应用脂肪酸组成研究热带东太平洋同域中上层鲨鱼营养生态位分化

物种对食物资源利用方式的差异,即营养生态位分化是物种共存的先决条件之一,对种间营养生态位的比较研究有助于了解同域分布物种的共存机制。脂肪酸组成可反映生物较长时间尺度的摄食信息,对探讨物种间营养生态位分化具有重要指示作用。热带东太平洋主要栖息有8种大型中上层鲨鱼,大青鲨(Prionace glauca)、大眼长尾鲨(Alopias superciliosus)、镰状真鲨(Carcharhinus falciformis)、长鳍真鲨(Carcharhinus longimanus)、浅海长尾鲨(Alopias pelagicus)、尖吻鲭鲨(Isurus oxyrinchus)、路氏双髻鲨(Sphyrna lewini)和锤头双髻鲨(Sphyrna zygaena),通过比较其肌肉脂肪酸组成,分析种间食性差异,营养关系及营养生态位分化。结果表明,尖吻鲭鲨营养级相对较高,大青鲨相对较低。3种鼠鲨与5种真鲨存在食性差异或栖息地隔离。浅海长尾鲨与大眼长尾鲨营养生态位重叠程度较高,存在激烈的资源竞争。大青鲨与镰状真鲨生态位宽度较大,表征其对环境的可塑性较强;尖吻鲭鲨和路氏双髻鲨生态位宽度较小,表现为其食性的特化。本研究解释了脂肪酸组成分析在鲨鱼摄食研究中的潜在应用,对分析大洋性鲨鱼的营养生态位分化,资源分配方式及同域共存机制有一定的应用价值。     

Trophic consequences of non‐native species for commercial fish in a backwater bay of the Three Gorges Reservoir,Southwest China

Trophic niche overlap in native and alien fish species can lead to competitive interactions whereby non‐native fishes outcompete indigenous individuals and eventually affect the viability of natural populations. The species Erythroculter mongolicus and Erythroculter ilishaeformis (belonging to the Culterinae), which are two commercially important fish species in the backwater bay of the Pengxi River in the Three Gorges Reservoir (TGR), were threatened by competition from the non‐native Coilia ectenes (lake anchovy). The latter is an alien species introduced into the lower reaches of the Yangtze River in China and now widespread in the TGR. The trophic consequences of non‐native lake anchovy invasion for E. mongolicus and E. ilishaeformis were assessed using stable isotope analysis (δ¹³C and δ¹⁵N) and associated metrics including the isotopic niche, measured as the standard ellipse area. The trophic niche of native E. mongolicus had little overlap (<15%) with the alien fish species and was significantly reduced in size after invasion by lake anchovy. This suggests that E. mongolicus shifted to a more specialized diet after invasion by lake anchovy. In contrast, the trophic niche overlap of native fish E. ilishaeformis with the alien fish species was larger (>50%) and the niche was obviously increased, implying that fish in this species exploited a wider dietary base to maintain their energetic requirements. Thus, marked changes for the native E. mongolicus and E. ilishaeformis were detected as the trophic consequences of invasion of non‐native lake anchovy.     

Pulsed resource availability changes dietary niche breadth and partitioning between generalist rodent consumers

Identifying the mechanisms that structure niche breadth and overlap between species is important for determining how species interact and assessing their functional role in an ecosystem. Without manipulative experiments, assessing the role of foraging ecology and interspecific competition in structuring diet is challenging. Systems with regular pulses of resources act as a natural experiment to investigate the factors that influence the dietary niches of consumers. We used natural pulses of mast‐fruiting of American beech (Fagus grandifolia) to test whether optimal foraging or competition structure the dietary niche breadth and overlap between two congener rodent species (Peromyscus leucopus and P. maniculatus), both of which are generalist consumers. We reconstructed diets seasonally over a 2‐year period using stable isotope analysis (δ¹³C, δ¹⁵N) of hair and of potential dietary items and measured niche dynamics using standard ellipse area calculated within a Bayesian framework. Changes in niche breadth were generally consistent with predictions of optimal foraging theory, with both species consuming more beechnuts (a high‐quality food resource) and having a narrower niche breadth during masting seasons compared to nonmasting seasons when dietary niches expanded and more fungi (a low‐quality food source) were consumed. In contrast, changes in dietary niche overlap were consistent with competition theory, with higher diet overlap during masting seasons than during nonmasting seasons. Overall, dietary niche dynamics were closely tied to beech masting, underscoring that food availability influences competition. Diet plasticity and niche partitioning between the two Peromyscus species may reflect differences in foraging strategies, thereby reducing competition when food availability is low. Such dietary shifts may have important implications for changes in ecosystem function, including the dispersal of fungal spores.     

Food resource partitioning of the <Emphasis Type="Italic">Mustelus lunulatus</Emphasis> and <Emphasis Type="Italic">Mustelus henlei</Emphasis> (Elasmobranchii: Carcharhiniformes)

The feeding habits and trophic ecology of Mustelus lunulatus and Mustelus henlei in the central coast of the Colombian Pacific were evaluated and compared to determine whether there was trophic niche overlap or resource partitioning between these two sympatric shark species. A total of 59 prey items were identified and grouped into 10 taxonomic categories. Mustelus lunulatus fed in large proportion on Stomatopoda and Brachyura, whereas M. henlei fed almost exclusively on Teleostei. Dendrobranchiata, Cephalopoda, Anomura and Polychaeta complemented the diets of both species. There were significant differences in diet between the two species, and there was an ontogenetic diet shift in Mustelus lunulatus, with Stomatopoda being the main prey item of juveniles and Brachyura the main prey item of adults. Dietary overlap (by sex and size) was low between species, but it was high for each species, with significant overlap between juveniles and adults of M. lunulatus and M. henlei, and between males and females of M. henlei. There were differences in the trophic levels of the species, sexes and sizes. This study suggests there is food resource partitioning, and differing ecological function of the two Mustelus species in the food web of the study area.     

Foraging ecology and niche overlap in pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales from waters of the U.S. mid‐Atlantic coast

A complementary approach of stomach content and stable isotope analyses was used to characterize the foraging ecology and evaluate niche overlap between pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales stranded on the U.S. mid‐Atlantic coast between 1998 and 2011. Food habits analysis demonstrated both species were primarily teuthophagous, with 35 species of cephalopods, and 2 species of mesopelagic fishes represented in their overall diets. Pianka's Index of niche overlap suggested high overlap between whale diets (O_n = 0.92), with squids from the families Histioteuthidae, Cranchidae, and Ommastrephidae serving as primary prey. Pygmy sperm whales consumed slightly larger prey sizes (mean mantle length [ML] = 10.8 cm) than dwarf sperm whales (mean ML = 7.8 cm). Mean prey sizes consumed by pygmy sperm whales increased with growth, but showed no trend in dwarf sperm whales. Significant differences were not detected in δ¹⁵N and δ¹³C values of muscle tissues from pygmy (10.8‰ ± 0.5‰, ?17.1‰ ± 0.6‰), and dwarf sperm whales (10.7‰ ± 0.5‰, ?17.0‰ ± 0.4‰), respectively. Isotopic niche widths also did not differ significantly and dietary overlap was high between the two species. Results suggest the feeding ecologies of the pygmy and dwarf sperm whales are similar and both species occupy equivalent trophic niches in the region.     

New insights into the trophic ecology of the scalloped hammerhead shark,Sphyrna lewini,in the eastern tropical Pacific Ocean

Scalloped hammerhead shark, Sphyrna lewini, is considered a generalist predator, showing individual specializations and different trophic levels. This species inhabits both oceanic islands and coastal nursery areas in the eastern tropical Pacific (ETP) Ocean. Existing trophic ecology studies on S. lewini have been focused on stomach contents. This study provides new insights into its foraging preferences, habitat use, and trophic position, using stable isotope analysis (SIA) of muscle tissue. Stable isotope signatures of δ¹³C and δ¹⁵N were determined in S. lewini muscles (n?=?29) from the Ecuadorian Pacific in 2013. Trophic position (TP), isotopic niches, and overlap of S. lewini were estimated by sex, age, and maturity stages to infer their dietary habits throughout life stages. SIA revealed complex movement patterns related to sex and age classes of S. lewini, highlighting high degrees of dietary plasticity and habitat use, with a stronger relation to coastal regions than previously reported. This study provides crucial information regarding essential areas and the related migration behavior of S. lewini, with important implications for their conservation and management in the ETP.

     

Are howler monkey species ecologically equivalent? Trophic niche overlap in syntopic Alouatta guariba clamitans and Alouatta caraya

According to the principle of competitive exclusion, niche differentiation allows the stable coexistence of closely related species. We analyzed dietary profile and diversity, and dietary overlap between syntopic brown howlers (BR; Alouatta guariba clamitans) and black and gold howlers (BLG; A. caraya) in the Atlantic Forest of NE Argentina, with the objective of evaluating the degree of trophic niche overlap and potential interspecific competition for food. During 12 months, we collected data on feeding behavior of two groups of each howler species using the scan sampling method, together with data on food availability. Both at the group‐ and species‐level, we analyzed feeding behavior in terms of monthly percentages of time spent feeding on each food type and specific food item, dietary diversity (Shannon index H′), and we estimated dietary overlap using the percentage index and the Morisita–Horn index (C_H). Across months, both howlers showed species‐specific preferences for certain food items, and BLG had a more diverse diet (mean±SE, H′=2.77±0.08) than BR (H′=2.39±0.09). However, diets of both species overlapped extensively (percentage index=45.64±2.97%; C_H=0.6±0.05) and diets of conspecific groups did not overlap more than diets of groups of different species. Given their high degree of trophic overlap, syntopic BR and BLG meet one of the conditions necessary for interspecific food competition to occur. Although at present we lack direct evidence for interspecific competition in these howler species, we conclude that high levels of niche overlap may have an important role in maintaining the essentially parapatric distribution of howler species throughout the Neotropics. Am. J. Primatol. 72:173–186, 2010. © 2009 Wiley‐Liss, Inc.     

Contrasting life-history traits of two sympatric smooth-hound species: implication for vulnerability

In this study, life-history traits (maximum and average size, size at maturity and fecundity) of two congeneric smooth-hounds, Mustelus mustelus and Mustelus punctulatus, which share a geographical distribution and experience a similar fishing exploitation, were estimated and compared between species. The results indicated a lower maximum and average size, a lower size at maturity and a higher fecundity in M. punctulatus compared with those in M. mustelus. Considering that these two species co-occur in the same areas and are caught by the same fishing gears, the results indicate a higher vulnerability to exploitation of M. mustelus compared with that of M. punctulatus.     

Looking at the unseen: combining animal bio‐logging and stable isotopes to reveal a shift in the ecological niche of a deep diving predator

Understanding how marine top predators exploit their environment is a central topic in marine ecology. Among all methodologies used to investigate this part of ecology, electronic devices are very useful to track animals' movements and foraging habitats, but they do not provide any dietary information. Stable isotopes provide information on trophic levels but remain imprecise to identify small spatial‐scale habitats. In this study, we combined the two approaches to obtain a synoptic view of the foraging behaviour variability of southern elephant seals Mirounga leonina. Our results suggested marked differences in distribution, diving behaviour, foraging habitats, trophic levels, and dietary habits of elephant seals according to their sex and age. Thus, we characterized main foraging habitats over the Kerguelen‐Heard Plateau and the Antarctic shelf for juvenile males, while females foraged mainly in oceanic waters of the Polar Frontal Zone and the Antarctic Zone. In addition, we highlighted the ontogeny of niche partitioning in this sexually dimorphic species. While females did not exhibit a major dietary shift in relation to their age and their breeding status, a different picture emerged for males. Young males had a trophic level identical to that of all females. However, at 3–4 yr of age, males showed a progressive increase in trophic level. The inter‐annual combination of bio‐logging and stable isotopes could provide a powerful tool to investigate possible shifts in ecological niche between years according to environmental changes.     

Niche overlap and diet composition of three sympatric coastal dolphin species in the southwest Atlantic Ocean

Sympatric species are expected to differ in ecological requirements to minimize niche overlap and avoid competition. Here we assess the trophic interactions among three coexisting dolphin species from southern Brazil: the franciscana dolphin (Pontoporia blainvillei), the Guiana dolphin (Sotalia guianensis), and the Lahille's bottlenose dolphin (Tursiops truncatus gephyreus). We evaluated temporal variation in carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values of bone collagen to examine potential dietary shifts resulting from increased fishing activity over the past three decades. We estimated the degree of niche overlap among these species and the contribution of potential prey sources to their diet. δ¹⁵N values were consistent among species and across years, while δ¹³C values increased for Guiana dolphins and decreased for bottlenose dolphins, suggesting changes in diet and/or foraging habitats through time. The similar δ¹³C and δ¹⁵N values and the high niche overlap between Guiana and bottlenose dolphins indicate that these species are primarily feeding on demersal prey. The franciscana diet is primarily composed of pelagic prey, resulting in a lower niche overlap in comparison with the other dolphin species. Our study provides further information about the foraging ecology of this unique dolphin community in southern Brazil with implications for its management and conservation.     

Generalist trophic ecology in a changing habitat: The case of the four‐striped mouse in a woody‐encroached savannah

Trophic generalists tolerate greater habitat change than specialists; however, few studies explore how generalist trophic ecology is affected. We established how the trophic ecology of an extreme generalist, Rhabdomys pumilio, changed in relation to a directionally changing woody‐encroached savannah in Eastern Cape, South Africa by investigating (a) foraging behaviour, (b) trophic niche and (c) feedback effects. (a) Giving‐up densities showed that R. pumilio preferred foraging in subcanopy microhabitat during the night as a result of lower thermoregulatory costs, but had similar preferences for sub‐ and intercanopy microhabitats during the day. (b) An isotope analysis revealed that the dietary composition and trophic niche occupied by R. pumilio differed among tree canopy cover levels (0%, 30% and 80%), which appeared to be related to changes in C₄ grass material and invertebrate availability. (c) Artificial seed patches suggested that R. pumilio was a potentially important postdispersal seed predator of the woody‐encroaching species, Vachellia karroo. Thus, an increase in tree canopy cover altered the trophic niche of R. pumilio by reducing foraging costs at night and providing alternative food resources in terms of availability and source. These findings demonstrate how an extreme generalist adapted to human‐induced habitat change through changes in its trophic ecology.     

Food‐web structure and mercury dynamics in a large subarctic lake following multiple species introductions

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Overlapping niches between two co-occurring invasive fish: the topmouth gudgeon Pseudorasbora parva and the common bleak Alburnus alburnus

Invasive fish species impact aquatic ecosystems and modify native communities, often leading to a decline in local species. These ecological impacts include the transmission of pathogens, predation, competition as well as hybridization. Two invasive fish species, the common bleak Alburnus alburnus and the topmouth gudgeon Pseudorabora parva, have both been recently found co-occurring in several regions of southern Europe, such as the Italian Arno River. Nonetheless, the trophic relationships among invasive fish species, especially cyprinids, remain poorly understood, and no studies have reported the trophic interaction between these two species. This study compared length–weight relationship and used stomach content and stable isotope analysis of two co-occurring populations in the Arno River to characterize the growth and overlap of potential trophic niches. It also found similar allometric growth in both species, a wider generalist trophic niche for P. parva and a more specialized niche for A. alburnus. A considerable niche overlap was found, suggesting that feeding competition can occur if resources were to be limited. Moreover, the niche of P. parva was more likely to overlap with that of A. alburnus than vice versa, suggesting that P. parva can be considered as a potential over competitor. Nonetheless, the authors found in the overlapping populations no evidence of realized competition, probably avoided through a combination of fine-scale mechanisms. They also highlighted that these two invasive species can co-exist and share resources, at least in an open ecosystem like a river, thus potentially doubling up their trophic impact on local communities.     

Feeding ecology and seasonal diet overlap between Stellifer brasiliensis and Stellifer stellifer in a tropical estuarine ecocline

Seasonal freshwater discharge was important for defining habitat utilization by different ontogenetic phases of Stellifer brasiliensis and Stellifer stellifer along the estuarine ecocline. The middle estuary was important as a nursery and feeding ground for young‐of‐the‐year, and a feeding ground for sub‐adults and adults of both species. These species are zoobenthivorous, but during their life cycle and between different habitats and seasons, their trophic guild can change to opportunist and zooplanktivore. During the late rainy season in the lower estuary, all phases of both species, except juveniles of S. brasiliensis and adults of S. stellifer, showed a niche overlap indicating similarity in prey utilization. The diet composition was qualitatively similar, showing an evident niche overlap of intra and interspecific competition among the Stellifer spp. Although the niches of these species appeared to significantly overlap, some resource partitioning patterns were apparent. The niche overlap was significantly reduced due to the seasonal difference in habitat use and prey consumption along the ecocline of the estuary by different ontogenetic phases. The ingestion of blue nylon fragments by both species was observed and quantified.     

Diet composition of the smooth dogfish (Mustelus canis) in the waters of Long Island,New York,USA

Mustelus canis, one of two species in the genus Mustelus found along the Northwest Atlantic coast and the second most abundant shark in the region, is beginning to comprise large portions of by-catch in various commercial fishing industries. This study analysed the gut contents of sharks taken from three locations in Long Island, NY (Long Beach, Shelter Island and Gardiners Bay) to examine sex- and site-specific diet composition. Our study indicates that smooth dogfish in these waters are opportunistic predators, showing a preference for crustaceans (i.e. Cancer irroratus, Libinia spp., Squilla empusa and Upogebia affinis). Dietary niche breadth was found to vary significantly and niche overlap was moderately low between sexes and between sites. While dietary components of M. canis discovered in this study corroborate other studies performed within the Northwestern Atlantic migratory range of M. canis, smooth dogfish diet varies considerably with region and time of year. Thus, future studies should include surveys of distribution patterns for common prey items and studies of caloric components of these prey items.     

Resource-use dynamics of co-occurring chondrichthyans from the First Coast,North Florida,USA

Recent studies on shark assemblages on the northeast Florida and southeast Georgia coast (hereafter referred to collectively as the “First Coast”) have demonstrated differences in species and age-class composition of catch from previously characterized estuaries and newly surveyed area beaches, demonstrating that these regions may provide a critical habitat to different segments (i.e., life stages) of local shark populations. In this study, carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) from muscle tissue and blood plasma were used to examine trophic dynamics (and temporal variability thereof) of the three dominant co-occurring species found along First Coast beaches (the Atlantic Sharpnose shark Rhizoprionodon terraenovae, Blacknose shark Carcharhinus acronotus and Blacktip shark Carcharhinus limbatus) to determine if they exhibit overlap in resource use along with spatial and temporal habitat use. Although considered spatially segregated from the beach species, a dominant, age-class species found in First Coast estuaries (juvenile Sandbar sharks Carcharhinus plumbeus) was also included in this analysis for comparison. Temporal variability of resource-use characteristics was detected at the species level. Resource-use overlap among species varied by tissue type and was generally higher for blood plasma, suggesting greater resource sharing over more recent time periods. Over longer time periods Atlantic Sharpnose and Blacktip sharks exhibited resource-use expansion, whereas Blacknose sharks exhibited a narrowing in resource use, suggesting a more specialized foraging strategy compared to the other species. The resource-use breadth of Sandbar sharks also expanded between blood plasma and muscle tissue. Significant size relationships were detected in Blacktip and Sandbar sharks, indicating ontogenetic resource shifts for both species. A diversity of highly productive resource pools likely support shark populations along the First Coast such that resource-use differentiation is not required to facilitate species co-occurrence. This work may shed light on understanding patterns of species co-occurrence as well as aid in future conservation efforts.     

Metazoan parasite communities and diet of the velvet belly lantern shark Etmopterus spinax (Squaliformes: Etmopteridae): a comparison of two deep‐sea ecosystems

By combining an examination of stomach contents yielding a snapshot of the most recent trophic niche and the structure of parasite communities reflecting a long‐term feeding niche, this study aimed at gaining more comprehensive information on the role of the small‐sized deep‐water velvet belly lantern shark Etmopterus spinax in the local food webs of the Galicia Bank and the canyon and valley system of the Avilés Canyon, which have been both proposed for inclusion in the Natura 2000 network of protected areas. As far as is known, this study provides the first comparative parasite infracommunity data for a deep‐sea shark species. Component parasite communities in E. spinax were relatively rich, whereas the infracommunities were rather depauperate, with similar low diversity at both localities. The significant differences in the composition and structure of both parasite communities and prey assemblages indicate differential effects of the two deep‐sea ecosystems on both long‐term and most recent trophic niches of E. spinax. These results underline the importance of the use of multivariate analyses for the assessment of geographical variation in shark populations based on parasites and diet data.     

Effects of water clarity and other environmental factors on trophic niches of two sympatric piscivores

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Food habits of the silky shark Carcharhinus falciformis (Müller & Henle, 1839) off the western coast of Baja California Sur,Mexico

The objective of this study was to establish the trophic niche of the silky shark and to determine the ecological role of this predator in the ecosystem close to Baja California. The trophic spectrum was analyzed from samples taken during summer and autumn (2000–2002) from the fishing camps of Punta Lobos and Punta Belcher on the western coast of Baja California Sur. A total of 263 stomach contents were analyzed (143 with food; 120 empty). The index of relative importance (IRI) showed that at Punta Lobos, silky sharks fed mainly on red crabs Pleuroncodes planipes (%IRI = 83%), whereas at Punta Belcher the main food item was the jumbo squid Dosidicus gigas (%IRI = 41%), followed by chub mackerel Scomber japonicus (%IRI = 33%). According to the Levin Index (Bi), the trophic niche breadth in silky sharks is low (Bi = <0.6), which means that silky sharks are specialist predators because they mainly consume three prey types: red crab, chub mackerel, and jumbo squid. The Shannon‐Wiener Index indicated that all trophic categories at Punta Belcher (0.85–1.22) had lower diversity than at Punta Lobos (0.50–1.6), because the silky shark feeds more on tropical prey found close to Punta Lobos. The Morisita‐Horn Index (Cλ) showed an overlap in the diet between the two areas analyzed and between sexes (Cλ = >0.6). The juveniles and adult females did not show any overlap. In the caloric analysis of the main prey, the jumbo squid (D. gigas) contributed the most calories to the silky shark diet (76%).     

Trophic niche similarities of sympatric Turdus thrushes determined by fecal contents,stable isotopes,and bipartite network approaches

An ecological niche has been defined as an n‐dimensional hypervolume formed by conditions and resources that species need to survive, grow, and reproduce. In practice, such niche dimensions are measurable and describe how species share resources, which has been thought to be a crucial mechanism for coexistence and a major driver of broad biodiversity patterns. Here, we investigate resource partitioning and trophic interactions of three sympatric, phylogenetically related and morphologically similar species of thrushes (Turdus spp.). Based on one year of data collected in southern Brazil, we investigated niche partitioning using three approaches: diet and trophic niche assessed by fecal analysis, diet and niche estimated by stable isotopes in blood and mixing models, and bipartite network analysis derived from direct diet and mixing model outputs. Approaches revealed that the three sympatric thrushes are generalists that feed on similar diets, demonstrating high niche overlap. Fruits from C3 plants were one of the most important food items in their networks, with wide links connecting the three thrush species. Turdus amaurochalinus and T. albicollis had the greatest trophic and isotopic niche overlap, with 90% and 20% overlap, respectively. There was partitioning of key resources between these two species, with a shared preference for fig tree fruits—Ficus cestrifolia (T. amaurochalinus PSIRI% = 11.3 and T. albicollis = 11.5), which was not present in the diet of T. rufiventris. Results added a new approach to the network analysis based on values from the stable isotope mixing models, allowing comparisons between traditional dietary analysis and diet inferred by isotopic mixing models, which reflects food items effectively assimilated in consumer tissues. Both are visualized in bipartite networks and show food‐consumers link strengths. This approach could be useful to other studies using stable isotopes coupled to network analysis, particularly useful in sympatric species with similar niches.