective tool for assessing the aquatic habits of extinct species.
Stable isotope analysis of mammalian tooth enamel is a valuable method for examining resource partitioning in modern and ancient environments where there is a mixture of C3 and C4 plants. However, before 7 Ma North American ecosystems were composed predominantly of C3 plants, complicating isotopic assessment of resource partitioning. Study of modern African and North American ecosystems has shown that niche partitioning among mammals may be discerned in communities dominated by C3 plants, suggesting that a similar approach may work for ancient C3 ecosystems. Here, such analyses are applied to explore resource use and niche partitioning in two ancient C3-dominated communities, one from California and one from Florida. Each locality, Black Hawk Ranch (California) and the Love Bone Bed (Florida), occurs in Miocene deposits that accumulated prior to the rapid increase in C4 ecosystems 7 Myr ago. δ13C and δ18O values were obtained from the tooth enamel of eight species from Black Hawk Ranch, and 15 species from the Love Bone Bed. Results from the 197 bulk isotope samples showed significant differences in δ13C among taxa at the Love Bone Bed, but no significant differences were observed among taxa at Black Hawk Ranch. At both localities, equids generally have more positive δ13C values than co-occurring taxa, suggesting that equids occupied more open habitats, whereas antilocaprids, camelids, and proboscideans have more negative values, implying utilization of more closed communities. One result of note is the positive δ13C values of Pediomeryx (Yumaceras) hamiltoni from the Love Bone Bed, which suggests that P. (Y.) hamiltoni incorporated abundant fiber, possibly grass, in the diet similar to the horses from this locality. The lack of significant differences among taxa at Black Hawk Ranch may indicate a relatively homogeneous flora, or presence of abundant resources permitting niche overlap, whereas the opposite is implied by the presence of significantly different isotope values among taxa at the Love Bone Bed. The results from this study highlight the utility of isotopic techniques allowing discernment of resource partitioning in C3-dominated landscapes such as those that persisted for the millions of years before the rapid increase in C4 ecosystems that occurred during the late Miocene.
Climatic and environmental shifts have had profound impacts on faunal and floral assemblages globally since the end of the Miocene. We explore the regional expression of these fluctuations in southwestern Europe by constructing long-term records (from ,11.1 to 0.8 Ma, late Miocene-middle Pleistocene) of carbon and oxygen isotope variations in tooth enamel of different large herbivorous mammals from Spain. Isotopic differences among taxa illuminate differences in ecological niches. The d 13 C values (relative to VPDB, mean 210.361.1%; range 213.0 to 27.4%) are consistent with consumption of C 3 vegetation; C 4 plants did not contribute significantly to the diets of the selected taxa. When averaged by time interval to examine secular trends, d 13 C values increase at ,9.5 Ma (MN9-MN10), probably related to the Middle Vallesian Crisis when there was a replacement of vegetation adapted to more humid conditions by vegetation adapted to drier and more seasonal conditions, and resulting in the disappearance of forested mammalian fauna. The mean d 13 C value drops significantly at ,4.223.7 Ma (MN14-MN15) during the Pliocene Warm Period, which brought more humid conditions to Europe, and returns to higher d 13 C values from ,2.6 Ma onwards (MN16), most likely reflecting more arid conditions as a consequence of the onset of the Northern Hemisphere glaciation. The most notable feature in oxygen isotope records (and mean annual temperature reconstructed from these records) is a gradual drop between MN13 and the middle Pleistocene (,6.320.8 Ma) most likely due to cooling associated with Northern Hemisphere glaciation.