31 research outputs found
Reconstructing ontogenetic movements in pelagic sharks coupling ocean models and stable isotope data in incrementally grown tissues
No full textEcological interactions in the marine pelagic environment are difficult to study, mostly because the open-ocean is vast and largely inaccessible. Migration is a common ecological trait in pelagic settings, with large impacts on community structure and dynamics, and ecosystem functioning. However, migratory predators are rapidly declining worldwide, with unclear ecological consequences.Pelagic sharks have declined regionally by > 90% in the past 15 years, largely as a result of overfishing and by-catch. Shark vulnerability to fishery capture depends on individual movements, and on the presence of movement traits across individuals, populations or species, which may implyshared vulnerability. Yet, the movements of pelagic sharks and other migratory oceanic animals are difficult to monitor or reconstruct.Natural-abundance stable isotopes allow retrospective movement reconstruction, by relating the isotopic composition of animal tissues to geographically indexed measurements or predictions of isotopic ratios at the base of the food web (isoscapes). Where incrementally grown, metabolically inert tissues are available, movements can be reconstructed throughout life. However, the application of stable isotopes in bulk tissues to study migration is complicated by mixed baseline and trophic effects and, in pelagic settings, by large uncertainties in the spatio-temporal distributions of isotopic baselines.In this study, I explored how the ontogenetic movements of two pelagic shark model species, the blue (Prionace glauca) and porbeagle (Lamna nasus) sharks, could be reconstructed using modelled global ocean carbon isoscapes, and carbon and nitrogen isotopes in bulk cartilage collagen and single amino acids from vertebrae.To provide a possible solution for poor sampling of isotopic baselines, I developed a process-based, mechanistic carbon isotope model, predicting the likely spatio-temporal distributions of the carbon isotopic composition of phytoplankton across the global ocean.To provide information on pelagic shark life-history traits, I recovered individual-level life history carbon and nitrogen isotope records for bulk cartilage collagen from vertebrae of sharks caught across the North Atlantic. I also recovered comparable carbon isotope records for single amino acids,producing the first compound-specific isotopic dataset of within-individual ontogenetic variance in sharks. Consistent ontogenetic isotope patterns across individuals of each species revealed species level life-history traits. Whilst the interpretation of traits for bulk collagen using modelled isoscapeswas ultimately limited from confounding influences from trophic level change, that of traits for essential amino acids conclusively demonstrated ontogenetic and transgenerational movement traits.During juvenile growth, blue sharks increasingly utilised foraging grounds with more positive carbon isotopic baselines, whereas porbeagles made increasing use of isotopically more negative grounds. Blue shark pupping and maternal foraging occurred in isotopically distinct grounds, with the possibility of natal homing by adult individuals. Pregnant female porbeagles, by contrast,migrated to isotopically distinct foraging grounds prior to giving birth.Isotope-derived information on ontogenetic movements complements tag-derived information over a snap-shot of the entire life of individuals, but explicit isoscape-based geo-location is limited by large uncertainties in isoscape models, and trophic influences on bulk tissue isotopiccompositions
Integrating metabolic performance, thermal tolerance, and plasticity enables for more accurate predictions on species vulnerability to acute and chronic effects of global warming
No full textPredicting species vulnerability to global warming requires a comprehensive, mechanistic understanding of sublethal and lethal thermal tolerances. To date, however, most studies investigating species physiological responses to increasing temperature have focused on the underlying physiological traits of either acute or chronic tolerance in isolation. Here we propose an integrative, synthetic approach including the investigation of multiple physiological traits (metabolic performance and thermal tolerance), and their plasticity, to provide more accurate and balanced predictions on species and assemblage vulnerability to both acute and chronic effects of global warming. We applied this approach to more accurately elucidate relative species vulnerability to warming within an assemblage of six caridean prawns occurring in the same geographic, hence macroclimatic, region, but living in different thermal habitats. Prawns were exposed to four incubation temperatures (10, 15, 20 and 25 °C) for 7 days, their metabolic rates and upper thermal limits were measured, and plasticity was calculated according to the concept of Reaction Norms, as well as Q10 for metabolism. Compared to species occupying narrower/more stable thermal niches, species inhabiting broader/more variable thermal environments (including the invasive Palaemon macrodactylus) are likely to be less vulnerable to extreme acute thermal events as a result of their higher upper thermal limits. Nevertheless, they may be at greater risk from chronic exposure to warming due to the greater metabolic costs they incur. Indeed, a trade-off between acute and chronic tolerance was apparent in the assemblage investigated. However, the invasive species P. macrodactylus represents an exception to this pattern, showing elevated thermal limits and plasticity of these limits, as well as a high metabolic control. In general, integrating multiple proxies for species physiological acute and chronic responses to increasing temperature helps providing more accurate predictions on species vulnerability to warming
SPATIAL-Lab/CombinedDynamicHOModel: FEE initial submission
No full textCode for the combined dynamic model by Magozzi et al. In review to predict local among-individual HO isotopic variance. Data files needed to run the scripts can be found at: https://www.dropbox.com/sh/z57sa9ezengplpf/AADKI2F46K1fM-ksjLyL5DxEa?dl=
Optimizing stable isotope sampling design in terrestrial movement ecology research
No full textThe recognition of adequate sampling designs is an interdisciplinary topic that has gained popularity over the last decades. In ecology, many research questions involve sampling across extensive and complex environmental gradients. This is the case for stable isotope analyses, which are widely used to characterize large-scale movement patterns and dietary preferences of organisms across taxa. Because natural-abundance stable isotope variation in the environment is incorporated into inert animal tissues, such as feathers or hair, it is possible to draw inferences about the type of food and water resources that individuals consumed and the locations where tissues were synthesized. However, modern stable isotope research can benefit from the implementation of robust statistical analyses and well-designed sampling approaches to improve geographic assignment interpretation. We employed hydrogen stable isotope simulations to study inferences regarding the probability of origin of migratory individuals and reveal gaps in sampling efforts while highlighting uncertainties of assignment model extrapolations. We present an integrative approach that explores multiple sampling strategies across species with different geographic ranges to understand advantages and limitations of animal movement inferences based on stable isotope data. We show the characteristics of different sampling strategies through geographic and isotopic gradients and establish a set of diagnostic tools that uncover the attributes of these gradients and evaluate uncertainties of model results. Our analysis demonstrates that sampling regimes should be evaluated in relation to specific research questions and study constraints, and that adopting a single method across species ranges can lead to a costly but less effective sampling strategy
Sensitivity of δ<sup>13</sup>C values of seabird tissues to combined spatial, temporal and ecological drivers: a simulation approach
No full textBiologging technologies have revolutionised our understanding of the foraging ecology and life history traits of marine predators, allowing for high resolution information about location, and in some cases, foraging behaviour of wild animals. At the same time, stable isotope ecologists have independently developed methods to infer location and foraging ecology (trophic geography). To date, relatively few studies have combined these two approaches, despite the potential wealth of complementary information. In marine systems, spatial and trophic information are coded in the isotopic composition of carbon and nitrogen in animal tissues, but interpretation of isotope values is limited by both the lack of reference maps (isoscapes) needed to relate the isotopic composition of an animal's tissues to a location, and the relatively large number of variables that could influence tissue isotope compositions. Simulation modelling can help to interpret measured tissue isotope compositions of migratory animals in the context of spatio-temporally dynamic isotopic baselines. Here, we couple individual-based movement models with global marine isotope models to explore the sensitivity of tissue δ13C values to a range of extrinsic (environmental) and intrinsic (behavioural, physiological) drivers. We use in-silico experiments to simulate isotopic compositions expected for birds exhibiting different movement and foraging behaviours and compare these simulated data to isotopic data recovered from biologger-equipped female northern giant petrels Macronectes halli incubating eggs on sub-Antarctic Marion Island. Our simulations suggest that in the studied system, time is a strong driver of isotopic variance. Accordingly, this implies that caution should be used when comparing δ13C values of marine predators’ tissues between seasons and years. We show how an in-silico experimental approach can be used to explore the sensitivity of animal tissue isotopic compositions to complex and often interacting drivers. Appreciation of the principle drivers behind isotopic variance specific to a given animal and geographic context can enhance inferences of geolocation as well as foraging behaviour, and can be applied to any mobile predator. Models can be relativey simple or complex and multi-layered depending on the level of ecological realism required. Future investigations can use other isoscapes, including terrestrial isoscapes and more complex or different movement models.</p
Mechanistic model predicts tissue{\textendash}environment relationships and trophic shifts in animal hydrogen and oxygen isotope ratios
No full textStatistical regression relationships between the hydrogen (H) and oxygen (O) isotope ratios (delta H-2 and delta O-18, respectively) of animal organic tissues and those of environmental water have been widely used to reconstruct animal movements, paleoenvironments, and diet and trophic relationships. In natural populations, however, tissue-environment isotopic relationships are highly variable among animal types and geographic regions. No systematic understanding of the origin(s) of this variability currently exists, clouding the interpretation of isotope data. Here, we present and apply a model, based on fundamental metabolic relationships, to test the sensitivity of consumer tissue H and O isotope ratios, and thus tissue-environment relationships, to basic physiological, behavioral, and environmental parameters. We then simulate patterns in consumer tissue isotopic compositions under several 'real-world' scenarios, demonstrating that the new model can reproduce-and potentially explain-previously observed patterns in consumer tissue H isotope ratios, including between-continent differences in feather-precipitation relationships and H-2-enrichment with trophic level across species. The model makes several fundamental predictions about the organic O isotope system, which constitute hypotheses for future testing as new data are obtained. By highlighting potential sources of variability and bias in tissue-environment relationships and establishing a framework within which such effects can be predicted, these results should advance the application of H and O isotopes in ecological, paleoecological, and forensic research
Sea Ice Dynamics and Planktonic Adaptations: A Study of Terra Nova Bay’s Mesozooplanktonic Community during the Austral Summer
No full textPhytoplankton and zooplanktonic communities form the base of the Antarctic food web. This study examines the evolution of the mesozooplanktonic system in Terra Nova Bay during the austral summer (December–February), focusing on the impact of sea ice dynamics and the resulting phytoplankton blooms. Terra Nova Bay (Ross Sea) offers a valuable context given its high productivity and ecological variability. Using a diachronic approach, we analyzed data spanning twelve years to understand how the system’s structure and functionality change over time. A novel key metric, Days since Sea Ice Melting, was employed to track shifts in phytoplankton community development and trophic dynamics. The results indicate that the system enters the summer season increasing primary productivity and creating the support for the development of a more complex and organized system during the season. The phytoplankton bloom recorded during mid-season, coped by an increase in biomass, is followed by the establishment of a well-organized grazing system. A secondary phytoplankton bloom is observed towards the end of the summer, but it does not significantly affect mesozooplankton communities. Overall, this study highlights the dynamic nature of Terra Nova Bay’s mesozooplanktonic community and evaluates the influence of climate change on Antarctic marine ecosystems
Combining simulation modeling and stable isotope analyses to reconstruct the last known movements of one of Nature’s giants
No full textThe spatial ecology of rare, migratory oceanic animals is difficult to study directly. Where incremental tissues are available, their chemical composition can provide valuable indirect observations of movement and diet. Interpreting the chemical record in incremental tissues can be highly uncertain, however, as multiple mechanisms interact to produce the observed data. Simulation modeling is one approach for considering alternative hypotheses in ecology and can be used to consider the relative likelihood of obtaining an observed record under different combinations of ecological and environmental processes. Here we show how a simulation modeling approach can help to infer movement behaviour based on stable carbon isotope profiles measured in incremental baleen tissues of a blue whale (Balaenoptera musculus). The life history of this particular specimen, which stranded in 1891 in the UK, was selected as a case study due to its cultural significance as part of a permanent display at the Natural History Museum, London. We specifically tested whether measured variations in stable isotope compositions across the analysed baleen plate were more consistent with residency or latitudinal migrations. The measured isotopic record was most closely reproduced with a period of residency in sub-tropical waters for at least a full year followed by three repeated annual migrations between sub-tropical and high latitude regions. The latitudinal migration cycle was interrupted in the year prior to stranding, potentially implying pregnancy and weaning, but isotopic data alone cannot test this hypothesis. Simulation methods can help reveal movement information coded in the biochemical compositions of incremental tissues such as those archived in historic collections, and provides context and inferences that are useful for retrospective studies of animal movement, especially where other sources of individual movement data are sparse or challenging to validate.© 2019 Trueman et al.
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ) and either DOI or URL of the article must be cited.NHM Repositor
Calibration chain transformation improves the comparability of organic hydrogen and oxygen stable isotope data
No full textStable hydrogen and oxygen isotopic compositions (δ2H and δ18O, respectively) of animal tissues have been used to infer geographical origin or mobility based on the premise that the isotopic composition of tissue is systematically related to that of local water sources. Isotopic data for known-origin samples are required to quantify these tissue–environment relationships. Although many of such data have been published and could be reused by researchers, differences in the standards used for calibration and analytical procedures for different datasets limit the comparability of these data. We develop an algorithm that uses results from comparative analysis of secondary standards to transform data among reference scales and estimate the uncertainty inherent in these transformations. We apply the algorithm to a compilation of known-origin keratin data published over the past ~20 years. We show that transformation improves the comparability of data from different laboratories, and that the transformed data suggest ecophysiologically meaningful differences in keratin–water relationships among different animal groups and taxa. The compiled data and algorithms are freely available in the ASSIGNR r-package to support geographical provenance research, and more generally offer a methodology overcoming several challenges in geochemical data integration and reuse
