Standard Ellipse Area Research Articles

Isotopic niche partitioning in two sympatric howler monkey species.

Ecological similarity between species can lead to interspecific trophic competition. However, when ecologically similar species coexist, they may differ in foraging strategies and habitat use, which can lead to niche partitioning. As the body tissues of consumers contain a stable isotope signature that reflects the isotopic composition of their diet, stable isotope analysis is a useful tool to study feeding behavior. We measured the isotopic niche width, which is a proxy for trophic niche width, of mantled (Alouatta palliata) and black (A. pigra) howler monkeys. Specifically, studied populations in allopatry and sympatry to assess whether these species showed niche partitioning. Between 2008 and 2012, we collected hair samples from 200 subjects (113 black and 87 mantled howler monkeys) and used continuous flow isotope ratio mass spectrometry to estimate δ13 C and δ15 N. We described the isotopic niche width of each species in allopatry and sympatry with the Bayesian estimation of the standard ellipse areas. In allopatry, isotopic niche width and isotopic variation were similar in both species. In sympatry, black howler monkeys had a significantly broader isotopic niche, which was mainly determined by high δ15 N values, and included the majority of mantled howler monkeys' isotopic niche. The isotopic niche of mantled howler monkeys did not differ between sympatry and allopatry. The coexistence of these ecologically similar species may be linked to trophic niche adjustments by one species, although the particular features of such adjustments (e.g., dietary, spatial, or sensory partitioning) remain to be addressed.

Ontogenetic shifts in trophic geography of jumbo squid, Dosidicus gigas, inferred from stable isotopes in eye lens

Incrementally-formed, metabolically-inert tissues have been used extensively to study marine animal trophic habitat retrospectively throughout their lifetime. In this study, sequential stable isotopic values of δ13C and δ15N in eye lenses were measured to investigate ontogenetic shifts in the trophic geography of Dosidicus gigas. A total of 617 segments from 73 lenses were examined with δ13C ranging from −20.45 to −15.47‰ and δ15N ranging from 4.34 to 18.74‰. A Generalized Additive Models (GAMs) result showed significantly increased isotopes across the eye lens which significantly differed between years and sexes. Sequential increasing but a variation in δ13C and δ15N values in eye lenses suggests that D. gigas opportunistically feeds on available prey but as it grows, it becomes progressively able to consume prey from higher trophic levels, perhaps to maximize feeding success. Analysis of variance (ANOVA) showed squid to have significant ontogenetic differences in δ13C but not in δ15N at different growth stages. These ontogenetic isotopic changes cannot be explained solely by trophic growth and may also be due to geographic movement. The corrected standard ellipse area (SEAc) of the embryonic, paralarval, juvenile, adult and dying phases were 10.802‰, 11.552‰, 9.152‰, 4.512‰ and 4.372‰, which suggests squid in early life span live in wide areas with different isotopic baseline values, but adult squid forage in the same habitat and become more specialized on particular prey. There were high and medium isotopic overlaps between the two consecutive stages for before juvenile and after juvenile, respectively, which reflect the squid nursery and foraging strategy. The lack of isotopic overlap between embryo and adult squid suggests that maternal squid have different trophic and spatial ecology compared with their offspring.

RKIN: Kernel-based method for estimating isotopic niche size and overlap.

The isotopic niche of consumers represents biologically relevant information on resource and habitat use. Several tools have been developed to quantify niche size and overlap. Nonetheless, methods adapted by spatial ecologists to quantify animal home ranges can be modified for use in stable isotope ecology when data are not normally distributed in bivariate space. We offer a tool that draws on existing spatial metrics, such as minimum convex polygon (MCP) and standard ellipse area (SEA), and add novel metrics using kernel utilization density (KUD) estimators to measure isotopic niche size and overlap. We present examples using empirical and simulated data to demonstrate the performance of the package kernel isotopic niches in r (rKIN) under various scenarios. Results of niche size from MCP, SEA and KUD were highly correlated but divergent among datasets. Overall, the KUD method produced the largest niche sizes and was more sensitive to the distribution of the isotopic data. Pairwise estimates of overlap were highly variable, likely because MCP and SEA inherently include or exclude unused areas in the resulting niche estimate. Four bandwidth methods (reference, normal scale, plug-in and biased cross-validation) produced comparable estimates of niche size and overlap at various sample sizes (10-40). Niche size and overlap were consistent across sample sizes >15. Use of rKIN will allow isotope ecologists to quantify niche shifts, expansions or contractions, as well as assess the performance of several estimation methods. The package also can be applied to other data types (e.g. principal component analysis, multi-dimensional scaling) so long as axes and measurement units are identical and can be converted to Cartesian coordinates.

Trophic ecology of Mexican Pacific harbor seal colonies using carbon and nitrogen stable isotopes.

There is limited information that provides a comprehensive understanding of the trophic ecology of Mexican Pacific harbor seal (Phoca vitulina richardii) colonies. While scat analysis has been used to determine the diet of some colonies, the integrative characterization of its feeding habits on broader temporal and spatial scales remains limited. We examined potential feeding grounds, trophic niche width, and overlap, and inferred the degree of dietary specialization using stable carbon and nitrogen isotope ratios (δ13C and δ15N) in this subspecies. We analyzed δ13C and δ15N on fur samples from pups collected at five sites along the western coast of the Baja California Peninsula, Mexico. Fur of natal coat of Pacific harbor seal pups begins to grow during the seventh month in utero until the last stage of gestation. Therefore pup fur is a good proxy for the mother’s feeding habits in winter (~December to March), based on the timing of gestation for the subspecies in this region. Our results indicated that the δ13C and δ15N values differed significantly among sampling sites, with the highest mean δ15N value occurring at the southernmost site, reflecting a well-characterized north to south latitudinal 15N-enrichment in the food web. The tendency identified in δ13C values, in which the northern colonies showed the most enriched values, suggests nearshore and benthic-demersal feeding habits. A low variance in δ13C and δ15N values for each colony (<1‰) and relatively small standard ellipse areas suggest a specialized foraging behavior in adult female Pacific harbor seals in Mexican waters.

82 Effects of Whole Body Vibration Training using Side-Alternating Vibration Platform with Tilt Table in Hospitalized Older Adults with Sarcopenia : A Randomized Controlled Pilot Study

Abstract Background and Aims Sarcopenia is defined as the loss of skeletal muscle mass and strength with increased age. Increased activity following whole body vibration (WBV) has been reported in patients with chronic illness, but few studies reported the effect of WBV on the physical function of patients with acute illness. This study aimed to investigate the effects of WBV training using vibration platform with tilt table on muscle mass and physical performance in adults with sarcopenia. Methods Inclusion criteria were as follow : 1) age more than 70 years old 2) unable to independently ambulate due to long term hospitalized care 3) patient who was diagnosed as sarcopenia. Participants were randomly allocated into WBV group using side-alternating vibration platform with tilt table vs. conventional physical therapy. In WBV group, subjects lied down on tilt table at 60 degree with bare foot. Then, subjects stood on the platform board which could vibrate. Initial evaluation included muscle power, muscle mass, hand grip force, balance test using Leonardo mechanography, Berg balance scale (BBS), timed get up &amp; go (TUG) test, gait speed and activities of daily living (ADL). Muscle power was evaluated using manual muscle test (MMT). In balance test using mechanography, as a center of path parameters, standard ellipse area (SEA), path length (PL) were evaluated. After 2 weeks, 2nd evaluation was conducted. Results A total of 15 were enrolled. There were no significant differences between two groups in demographic characteristics. At initial assessment, there were no significant differences in both groups except for SEA. After intervention, WBV group showed improvements in muscle mass, SEA, BBS, TUG, gait speed, ADL. However, there were no statistically significant differences in all outcomes at 2nd evaluation. Conclusion WBV training may improve muscle mass, ability of ambulation and ADL in hospitalized older adults with sarcopenia.

Assessing the relationship between diet and size-at-age in Pacific halibut (Hippoglossus stenolepis) using δ13C and δ15N analysis

The ecological mechanisms driving an observed decline in the mean size-at-age of adult Pacific halibut (Hippoglossus stenolepis) in the eastern North Pacific Ocean have yet to be defined. Here, we present the results of a study designed to investigate the relationship between one potential mechanism — diet — and size-at-age using carbon and nitrogen stable isotope analysis. Our results indicate significant differences in the skeletal muscle δ13C and δ15N values between size-at-age categories for each sex, with larger-size-at-age fish consuming diets with higher δ15N values, indicating higher trophic level feeding. Analysis of Bayesian standard ellipse areas showed that for females, intermediate size-at-age categories have the largest dietary range. For males, the largest dietary range was observed in the largest size-at-age category. Our results suggest a size-based stratification in dietary strategy for Pacific halibut with implications for observed declines in size-at-age.

Inter-regional variation in feeding patterns of skipjack tuna (Katsuwonus pelamis) inferred from stomach content, stable isotope and fatty acid analyses

Foraging habits of skipjack tuna, SKJ (Katsuwonus pelamis), were investigated in three Spanish marine regions (Balearic Sea, Alboran Sea and Gulf of Cadiz) using stomach content (SCA), stable isotope (SIA), and fatty acid (FA) analyses. The three methodological approaches yielded significant differences among locations. All the studied areas appear to serve as important foraging grounds for SKJ, but the diet composition significantly varied among them. The predominant prey species in the respective locations were the North Atlantic krill, Meganyctiphanes norvegica, in the Balearic Sea, the flyingfish, Exocœtus volitans, in the Alboran Sea, and the anchovy, Engraulis encrasicolus, in the Gulf of Cadiz. Regional differences were also found in δ13C and δ15N values; furthermore, the analysis of standard ellipse areas (SEAc) based on isotopic data showed that the broadest niche corresponded to SKJ from the Gulf of Cadiz, with no significant isotopic niche overlap between areas. Consistent with the SCA and stable isotope results, the FA composition varied among areas. Docosahexaenoic acid (DHA, 22:6n-3) was the most abundant FA in the SKJ muscle, showing its highest values in samples from the Gulf of Cadiz; this FA was the most effective in segregating SKJ geographical groups. In conclusion, this study provides evidence that SKJ in eastern Atlantic and western Mediterranean waters can easily adapt their diet to local prey availability. Furthermore, stable isotope signatures and FA profiles of muscle tissue prove to be reliable trophic markers that allow separation of populations occurring in different marine areas.

Trophic ecology of Penaeus chinensis (Decapoda: Dendrobranchiata: Penaeidae) and potential competitive interactions with other species in the Haizhou Bay determined by carbon and nitrogen stable isotope analysis

The Chinese white shrimp Penaeus chinensis is one of the most economically important crustacean species in China with respects to both capture and aquaculture. Stable carbon and nitrogen isotope ratios (δ13C and δ15N) was analyzed to reveal its potential dietary characteristics, in particular contributions of primary producers as food sources, as well as isotopic niche width and potential food competitions with materials from Haizhou Bay in Yellow Sea, a state-level germplasm source conservation and stock recovery area. The results confirmed that bivalves served as an important diet of P.chinensis and the prawn incorporated a mixture of benthic microalgae and marine phytoplankton as food sources, while terrestrial organic matter supposed to be made minimum contributions. Benthic microalgae overwhelmingly dominated in the dietary proportion (mode), and accounted for 90% of the food sources in comparison with the contribution of 10% of marine phytoplankton. Penaeus chinensis was closest to Charybdis japonica and Dorippe japonica in isotopic compositions. Trophic niche widths were similar in P.chinensis and D. japonica, and they were larger than that of C.japonica, as determined by the sizes of SEAb (Bayesian standard ellipse areas). The overlaps of standard ellipse areas of P.chinensis with C. japonica and D. japonica were 98.5% and 86.5% respectively, indicating intense competition for food between P.chinensis and the other two species. In the views of food availability and competition, biomasses of benthic microalgae, bivalves and C.japonica and D.japonica may regulate the population of P.chinensis in Haizhou Bay.

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.

Physical and Tactical Demands of the Goalkeeper in Football in Different Small-Sided Games.

Background: Several studies have examined the differences between the different small-sided game (SSG) formats. However, only one study has analysed how the different variables that define SSGs can modify the goalkeeper’s behavior. The aim of the present study was to analyze how the modification of the pitch size in SSGs affects the physical demands of the goalkeepers. Methods: Three professional male football goalkeepers participated in this study. Three different SSG were analysed (62 m × 44 m for a large pitch; 50 m × 35 m for a medium pitch and 32 m × 23 m for a small pitch). Positional data of each goalkeeper was gathered using an 18.18 Hz global positioning system. The data gathered was used to compute players’ spatial exploration index, standard ellipse area, prediction ellipse area The distance covered, distance covered in different intensities and accelerations/decelerations were used to assess the players’ physical performance. Results and Conclusions: There were differences between small and large SSGs in relation to the distances covered at different intensities and pitch exploration. Intensities were lower when the pitch size was larger. Besides that, the pitch exploration variables increased along with the increment of the pitch size.

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.

Niche-related processes in island intertidal communities inferred from stable isotopes data

Abstract It is well recognized that niche-based processes are intimately related to most important ecological theories such as natural selection and island biogeography. Current niche approaches involving stable isotope analysis (SIA) have been used to clarify niche population and community dynamics, mainly through carbon and nitrogen signatures in organisms modeled in an isotopic δ-space. We modeled over a thousand δ13C and δ15N samples from six intertidal rocky reefs, three in oceanic islands and three in mainland coastal habitats, to test whether island reef communities follow the prediction of ecological release and vacant niche theories and exhibit higher niche width, resource exploitation and trophic diversity if compared to mainland communities. Additionally, we used an endemic island species to verify if, as hypothesized, niche was conserved along the evolutionary history of the species in relation its mainland sister species. Our results indicate that niche width (standard ellipse area), resource exploitation range (δ13C range) and trophic heterogeneity were higher in island communities in comparison to mainland communities. We found that the niche of island endemic species was more similar to the niche of mainland sister species than to the niche of confamiliar sympatric species suggesting that island endemic species have retained their ancestral niche. Niche expansion processes in island populations commonly occurred in response to ecological release effects, which are associated with lower biotic resistance (competition and predation pressure) in depauperate island communities. Although niche expansion by competition release is well-known for island terrestrial fauna, to this day evidence for marine organisms, mainly at a community-scale, had remained weak. Based on our results island communities may be prone to biological invasions into vacant niches promoted by anthropogenic activities. More research is needed to understand how potential invasions can affect island intertidal reef communities.

Intraspecific differences in relative isotopic niche area and overlap of co-occurring sharks

Few studies have assessed whether patterns of resource partitioning among sympatric marine predators vary between different habitats. This type of data is important for understanding food web functioning as well as for supporting an ecosystem-based fisheries management plan. In this study, we used δ13C and δ15N stable isotope analysis to assess the relative isotopic niche area (i.e., which species has the largest and smallest isotopic niche area within a study site) and core isotopic niche overlap between 299 sharks of 11 co-occurring shark species that vary in size, diet and behavior in three coastal study areas in South Florida. Overall, results show that the relative isotopic niche area and patterns of core isotopic niche overlap between some sympatric shark species varied between sites, suggesting plasticity in resource use and competitive interactions between shark species (e.g., 85% of blacktip shark Carcharhinus limbatus standard ellipse area overlapped with the blacknose shark C. acronotus ellipse in Biscayne Bay, but there was no overlap between these species’ ellipses in nearby Florida Bay). Therefore, patterns of resource use and trophic interactions documented among species from one site may not be applicable to a neighboring location. These findings may have implications for food web models that incorporate trophic data from different areas for a species when local data are unavailable.

Trophic partitioning between abundant demersal sharks coexisting in the North Aegean Sea

AbstractWe examined the feeding ecology (diet, trophic width and trophic position) of five demersal shark species (Mustelus mustelus Linnaeus, 1758, Galeus melastomus Rafinesque, 1810, Scyliorhinus canicula Linnaeus, 1758, Scyliorhinus stellaris Linnaeus, 1758, Squalus blainville, Risso, 1826) coexisting in the north-eastern Aegean Sea (around Gökçeda Island) by combining stomach content and stable isotope analyses. The results indicate clear differences in diet between the five sharks. Cephalopods were mainly found in diet of S. stellaris and M. mustelus and the stomachs of G. melastomus, S. canicula and S. blainville included fish. S. blainville showed the highest trophic position in respect of stable isotope analysis (TPsia = 4.89) around Gökçeada Island. It was followed by G. melastomus (TPsia = 4.57). Direct isotopic values (both stable nitrogen and carbon) and isotopic niche width based on the Standard Ellipse Area (SEA) clearly differed among the five shark species. In particular, S. blainville was isotopically segregated from the other shark species studied, showing a narrow isotopic trophic niche and higher trophic level. In contrast, M. mustelus had the widest trophic niche of the five species studied. The niche width of S. stellaris was narrower than M. mustelus and S. canicula but wider than S. blainville and G. melastomus. SEA showed that G. melastomus has a specialized feeding strategy in the area. There is no overlap between S. canicula and S. stellaris in trophic width.

Behavioural plasticity and trophic niche shift: How wintering geese respond to habitat alteration

Abstract The accelerated rate of human‐induced environmental change poses a significant challenge for wildlife. The ability of wild animals to adapt to environmental changes has important consequences for their fitness, survival, and reproduction. Behavioural flexibility, an immediate adjustment of behaviour in response to environmental variability, may be particularly important for coping with anthropogenic change. The main aim of this study was to quantify the response of two wintering goose species (bean goose Anser fabalis and lesser white‐fronted goose Anser erythropus) to poor habitat condition at population level by studying foraging behaviour. In addition, we tested whether behavioural plasticity could alter trophic niche. We characterised foraging behaviours and calculated daily home range (HR) of the geese using global positioning system tracking data. We calculated standard ellipse areas to quantify niche width using the δ13C and δ15N values of individual geese. We linked behavioural plasticity with habitat quality using ANCOVA (analysis of covariance) models. We also tested the correlation between standard ellipse areas and HR using ANCOVA model. We found significant differences in geese foraging behaviours between years in their daily foraging area, travel distance and speed, and turning angle. Specifically, the birds increased their foraging area to satisfy their daily energy intake requirement in response to poor habitat conditions. They flew more sinuously and travelled faster and longer distances on a daily basis. For the endangered lesser white‐fronted goose, all behaviour variables were associated with habitat quality. For bean goose, only HR and turning angle were correlated with habitat quality. The birds, especially the lesser white‐fronted goose, may have had a higher trophic position under poor conditions. Our findings indicate that wintering geese showed a high degree of behavioural plasticity. However, more active foraging behaviours under poor habitat condition did not lead to a broader trophic niche. Habitat availability could be responsible to the divergent responses of foraging HR and isotopic niche to human‐induced environmental change. Therefore, maintaining natural hydrological regimes during the critical period (i.e. September–November) to ensure that quality food resources are available is central to the future of populations of geese within the East Asian–Australasian Flyway.

Resources utilization and trophic niche between silver carp and bighead carp in two mesotrophic deep reservoirs

Resources utilization and trophic structure in aquatic food webs play important roles in the ecosystem stability and functioning. Silver carp (SC, Hypophthalmichthys molitrix) and bighead carp (BC, Hypophthalmichthys nobilis) are intensively stocked in lakes and reservoirs in China and share similar food resources and trophic positions in water bodies. To better understand the ecological roles of SC and BC in natural freshwater, two mesotrophic reservoirs (Nanwan and Nianyushan) were selected to compare resource utilization and the trophic niche of these two fish species. Data analysis using Bayesian mixing model showed that SC was more like a fine particulate organic matter (fPOM) feeder, while BC consumed more coarse particulate organic matter (cPOM) and displayed a higher trophic position in both reservoirs. In contrast, niche breadths represented by the corrected standard ellipse area (SEAC) were essentially the same for SC and BC in Nanwan (SEAC = 6.1 for SC and BC), but much larger for silver carp in Nianyushan (SEAC for SC: 11.6, SEAC for BC: 4.2). The high stocking ratio of SC/BC in Nianyushan was the probable reason for the large SEAC of silver carp, which suggested that silver carp could use more food resources and become more competitive with a higher stocking biomass ratio. The results indicated that the trophic partitioning of filter feeders might be regulated by the stocking biomass ratio of the fish to some extent.

Spatial diet overlap and food resource in two congeneric mullet species revealed by stable isotopes and stomach content analyses

Food partitioning among coexisting species in different habitats remains an important research topic in trophic ecology. In this work, we combined carbon and nitrogen stable isotope ratios and stomach content analyses to investigate differences in diet and niche overlap of two congeneric juvenile mullet species (Mugil curema and Mugil liza) coexisting in a marine surf-zone and an estuarine zone in southern Brazil (29oS). These habitats have contrasting levels of food availability, especially in terms of prey diversity, with higher microalgae diversity in the estuary than in the marine surf-zone. In these contrasting conditions, we predicted that both mullet species will have (a) higher niche overlap and smaller niche breadth at the marine surf-zone due to the common exploration of highly abundant surf-zone diatoms and (b) lower niche overlap and higher niche breadth inside the estuary due to selective feeding on more diverse food resources. Isotope niche areas (measured as standard ellipse areas) were higher in the estuary (6.10 and 6.18) than in the marine surf-zone (3.68 and 3.37) for both M. curema and M. liza, respectively. We observed an overlap of 52% in isotopic niches of both species in the marine surf-zone and none in the estuary. We also found contrasting patterns in the diet composition between species according to the habitat. At the marine surfzone, diatoms of the classes Bacillariophyceae and Coscinodiscophyceae dominated (> 99%) the food content of both mullet species. In contrast, green algae, cyanobacteria, dinoflagellates and flagellates comprised the diet of both species in the estuary. These results could be explained by spatial differences in food availability (especially regarding diversity of microalgae) between both habitats. At the marine site, both species explored the most abundant microalgae available (mostly the surf-zone diatom Asterionellopsis cf. guyunusae and fragments of Coscinodiscus), whereas in the estuary both species shifted their diets to explore the greater diversity of microalgae resources. Overall, our findings revealed that niche partitioning theory could not fully predict changes in breadth and overlap of food niches of estuarine dependent fish species with complex life cycles encompassing marine to estuarine systems with contrasting food availabilities.

Morphology and stable isotope analysis demonstrate different structuring of bat communities in rainforest and savannah habitats.

Bats play important ecological roles in tropical systems, yet how these communities are structured is still poorly understood. Our study explores the structure of African bat communities using morphological characters to define the morphospace occupied by these bats and stable isotope analysis to define their dietary niche breadth. We compared two communities, one in rainforest (Liberia) and one in savannah (South Africa), and asked whether the greater richness in the rainforest was due to more species ‘packing’ into the same morphospace and trophic space than bats from the savannah, or some other arrangement. In the rainforest, bats occupied a larger area in morphospace and species packing was higher than in the savannah; although this difference disappeared when comparing insectivorous bats only. There were also differences in morphospace occupied by different foraging groups (aerial, edge, clutter and fruitbat). Stable isotope analysis revealed that the range of δ13C values was almost double in rainforest than in savannah indicating a greater range of utilization of basal C3 and C4 resources in the former site, covering primary productivity from both these sources. The ranges in δ15N, however, were similar between the two habitats suggesting a similar number of trophic levels. Niche breadth, as defined by either standard ellipse area or convex hull, was greater for the bat community in rainforest than in savannah, with all four foraging groups having larger niche breadths in the former than the latter. The higher inter-species morphospace and niche breadth in forest bats suggest that species packing is not necessarily competitive. By employing morphometrics and stable isotope analysis, we have shown that the rainforest bat community packs more species in morphospace and uses a larger niche breadth than the one in savannah.

Stable isotopes indicate that zebra mussels (Dreissena polymorpha) increase dependence of lake food webs on littoral energy sources

Abstract The influence of zebra mussels (Dreissena polymorpha) on phytoplankton abundance is well known, but their community‐level impact on energy flow is less clear. Reduced phytoplankton abundance could increase reliance of fish and aquatic invertebrates on alternative energy sources such as epiphyton and benthic algae. We assessed impacts of zebra mussels on energy flow by comparing food webs in two Minnesota, USA, lakes during summers of 2013 and 2014. Lake Carlos had a dense population of zebra mussels, while upstream Lake Ida was free of zebra mussels until this study began and maintained low densities during our study. We used baseline‐corrected (BC) δ13C to test whether fish and littoral invertebrate primary and secondary consumers were more reliant on littoral carbon in Carlos compared to Ida. We also used BC δ15N to determine if trophic position of fish species differed between lakes. Lastly, we compared isotopic niche space by estimating standard ellipse areas for fish species in Carlos and Ida lakes, and tested whether the community‐level range of trophic levels, reliance on littoral carbon and standard ellipse area differed between lakes. Results showed invertebrate secondary consumers had more enriched BC δ13C in Carlos than in Ida, indicating greater reliance on littoral energy. Mixing models indicated that 10 of 11 fish species were more reliant on littoral carbon in Carlos, with littoral carbon use in the 10 species 1.5‐fold higher in Carlos. Isotopic niche analysis also showed increased littoral reliance in Carlos fish, as the same 10 fish species in Carlos had statistically distinct ellipses that were enriched in δ13C. Mixing models also indicated that seven of 11 fish species analysed had significantly higher trophic positions in Lake Carlos. In contrast, community‐scale metrics for fish showed no difference between lakes in the range of trophic levels, range of reliance on littoral energy, or size of standardised ellipse area of isotopic niche space. This indicates that, despite most individual fish species increasing their reliance on littoral energy and shifting upwards in trophic position, the overall size of the community isotopic niche area remained similar between lakes. Our results indicate that zebra mussels have community‐wide impacts on energy flow in lakes, with invertebrate predators and many species of fish increasing their reliance on littoral energy sources, and most species of fish shifting to higher trophic positions. A key question is whether increased water clarity associated with zebra mussels can increase littoral production sufficiently to compensate for higher demand. If not, it is plausible that invertebrate and fish production will decline due to increased intra‐ and inter‐specific competition.

Comparative study of trophic and elemental characteristics of zooplankton in deep (500–3500 m) and shallow (0–200 m) layers

The deep sea has limited food resources and is considered one of the most rigorous environments on Earth. In contrast, zooplankton and their food supply are abundant in shallow sea layers. In this study, the trophic and elemental characteristics of zooplankton taxa in the deep and shallow layers were explored with respect to trophic position, trophic niche overlap among taxa, and growth performance. Our results showed that higher values of δ15N were detected in most taxa or taxa groups in the deep layer compared to similar taxa in the shallow layer, indicating that depth-dependent δ15N values existed in most zooplankton taxa. A lower isotopic niche overlap was detected among taxa in the shallow layer, since the overlap of SEAc (standard ellipse area corrected for small sample sizes) between pairs of taxa was lower in the shallow layer than in the deep layer. In the deep layer, SEAc values of taxa were higher than those in the shallow layer respectively, showing higher isotopic niche widths. This could be due to the high trophic diversity of each taxa in the deep layer and the area sampled actually including at least two zones (mesopelagic and bathypelagic). From an ecological stoichiometry perspective, most taxonomic groups in the deep layer exhibited higher C:P and N:P ratios than similar taxa in the shallow layer, suggesting lower maximal growth rates in the deep layer. Lower growth rates potentially reduce the consumption of limited resources in the deep layer, and higher growth rates in the shallow layer facilitate the rapid exploitation of abundant resources and allow zooplankton to flourish.