Food niche segregation between two herbivorous cyprinid species in a turbid lake

The diet and growth of two cyprinids, roach Rutilus rutilus and rudd Scardinius erythrophthalmus, in the clay-turbid Kirkkojärvi basin in Lake Hiidenvesi (Finland) were studied. Young R. rutilus fed mainly on detritus, molluscs, chironomids and zooplankton, while older individuals consumed mostly detritus, molluscs and filamentous algae. In the food of S. erythrophthalmus , detritus was less prevalent and animal food and plants contributed to most of the diets. The animal food of S. erythrophthalmus consisted mostly of surface insects. Of the plant food, the macrophytes Potamogeton obtusifolius and Ranunculus circinatus had the highest representation, while the proportion of filamentous algae was low. The growth rate of S. erythrophthalmus was significantly higher than that of R. rutilus . The results suggested that the species composition of vascular macrophytes was not favourable for R. rutilus . Small submerged species suitable for R. rutilus were absent and they fed on filamentous algae and detritus, which resulted in a slow growth rate. The results suggested that in a clay-turbid lake the food spectrum is more suitable for S. erythrophthalmus than for R. rutilus . In such conditions, R. rutilus may have no benefit from its generalistic feeding abilities.     

Trophic niche width,offspring condition and immunity in a raptor species

Strategies developed by organisms to maximize foraging efficiency have a strong influence on fitness. The way in which the range of food resources is exploited has served to classify species, populations and individuals from more specialist (narrow trophic niche) to more generalist (broad trophic niche). Recent studies have provided evidence that many of the considered generalist species/populations are actually composed of different specialist individuals (individual specialization). Even the existence of generalism as an adaptive strategy has been questioned. In this study, we investigated the relationship between trophic niche width, individual quality and offspring viability in a population of common kestrel Falco tinnunculus during 4 years. We showed that the diet of kestrels varied significantly among years and that individuals of better quality fed their offspring with a higher diversity of prey species and a higher amount of food. Moreover, body condition and immune response of nestlings were positively correlated with diversity of prey delivered by parents. Our study suggests that generalism has the potential to increase fitness and that broadening the trophic niche may be an adaptive strategy in unpredictable environments.     

Trophic relationships of two species of grebe on a prairie lake based on stable isotope analysis

Loch Leven, U.K., contains brown trout (Salmo trutta), eel (Anguilla anguilla), minnow (Phoxinus phoxinus), perch (Perca fluviatilis), pike (Esox lucius) and three-spined stickleback (Gasterosteus aculeatus), with brook lamprey (Lampetra planeri) and stone loach (Barbatula barbatula) also present in its tributaries. Arctic charr (Salvelinus alpinus), Atlantic salmon (Salmo salar) and flounder (Platichthys flesus) are now extinct. The brown trout population has supported a world-renowned recreational fishery for over a century, although a decline in fishery performance led to extensive stocking between 1983 and 2006, including with non-native rainbow trout (Oncorhynchus mykiss). This review combines historical information with contemporary gill-net and hydroacoustic surveys. In 2008, brown trout, perch and three-spined sticklebacks were abundant, but pike and stone loach were rare. The obstruction of migratory routes was probably responsible for the loss of Atlantic salmon and flounder, while a lowering of water level likely caused the extinction of Arctic charr and contributed to a reduction in pike abundance. Perch abundance has fluctuated markedly, being influenced by disease and eutrophication, although a reduction in nutrients and associated recovery of macrophytes are likely to have benefitted this species. Although the brown trout population has undoubtedly shown a long-term decline, individuals are currently in excellent condition.     

Trophic niche changes associated with habitat fragmentation in a Neotropical bat species

Habitat fragmentation could alter ecological traits including species trophic habits. Here, we used carbon and nitrogen stable isotope ratios to establish differences in isotopic niche width and food resource use between forest fragments and the continuous forest for the phyllostomid frugivorous bat Artibeus lituratus. Using mist nests, we captured bats from two forest fragments and two sites in continuous forest, and sampled from each individual captured three body tissues with contrasting turnover rates (skin, muscle, and liver). Samples were collected between February and March (austral summer) and between August and September (austral winter). In addition, in each sampling site and season we collected potential food resources (fruits and insects) consumed by our A. lituratus. Our findings indicate that A. lituratus had a predominantly omnivorous diet, with high consumption of insects during summer in forest fragments. The increasing consumption of insects in these fragments seems to have led to a wider isotopic niche, in relation to the continuous forest. Because A. lituratus is typically a seed disperser, changes in trophic habits in the forest fragments from frugivory to insectivory may diminish their role in forest regeneration. Abstract in Portuguese is available with online material.     

Trophic interactions and habitat segregation between competing Daphnia species

Summary Two commonly coexisting species of Daphnia segregate by habitat in many stratified lakes. Daphnia pulicaria is mostly found in the hypolimnion whereas D. galeata mendotae undergoes diel vertical migration between the hypolimnion and the epilimnion. I examined how habitat segregation between these two potentially competing species might be affected by trophic interactions with their resources and predators by performing a field experiment in deep enclosures in which I manipulated fish predation, nutrient levels, and the density of epilimnetic Daphnia. The results of the experiment indicate that habitat use by D. pulicaria can be jointly regulated by competition for food from epilimnetic Daphnia and predation by fishes. Patterns of habitat segregation between the two Daphnia species were determined by predation by fish but not by nutrient levels: The removal of epilimnetic fish predators resulted in higher zooplankton and lower epilimnetic phytoplankton densities and allowed D. pulicaria to expand its habitat distribution into the epilimnion. In contrast, increased resource productivity resulted in higher densities of both Daphnia species but did not affect phytoplankton levels or habitat use by Daphnia. The two species exhibit a trade-off in their ability to exploit resources and their susceptibility to predation by fish. D. g. mendotae (the less susceptible species) may thus restrict D. pulicaria (the better resource exploiter) from the epilimnion when fish are common due to lower minimum resource requirements than those needed by D. pulicaria to offset the higher mortality rate imposed by selective epilimnetic fish predators. D. g. mendotae does not appear to have this effect in the absence of fish.     

Trophic niche width and overlap of two sympatric gulls in the southwestern mediterranean

The diets of two potential competitor species, Audouin's Larus audouinii and yellow-legged gulls Larus cachinnans, were examined while they bred at the Chafarinas Islands during 1993, 1994, and 1995. Data were collected during two commercial fishing regimes: (1) trawling and purse seine fisheries, and (2) diurnal trawlers only. Since the food supply for the gulls in this area was heavily reliant on the activity of purse seine fisheries, these contrasting situations allowed us to analyze short-term effects, induced by daily changes in food supply, on niche width, dietary shift, and niche overlap between the two species. Overall, both species relied mainly on fish for food, especially Clupeiforms, in the case of Audouin's gull irrespective of the fishing situation, and in the case of the yellow-legged gull, only when purse seine fishing was in operation. When purse seine boats did not operate (food shortage), yellow-legged gulls broadened their niche, consuming equal amounts of all the feeding resources, and they showed a dietary shift toward a greater consumption of prey from refuse tips. In contrast, Audouin's gulls did not change their niche width, but showed a slight dietary shift away from the consumption of epipelagic fish, compensated by an increase in reliance on benthic-mesopelagic resources. Niche overlap was clearly higher on days when both fishing fleets operated, probably because a superabundant food resource facilitates high overlap without affecting coexistence between the two species. Since our study was developed on the basis of daily variations in food supply, and competition effects are to be expected on a longer-term basis, these changes can be seen as the outcome of the coexistence of two species in stable competitive equilibrium. Received: 4 October 1996 / Accepted: 20 May 1997     

Trophic interactions and the relationship between species diversity and ecosystem stability

Several theoretical studies propose that biodiversity buffers ecosystem functioning against environmental fluctuations, but virtually all of these studies concern a single trophic level, the primary producers. Changes in biodiversity also affect ecosystem processes through trophic interactions. Therefore, it is important to understand how trophic interactions affect the relationship between biodiversity and the stability of ecosystem processes. Here we present two models to investigate this issue in ecosystems with two trophic levels. The first is an analytically tractable symmetrical plant-herbivore model under random environmental fluctuations, while the second is a mechanistic ecosystem model under periodic environmental fluctuations. Our analysis shows that when diversity affects net species interaction strength, species interactions--both competition among plants and plant-herbivore interactions--have a strong impact on the relationships between diversity and the temporal variability of total biomass of the various trophic levels. More intense plant competition leads to a stronger decrease or a lower increase in variability of total plant biomass, but plant-herbivore interactions always have a destabilizing effect on total plant biomass. Despite the complexity generated by trophic interactions, biodiversity should still act as biological insurance for ecosystem processes, except when mean trophic interaction strength increases strongly with diversity.     

Seasonal niche segregation of two sympatric xenocyprinid fishes

Xenocypris microlepis (Bleeker, 1871) and Xenocypris davidi (Bleeker, 1871) are two closely related xenocyprinid species potentially subject to exploitative competition. They often coexist in many freshwater ecosystems, which offers an opportunity to analyze their relationships. The present study describes the seasonal feeding habits of age‐3 X. microlepis and X. davidi in Xin'anjiang Reservoir, located in Zhejiang, China, as determined by stable isotope analysis. Particulate organic matter (POM; 50%) and periphyton (50%) were the major items observed in the X. microlepis diet, whereas periphyton (>60%) was prevalent in the X. davidi diet. Seasonal variations were observed in the diet compositions of both xenocyprinid species. Whereas X. microlepis tended to ingest more sediment organic matter (SOM) in autumn than in spring and summer, SOM was the secondary food item for X. davidi over the three seasons. The seasonal diet shift observed in this work indicates niche segregation of the sympatric pair. The results of this study contribute to the current knowledge of seasonal trophic interactions in predator–prey systems where sympatric xenocyprinids are present.     

Trophic niche partitioning between two prey and their incidental predators revealed various threats for an endangered species

Documenting trophic niche partitioning and resource use within a community is critical to evaluate underlying mechanisms of coexistence, competition, or predation. Detailed knowledge about foraging is essential as it may influence the vital rates, which, in turn, can affect trophic relationships between species, and population dynamics. The aims of this study were to evaluate resource and trophic niche partitioning in summer/autumn between the endangered Atlantic‐Gaspésie caribou (Rangifer tarandus caribou) population, moose (Alces americanus) and their incidental predators, the black bear (Ursus americanus) and coyote (Canis latrans), and to quantify the extent to which these predators consumed caribou. Bayesian isotopic analysis showed a small overlap in trophic niche for the two sympatric ungulates suggesting a low potential for resource competition. Our results also revealed that caribou occupied a larger isotopic niche area than moose, suggesting a greater diversity of resources used by caribou. Not surprisingly, coyotes consumed mainly deer (Odocoileus virginianus), moose, snowshoe hare (Lepus americanus), and occasionally caribou, while bears consumed mainly vegetation and, to a lesser extent, moose and caribou. As coyotes and bears also feed on plant species, we documented trophic niche overlap between caribou and their predators, as searching for similar resources can force them to use the same habitats and thus increase the encounter rate and, ultimately, mortality risk for caribou. Although the decline in the Gaspésie caribou population is mostly driven by habitat‐mediated predation, we found evidence that the low level of resource competition with moose, added to the shared resources with incidental predators, mainly bears, may contribute to jeopardize the recovery of this endangered caribou population. Highlighting the trophic interaction between species is needed to establish efficient conservation and management strategies to insure the persistence of endangered populations. The comparison of trophic niches of species sharing the same habitat or resources is fundamental to evaluate the mechanisms of coexistence or competition and eventually predict the consequences of ecosystem changes in the community.     

Trophic and spatial interrelationships in the fish species of an Ontario temperate lake

Synopsis Analysis of the fish faunas of Lake Opinicon and other small, cold temperate Ontario water bodies shows that the component species differ in body size, morphology, abundances, habitats, diurnal and seasonal habitat utilization patterns, diets, dietary changes with age, reproductive strategies, and population turnover rates. These differences are detailed.The number of species occurring in a lake is partly due to historic factors, the number of habitats available, and morphological, behavioral and ecological adaptations that, by channelling their owners towards alternative resources, permit species to co-occur. Diet overlap values between most species are low except for the congeneric bluegill and pump-kinseed sunfishes, where values are moderate. These are the two commonest species in the lake and other parameters must increase the ecological differences between these two species.Lake Opinicon is a highly variable ecosystem. Part of this variability stems from the seasonal nature of the environment and the fact that different resources reach their peak abundance at different times of the year. Ecological overlap levels between fish species fluctuate greatly in the course of the season as species switch from, or move on to, different resources. Population levels in different habitats also vary seasonally. Species adaptations and interaction patterns were presumably evolved over a long period; most of these adaptations undoubtedly developed before the component species colonized the lake.This paper forms part of the proceedings of a mini-symposium convened at Cornell University, Ithaca, N.Y., 18–19 May 1976, entitled Patterns of Community Structure in Fishes (G. S. Helfman, ed.).     

Experimental evidence for niche segregation in a sister species pair of non-biting midges

The principle of limiting similarity states that closely related species need to partition resources of the habitat in order to coexist in the same general area. We tested this hypothesis experimentally with a sister species pair of non-biting midges (Chironomus riparius and C. piger) by assessing their relative larval fitness under several concentrations of nitrite and temperature regimes, as suggested by the observed habitat segregation in a previous field study. Both chironomid species often occur in eutrophic habitats like agricultural areas or industrial point source effluents. Based on field observations, we hypothesised C. piger to tolerate higher nitrite concentrations, higher temperatures and larger temperature ranges than C. riparius. As predicted, C. piger coped better with higher nitrite concentrations. Against the expectations, C. riparius had a tendentially higher fitness at both higher constant temperatures and larger daily temperature ranges. However, the interaction of both stressors favoured C. piger in warm high-nitrite habitats thus concurring to the field observations. The complex interaction of candidate environmental factors with antagonistic effects found here emphasises thus the necessity to experimentally assess field observations of niche segregation.     

Somato-dendritic synapses in the paraventricular organ of two anuran species

Summary The ultrastructure of the paraventricular organ ofXenopus laevis andRana esculenta has been investigated. Special attention has been paid to contact regions between nerve cells of the paraventricular organ and other nerve cells.According to the results of the glutaraldehyde-osmium tetroxide fixation as well as the zinc iodide-osmium method, it appears that the perikarya of several nerve cells of the paraventricular organ make synaptic contacts with dendrites of other nerve cells. It is suggested that the presence of the somato-dendritic synapses is a morphological indication for the sensory function of the nerve cells.Thanks are due to Prof. Dr. P. G. W. J. van Oordt for his interest and the many helpful discussions, and to Mr. H. van Kooten and his co-workers for their skilful photographic assistance.     

Trophic niche segregation among herbivorous serrasalmids from rapids of the lower Xingu River,Brazilian Amazon

In the Amazon Basin, several species of herbivorous serrasalmid fishes inhabit rapids, but it is unknown if they partition food resources during the annual low-water period when fish densities are high within greatly reduced volume of aquatic habitat. We investigated the trophic ecology of juveniles and adults of three species, Myleus setiger, Ossubtus xinguense, and Tometes kranponhah, common in rapids of the Xingu River during the low-water period. Diets, stable isotope ratios of muscle tissue, and functional traits were analyzed for 59 specimens of M. setiger, 175 of O. xinguense and 215 of T. kranponhah. The three species overlapped in dietary and isotopic space, with adult O. xinguense being most divergent. Juvenile and adult T. kranponhah and juvenile O. xinguense, two groups with broad diets, had lowest trophic positions estimated from isotopic data. Adult O. xinguense had the highest trophic position despite having large amounts of Podostemaceae in the diet. High trophic overlap during the low-water period suggests that either food resources are not limiting, or niches are partitioned by other means. Differences in functional traits of the three serrasalmids could be associated with differential efficiencies of swimming and feeding within microhabitats that vary according to water velocity and/or structural complexity.

     

Co-existence and niche segregation of three small bovid species in southern Mozambique

Niche segregation among three small antelopes – red duiker, common duiker and suni – was investigated in a coastal savanna woodland/forest mosaic. It was expected that these similar‐sized concentrate selectors would show differentiation in diet choice to decrease competition. Diet composition did not vary significantly among the different vegetation types. For all three antelope species, the number of dietary items was large, with a minimum of 70 different food items per species. Dietary specialization was low, with only 10% of the food items being exclusively used by each of the species. The ranks of food items were positively correlated among species in the wet season, but not in the dry season. Diet breadth significantly decreased in the dry season. The use of exclusive species was significantly larger in the dry season with lowest values recorded for the common duiker. Diet overlap in the wet season was considerable, but significantly decreased in the dry season, the time of food scarcity. The dry season data showed evidence for niche segregation, although this was not based on displacement. As niche segregation in the dry season was coupled to a random apportionment of diet items among antelope species, it cannot be interpreted as the result of competitive displacement.     

Call differences and calling site segregation in anuran species from central Amazonian floating meadows

Summary The acoustic behaviour of 15 sympatric and synchronically breeding species of frogs in an area of floating meadows near Manaus (Brazil) was studied for a period of 8 months. The calling positions of each species can be identified with certain physiognomic types of vegetation.Sound analyses were used to compare the mating calls. The main variables are dominant frequency, call duration and pulse repetition rate. Each of the 15 species has a distinct mating call and differs from the acoustic behaviour of each other one. Eleven species are separated in their dominant frequency ranges within their specific calling sites. Species sharing emphasised frequency ranges within identical calling sites differ greatly in at least two temporal variables.The roles of calling position, spectral, and temporal features of mating calls in species recognition and premating reproductive isolation are discussed.     

Habitat overlap/niche segregation in two Umbilicaria lichens: a possible mechanism

Summary Umbilicaria muhlenbergii and Umbilicaria papulosa are two similar lichens which show extensive habitat overlap. Current theory predicts that for those resources that are limited, and of critical importance to both species, segregation is demand for or use of those resources ought to be present. Controlled experiments showed that the upper and lower cortical surfaces of the two species functioned in very different ways so that U. muhlenbergii is wetted most rapidly by runoff and mist-like precipitation whereas U. papulosa is wetted most rapidly by large raindrops. An analysis of the meteorological conditions in the natural habitat for the two lichens shows that the four months providing significant productivity in U. papulosa are the same months with a very high frequency of thunderstorms (which produce large drops). Conversely, the months which produce the greatest production in U. muhlenbergii are spread out over most of the year. When water is supplied after periods of dryness, the two species absorb it at different times and from different sources. This difference supports current ideas about niche segregation in plants but represents the first time it has been demonstrated for lichens.     

Habitat niche specialization in an understory species in a warm temperate forest

Relationships between microhabitat variables; understory light conditions in summer and winter, altitude, slope inclination and topographic categories (valley, ridge, and slope) and the distribution of Aucuba japonica Thunb. (Cornaceae), a common understory shrub species in Japan were examined using non-contagious 66, 20 × 20 m² quadrats. The Morishita’s I _δ suggested that A. japonica distributions were strongly heterogeneous among the quadrats. Therefore positive spatial autocorrelation of A. japonica at a within-quadrat level (≤20 m) was obvious. Moran’s I statistics showed a significant positive spatial autocorrelation in A. japonica abundance within the distance shorter than 60 m. But the partial Mantel tests suggested that the mass effect from neighboring quadrats would little explain A. japonica abundance in a quadrat. The partial Mantel tests also clearly showed that A. japonica distributions were strongly structured by topography and understory light conditions. Using Monte Carlo randomization tests, we found that A. japonica was aggregately distributed in quadrats in valley which were covered by deciduous canopies. Better understory light conditions in winter together with valley edaphic conditions may increase the abundance of A. japonica there. It is concluded that habitat niche specialization is important in structuring distribution of A. japonica in this forest community.     

Trophic niche segregation allows range‐extending coral reef fishes to co‐exist with temperate species under climate change

Changing climate is forcing many terrestrial and marine species to extend their ranges poleward to stay within the bounds of their thermal tolerances. However, when such species enter higher latitude ecosystems, they engage in novel interactions with local species, such as altered predator–prey dynamics and competition for food. Here, we evaluate the trophic overlap between range‐extending and local fish species along the east coast of temperate Australia, a hotspot for ocean warming and species range extensions. Stable isotope ratios (δ¹⁵N and δ¹³C) of muscle tissue and stomach content analysis were used to quantify overlap of trophic niche space between vagrant tropical and local temperate fish communities along a 730 km (6°) latitudinal gradient. Our study shows that in recipient temperate ecosystems, sympatric tropical and temperate species do not overlap significantly in their diet—even though they forage on broadly similar prey groups—and are therefore unlikely to compete for trophic niche space. The tropical and temperate species we studied, which are commonly found in shallow‐water coastal environments, exhibited moderately broad niche breadths and local‐scale dietary plasticity, indicating trophic generalism. We posit that because these species are generalists, they can co‐exist under current climate change, facilitating the existence of novel community structures.     

Acoustic niche partitioning among seven cuckoo species in a forest in eastern China

Acoustic communication among birds plays an important role in attracting mates and defending territories. For the successful transmission of songs, individuals of different species often avoid singing at the same time to reduce acoustic interference from background noise and overlapping signals from heterospecifics. Such behavioural acoustic niche partitioning may occur especially among closely related species due to their ecological similarities. In this study, we recorded bird sounds in a subtropical forest in China in May–June 2019 and detected seven cuckoo species. Extracting characteristics of the cuckoo calls, we found that only four of the 21 pairs of species overlapped in frequency range, and 19 pairs were classified accurately using a linear discriminant analysis classifier based on their features. The remaining two species pairs could be separated based on temporal or spatial distribution patterns. We also analysed the temporal distribution patterns and overlap time of the calls, finding that the seven species exhibit partitioning in at least one of three acoustic dimensions (site, frequency, activity time). We conclude that the seven sympatric cuckoo species were strongly partitioned in acoustic signal space and minimally masked each other's signals.