Modern Food Webs Research Articles

A new era of isotope ecology: Nitrogen isotope ratio of amino acids as an approach for unraveling modern and ancient food web.

Food web research is rapidly expanding through study of natural fractional abundance of 15N in individual amino acids. This paper overviews the principles of this isotope approach, and from my perspective, reanalyzes applications, and further extends the discussion. It applies kinetic isotope effects that enriches 15N in certain amino acids associated with the metabolic processes, which was clearly demonstrated by observations of both natural ecosystem and laboratory experiments. In trophic processes 'trophic amino acids' such as glutamic acid that significantly enrich 15N, whereas 'source amino acids' such as phenylalanine and methionine show little 15N enrichment. Through various applications conducted over the years, the principles of the method have shown to operate well and disentangle complex food webs and relevant problems. Applications include food chain length estimate, nitrogen resource assessment, tracking fish migration, and reconstruction of paleodiet. With this approach, considerations of a wide range of classical issues have been reinvigorated, while in the same time, new challenging frontiers are emerging.

Tooth enamel nitrogen isotope composition records trophic position: a tool for reconstructing food webs

Nitrogen isotopes are widely used to study the trophic position of animals in modern food webs; however, their application in the fossil record is severely limited by degradation of organic material during fossilization. In this study, we show that the nitrogen isotope composition of organic matter preserved in mammalian tooth enamel (δ15Nenamel) records diet and trophic position. The δ15Nenamel of modern African mammals shows a 3.7‰ increase between herbivores and carnivores as expected from trophic enrichment, and there is a strong positive correlation between δ15Nenamel and δ15Nbone-collagen values from the same individuals. Additionally, δ15Nenamel values of Late Pleistocene fossil teeth preserve diet and trophic level information, despite complete diagenetic loss of collagen in the same specimens. We demonstrate that δ15Nenamel represents a powerful geochemical proxy for diet that is applicable to fossils and can help delineate major dietary transitions in ancient vertebrate lineages.

Reconstructing trophic position over the past century for five Puget Sound fish species

The comparison of historical and modern food web dynamics allows ecologists to test whether the trophic connectivity we observe today is ‘normal’ in its historical context. Fish densities and abundances have changed across time, making it likely that fish trophic interactions and their trophic positions have also changed. Historical trophic data of marine fishes can now be extracted from the tissues of fluid-preserved specimens held in natural history collections via compound-specific stable isotope analysis of amino acids (CSIA-AA) of nitrogen. We conducted CSIA-AA to quantify trophic position change over the past century in 5 ecologically important fishes of Puget Sound, Washington, USA: Pacific hake Merluccius productus, walleye pollock Gadus chalcogrammus, copper rockfish Sebastes caurinus, English sole Parophrys vetulus, and Pacific herring Clupea pallasii, and examined the canonical trophic (glutamic acid) and source (phenylalanine) amino acids. For all fishes except copper rockfish, trophic position, glutamic acid, and phenylalanine values remained similar across time. For copper rockfish, glutamic acid but not phenylalanine values increased over time, indicating an increase in this species’ trophic position. The observed increase in copper rockfish trophic position may be a function of diet switching and declining prey quality rather than a consequence of rockfish consuming higher trophic level prey. This study leverages more than 100 yr of trophic data of fishes representing various feeding guilds and demonstrates that some fish species may be more trophically resilient to major environmental change than expected. Efforts should be made to identify and conserve the trophic interactions of species experiencing change.

Seasonality or short-term mobility among trophy head victims and villagers?: Understanding late-life dietary change in the pre-Hispanic Andes through stable isotope analysis (δ13C/δ15N) of archaeological hair keratin and bone collagen

ObjectivesThis study aims to determine whether adults from the site of Uraca in the Lower Majes Valley, Arequipa, Peru altered their diets in late-life—if so, were those short-term changes related to accessing distinct foods during periods of short-term mobility, seasonal subsistence strategies without accompanying mobility, or some other type of short-term change. We address these questions by comparing stable isotope variability (δ13C/δ15N) of Uraca hair keratin and bone collagen to published archaeological hair data from Peru. We propose and apply a landscape bioarchaeology approach—here, the spatially-informed meta-analysis of published δ13C/δ15N data from archaeological hair keratin of known provenience—to determine thresholds for different types of short-term dietary change. Materials and methodsWe conducted stable isotope analysis (δ13C/δ15N) of archaeological hair keratin (n = 40 samples) and bone collagen (n = 5 samples) from Uraca, including adult male trophy heads and adult male and female villagers. We then compiled published archaeological hair keratin data from the Andes and coded the 11 sites according to biogeographical zones. We compared late-life averages for the entire dataset (n = 131 segments) and ranges for individuals with more than six months of data (n = 101 segments) between sites and between subgroups based on elevational zones, sex, and trophy subgroupings. We compiled archaeological and modern baseline food web data for the region (n = 401 samples) and compared hair data adjusted to diet. ResultsMeta-analysis shows greater late-life median δ13Ckeratin (VPDB) and δ15Nkeratin (AIR) for yunga vs. coastal burials, greater δ13Ckeratin (VPDB) ranges for coastal burials, greater δ15Nkeratin (AIR) ranges for females, greater median δ15Nkeratin (AIR) for trophy individuals, and greater δ13Ckeratin (VPDB) ranges for trophy individuals. Given these distinct late-life diets and ranges for coastal and yunga burials relative to southern Peruvian food web data, two females and three trophy individuals from Uraca likely changed diets during a short-term move, while the remainder show no evidence for dietary change. DiscussionThese analyses demonstrate distinct dietary practices between coastal and yunga groups, between males and females, and between trophy head victims and non-trophy villagers. Understanding the nature of late-life dietary change through a comparative synthesis of archaeological hair provides key insights into individual life trajectories, communal practices, mobility, and foodways relative to altitudinally-variable landscapes of the Peruvian Andes.

Disentangling ecological and taphonomic signals in ancient food webs

AbstractAnalyses of ancient food webs reveal important paleoecological processes and responses to a range of perturbations throughout Earth's history, such as climate change. These responses can inform our forecasts of future biotic responses to similar perturbations. However, previous analyses of ancient food webs rarely accounted for key differences between modern and ancient community data, particularly selective loss of soft-bodied taxa during fossilization. To consider how fossilization impacts inferences of ancient community structure, we (1) analyzed node-level attributes to identify correlations between ecological roles and fossilization potential and (2) applied selective information loss procedures to food web data for extant systems. We found that selective loss of soft-bodied organisms has predictable effects on the trophic structure of “artificially fossilized” food webs because these organisms occupy unique, consistent food web positions. Fossilized food webs misleadingly appear less stable (i.e., more prone to trophic cascades), with less predation and an overrepresentation of generalist consumers. We also found that ecological differences between soft- and hard-bodied taxa—indicated by distinct positions in modern food webs—are recorded in an early Eocene web, but not in Cambrian webs. This suggests that ecological differences between the groups have existed for ≥48 Myr. Our results indicate that accounting for soft-bodied taxa is vital for accurate depictions of ancient food webs. However, the consistency of information loss trends across the analyzed food webs means it is possible to predict how the selective loss of soft-bodied taxa affects food web metrics, which can permit better modeling of ancient communities.

Temporal and population trends in human exploited pinnipeds from Tierra del Fuego

Archaeological sites on the coast of Tierra del Fuego, Argentina, provide a biogeochemical record that can inform us about those ecological dynamics. An abundance of southern fur seal (Arctocephalus australis) and southern sea lion (Otaria flavescens) remains provide a valuable resource to reconstruct ancient and modern food webs. To quantify ecological relationships, we measured bulk stable isotope ratios from bone collagen in otariids and other associated animals, several of which are potential otariid prey. Variations in bulk stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) are linked to potential dietary differences and habitat specialization between coastal areas or the open ocean in populations ranging in age from 7000 cal. Years BP to modern. We observed increases in the variability of these isotopic compositions over time, which suggests a diversity in the diets and habitats of otariids. Shifts in marine food webs occurred during the transition from subsistence hunting of otariids to industrial hunting and expanded human influence. We conclude that direct human influences, such as hunting and habitat alteration, were the major drivers of ecological change in southern South American marine ecosystems.

Scientists' warning on endangered food webs

Abstract. All organisms are ultimately dependent on a large diversity of consumptive and non-consumptive interactions established with other organisms, forming an intricate web of interdependencies. In 1992, when 1700 concerned scientists issued the first “World Scientists' Warning to Humanity”, our understanding of such interaction networks was still in its infancy. By simultaneously considering the species (nodes) and the links that glue them together into functional communities, the study of modern food webs – or more generally ecological networks – has brought us closer to a predictive community ecology. Scientists have now observed, manipulated, and modelled the assembly and the collapse of food webs under various global change stressors and identified common patterns. Most stressors, such as increasing temperature, biological invasions, biodiversity loss, habitat fragmentation, over-exploitation, have been shown to simplify food webs by concentrating energy flow along fewer pathways, threatening long-term community persistence. More worryingly, it has been shown that communities can abruptly change from highly diverse to simplified stable states with little or no warning. Altogether, evidence shows that apart from the challenge of tackling climate change and hampering the extinction of threatened species, we need urgent action to tackle large-scale biological change and specifically to protect food webs, as we are under the risk of pushing entire ecosystems outside their safe zones. At the same time, we need to gain a better understanding of the global-scale synergies and trade-offs between climate change and biological change. Here we highlight the most pressing challenges for the conservation of natural food webs and recent advances that might help us addressing such challenges.

Ecological Legacy of DDT Archived in Lake Sediments from Eastern Canada.

Historic forest management practices led to widespread aerial application of insecticides, such as dichlorodiphenyltrichloroethane (DDT), to North American conifer forests during ∼1950-1970. Lake basins thus may provide an important archive of inputs and aquatic responses to these organochlorines. We use dated sediment cores from five study lakes in multiple watersheds in New Brunswick (NB), Canada, to provide a regional paleo-ecotoxicological perspective on this potential legacy stressor in remote lake ecosystems. Peak sedimentary levels of p, p'- and o, p'-DDT (ΣDDT) and breakdown products ΣDDE (dichlorodiphenyldichloroethylene) and ΣDDD (dichlorodiphenyldichloroethane) generally occurred during the 1970s to 1980s. Sediments exceeded probable effect levels (PELs) by ∼450 times at the most impacted lake. Modern sediments in all study lakes still contained levels of DDT-related compounds that exceed PELs. For the first time, we show that aerial applications of DDT to eastern Canadian forests likely resulted in large shifts to primary consumers within several lake food webs, principally through lake-specific impacts on zooplankton community composition. Modern pelagic zooplankton communities are now much different compared to communities present before DDT use, suggesting that a regional organochlorine legacy may exist in the modern food webs of many remote NB lakes.

Back to the future? Late Holocene marine food web structure in a warm climatic phase as a predictor of trophodynamics in a warmer South-Western Atlantic Ocean.

Stable carbon and nitrogen isotope ratios in the skeletal elements of both ancient and modern marine species from the Beagle Channel were used to compare the structure of Late Holocene and modern food webs, and predict potential changes as a result of a Sea Surface Temperature (SST) increase in the region. Complementary, ancient and modern shells of limpets and mussels were isotopically analysed to explore changes in the isotopic baseline and compare marine food webs through time after an appropriate correction for baseline shifts. Results confirmed a declining pattern of marine primary productivity during the Late Holocene in the Beagle Channel. In general, the isotopic niches overlapped largely in the ancient food web in comparison to the current marine one, with the exception of that of cormorants (Phalacrocorax sp.). Our data suggest that all the species that have undergone intense human exploitation (Arctocephalus australis, Otaria flavescens and Merluccius sp.) significantly increased their trophic levels. The most important finding of this work was the very high isotopic overlap between snoek (Thyrsites atun) and hake (Merluccius sp.) during the Late Holocene. Increasing SST as a result of global warming could favour the recolonization of the southern South-Western Atlantic Ocean by snoek from the South-Eastern Pacific Ocean, with a potential impact on the landings of the economically important Argentine and Austral hake. These findings highlight the relevance of using zooarchaeological remains for providing predictions about marine food webs changes in the near future.

Assimilation of ancient organic carbon by zooplankton in Tibetan Plateau lakes is depending on watershed characteristics

AbstractAncient (i.e., radiocarbon depleted) organic carbon (OC) is exported from ice sheet, glacier, and permafrost systems and may be buried, respired, or assimilated in downstream aquatic systems. Few studies have explored the potential use of this ancient OC in lake food webs. We combined natural abundance radiocarbon and stable carbon isotope data (Δ14C andδ13C) to study ancient OC utilization by zooplankton in six lakes covering a large climate gradient on the central and peripheral Tibetan Plateau. A depleted Δ14C signature of dissolved and particulate OC was found in the inflowing streams and lakes, ranging from – 49‰ to – 569‰, corresponding to radiocarbon ages between 403 yr and 6757 yr. The Δ14C values for zooplankton in the lakes ranged from – 45‰ to – 264‰, reflecting that zooplankton obtain14C‐depleted signatures through assimilation of ancient OC and/or indirectly through consumption of phytoplankton or aquatic plant utilizing14C‐depleted inorganic carbon. Moreover, ancient OC from inflowing streams contributed more to zooplankton diets in the temperate glacier area than in the cold glacier area. Assimilation of ancient OC by zooplankton in lakes is not only affected by drainage basin characteristics, such as the recharge coefficient of the lake, but also by the biogeochemical properties of OC. Use of ancient OC by zooplankton in high‐altitude lakes may constitute an important link between the contemporary aquatic food webs and the glaciated watersheds. Our findings have important implications for the contribution of ancient carbon to the modern lake food webs of high‐altitude and polar lakes.

Zinc isotope ratios of bones and teeth as new dietary indicators: results from a modern food web (Koobi Fora, Kenya).

In order to explore the possibilities of using zinc (Zn) stable isotope ratios as dietary indicators, we report here on the measurements of the ratio of stable isotopes of zinc (66Zn/64Zn, expressed here as δ66Zn) in bioapatite (bone and dental enamel) of animals from a modern food web in the Koobi Fora region of the Turkana Basin in Kenya. We demonstrate that δ66Zn values in both bone and enamel allow a clear distinction between carnivores and herbivores from this food web. Differences were also observed between browsers and grazers as well as between carnivores that consumed bone (i.e. hyenas) compared to those that largely consume flesh (i.e. lions). We conclude that Zn isotope ratio measurements of bone and teeth are a new and promising dietary indicator.

Expanding the Isotopic Toolbox: Applications of Hydrogen and Oxygen Stable Isotope Ratios to Food Web Studies

The measurement of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H) and oxygen (δ18O) isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applications using δ2H and, to a lesser extent, δ18O values have demonstrated potential for these elements to provide novel insights in modern food web studies. We explore the advantages and challenges associated with three applications of δ2H and δ18O values in food web studies. First, large δ2H differences between aquatic and terrestrial ecosystem end members can permit the quantification of energy inputs and nutrient fluxes between these two sources, with potential applications for determining allochthonous vs. autochthonous nutrient sources in freshwater systems and relative aquatic habitat utilization by terrestrial organisms. Next, some studies have identified a relationship between δ2H values and trophic position, which suggests that this marker may serve as a trophic indicator, in addition to the more commonly used δ15N values. Finally, coupled measurements of δ2H and δ18O values are increasing as a result of reduced analytical challenges to measure both simultaneously and may provide additional ecological information over single element measurements. In some organisms, the isotopic ratios of these two elements are tightly coupled, whereas the isotopic disequilibrium in other organisms may offer insight into the diet and physiology of individuals. Although a coherent framework for interpreting δ2H and δ18O data in the context of food web studies is emerging, many fundamental uncertainties remain. We highlight directions for targeted research that will increase our understanding of how these markers move through food webs and reflect ecological processes.

Exploring paleo food-webs in the European Early and Middle Pleistocene: A network analysis

Food webs are networks of feeding (trophic) interactions among species. As any other network approach, research on food webs focuses its analysis on the structure of direct and indirect interactions among diverse species, rather than looking at the particularities of certain taxa. In recent times, scholars have collected an impressive amount of empirical food-web data to study present day terrestrial and aquatic habitats.More restrictively, this approach has also been applied to trophic interactions represented in the fossil record of extinct ecosystems. Nevertheless, to our knowledge, none of them has addressed the role played by the different Pleistocene hominin species as part of such food-webs. In this work, we aim at filling this gap by focusing on the Early and Middle Pleistocene paleo-communities in Western Eurasia. Our goal is to improve our understanding on changes experienced by large mammals' interactions during this period, and shed some light on the influence of and on Homo species of those changes.We have constructed up to 27 paleo food-webs from the archaeo-paleontological record of European assemblages, covering from the Middle Villafranchian to the Late Galerian. Only large mammals have been considered, including a couple of Homo species that are present in 8 food-webs. Then, we have developed a two-steps analysis. First, we have calculated the main structural features of all the networks, and have compared them across geographical areas, periods and cases with and without Homo species. Second, we have calculated different structural centrality measures in order to assess the relevance of Homo species in their corresponding food-webs.The obtained results show that the Pleistocene food webs under study shared basic features with modern food webs, although differences in the values of some parameters might be significant. Moreover, when comparing the networks across periods, we found a marked change that could be related to the Mid-Pleistocene Revolution. Finally, our results also highlight the trophic position of hominins in the web as a central species that channeled energy fluxes.

Effects of decalcification on bulk and compound-specific nitrogen and carbon isotope analyses of dentin.

For bulk carbon and nitrogen isotope analysis of dentin, samples are typically decalcified. Since the non-protein carbon in dentin is low, whole sample analysis may produce reliable data. Compound-specific isotope analysis (CSIA) of bone and tooth dentin protein is a powerful tool for reconstructing the flow of carbon and nitrogen in modern and past food webs. Decalcification has also been used to prepare bone and dentin samples for CSIA, but the effects of this process on bulk dentin, amino acid composition, and their specific isotope values are not known. The bulk isotope values of raw and decalcified dentin from a sperm whale tooth were measured to determine the effects of decalcification and the accuracy of untreated dentin results. CSIA was also performed on decalcified and raw dentin to examine differences in the amino acid isotope values and molar composition between these two approaches. Analysis of raw dentin yields precise and accurate bulk isotope measurements for this animal. The isotopic values of decalcified samples and raw dentin for individual amino acids were similar, but the average of the isotope value offsets between the two sample types was significant. The presence of inorganic material complicated raw sample processing for individual amino acid isotope values, and may have contributed to the isotopic differences between decalcified and raw samples. Decalcification is not needed to measure bulk isotope values in dentin from this modern odontocete, probably because the lipid and carbonate concentrations are low and the carbon isotope values of dentin protein and carbonate are similar. This method should not be applied in some cases (e.g., with fossil dentin and modern bone). Decalcification should still be used prior to CSIA since significant matrix issues occur with raw dentin processing and decalcification does not alter the amino acid molar composition or isotopic values of dentin.

Sample acidification significantly alters stable isotope ratios of sulfur in aquatic plants and animals

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 493:1-8 (2013) - DOI: https://doi.org/10.3354/meps10560 FEATURE ARTICLE Sample acidification significantly alters stable isotope ratios of sulfur in aquatic plants and animals Rod M. Connolly1,*, Thomas A. Schlacher2 1Australian Rivers Institute - Coast and Estuaries, and School of Environment, Gold Coast Campus, Griffith University, Queensland 4222, Australia 2Faculty of Science, University of the Sunshine Coast, Maroochydore DC, Queensland 4558, Australia *Email: r.connolly@griffith.edu.au ABSTRACT: Sulfur stable isotopes are increasingly being used as tracers of material processing in studies of both modern and historical food webs. Preparation of plant and animal material for isotope analysis routinely includes steps that remove inorganic material not normally assimilated by consumers. Whereas acidification of samples is known to assist with this for some elements (carbon), it can produce unwanted effects for others (nitrogen). Here we tested the effects of acidification on sulfur isotopes by comparing isotope ratios of paired acidified and non-acidified samples of seagrass, epiphytic algae growing on seagrass and animal consumers (3 types of crustaceans: amphipods, copepods and isopods). Acid treatment resulted in significant losses of elemental sulfur from the tissues and changes in sulfur isotope ratios of samples. The artificial depletion of the heavy sulfur isotope decreased sulfur isotope ratios by 2.6‰ on average, and by as much as 7.0‰ in individual samples. Acidification of samples prior to sulfur isotope analysis results in invalid ratios and should not be used. KEY WORDS: Acid digestion · Amino acids · Carbonate · DMSP · Seagrass · Stable isotope analysis Full text in pdf format Information about this Feature Article NextCite this article as: Connolly RM, Schlacher TA (2013) Sample acidification significantly alters stable isotope ratios of sulfur in aquatic plants and animals. Mar Ecol Prog Ser 493:1-8. https://doi.org/10.3354/meps10560 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 493. Online publication date: November 20, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Millennial‐aged organic carbon subsidies to a modern river food web

Recent studies indicate that highly aged material is a major component of organic matter transported by most rivers. However, few studies have used natural 14C to trace the potential entry of this aged material into modern river food webs. Here we use natural abundance 14C, 13C, and deuterium (2H) to trace the contribution of aged and contemporary organic matter to an important group of consumers, crustacean zooplankton, in a large temperate river (the Hudson River, New York, USA). Zooplankton were highly 14C depleted (mean delta14C = -240 per thousand) compared to modern primary production in the river or its watershed (delta14C = -60 per thousand to +50 per thousand). In order to account for the observed 14C depletion, zooplankton must be subsidized by highly aged particulate organic carbon. IsoSource modeling suggests that the range of the aged dietary subsidy is between approximately 57%, if the aged organic matter source was produced 3400 years ago, and approximately 21%, if the organic carbon used is > or = 50 000 years in age, including fossil material that is millions of years in age. The magnitude of this aged carbon subsidy to river zooplankton suggests that modern river food webs may in some cases be buffered from the limitations set by present-day primary production.

Compilation and network analyses of cambrian food webs.

A rich body of empirically grounded theory has developed about food webs—the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple “niche model,” which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body plans, and trophic roles during the Cambrian radiation. More research is needed to explore the generality of food-web structure through deep time and across habitats, especially to investigate potential mechanisms that could give rise to similar structure, as well as any differences.

Early Cambrian origin of modern food webs: evidence from predator arrow worms

Although palaeontological evidence from exceptional biota demonstrates the existence of diverse marine communities in the Early Cambrian (approx. 540-520 Myr ago), little is known concerning the functioning of the marine ecosystem, especially its trophic structure and the full range of ecological niches colonized by the fauna. The presence of a diverse zooplankton in Early Cambrian oceans is still an open issue. Here we provide compelling evidence that chaetognaths, an important element of modern zooplankton, were present in the Early Cambrian Chengjiang biota with morphologies almost identical to Recent forms. New information obtained from the lowermost Cambrian of China added to previous studies provide convincing evidence that protoconodont-bearing animals also belonged to chaetognaths. Chaetognaths were probably widespread and diverse in the earliest Cambrian. The obvious raptorial function of their circumoral apparatuses (grasping spines) places them among the earliest active predator metazoans. Morphology, body ratios and distribution suggest that the ancestral chaetognaths were planktonic with possible ecological preferences for hyperbenthic niches close to the sea bottom. Our results point to the early introduction of prey-predator relationships into the pelagic realm, and to the increase of trophic complexity (three-level structure) during the Precambrian-Cambrian transition, thus laying the foundations of present-day marine food chains.

Predicting diet, trophic level and palaeoecology from bone stable isotope analysis: a comparative study of five red deer populations

C and N stable isotope ratios of red deer (Cervus elaphus) bone collagen (154 individuals) from five modern populations occupying geographically different habitats are reported. No significant difference was observed between deer occupying forested and non-forested environments subject to similar climatic conditions suggesting a simple "canopy effect" is not observed. Mean population delta13C is negatively correlated with temperature whereas mean population delta15N is positively correlated with temperature. A weak but significant positive correlation was observed between deer age and collagen delta13C values from the Isle of Rum population (Scotland). The amount of intra-population isotope variability is not consistent among populations; thus significant numbers of individuals from each species are required for modern food web studies, for palaeodietary baseline data, and for palaeoecological studies.

Enamel diagenesis at South African Australopith sites: Implications for paleoecological reconstruction with trace elements

Elemental ratio data from archaeological and paleontological bone have often been used for paleoecological reconstruction, but recent studies have shown that, even when solubility profiling techniques are employed in an attempt to recover biogenic signals, bone is an unreliable material. As a result, there has been renewed interest in using enamel for such studies, as it is known to be less susceptible to diagenesis. Nevertheless, enamel is not immune from diagenetic processes, and several studies have suggested that paleoecologically relevant elements may be altered in fossil enamel. Here, we investigate Sr, Ba, Zn, and Pb compositions of enamel from South African karstic cave sites in an effort to ascertain whether or not this material provides reliable paleoecological information. We compared enamel data for mammals from three fossil sites aged 1.8–3.0 Ma, all of which are on dolomites, with data from modern mammals living on dolomitic and granitic substrates. Sr/Ca and Ba/Ca are about three times higher in enamel from modern mammals on granites than those living on dolomites, stressing the need for geologically appropriate modern/fossil comparisons. After pretreatment with dilute acid, we found no evidence of increased Sr/Ca, Ba/Ca, or Pb/Ca in fossil enamel. In contrast, Zn/Ca increased by over five times at one site (Makapansgat), but much more subtly elsewhere. Ecological patterning in Sr/Ca, Ba/Ca, and Sr/Ba ratios was also retained in fossil enamel. This study suggests that Sr/Ca, Ba/Ca, and Pb/Ca data likely preserve paleoecological information from these sites, but also demonstrates that geologically similar sites can differ in the degree to which they impart certain elements (Zn in this case) to fossils. Thus, screening is probably necessary on a site-by-site basis. Lastly, further investigation of elemental distributions in modern foodwebs is necessary before elemental ratio analysis can become a common tool for paleoecological reconstruction.