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Sharks are essential components of marine communities, and their removal might simplify ecosystems and lead to unpredictable and detrimental effects on the food web. Comparing the isotopic niche of species between archaeological and modern communities can provide information to assess temporal changes in the ecological dynamics of communities. Here, stable isotope analysis was used to compare food web topology metrics between two shark guilds or communities, a late Holocene archaeological community (AC) dating from 700 to 500 years ago and a modern community (MC) trophic web, both from South Brazil. In the same line of comparison, we assess the trophic position of a top predator, Carcharias taurus. Results showed topological temporal differences such as higher trophic redundancy and higher patterns of niche overlap in the AC. Higher trophic redundancy could be expected in late Holocene food webs, as similar studies also observed these findings. In contrast, the MC showed less dense packing of species within the isotopic niche space, thus higher niche partitioning and higher trophic diversity, suggesting changing ecological interaction dynamics. We found that Carcharias taurus has increased its trophic level, possibly due to a release from the intraspecific competition and a dietary shift towards larger prey items. We suggest that anthropic impacts, such as overfishing, may cause these differences in the trophic position of this species. We also advocate that this study method might help future trophic reconstructions using shark teeth, as information about past marine environments is scarce, and could serve as a baseline for future studies., Author(s): Guilherme Burg Mayer [sup.1] [sup.2] , Renato Hajenius Aché de Freitas [sup.2] Author Affiliations: (1) grid.411237.2, 0000 0001 2188 7235, Programa de Pós-Graduação em Ecologia, Departamento de Ecologia e [...]

Feeding habits and habitat use inform ecosystem-based management strategies for commercial fish species. A consumer's diet can be assessed through stomach content analysis (SCA), bulk stable isotope analysis (BSIA) and compound-specific stable isotope analysis of amino acids (CSIA-AA). Our research establishes the first approach combining these traditional and novel techniques to provide insight on the movements and trophic ecology of dolphinfish (Coryphaena hippurus) in the Mexican Central Pacific (MCP) during 2013. Dolphinfish SCA (n = 311), muscle [delta].sup.15N and [delta].sup.13C BSIA (n = 148), and [delta].sup.15N CSIA-AA (n = 9) were performed to assess trophic and movement patterns. Diet was composed of 59 prey items. According to the Prey-Specific Index of Relative Importance, the main prey were Argonauta spp. (24%), Portunus xantusii (11%), Dosidicus gigas (7%), and Selar crumenophthalmus (7%). Diet differed between seasons and age class but not by sex. Trophic position did not change with body size based on SCA or SIA with average estimates of 3.5, 4.1, and 4.3 based on BSIA, CSIA, and SCA, respectively. Adult dolphinfish showed a shift in their isotopic niche; bulk [delta].sup.15N values varied widely in adults (â 10â°) suggesting movements through different isoscapes while juveniles had more constrained values consistent with residency within the regional isoscapes. These results were supported by differences in source amino acid [delta].sup.15N mean values between juveniles (4.6â°) and adults (0.8â°). Our findings suggest that the MCP is a migration corridor for dolphinfish between foraging areas across the Eastern Tropical Pacific., Author(s): Sergio A. Briones-Hernández [sup.1] , Víctor H. Galván-Piña [sup.2] , Bernabé Aguilar-Palomino [sup.2] , Fernando R. Elorriaga-Verplancken [sup.1] , A. Vianney Barajas-Calderón [sup.1] , Antonio Delgado-Huertas [sup.3] , Brittany [...]

Fish foraging and energy flow between trophic levels are predicted to decline with freshwater browning due to decreased light availability. Studies investigating these predictions have focused on juvenile and adult fishes; however, the larval stage represents a 'critical period' in development. We investigated the indirect (i.e., prey availability) versus direct (i.e., visual foraging) effects of browning on zooplankton-larval fish interactions by altering water colour with SuperHume (absorbance at 440 nm = 1.6-10.8 [m.sup.-1]). Phytoplankton and zooplankton densities were monitored across treatments for 1 month to simulate the time leading up to fish spawning in the spring. Larval largemouth bass (Micropterus salmoides) were then introduced to assess indirect effects on fish feeding, growth, and survival. Direct effects on largemouth bass and bluegill (Lepomis macrochirus) foraging on zooplankton were determined with separate short-term experiments. Browning did not directly alter the ability of larvae to capture prey. However, indirect effects on larval fish foraging, growth, and survival were observed as phytoplankton and zooplankton abundance decreased with increased browning. Our data suggest browning may reduce energy transfer to larval fish due to a reduction in prey but not visual foraging. Le brunissement de l'eau douce devrait s'accompagner de diminutions de la quete de nourriture par les poissons et des flux energetiques entre niveaux trophiques en raison de la reduction de la disponibilite de lumiere en decoulant. Les etudes qui se penchent sur ces predictions se sont interessees aux poissons juveniles ou adultes; le stade larvaire represente toutefois une << periode critique >> du developpement. Nous avons examine les effets indirects (c.-a-d., la disponibilite de proies) et directs (c.-a-d., la quete visuelle de nourriture) du brunissement sur les interactions entre zooplancton et larves de poisson en modifiant la couleur de l'eau avec du SuperHume (absorbance a 440 nm = 1,6-10,8 [m.sup.-1]). Les densites de phytoplancton et de zooplancton ont ete mesurees pour les differents traitements pendant 1 mois, afin de simuler la periode precedant le frai des poissons au printemps. Des larves d'achigan a grande bouche (Micropterus salmoides) ont ensuite ete introduites, afin d'evaluer les effets indirects sur l'alimentation, la croissance et la survie des poissons. Les effets directs sur des achigans a grande bouche et des crapets arlequin (Lepomis macrochirus) s'alimentant de zooplancton ont ete determines par d'autres experiences de courte duree. Le brunissement n'a pas modifie directement la capacite des larves de capturer des proies. Des effets indirects sur la quete de nourriture, la croissance et la survie des larves de poisson ont toutefois ete observes au fil de la diminution de l'abondance du phytoplancton et du zooplancton a mesure que le brunissement augmentait. Nos donnees donnent a penser que le brunissement pourrait reduire le transfert d'energie aux larves de poisson en raison d'une reduction des proies, mais non la quete visuelle de nourriture. [Traduit par la Redaction], Introduction In recent decades, many freshwater and coastal ecosystems in the Northern Hemisphere have become browner in colour due to an increased export of chromophoric dissolved organic matter (cDOM) from [...]

Using carbon and nitrogen stable isotope values, we analyzed the trophic position (TP) and the isotopic niche width of lanternfishes from three different areas in the Southern Pacific Ocean. Fishes from Perú had slightly higher [delta].sup.13C values compared with fish from Chilean areas. In contrast, [delta].sup.15N values increased with latitude (North to South). Myctophids TP differed between the three study areas (highest in Central Chile, lowest in Peru). Peruvian fishes had a smaller isotopic niche than the lanternfishes of those from Chile., Author(s): Carolina Cárcamo [sup.1] , Pepe Espinoza [sup.2] [sup.3] , Carlos Canales-Cerro [sup.4] , Stephanny Curaz-Leiva [sup.5] , Ana Brisca Guzman-Castellanos [sup.1] [sup.6] , Ivonne Quintanilla [sup.7] , Fernanda Vargas [...]

What Do Gulls Do at Night? Devon McClain, Andrews University and Camp Au Sable; Shandelle Henson and James Hayward, Andrews University; Gordon Atkins, Andrews University and Camp Au Sable Much [...]

Nitrogen stable isotopes ([delta].sup.15N) are typically used to estimate trophic position, providing insight into ecological roles and broader food web structure. Ecological inferences drawn from these estimates rely on quantification of isotopic baselines, i.e., low trophic level organisms reflecting the predominant nitrogen sources that support food web biomass. When baselines vary due to environmental (e.g., temperature) or anthropogenic factors (e.g., nutrient run-off), interpretation of trophic position based on [delta].sup.15N may not be ecologically sound. Here, we tested the effects of assuming stable versus spatially variable [delta].sup.15N baselines used to estimate the trophic position of a cosmopolitan estuarine predator-juvenile bull sharks (Carcharhinus leucas). Sampling across the San Antonio Bay system, TX, USA revealed that baseline consumers exhibited spatially variable [delta].sup.15N values, which were strongly associated with capture salinity representing the influence of anthropogenically introduced nitrogen largely from fluvial run-off. As a result, estimates of bull shark trophic position differed based on baseline assumptions-sharks exhibited an ontogenetic shift in trophic position when spatial variability of baseline [delta].sup.15N was accounted for, while an uncorrected approach indicated no relationship between body size and trophic position. Diet data supported ontogenetic shifts in bull shark diets, with increased consumption of larger-bodied prey among older individuals. Evaluation of isotopic baselines in spatially dynamic ecosystems like estuaries is essential, especially for highly mobile species like sharks that traverse dynamic isoscapes. A literature review revealed that only 16% of studies leveraging stable isotopes to assess the trophic ecology of sharks have accounted for potential spatial variability of isotopic baselines. As such, greater consideration of variability in isotopic baselines is important moving forward considering the ubiquitous application of this technique by ecologists., Author(s): Philip Matich [sup.1] , Oliver N. Shipley [sup.2] , Ornella C. Weideli [sup.3] Author Affiliations: (1) grid.264764.5, Marine Biology Department, Texas A & M University at Galveston, , 1001 [...]

Differences in phenological responses to climate change among species can desynchronise ecological interactions and thereby threaten ecosystem function. To assess these threats, we must quantify the relative impact of climate change on species at different trophic levels. Here, we apply a Climate Sensitivity Profile approach to 10,003 terrestrial and aquatic phenological data sets, spatially matched to temperature and precipitation data, to quantify variation in climate sensitivity. The direction, magnitude and timing of climate sensitivity varied markedly among organisms within taxonomic and trophic groups. Despite this variability, we detected systematic variation in the direction and magnitude of phenological climate sensitivity. Secondary consumers showed consistently lower climate sensitivity than other groups. We used mid-century climate change projections to estimate that the timing of phenological events could change more for primary consumers than for species in other trophic levels (6.2 versus 2.5-2.9 days earlier on average), with substantial taxonomic variation (1.1-14.8 days earlier on average)., Numerous long-term ecological changes have been attributed to climate change (1). Shifts in the seasonal timing of recurring biological events such as reproduction and migration (that is, phenological changes) have [...]

We tested joint effects of predator loss and increased resource availability on the grazers' trophic level and the propagation of trophic interactions in a benthic food web by excluding larger predatory fish from cages and manipulating nutrients in the coastal zone of the Baltic Sea. The combination of nutrient enrichment and excluding larger predators induced an increase in medium-sized predatory fish (three-spined stickleback). The meso-predator fish in turn did not change the total abundance of the invertebrate herbivores, but did cause a substantial shift in their community composition towards the dominance of gastropods by reducing amphipods by 40-60%, while gastropods were left unchanged. The shift in grazer composition generated a 23 times higher producer biomass, but only under nutrient enrichment. Our results show that top-predator declines can substantially shift the species composition at the grazers' level, but that cascading effects on producers by a trophic cascade strongly depend on resource availability., Author(s): Katrin Sieben [sup.1] , Anneke D. Rippen [sup.1] , Britas Klemens Eriksson [sup.1] Author Affiliations: (1) grid.4830.f, 0000000404071981, Department of Marine Benthic Ecology and Evolution, Centre for Ecological and [...]

Quantifying the nutritional quality of forage fish is integral for understanding upper trophic levels as forage fish are the dominant prey for top predator fish, marine mammals, and sea birds. Many existing reports documenting body composition of forage species are not comparable due to confounding effects. This study systematically assessed the variability in proximate composition and energy content of 16 forage species in southeastern Alaska (57.2626 N/133.7394 W) between 2001 and 2004. Variation in energy and lipid contents was related to habitat, epipelagic planktivores varying most, mesopelagics intermediate, and demersal species relatively invariable. Season was the greatest source of variation as a result of short growing seasons at high latitude and energy allocation strategies for reproduction and growth. Among species that varied seasonally, energy and lipid increased over summer and declined during winter. Annual differences in body composition occurred during periods of peak energy content. Sampling recommendations and guidance for bioenergetics models are provided., Author(s): Johanna J. Vollenweider [sup.1] , Ron A. Heintz [sup.1] , Lawrence Schaufler [sup.1] , Robert Bradshaw [sup.1] Author Affiliations: (1) grid.474331.6, 0000 0001 2231 4236, Alaska Fisheries Science Center, [...]

Coprolites offer insights into the diets of the animals that produced them, and thereby also provide a unique perspective of the paleoenvironments and paleoecosystems that existed during their deposition. Late [...]

Food webs depict who eats whom in communities. Ecologists have examined statistical metrics and other properties of food webs, but mainly due to the uneven quality of the data, the results have proved controversial. The qualitative data on which those efforts rested treat trophic interactions as present or absent and disregard potentially huge variation in their magnitude, an approach similar to analyzing traffic without differentiating between highways and side roads. More appropriate data are now available and were used here to analyze the relationship between trophic complexity and diversity in 59 quantitative food webs from seven studies (14-202 species) based on recently developed quantitative descriptors. Our results shed new light on food-web structure. First, webs are much simpler when considered quantitatively, and link density exhibits scale invariance or weak dependence on food-web size. Second, the 'constant connectance' hypothesis is not supported: connectance decreases with web size in both qualitative and quantitative data. Complexity has occupied a central role in the discussion of food-web stability, and we explore the implications for this debate. Our findings indicate that larger webs are more richly endowed with the weak trophic interactions that recent theories show to be responsible for food-web stability. Key words: connectance; diversity; ecological network; food-web stability; scaling; stability; trophic complexity and species diversity.

The flow of energy and nutrients between trophic levels is affected by both the trophic structure of food webs and the diversity of species within trophic levels. However, the combined effects of trophic structure and diversity on trophic transfer remain largely unknown. Here we ask whether changes in consumer diversity have the same effect as changes in resource diversity on rates of resource consumption. We address this question by focusing on consumer--resource dynamics for the ecologically important process of decomposition. This study compares the top-down effect of consumer (detritivore) diversity on the consumption of dead organic matter (decomposition) with the bottom-up effect of resource (detrital) diversity, based on a compilation of 90 observations reported in 28 studies. We did not detect effects of either detrital or consumer diversity on measures of detrital standing stock, and effects on consumer standing stock were equivocal. However, our meta-analysis indicates that reductions in detritivore diversity result in significant reductions in the rate of decomposition. Detrital diversity has both positive and negative effects on decomposition, with no overall trend. This difference between top-down and bottom-up effects of diversity is robust to different effect size metrics and could not be explained by differences in experimental systems or designs between detritivore and detrital manipulations. Our finding that resource diversity has no net effect on consumption in 'brown' (detritus--consumer) food webs contrasts with previous findings from 'green' (plant--herbivore) food webs and suggests that effects of plant diversity on consumption may fundamentally change after plant death. Key words: biodiversity and ecosystem function; detrital processing; resource consumption; trophic structure; trophic transfer.

Stable isotope ratios (typically of carbon and nitrogen) provide one representation of an organism's trophic niche and are widely used to examine aspects of food web structure. Yet stable isotopes have not been applied to quantitatively characterize community-wide aspects of trophic structure (i.e., at the level of an entire food web). We propose quantitative metrics that can be used to this end, drawing on similar approaches from ecomorphology research. For example, the convex hull area occupied by species in [[delta].sup.13]C-[[delta].sup.15]N niche space is a representation of the total extent of trophic diversity within a food web, whereas mean nearest neighbor distance among all species pairs is a measure of species packing within trophic niche space. To facilitate discussion of opportunities and limitations of the metrics, we provide empirical and conceptual examples drawn from Bahamian tidal creek food webs. These examples illustrate how this methodology can be used to quantify trophic diversity and trophic redundancy in food webs, as well as to link individual species to characteristics of the food web in which they are embedded. Building from extensive applications of stable isotope ratios by ecologists, the community-wide metrics may provide a new perspective on food web structure, function, and dynamics. Key words: biodiversity; diet; ecomorphology; food webs; functional groups; niche; predator-prey imeractions; trophic guild; trophic redundancy.