Degree Of Individual Specialization Research Articles

First data on the consumed prey by Speleomantes italicus from the Republic of San Marino

We here present the first study on the consumed prey by an epigean population of the Italian cave salamander (Speleomantes italicus) from the Republic of San Marino. Using the harmless technique of stomach flushing, we aimed to provide the first data on the diet and on the degree of individual specialization that characterizes the studied population. We performed two-night surveys (one in autumn 2022 and one in spring 2023) in which we opportunistically searched for salamanders in forested areas and dry walls. Captured salamanders were sexed, weighed, photographed, measured and stomach flushed. Overall, we inspected the stomach contents of 67 individuals, recognizing 1,018 prey items belonging to 28 different prey categories. The examined population was mainly composed by generalist individuals, and no differences in number and diversity of prey consumed were observed among salamanders. Contrarily to what has been observed in other Speleomantes species, flying prey provided a minor contribution to the diet of the investigated population. Our study produced the first information on the diet of Speleomantes italicus from the Republic of San Marino, representing the starting point for future assessments on the dietary habits of this specific population.

Geographical, temporal, and individual-based differences in the trophic ecology of female Cape fur seals.

Information on resource use and trophic dynamics of marine predators is important for understanding their role in ecosystem functioning and predicting population-level responses to environmental change. Where separate populations experience different local environmental conditions, geographic variability in their foraging ecology is often expected. Within populations, individuals also vary in morphology, physiology, and experience, resulting in specialization in resource use. In this context, isotopic compositions of incrementally grown tissues such as keratinous hairs offer a valuable opportunity to study long-term variation in resource and habitat use. We investigated the trophic ecology of female Cape fur seals (Arctocephalus pusillus pusillus) using carbon and nitrogen isotopic compositions of serially sampled whiskers collected at four breeding sites along the coast of South Africa. Drawing on over 900 isotopic measurements, we assessed geographic variability in isotopic niche width between colonies and the degree of individual specialization. We found slight, but clear geographic differences in isotopic ratios and isotopic niche widths, seemingly related to ecological setting, with niche widths being proportional to the area of available shelf and shelf-slope habitat surrounding the colony. We further identified periodic oscillations in isotopic ratios, which likely reflect temporal patterns in foraging distribution and prey type, linked to shifts in the availability of prey resources and their interaction with constraints on individual females throughout their breeding cycle. Finally, individual specialization indices revealed that each of the study populations contain specialist individuals that utilize only a small subset of the total population niche width. The degree of individual specialization was, however, not consistent across colonies and may reflect an interactive influence between density-dependent effects and habitat heterogeneity. Overall, this study provides important information on the trophic ecology of Cape fur seals breeding in South Africa and highlights the need to consider geographic and individual variability when assessing the foraging ecology of marine predators.

Diet and disturbance: Seaside Sparrow resource use driven by oiling and Hurricane Isaac

The 2010 Deepwater Horizon (DWH) disaster led to extensive oil deposition in Louisiana’s coastal wetlands, followed two years later by Hurricane Isaac. These disturbances led to changes in saltmarsh invertebrate communities, potentially affecting higher-level predators and the saltmarsh food web. Seaside Sparrows (Ammospiza maritima) are ubiquitous, year-round residents of the coastal saltmarsh affected by the DWH spill, where they consume diverse invertebrates and may be considered an indicator species for the ecosystem’s integrity. We used DNA metabarcoding to evaluate prey consumed by Seaside Sparrows to understand how sparrows responded to residual contamination from the DWH oil spill and ecosystem disturbance caused by Hurricane Isaac. To do so, we evaluated metrics of diet (prey richness, diversity, overall diet composition) and resource use (total niche width, individual specialization) from 2011 to 2017 on oiled, unoiled, and reference sites. We found that while diet composition varied across years and site type, Hurricane Isaac had an even greater effect on the richness and diversity of prey consumed. Resource use—as measured by the total niche width of the populations and degree of individual specialization—was most stable on unoiled sites compared to unoiled and reference sites. Finally, we analyzed resource use for each combination of site type and year (i.e.: “2014 oiled sites”), which indicated a strong correlation between individual specialization and total niche width: as total niche width increased, individuals became more specialized, following the predictions of the Niche Variation Hypothesis.

Human food subsidies drive individual specialization and intrapopulation dietary differences in a generalist predator

AbstractGeneralist species can exhibit individual specialization (IS), where individuals adopt specialized foraging behaviors not attributable to age, sex, or social dominance. While IS increases with the diversity of available foraging resources (ecological opportunity), the potential impact of human food subsidies on ecological opportunity is unknown. We quantified the isotopic niche width of Steller's Jays (Cyanocitta stelleri), a synanthropic predator and dietary generalist, across a gradient of human land‐use categories ranging from subsidized (park campgrounds) to unsubsidized (forest interior) habitats in a protected area in California. We asked (1) if isotopic niche width was better predicted by individual foraging behavior than sex, social dominance, or habitat category (indicating IS) and (2) if degree of IS exhibited by jays increased with the availability of human food subsidies. We characterized the isotopic niche space occupied by individual jays relative to the population using carbon (δ13C) and nitrogen (δ15N) isotope values. Using linear models, we found that jay diet variation was best explained by individual behavior and habitat use rather than by sex or social dominance. While the degree of IS increased with the availability of human foods, individual jays exhibited a variety of foraging behaviors in all habitats that were segregated by foraging stratum and use of human foods. Individual diet also determined the degree of specialization, as jays that specialized on human foods had the narrowest niche width regardless of habitat. Management efforts targeted at generalist wildlife exhibiting large degrees of IS should therefore account for the impact of food subsidies on foraging behavior. Approaches that involve aversive conditioning may fail where highly specialized individuals are unlikely to encounter treatments; therefore, we recommend simultaneous efforts to limit human food subsidies (e.g., information campaigns and improved containment of human food and food waste), and deployment across the largest possible extent of foraging microhabitats and substrates in order to ensure exposure of whole populations to emetic eggs.

Linking agricultural practices to lizard trophic behaviour: An ecological approach

Among intensive agricultural practices, pesticides, mowing, and heavy agricultural machineries have become an important tool to maximize harvesting and secure animal husbandry. However, they are also cause of agricultural ecosystem decline, often leading to degradation of key micro-habitat features for many species, higher predation risk and lower food availability. We investigated the diet and foraging ecology of the Italian wall lizard in agricultural areas to determine whether different management practices (conventional, organic, and control) can affect (i) the structure of the trophic niche of the species; (ii) prey diversity, the degree of individual specialization, and the overall population feeding strategy; (iii) lizards' health status. Faecal pellets were collected for diet composition analyses, while prey diversity in the environment was estimated by placing adhesive traps. Lizards' body condition did not differ among management type although males from control field resulted slightly larger than those from conventional and organic areas. The species showed a generalist (conventional and organic areas) and mixed (control area) feeding strategy with a preference for coleopterans. Although a different prey diversity was found in control areas compared to organic and conventional ones, diet composition and the importance of specific food items was similar among management types. This may suggest that management activities may have affected the overall prey availability and indirectly influenced lizard trophic behaviour. Our study provides a comprehensive knowledge on the feeding ecology of P. siculus in managed habitats, which may have useful implications for the overall conservation of lizards in agricultural environments.

Feeding Strategies of Co-occurring Newt Species across Different Conditions of Syntopy: A Test of the “Within-Population Niche Variation” Hypothesis

Intraspecific trait variation in generalist animals is widespread in nature, yet its effects on community ecology are not well understood. Newts are considered opportunistic feeders that may co-occur in different syntopic conditions and represent an excellent model for studying the role of individual feeding specialization in shaping the population dietary strategy. Here, we investigated the diet of three newt species from central Italy occurring in artificial habitats in different coexistence conditions to test the predictions of the niche width (NW) variation hypotheses. Population NW did not vary among species and between presence and absence of coexisting species. An overall positive relationship between individual specialization and population NW was observed. However, this pattern was disrupted by the condition of syntopy with newt populations showing an individual NW variation invariant with population NW in presence of coexisting species, whereas it was larger in populations occurring alone. The observed pattern of newt behavior was not consistent with any of the proposed scenarios. We found a consistent pattern with the degree of individual specialization being (1) size-dependent (specialized individuals increasing within larger sized species) and (2) assemblage-complexity-dependent (specialized individuals increasing in syntopic populations in comparison to singly populations).

Specialized foraging habits of adult female California sea lions Zalophus californianus

AbstractIndividual foraging specialization occurs when organisms use a small subset of the resources available to a population. This plays an important role in population dynamics since individuals may have different ecological functions within an ecosystem related to habitat use and prey preferences. The foraging habitat fidelity and degree of specialization of California sea lions (Zalophus californianus) were evaluated by analyzing the stable isotopes values of carbon and nitrogen in vibrissae collected from 16 adult females from the reproductive colony on Santa Margarita Island, Magdalena Bay, Mexico, in 2012 and 2013. Based on the degree of individual specialization in δ15N, 62.5% of the females assessed can be considered specialist consumers focusing on the same prey or different prey from the same trophic level. The degree of individual specialization in δ13C indicated that 100% of the individuals showed fidelity to their foraging habitat as some fed in the lagoon, others foraged along the coast, and a third group preferred prey from the pelagic environment during both the breeding and nonbreeding seasons, suggesting diversification of foraging areas. Foraging area fidelity persisted despite the 2°C increase in the sea surface temperature over the course of the study period.

Stable isotopes reveal opportunistic foraging in a spatiotemporally heterogeneous environment: Bird assemblages in mangrove forests.

Environmental heterogeneity can foster opportunistic foraging by mobile species, resulting in generalized resource and habitat use. Determining species’ food web roles is important to fully understand how ecosystems function, and stable isotopes can provide insight into the foraging ecology of bird assemblages. We investigated flexibility of food choice in mangrove bird assemblages of northeast Australia by determining whether species’ carbon and nitrogen isotopic values corresponded to foraging group classification described in the literature, such as groups of species that are omnivorous or insectivorous. Subsequently, we evaluated foraging group isotopic niche size, overlap, degree of individual specialisation, and the probable proportions of coastal resources that contribute to their collective diets. We found that mangrove birds are more opportunistic when foraging than expected from previous diet studies. Importantly, relationships between the dietary diversity of species within a foraging group and isotopic niche size are spatially inconsistent, making inferences regarding foraging strategies difficult. However, quantifying individual specialisation and determining the probable relative contributions of coastal resources to the collective diet of isotope-based foraging groups can help to differentiate between specialised and generalised foraging strategies. We suggest that flexibility in mangrove bird foraging strategy occurs in response to environmental heterogeneity. A complementary approach that combines isotopic analysis with other dietary information (collated from previous diet studies using visual observation or gut content analyses) has provided useful insight to how bird assemblages partition resources in spatiotemporally heterogeneous environments.

Drivers of individual niche variation in coexisting species.

Although neglected by classic niche theory, individual variation is now recognized as a prevalent phenomenon in nature with evolutionary and ecological relevance. Recent theory suggests that differences in individual variation across competitors can affect species coexistence and community patterns. However, the degree of individual variation is flexible across wild populations and we still know little about the ecological drivers of this variation across populations of single species and, especially, across coexisting species. Here, we aimed to (a) elucidate the major drivers of individual niche variation in natural communities and (b) to determine how consistent this variation is across coexisting species and communities. We analysed natural patterns of individual-level niche variation in four species of coexisting generalist frogs across a wide range of tropical communities. Specifically, we used gut contents and stable isotopes (δ13 C and δ15 N) from frog species and their prey to quantify individual niche specialization. Then, we combined data on local community structure, availability of prey, phylogenetic relationships and predator-prey size models to test how this variation is related to four ecological factors which are predicted to be key drivers of individual specialization: intraspecific competition, interspecific competition, ecological opportunity (i.e., diversity of resources) and predation. We found that the degree of individual trophic specialization varied by up to ninefold across populations within the same species. This sizable variation in trophic specialization across populations was at least partially explained by gradients of density of competitors (both conspecifics and heterospecifics) and intraguild predation. However, the specific relationships between individual specialization and these ecological gradients were strongly species-specific. As consequences, the identity of the species with more individual variation changed among sites and there was typically no spatial correlation in the degree of individual specialization across coexisting species. Our results show that individual niche specialization within and across species can be strongly context-dependent and that hierarchies of individual variation among coexisting species are not necessarily consistent across communities. Recent theory suggests that this pattern could lead to concurrent changes in competitive interactions across sites and thereby could play a key role in species coexistence at the landscape level. Our results suggest that individual variation across and within coexisting species has the potential to affect not only species coexistence at local communities, but also regional diversity patterns.

Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes

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 578:243-251 (2017) - DOI: https://doi.org/10.3354/meps12124 Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes Joan Navarro1,2,*, David Grémillet2, Francisco J. Ramirez1, Isabel Afán1, Willem Bouten3, Manuela G. Forero1 1Estación Biológica de Doñana CSIC, Avda. Américo Vespucio s/n, Sevilla 41092, Spain 2Centre d’Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, 34293 Montpellier, France 3Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics IBED, University of Amsterdam, PO Box 94248, 1090 GE Amsterdam, The Netherlands *Corresponding author: joan@ebd.csic.esAdvance View was available online May 15, 2017 ABSTRACT: Population expansions of successful species have gained importance as a major conservation and management concern. The success of these ‘winners’ is widely attributed to their high adaptability and behavioural plasticity, which allow them to efficiently use opportunities provided by human-modified habitats. However, most of these studies consider conspecifics as ecological equivalents, without considering the individual components within populations. This is critical for a better understanding of the main ecological mechanisms related to the success of winning species. Here, we investigated the spatial ecology of the opportunistic yellow-legged gull Larus michahellis, a clear example of a winning species in southern Europe, to examine its degree of individual specialization in habitat use. To test for such individual strategies, we applied specialization metrics to spatial data obtained from 18 yellow-legged gulls that were GPS-tracked simultaneously during the breeding season. The results revealed that population-level generalism in habitat use in the yellow-legged gull arises through varying levels of individual specialization, and individual spatial segregation within each habitat. Importantly, we found that the combination of individual specialization and individual spatial segregation may reduce intra-specific competition, with these 2 important mechanisms driving the success of this winning species. KEY WORDS: Foraging strategies · Gulls · GPS · Habitat use · Individual specialization · Movement ecology · Opportunistic seabirds · Seabird · Spatial ecology · Winning species Full text in pdf format PreviousNextCite this article as: Navarro J, Grémillet D, Ramirez FJ, Afán I, Bouten W, Forero MG (2017) Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes. Mar Ecol Prog Ser 578:243-251. https://doi.org/10.3354/meps12124 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 578. Online publication date: August 31, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 32:309-319 (2017) - DOI: https://doi.org/10.3354/esr00812 Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry Megan G. Chevis1,2, Brendan J. Godley1, James P. Lewis3, Julie Jackson Lewis2, Kylie L. Scales4,5, Rachel T. Graham2,* 1Centre for Ecology and Conservation, University of Exeter, Penryn Campus, TR10 9EZ, UK 2MarAlliance, 32 Coconut Drive/PO Box 283, San Pedro, Ambergris Caye, Belize 3Amphibian Survival Alliance, International Conservation House, 7078 Airlie Road, Warrenton, VA 20187, USA 4Institute of Marine Sciences, University of California, Santa Cruz, CA 95064, USA 5NOAA Southwest Fisheries Center, Environmental Research Division, 99 Pacific Street, Suite #255A, Monterey, CA 93950, USA *Corresponding author: rachel@maralliance.org ABSTRACT: Understanding the ecological interactions that underlie marine ecosystem functioning requires sufficient data describing habitat use by mobile species. Hawksbill turtles Eretmochelys imbricata are considered a key species in coral reef-associated communities, owing to their specific foraging preferences, yet new information is still revealing details of the spatial and temporal aspects of habitat use. We used passive acoustic telemetry to monitor the movements of 18 juvenile hawksbills (minimum curved carapace length: 32.0-59.7 cm, mean ± SD = 43.9 ± 6.7 cm) at a developmental foraging site in a Mesoamerican barrier reef, Lighthouse Reef Atoll in Belize (tracking duration 10-1414 d, mean ± SD = 570 ± 484 d). Although specific home ranges were difficult to quantify, several turtles showed high site fidelity over timescales of months to years, with occasional wide-ranging use of the atoll. Diel variation in the number of detections received strongly suggest nocturnal resting. Long-term tracking data reveal 3 degrees of site fidelity across the atoll, based on the number of detection days near individual stations: high residency (n = 4 turtles), sequential residency (n = 5), and transient behavior (n = 4). These variations in movement raise questions about the differentiation of foraging habitats and degree of individual specialization within this population, as well as the influences of microhabitats and human disturbance. KEY WORDS: Spatial ecology · Home range · Belize · Habitat use · Site fidelity · Marine megafauna · World Heritage Site Full text in pdf format Supplementary material PreviousNextCite this article as: Chevis MG, Godley BJ, Lewis JP, Jackson Lewis J, Scales KL, Graham RT (2017) Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry. Endang Species Res 32:309-319. https://doi.org/10.3354/esr00812 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 32. Online publication date: March 28, 2017 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2017 Inter-Research.

Latitudinal variation in ecological opportunity and intraspecific competition indicates differences in niche variability and diet specialization of Arctic marine predators.

Individual specialization (IS), where individuals within populations irrespective of age, sex, and body size are either specialized or generalized in terms of resource use, has implications on ecological niches and food web structure. Niche size and degree of IS of near‐top trophic‐level marine predators have been little studied in polar regions or with latitude. We quantified the large‐scale latitudinal variation of population‐ and individual‐level niche size and IS in ringed seals (Pusa hispida) and beluga whales (Delphinapterus leucas) using stable carbon and nitrogen isotope analysis on 379 paired ringed seal liver and muscle samples and 124 paired beluga skin and muscle samples from eight locations ranging from the low to high Arctic. We characterized both within‐ and between‐individual variation in predator niche size at each location as well as accounting for spatial differences in the isotopic ranges of potential prey. Total isotopic niche width (TINW) for populations of ringed seals and beluga decreased with increasing latitude. Higher TINW values were associated with greater ecological opportunity (i.e., prey diversity) in the prey fish community which mainly consists of Capelin (Mallotus villosus) and Sand lance (Ammodytes sp.) at lower latitudes and Arctic cod (Boreogadus saida) at high latitudes. In beluga, their dietary consistency between tissues also known as the within‐individual component (WIC) increased in a near 1:1 ratio with TINW (slope = 0.84), suggesting dietary generalization, whereas the slope (0.18) of WIC relative to TINW in ringed seals indicated a high degree of individual specialization in ringed seal populations with higher TINWs. Our findings highlight the differences in TINW and level of IS for ringed seals and beluga relative to latitude as a likely response to large‐scale spatial variation in ecological opportunity, suggesting species‐specific variation in dietary plasticity to spatial differences in prey resources and environmental conditions in a rapidly changing ecosystem.

Does intraspecific competition promote variation? A test via synthesis.

Competitive diversification, that is, when increasing intraspecific competition promotes population niche expansion, is commonly invoked in evolutionary studies and currently plays a central role in how we conceptualize the process of adaptive diversification. Despite the frequency with which this idea is cited, the empirical evidence for the process is somewhat limited, and the findings of these studies have yet to be weighed objectively through synthesis. Here, we sought to fill this gap by reviewing the existing literature and collecting the data necessary to assess the evidence for competition as a diversifying force. Additionally, we sought to test a more recent hypothesis, which suggests that competition can act to both promote and inhibit dietary diversification depending on the degree to which a consumer depletes its resources. The surprising result of this synthesis was that increasing competition did not have a mean positive effect on population‐level diet breadth or the degree of individual specialization. Instead, we found that increasing intraspecific competition had a restricting effect on population‐level diet breadth in as many cases as it had a diversifying effect. This wide disparity in the effect of competition on consumer diet variation was negatively related to a metric for consumer resource depletion. Altogether, these findings call into question a long‐standing assumption of basic evolutionary models and lend some support to recent theoretical predictions. Specifically, these findings support the idea that competition is primarily diversifying for species with a small effect (per unit biomass) on their resources and that resource depletion limits the diversifying effect of competition for consumers with larger ecological effects.

Determinants of individual foraging specialization in large marine vertebrates, the Antarctic and subantarctic fur seals

The degree of individual specialization in resource use differs widely among wild populations where individuals range from fully generalized to highly specialized. This interindividual variation has profound implications in many ecological and evolutionary processes. A recent review proposed four main ecological causes of individual specialization: interspecific and intraspecific competition, ecological opportunity and predation. Using the isotopic signature of subsampled whiskers, we investigated to what degree three of these factors (interspecific and intraspecific competition and ecological opportunity) affect the population niche width and the level of individual foraging specialization in two fur seal species, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis), over several years. Population niche width was greater when the two seal species bred in allopatry (low interspecific competition) than in sympatry or when seals bred in high-density stabilized colonies (high intraspecific competition). In agreement with the niche variation hypothesis (NVH), higher population niche width was associated with higher interindividual niche variation. However, in contrast to the NVH, all Antarctic females increased their niche width during the interbreeding period when they had potential access to a wider diversity of foraging grounds and associated prey (high ecological opportunities), suggesting they all dispersed to a similar productive area. The degree of individual specialization varied among populations and within the annual cycle. Highest levels of interindividual variation were found in a context of lower interspecific or higher intraspecific competition. Contrasted results were found concerning the effect of ecological opportunity. Depending on seal species, females exhibited either a greater or lower degree of individual specialization during the interbreeding period, reflecting species-specific biological constraints during that period. These results suggest a significant impact of ecological interactions on the population niche width and degree of individual specialization. Such variation at the individual level may be an important factor in the species plasticity with significant consequences on how it may respond to environmental variability.

Is different degree of individual specialization in three spider species caused by distinct selection pressures?

Individual specialization (IS), i.e. the relatively narrower niche of individuals compared to their population, can be caused by the interplay between intrinsic and extrinsic factors. We studied IS on prey type and size in three congeneric euryphagous sympatrically occurring species: Philodromus albidus, Philodromus aureolus, and Philodromus cespitum. We performed prey acceptance experiments in standardized laboratory conditions using adult females. We also studied possible factors affecting IS. As intrinsic factors, we measured aggressiveness toward prey and spider size as the measures of behavioral and morphological differences, respectively. As extrinsic factors, we studied the composition of the guild of actively hunting spiders in the area from where the philodromids were collected. We computed the degree of inter- and intraspecific crowding as a measure of inter- and intraspecific competition, respectively. Then we computed competition coefficients from census data in order to estimate the strength of interspecific competition among three species. There was no IS on prey type in any studied species. In terms of prey size, only P. albidus was found to be individually specialized, while there was no IS in the other two species. There was a significant effect of aggressiveness, but no significant effect of body size on IS in P. albidus. This species was the least aggressive of the studied species. The philodromids were the dominant actively hunting spiders in the study area. P. albidus was exposed to a relatively higher degree of interspecific than intraspecific competition, whereas in the other philodromids the situation was reversed. The presence of interspecific competition between P. albidus and the other two species was confirmed by the census data analysis. We documented context-dependent IS in Philodromus species. We argue that the higher degree of IS in P. albidus was influenced by interference competition mainly from the other two philodromid species. The niches of the other two species were influenced by food limitation, which decreased their IS.

Temporal consistency and individual specialization in resource use by green turtles in successive life stages

Not all individuals in a population use the same subset of dietary and habitat resources. Patterns of individual specialization have been documented in an increasing number of organisms, but often without an associated time scale over which niche specialization was observed. We examined the patterns in individual resource use through time and in relation to the population with metrics of temporal consistency and degree of individual specialization. We used stable isotope analysis of carbon and nitrogen in successive subsections of scute tissue from the carapace to compare foraging patterns in three successive life stages of the green turtle (Chelonia mydas). Temporal consistency was measured as the mean within-individual variation in stable isotope values through time, whereas the degree of individual specialization was a ratio of the individual variation to that of the population. The distinction between these two parameters is important, as the metric of temporal consistency quantifies the regularity of individual resource use, and the degree of individual specialization indicates what proportion of the population niche an average individual uses. The scute record retains a chronological history of resource use and was estimated to represent a minimum 0.8 years in juveniles to a maximum of 6.5 years in adults. Both temporal consistency and individual specialization varied significantly among life stages. Adults were highly consistent in resource use through time and formed a generalist population with individual specialists maintaining long-term patterns in resource use. Oceanic and neritic juvenile life stages exhibited less temporal consistency in resource use with less individual specialization than adults. These observations are important when considering the ecological roles filled by green turtles in each life stage; also, individual differences in resource use may result in differential fitness consequences.

Spécialisation individuelle et division sociale du travail : Une lecture dynamique d'A. Smith, A. Marshall et A. Young

Résumé Smith a considéré la spécialisation individuelle comme une conséquence négative à subir en matière de développement humain. Cette approche a été reprise par le courant marxiste autour du thème de l’aliénation. Pour Marshall au contraire, la mécanisation de l’industrie permet progressivement une réduction du degré de spécialisation individuelle. Pour Young, l’expansion des systèmes mécanisés est lui-même un processus de division du travail entre industries et elle est devenue la principale source des rendements croissants. Suivant cette approche, la division sociale du travail, contrairement à l’idée de Smith et de Marx, permet de sortir du déterminisme de l’aliénation.

Stress Tolerance of Ecosystems

It is conventionally argued that a stable ecosystem, namely one with high species-diversity and high constancy in physical parameters, is less sensitive to additional stress than a system with varying physical parameters and low species-diversity. By this logic, the Baltic would be more susceptible to additional stress, such as that of pollution, than the North Sea.Examples of irreparable damage to some of the most stable ecosystems in the world, such as coral reefs and tropical rain-forests, suggest, on the contrary, that these systems are more vulnerable than low-diversity ecosystems, such as a brackish-water zone in the mouth of a river or a coniferous forest in a temperate region.Studies of stress tolerance in estuaries showed that the species already living under stress, such as that of reduced and changing salinities, were more tolerant to pollution than species in a less fluctuating environment. This adaptability to environmental changes seems to be characteristic of ecosystems with a low degree of individual specialization and high genetic diversity (i.e. a large number of alleles). Following this conclusion, we question the underlying assumptions in the statement that for example the Baltic Sea, which can be regarded as a large estuary, is an area particularly susceptible to stress; purely marine ecosystems are probably more sensitive.Ecosystem stress-tolerance should be made a top priority in ecological research; this is a necessity inter alia for future localization of industries, in order to minimize their effects on the environment.