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65 results for “isotopic niche”
Data from: Integrating isotopic and nutritional niches reveals multiple dimensions of individual diet specialisation in a marine apex predator
<ol> <li>Dietary specializations are important determinants of ecological structure, particularly in species with high per-capita trophic influence like marine apex predators. These species are, however, among the most challenging in which to establish spatiotemporally integrated diets.</li> <li>We introduce a novel integration of stable isotopes with a multidimensional nutritional niche framework that addresses the challenges of establishing spatiotemporally integrated nutritional niches in wild populations, and apply the framework to explore individual diet specialization in a marine apex predator, the white shark (<em>Carcharodon carcharias</em>).</li> <li>Sequential tooth files were sampled from juvenile white sharks to establish individual isotopic (δ-space; δ<sup>13</sup>C, δ<sup>15</sup>N, δ<sup>34</sup>S) niche specialization. Bayesian mixing models were then used to reveal individual-level prey (p-space) specialization, and further combined with nutritional geometry models to quantify the nutritional (N-space) dimensions of individual specialization and their relationships to prey use.</li> <li>Isotopic and mixing model analyses indicated juvenile white sharks as individual specialists within a broader, generalist, population niche. Individual sharks differed in their consumption of several important mesopredator species, which suggested among-individual variance in trophic roles in either pelagic or benthic food webs. However, variation in nutrient intakes was small and not consistently correlated with differences in prey use, suggesting white sharks as nutritional specialists and that individuals could use functionally and nutritionally different prey as complementary means to achieve a common nutritional goal.</li> <li>We identify how degrees of individual specialisation can differ between niche spaces (δ-, p- or N-space), the physiological and ecological implications of this, and argue that integrating nutrition can provide stronger, mechanistic links between diet specialisation and its intrinsic (fitness/performance) and extrinsic (ecological) outcomes. Our time-integrated framework is adaptable for examining the nutritional consequences and drivers of food use variation at the individual, population or species level.</li> </ol>
Isotopes complement morphology: Niche partitioning among greenbuls in the Afrotropical lowland forest
<p><a name="_Hlk153960869"></a>Biodiversity plays a vital role in ecosystem functioning, so understanding how species coexist is a cornerstone of ecology. However, despite decades of research, our current knowledge is incomplete due to methodological limitations and sampling bias, particularly in the species-rich tropics. In this study, we combined bill and body morphological traits with stable isotopes in feathers to quantify niche differentiation among six co-occurring greenbul taxa, a diverse group of frugivorous and insectivorous passerines with remarkable similarities in body shape, in the lowland rainforests of Mt. Cameroon, West Central Africa. Our results showed that the greenbul’s niche space was primarily differentiated by variations in body morphology, with Yellow-lored Bristlebill <em>Bleda notatus</em> and Eastern Bearded Greenbul <em>Criniger chloronotus</em> occupying ecological niches distinct from the remaining four taxa, while bill morphology indicated substantial overlap between the taxa. In addition, isotopic composition of the feathers revealed a separation of Western Greenbul <em>Arizelocichla tephrolaema</em> from the other taxa. Our results show that the integration of morphological and isotopic data can provide robust estimates of niche overlaps, providing evidence for the differentiation of ecological roles. This highlights the importance of integrating variable traits to improve our understanding of how animals exploit the multidimensional niche space that enables their coexistence.</p>
Data from: Isotopic niche overlap among foraging marine turtle species in the Gulf of Mexico
<p>R codes and corresponding dataset for "Isotopic niche overlap among foraging marine turtle species in the Gulf of Mexico" by Weber et al. for publication. </p> <p>The "MasterDB" dataset contains the bulk stable isotope data (C, N, S) for loggerhead, green, and Kemp's ridley turtles sampled off the coast of Crystal River, Florida from 2016 to 2022. The "SIA_Values" dataset presents the data in the appropriate format for the nicheRover R package. Both metadata .csv files contain all metadata necessary for interpretation. </p>
Data from: Isotopic niche variation from the Holocene to today reveals minimal partitioning and individualistic dynamics among four sympatric desert mice
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Data from: Spider webs, stable isotopes and molecular gut content analysis: multiple lines of evidence support trophic niche differentiation in a community of Hawaiian spiders
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Data from: Isotopic niches support the resource breadth hypothesis
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Data from: Integrating isotopic and nutritional niches reveals multiple dimensions of individual diet specialisation in a marine apex predator
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Seasonal isotopic niche of a rodent: High between-individual variation but no changes in individual niche width during the rich-resource period
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Floods connect tropical river-floodplain food webs but shrink fish community isotopic trophic niches
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Quantifying temporal variation in dietary niche to reveal drivers of past population declines; stable isotope, harvest trends, and land use
<p><b>1.</b> Given the long and dynamic history of anthropogenic disturbances to ecosystems, it is difficult to determine the drivers of past population declines. These uncertainties dilute the efficacy of conservation efforts and might hinder species and ecosystem recovery.</p> <p><b>2.</b> Niche quantification can be a useful tool for understanding drivers of past population declines. Niche parameters reflect key resources used, providing insight into the conditions needed to achieve population stability. By reconstructing a population's niche position and space over a period of decline and comparing to historic baselines, shifts in the realized niche of a species can be assessed. Comparing shifts to historic information on resource availability and timing of declines can allow practitioners to identify probable drivers of species decline.</p> <p><span><b>3.</b> We demonstrated the utility of this technique by reconstructing parameters of isotopic dietary niche over a 130 year period and comparing isotopic niche reconstructions to land use and crop harvests during this same period via regression and Bayesian standard ellipsoid (SIBER) analyses. We use a formerly widespread but now endangered species, the eastern spotted skunk (<i>Spilogale putorius</i>), addressing the hypothesis that land use change and agricultural intensification led to a historical collapse of key dietary resources which correlates with population declines in this species. To help control for isotopic variability unrelated to population decline, we compare trends to those of a secure, but ecologically similar generalist mesocarnivore, the striped skunk (<i>Mephitis mephitis</i>), across the same spatiotemporal scale. </span></p> <p><b>4.</b> We present evidence that historic dietary changes occurred in spotted skunks in the early 1900s but not to the same degree in striped skunks. Changes in isotopic composition correspond with the temporal period of decline and are explained by concurrent changes in land use. These results support the hypothesis that loss of key dietary resources as a result of land use change and agricultural intensification played a significant role in population declines of spotted skunks in this region.</p>
Data from: Intra- and interspecific niche variation as reconstructed from stable isotopes in two ecologically different Ethiopian Rift Valley lakes
1. The concept of species niches has enhanced our understanding of community assembly and food web structure in a variety of ecosystem types. Niche-based species sorting profoundly determines community composition along strong environmental gradients, while interspecific interactions tend to be more important within habitats at local spatial scales. The role of intraspecific niche variation in community assembly and ecosystem functioning has only recently been highlighted. 2. The present study undertakes a quantitative comparison of the trophic structure of fish communities in two iconic Ethiopian Rift Valley lakes, Lake Abaya and Lake Chamo, which are biodiversity hotspots with high societal importance. The lakes differ strongly in ecology: whereas Lake Abaya is turbid due to a very high sediment loading, Lake Chamo is a clear-water lake, which in recent years is, however, rapidly becoming more turbid. Using stable isotopes, we compare the structure of the food web in both lakes, and investigate the degree to which differences in trophic structure between the two lakes are mediated by changes in species composition with fixed within-species niches or rather by flexibility in food acquisition within species. 3. Different food web compartments, including fish and the main basal sources, were sampled in both lakes. We used Bayesian stable isotope mixing models and Bayesian community-wide metrics for a quantitative comparison of the food web structure between the two lakes. 4. We demonstrate that the isotopic niche of the fish community in Lake Abaya is larger and more diversified compared to that in Lake Chamo. Sediment organic material seems to be a major energy source for fish in Abaya, while zooplankton is a dominant source for fish in Chamo. This is consistent with the different ecology of the two lakes, where high turbidity impedes primary and secondary production in Abaya. Differences in trophic structure between the two lakes resulted from intraspecific isotopic niche variation rather than from compositional variation between fish communities. 5. Our results point to the importance of intraspecific variation in feeding ecology of fish communities inhabiting two large Ethiopian Rift Valley Lakes with distinct environmental conditions. We anticipate that the approach we used has strong potential to explore large-scale patterns in food web organization in relation to niche variation across different types of ecosystems.
Data from: Individual growth as a non-dietary determinant of the isotopic niche metrics
1. Quantitative analytical approaches for isotopic niche analysis in the trophic diversity studies are proliferating rapidly; however, the assumptions behind the isotopic niche applications are rarely tested. One of the main assumptions is independence of the niche metrics and physiological status of the animals. The aim of this experimental study was to test the relationship between growth and Layman's metrics of isotopic niche in consumers eating the same food but in different quantities and growing at different rates. 2. Based on research indicating that individual variability in isotopic fractionation increases under suboptimal conditions, I hypothesized that a group of consumers originating from the same population and exposed to food limitation would have greater estimates of the niche breadth and diversity as a result of higher inter-individual variability in growth rate and stable isotope signatures than in non-limiting feeding conditions. This hypothesis was tested using Baltic mysids Neomysis integer fed isotopically uniform diet under laboratory conditions and analyzing individual growth and stable isotope signature in concert. 3. As hypothesized, mysid growth rate was a significant negative predictor of most niche metrics. These effects were related to both increased inter-individual variability and higher trophic fractionation in malnourished animals, whereas in actively growing mysids lower fractionation was observed together with lower values for niche size, isotopic range and trophic diversity. 4. These findings challenge how we interpret the intrapopulation isotopic variance and evaluate isotopic evidence of individual specialization and call for integrated approaches for isotopic niche and growth assessment.
Data from: Isotopic niche reflects stress-induced variability in physiological status
The isotopic niche has become an established concept in trophic ecology. However, the assumptions behind this approach have rarely been evaluated. The evidence is accumulating that physiological stress can affect both magnitude and inter-individual variability of the isotopic signature in consumers via alterations in metabolic pathways. We hypothesized that stress factors (inadequate nutrition, parasite infestations, and exposure to toxic substances or varying oxygen conditions) might lead to suboptimal physiological performance and altered stable isotope signatures. The latter can be misinterpreted as alterations in isotopic niche. This hypothesis was tested by inducing physiological stress in the deposit-feeding amphipod Monoporeia affinis exposed to either different feeding regimes or contaminated sediments. In the amphipods, we measured body condition indices or reproductive output to assess growth status and δ13C and δ15N values to derive isotope niche metrics. As hypothesized, greater isotopic niche estimates were derived for the stressed animals compared to the control groups. Moreover, the δ15N values were influenced by body size, reproductive status and parasite infestations, while δ13C values were influenced by body size, oxygen conditions and survival. Using regression analysis with isotope composition and growth variables as predictors, we were able to discriminate between the amphipods exposed to nutritionally or chemically stressful conditions and those in the control groups. Thus, interpretation of isotopic niche can be confounded by natural or anthropogenic stressors that may induce an apparent rather than a dietary change in isotopic niche. These findings stress the importance of including measures of growth and health status when evaluating stable isotope data in food web studies.
Data from: Do deposit-feeders compete? Isotopic niche analysis of an invasion in a species-poor system
Successful establishment of invasive species is often related to the existence of vacant niches. Competition occurs when invaders use the same limiting resources as members of the recipient community, which will be reflected in some overlap of their trophic niches. The concept of isotopic niche has been used to study trophic niche partitioning among species. Here, we present a two-year field study comparing isotopic niches of the deposit-feeding community in a naturally species-poor system. The isotopic niche analyses showed no overlap between a recent polychaete invader and any of the native species suggesting that it has occupied a vacant niche. Its narrow isotopic niche suggests specialized feeding, however, the high d15N values compared to natives are most likely due to isotope fractionation effects related to nitrogen recycling and a mismatch between biological stoichiometry of the polychaete and the sediment nitrogen content. Notably, highly overlapping isotopic niches were inferred for the native species, which is surprising in a food-limited system. Therefore, our results demonstrate that invaders may broaden the community trophic diversity and enhance resource utilization, but also raise questions about the congruence between trophic and isotopic niche concepts and call for careful examination of assumptions underlying isotopic niche interpretation.
Data from: Broad and flexible stable isotope niches in invasive non-native Rattus spp. in anthropogenic and natural habitats of central eastern Madagascar
Background: Rodents of the genus Rattus are among the most pervasive and successful invasive species, causing major vicissitudes in native ecological communities. A broad and flexible generalist diet has been suggested as key to the invasion success of Rattus spp. Here, we use an indirect approach to better understand foraging niche width, plasticity, and overlap within and between introduced Rattus spp. in anthropogenic habitats and natural humid forests of Madagascar. Results: Based on stable carbon and nitrogen isotope values measured in hair samples of 565 individual rodents, we found that R. rattus had an extremely wide foraging niche, encompassing the isotopic space covered by a complete endemic forest-dwelling Malagasy small mammal community. Comparisons of Bayesian standard ellipses, as well as (multivariate) mixed-modeling analyses, revealed that the stable isotope niche of R. rattus tended to change seasonally and differed between natural forests and anthropogenic habitats, indicating plasticity in feeding niches. In co-occurrence, R. rattus and R. norvegicus partitioned feeding niches. Isotopic mismatch of signatures of individual R. rattus and the habitat in which they were captured, indicate frequent dispersal movements for this species between natural forest and anthropogenic habitats. Conclusions: Since R. rattus are known to transmit a number of zoonoses, potentially affecting communities of endemic small mammals, as well as humans, these movements presumably increase transmission potential. Our results suggest that due to their generalist diet and potential movement between natural forest and anthropogenic habitats, Rattus spp. might affect native forest-dependent Malagasy rodents as competitors, predators, and disease vectors. The combination of these effects helps explain the invasion success of Rattus spp. and the detrimental effects of this genus on the endemic Malagasy rodent fauna.
Data from: Isotopic niche partitioning between two apex predators over time
1. Stable isotope analyses have become an important tool in reconstructing diets, analyzing resource use patterns, elucidating trophic relations among predators and understanding the structure of food webs. 2. Here, we use stable carbon and nitrogen isotope ratios in bone collagen to reconstruct and compare the isotopic niches of adult South American fur seals (Arctocephalus australis); n = 86) and sea lions (Otaria flavescens); n = 49) –two otariid species with marked morphological differences– in the Río de la Plata estuary (Argentina - Uruguay) and the adjacent Atlantic Ocean during the second half of the 20th century and the beginning of the 21st century. Samples from the middle Holocene (n = 7 fur seals and n = 5 sea lions) are also included in order to provide a reference point for characterizing resource partitioning before major anthropogenic modifications of the environment. 3. We found that the South American fur seals and South American sea lions had distinct isotopic niches during the middle Holocene. Isotopic niche segregation was similar at the beginning of the second half of the 20th century, but has diminished over time. 4. The progressive convergence of the isotopic niches of these two otariids during the second half of the 20th century and the beginning of the 21st century is most likely due to the increased reliance of South American fur seals on demersal prey. 5. This recent dietary change of South American fur seals can be explained by at least two non-mutually exclusive mechanisms: (i) the decrease in the abundance of sympatric South American sea lions as a consequence of small colony size and high pup mortality resulting from commercial sealing; and (ii) the decrease in the average size of demersal fishes due to intense fishing of the larger class sizes, which may have increased their accessibility to those eared seals with a smaller mouth gape, i.e., South American fur seals of both sexes and female South American sea lions.
Isotopic niche overlap between sympatric Australian snubfin and humpback dolphins
<p>Ecological niche theory predicts the coexistence of closely related species is promoted by resource partitioning and leads to the use of different ecological niches. Australian snubfin (<em>Orcaella heinsohni</em>) and humpback (<em>Sousa sahulensis</em>) dolphins live in sympatry throughout most of their range in northern Australia. We compared stable isotope ratios of carbon (δ<sup>13</sup>C) and nitrogen (δ<sup>15</sup>N) in their skin to investigate resource partitioning between these ecologically similar species. Skin samples were collected from live Australian snubfin (n = 31) and humpback dolphins (n = 23) along the east coast of Queensland in 2014-2015. Both species had similar δ<sup>13</sup>C and δ<sup>15</sup>N values and high (>50%) isotopic niche space overlap, suggesting that they feed at similar trophic levels, have substantial dietary overlap, and both rely on similar basal food resources. Despite similarities, snubfin dolphins were more likely to have a larger δ<sup>15</sup>N than humpback dolphins, indicating they may forage on a wider diversity of prey. Humpback dolphins were more likely to have a larger δ<sup>13</sup>C range suggesting they may forage on a wider range of habitats. Overall results suggest that subtle differences in habitat use, and prey selection are likely the principal resource partitioning mechanisms enabling co-existence of Australian snubfin and humpback dolphins.</p>
Data from: Functional traits and environmental conditions predict community isotopic niches and energy pathways across spatial scales
1. Despite ongoing research in food web ecology and functional biogeography, the links between food-web structure, functional traits and environmental conditions across spatial scales remain poorly understood. Trophic niches, defined as the amount of energy and elemental space occupied by species and food webs, may help bridge this divide. 2. Here, we ask how the functional traits of species, the environmental conditions of habitats and the spatial scale of analysis jointly determine the characteristics of trophic niches. We used isotopic niches as a proxy of trophic niches, and conducted analyses at spatial scales ranging from local food webs and metacommunities to geographically distant sites. 3. We sampled aquatic macroinvertebrates from 104 tank bromeliads distributed across five sites from Central to South America, and compiled the macroinvertebrates' functional traits and stable isotope values (δ15N and δ13C). We assessed how isotopic niches within each bromeliad were influenced by the functional trait composition of their associated invertebrates and environmental conditions (i.e., habitat size, canopy cover, and detrital concentration). We then evaluated whether the diet of dominant predators and, consequently, energy pathways within food webs, reflected functional and environmental changes among bromeliads across sites. Finally, we determined the extent to which the isotopic niches of macroinvertebrates within each bromeliad contributed to the metacommunity isotopic niches within each site, and compared these metacommunity-level niches over biogeographic scales. 4. At the bromeliad level, isotopic niches increased with the functional richness of species in the food web and the detrital concentration in the bromeliad. The diet of top predators tracked shifts in prey biomass along gradients of canopy cover and detrital concentration. Bromeliads that grew under heterogeneous canopy cover displayed less trophic redundancy and therefore combined to form larger metacommunity isotopic niches. Finally, the size of metacommunity niches depended on within-site heterogeneity in canopy cover. 5. Our results suggest that the trophic niches occupied by food webs can predictably scale from local food webs to metacommunities to biogeographic regions. This scaling process is determined by both the functional traits of species and heterogeneity in environmental conditions.
Data from: Isotopic and dietary niches as indicators for resource partitioning in the gleaner bats M. bechsteinii, M. nattereri, and P. auritus
The n-dimensional ecological niche summarizes all living requirements of a species. According to the competition and niche theory, co-occurring species have to differ in at least one dimension to live in stable coexistence. Measuring the overall ecological niche within natural ecosystems is probably impossible but methods that describe several dimensions at once like the isotopic niche are good approximations. However, the impact of each factor contributing to the isotopic niche might be difficult to estimate. The dietary niche, as one part of the isotopic niche, can be examined with high resolution using molecular techniques. In this study we aimed to improve our understanding of species coexistence. We outlined the importance of the isotopic and dietary niches in the context of resource partitioning using the bat species M. bechsteinii, M. nattereri, and P. auritus of the gleaner guild as examples. The dietary and isotopic niches were estimated with stable isotope analysis and molecular fecal analysis. We tested (i) how distinct the occupied dietary niches of members of the same guild are and (ii) how similar the dietary and isotopic niches are to each other. While the inter-specific overlap was high for the dietary niche, no overlap could be observed for the isotopic niche. In general, the isotopic niche can describe a more complete picture of the ecological niche, while the dietary niche provides highly detailed information. The combination of both niches might advance our understanding of stable species coexistences.
Data from: The effects of spatial scale and isoscape on consumer isotopic niche width
1. The mean and variance of ecological variables are dependent on sampling attributes such as the coverage of environmental heterogeneity (sampling extent) and spatial scale. Trophic niche width is often approximated by bulk tissue stable isotopes of C and N, i.e. the population isotopic niche. However, recent studies suggest that environmental heterogeneity (experienced by individuals) may be more important in defining the isotopic niche width than trophic variability. We hypothesised that isotopic niche width will increase monotonically with spatial scale, largely produced by environmental variation, e.g. nutrient source. 2. To refine this hypothesis, by describing the shapes of isotope scaling curves, we explored a previously published dataset describing three Chilean intertidal species representing different feeding guilds (grazing snails, suspension feeding mussel). We tested these hypotheses on a new, larger dataset describing three functionally-analogous intertidal species from Northern Ireland. We generated isotopic variance-area curves from a spatially-explicit bootstrap and investigated the scale-dependency of environment-isotope relationships, including wave exposure and sub-habitat heterogeneity. 3. Spatial scale explained 50% of the variance in population isotopic niche widths (bivariate C-N ellipse area) by simple, non-linear relationships. Finer scales (< 1 to 10 km lag) accounted for most variance. Scale dependence was strong for ẟ15N variance, of which > 40% was explained by modelling linear coefficients. A ẟ15N baseline gradient, or isoscape, dominated ẟ15N variance scaling patterns, from sheltered, terrestrially-influenced embayments to exposed, pelagic-dominated coastline. Consumer ẟ13C variance had a weaker scale-dependence, plateauing at mesoscales (> 20 km lag). 4. We show that isotopic niche width is strongly dependent on sampling spatial extent, which controls the environmental heterogeneity experienced by individual consumers. Environmental heterogeneity must be accounted for before isotopic niche width can be considered to accurately represent trophic niche width. Studies conducted at different spatial scales are likely to identify different environment-isotope relationships. 5. We recommend that spatial scale should be incorporated into sampling designs explicitly, easiest by maintaining a consistent lag distance or area within which populations are sampled. Identified isoscapes can be de-trended, where necessary.
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