Specialization and noncompetitive resource partitioning among sponge-eating dorid nudibranchs

Summary Habitat and food resource partitioning ecologically isolate six species of Pacific Northwest dorid nudibranchs. Food resources along a gradient of sponge skeletal structure are partitioned between two exploitive guilds. The guilds are characterized by mutually exclusive predatory and digestive adaptations which allow efficient processing of sponges with poorly- or well-organized skeletons. Habitats along a depth gradient are partitioned within guilds. For a dorid species, feeding rates, extraction efficiencies and food quality are virtually identical for sponges with the appropriate extreme (either poorly- or well-organized) and intermediate skeletal organizations, but growth and reproductive rates supported by the former prey type are twice those supported by the latter prey type. Prey types with the appropriate extreme skeletal organization are thus optimal food and specialization to that food is expected. When two divergent specialist species co-occur, food resource partitioning is demonstrable but arises from self-stabilizing specializations to maximize net energy accumulation and not from competitive interactions. Habitat partitioning is viewed as arising from prey distributions and dorid physiological tolerances. This system represents an example of morphological and behavioral specializations giving rise to resource partitioning as opposed to competition giving rise to resource partitioning and subsequent morphological and behavioral specializations.     

Prey diversity as a driver of resource partitioning between river‐dwelling fish species

Although food resource partitioning among sympatric species has often been explored in riverine systems, the potential influence of prey diversity on resource partitioning is little known. Using empirical data, we modeled food resource partitioning (assessed as dietary overlap) of coexisting juvenile Atlantic salmon (Salmo salar) and alpine bullhead (Cottus poecilopus). Explanatory variables incorporated into the model were fish abundance, benthic prey diversity and abundance, and several dietary metrics to give a total of seventeen potential explanatory variables. First, a forward stepwise procedure based on the Akaike information criterion was used to select explanatory variables with significant effects on food resource partitioning. Then, linear mixed‐effect models were constructed using the selected explanatory variables and with sampling site as a random factor. Food resource partitioning between salmon and bullhead increased significantly with increasing prey diversity, and the variation in food resource partitioning was best described by the model that included prey diversity as the only explanatory variable. This study provides empirical support for the notion that prey diversity is a key driver of resource partitioning among competing species.     

Differential diet breadths and species coexistence in leafroller-hunting eumenid wasps

There are, at least, three possible ways in which similar species coexist; resource partitioning, interference competition, and exploitation competition. Here, I investigated which way contributed to the coexistence of leafroller-hunting eumenid wasp species. Resource partitioning and, in addition, differential diet breadths proved to promote species coexistence in this case. First, I analyze the prey records and diet overlap of four eumenid species in a local area. The larger two eumenids hunted similar-sized prey items and had similar potential taxonomic prey uses. But the diet breadth of the subsocial eumenid was much wider than that of the solitary one. As a result, the diet overlap between the two large eumenids decreased. This was because the solitary eumenid attend repeatedly to the same hunting site inhabited by one abundant prey species, while the subsocial one made random hunting. On the other hand, the two medium-sized eumenids partitioned resources according to prey size. Secondly, I related these results to prey choice by several other species of eumenid obtained from literature sources. Ten Japanese common eumenids were divided into four groups according to their prey size. In each of the four groups, 2 to 3 wasp species differentiated the habitat (1 group) or coexisted by means of differential diet breadths (parallel with differential sociality, 2 groups).     

Dietary opportunism,resource partitioning,and consumption of coffee berry borers by five species of migratory wood warblers (Parulidae) wintering in Jamaican shade coffee plantations

Diets reflect important ecological interactions, but are challenging to quantify for foliage‐gleaning birds. We used regurgitated stomach samples from five primarily insectivorous species of long‐distance migrant warblers (Parulidae) wintering in two moderate‐elevation shade coffee farms in Jamaica to assess both foraging opportunism and prey resource partitioning. Our results, based primarily on 6120 prey items in 80 stomach samples collected during a one‐week period in March 2000, confirm opportunism. The diets of all five warblers, including American Redstarts (Setophaga ruticilla), Black‐and‐White Warblers (Mniotilta varia), Black‐throated Blue Warblers (S. caerulescens), Northern Parulas (S. americana), and Prairie Warblers (S. discolor), overlapped strongly based on consumption of the same prey types, even many of the same prey species (4 of 10 interspecific overlaps >0.9, range = 0.74–0.97). Moreover, all five species fed on similarly small, often patchily distributed prey, including coffee berry borers (Hypothenemus hampei; Coleoptera, Curculionidae). Nonetheless, permutational multivariate analysis of variance also revealed that the diets of these species differed significantly, primarily with respect to prey mobility (winged vs. sessile); American Redstarts fed on the most mobile prey, and Northern Parulas on the least mobile prey and a relatively restricted set of prey taxa compared to the other four species of warblers. Overall, our results suggest both dietary opportunism consistent with a migratory life‐history, and interspecific resource partitioning consistent with differences in morphology and foraging behavior during a food‐limited season. Having provided evidence of the three necessary conditions, namely intraspecific competition, resource limitation, and interspecific overlap in resource use, the results of our study, in combination with those of other studies, also provide evidence of interspecific competition among wintering migrant insectivores. We thus argue that diffuse interspecific exploitative food competition may be more important than previously recognized.     

Feeding of an Iberian stream cyprinid assemblage: seasonality of resource use in a highly variable environment

Food resource use by seven cyprinids from an Iberian stream was analysed over 9 months. Differences in food resource use were found both between species and within species between seasons. Plant material was a more important food for carp, nase, goldfish and barbel than for gudgeon, roach and chub, irrespective of the season. Chironomid larvae were the staple animal food for the former five species throughout the year. Roach and chub, especially the latter, displayed large seasonal variations in prey use, with chironomid larvae only being important during autumn. Ephemerellid nymphs and ephemeropteran imagos dominated the animal diet of chub during spring and summer, respectively. Dipteran adults and Formicidae were the most important prey for roach during spring and summer, with other common prey being ephemerellid nymphs and hydropsychid larvae. Food resource overlap among the three dominant species (roach, barbel and chub) displayed a large seasonal variation. High overlaps were observed during autumn when these species used the same resources. During summer overlaps were much lower with each species specialising on different prey. The remaining less abundant species had large diet overlaps amongst themselves and with barbel, over all seasons. It is suggested that morphological constraints, habitat partitioning and temporal changes in food resource limitation may be involved in producing these patterns of food resource use.     

One meadow for two sparrows: resource partitioning in a high elevation habitat

Resource partitioning is the basis of the coexistence of sympatric species and has therefore received much attention in ecological studies. However, how variation in environmental conditions (and particularly natural variation in resource availability) can influence resource partitioning in free-ranging animals is not well understood. In the present study, we addressed the hypothesis that natural changes in the availability of food resources affect food partitioning between sympatric species. To do so, we examined temporal changes in the plasma isotopic signature (δ(15)N and δ(13)C) of syntopic Lincoln's sparrows Melospiza lincolnii and white-crowned sparrows Zonotrichia leucophrys, in parallel with seasonal changes in habitat maturity and food availability from spring to early summer. We found no apparent trophic segregation between Lincoln's and white-crowned sparrows when resources were scarce in spring. But, interestingly, as resource availability and the number of breeding birds increased, Lincoln's sparrows showed lower δ(15)N values than white-crowned sparrows, as they consumed more prey from lower trophic levels and less prey from higher trophic levels. This feeding divergence between sympatric species may be explained (1) by a change in foraging preferences and opportunities for Lincoln's sparrows and (2) by the abundance of competitors that increased faster than resources, thus promoting interspecific competition and trophic segregation. These results provide clear evidence that trophic segregation is dynamically tied to variation in environmental conditions, which are therefore fundamental to consider when examining resource partitioning between co-existing species.     

Comparative feeding ecology of sympatric Solea solea and S. senegalensis, within the nursery areas of the Tagus estuary, Portugal

Among the stomach contents of 609 individuals of Solea solea and 1104 of S. senegalensis the main food items of S. solea were Corophium spp. and Hediste diversicolor, and of S. senegalensis were Corophium spp., H. diversicolor and Scrobicularia plana. For both species, the importance of larger prey items in the diet, namely H. diversicolor and Crangon crangon, increased with fish size. Feeding activity of S. solea and S. senegalensis increased in spring and summer. Short-term variations were particularly related to the tidal cycle and the two species fed in intertidal areas. Dietary dierences between the two nursery areas reflected prey availability mainly. Although intra- and interspecific length classes overlapped in diet, potential interspecific competition was probably minimized by a dierential habitat use pattern.     

The dietary basis for temporal partitioning: food habits of coexisting Acomys species

Two rodent species of the genus Acomys coexist on rocky terrain in the southern deserts of Israel. The common spiny mouse (A. cahirinus) is nocturnally active whereas the golden spiny mouse (A. russatus) is diurnally active. An early removal study suggested that competition accounts for this pattern of temporal partitioning: the golden spiny mouse is forced into diurnal activity by its congener. Theoretically, temporal segregation should facilitate coexistence if the shared limiting resources differ at different times (primarily among predators whose prey populations have activity rhythms), or if they are renewed within the period of the temporal segregation. We studied food preferences of the two Acomys species in a controlled cafeteria experiment in order to assess resource overlap and the potential for competition for food between the two species. We found no significant difference in food preferences between species. The dietary items preferred by both were arthropods. We also carried out a seasonal study of the percentage and identity of arthropods taken in the field by individuals of the two species. Individuals of both species took on annual average a high percentage of arthropods in their diets. Seasonal diet shifts reflect seasonal abundance of arthropods at Ein Gedi during day and night. Diurnal activity may also reduce interspecific interference competition between A. russatus and A. cahirinus. However, the strong interspecific dietary overlap in food preference, the heavy reliance on arthropods in spiny mouse diets, and the seasonal and circadian differences in arthropod consumption suggest that prey partitioning may be a viable mechanism of coexistence in this system. Received: 6 July 1998 / Accepted: 10 May 1999     

Pitcher plant facilitates prey capture in a sympatric congener

Carnivorous plants avoid below-ground competition for nitrogen by utilizing an alternative nitrogen resource—invertebrate prey, but it remains unclear if sympatric carnivorous plants compete for prey resources. The aim of this study was to investigate if exploitative prey-resource competition occurs between the two sympatric pitcher plant species, Nepenthes rafflesiana and N. gracilis in Singapore. We first investigated if prey-resource partitioning occurs between these two species, and then investigated niche shift in N. gracilis by examining its pitcher contents along an in situ gradient of N. rafflesiana interspecific competition. Our results showed clear evidence of resource partitioning between the two species, but contrary to the expectation of competition, proximity to N. rafflesiana pitchers correlated with higher total prey numbers in N. gracilis pitchers. Our multivariate model of prey assemblages further suggested that N. rafflesiana facilitates N. gracilis prey capture, especially in several ant taxa that are trapped by both species. Concurrently, we found strong evidence for intraspecific competition between N. gracilis pitchers, suggesting that prey resources are exhaustible by pitcher-predation. Our results show that resource partitioning can be associated with facilitative interactions, instead of competition as is usually assumed. Facilitation is more typically expected between phylogenetically distant species, but divergences in resource acquisition strategies can permit facilitation between congeners.     

Specialisation in prey capture drives coexistence among sympatric spider‐hunting wasps

1. Sister taxa that coexist in the same space and time often face competition due to the use of similar resources. However, some closely related species can adopt fine‐grained specialisation in resource use to coexist. This study investigated niche overlap between three sympatric spider‐hunting wasp species of the genus Trypoxylon (Hymenoptera: Crabronidae) known to nest in three of the habitats found in the study area. 2. First, the co‐occurrence of these wasp species in the three habitats was estimated, as a proxy for potential competition. Then, the following hypotheses were tested: (i) niche partitioning is seen more often between species that co‐occur in a habitat, whereas there is niche overlap between species nesting in distinct habitats (prey specialisation hypothesis); and (ii) wasp species capture prey according to their size (physical constraint hypothesis). 3. Two pairs of wasp species were found consistently nesting in the same habitat. Niche partitioning based on prey taxa occurred regardless of the habitat preference. It was also found that differences in the size of wasps reflected distinctions in the size of their prey. 4. These findings were consistent over the years, showing that the significance of specialisation in foraging activities and physical constraints during prey capture can play key roles in the coexistence of sympatric species. The distinctions in the foraging strategies of these wasps are discussed, as well as potential mechanisms driving the evolution in prey specialisation, with insights for future studies.     

Food partitioning among carnivores within feeding guild structure of fishes inhabiting a mudflat ecosystem of Indian Sundarbans

The present study was aimed to determine dietary composition and feeding guild structure of the fishes inhabiting mudflat habitat of Indian Sundarbans. In addition, partitioning of food resources by the fish species belonging to the carnivorous feeding guild was also performed to understand the survival strategies of fish in a mudflat estuarine habitat. Seventeen prey categories were isolated from the stomachs of 31 studied fish species. Overall, five feeding guilds (viz. plankti-benthivore: 12 species, herbivore: one species, detritivore: three species, omnivore: one species and carnivore: 14 species) were identified on the basis of the prey abundance within their stomachs, considering 64 % Bray–Curtis similarity. Among the carnivorous, maximum trophic richness was obtained for Uroconger lepturus followed by Ophichthus apicalis. Teleost and decapods were the main animal prey items preferred by majority of the carnivorous fishes. However, O. apicalis and Terapon jarbua showed their preference toward maximum number of prey categories among carnivores, which was also ratified by the high values for standardized niche breadth presented by them. The maximum degree of interspecific dietary overlap was found between Uropterygius marmoratus and Pseudapocryptes elongatus as both of them were recognized as cranci-piscivore. The lowest was observed between Hyporhamphus limbatus and Coilia neglecta. As food resources are not limiting in the mudflats of Indian Sundarbans, the general patterns of resource partitioning and niche differentiation in resident ecological communities will improve the understanding of the mechanisms underlying species coexistence and community structure.     

Trophic relationships among concentrated populations of small fishes in seagrass meadows

Changes in available food and utilized foods for a densely populated guild of animals can uncover periods of niche displacement among particular consumer species or their separate size classes. Dense populations of small fishes and their foods were çensussed for 13 months and studied experimentally in shoalgrass and turtlegrass meadows of Redfish Bay, Texas. Feeding habits were determined with respect to prey availability, and illustrated the extent to which seasonal partitioning of food corresponded to food depletion among these abundant consumers in seagrass meadow food webs. The darter goby, code goby, pinfish, and Gulf pipefish were the most common species throughout the year. Although the darter goby did not show distinct ontogenetic changes in food habits, the code goby, Gulf pipefish, and pinfish demonstrated major ontogenetic progressions of foods selected.Food availability in the seagrass meadows changed seasonally. When major prey such as amphipods were abundant, during spring, many fish species showed high overlap in food use. Regardless of food availability, the code goby and Gulf pipefish fed mainly on amphipods or copepods. The more common darter goby and pinfish seasonally changed their diets with changes in food availability; the darter goby and pinfish were more carnivorous during spring, but they largely consumed epiphytic algae during summer. Cage experiments were used to monitor foods confined with elevated densities of pinfish and darter gobies, relative to control cages at natural overall densities. Prey items in the former cages decreased sharply, with corresponding dietary shifts by these common fishes. During resource depletion, these changes in resource use by these naturally concentrated consumers appeared as temporary partitioning of available resources. This shift occurred during both natural (seasonal) and experimental depletions of food, and appears to result from increased interspecific and intraspecific competition during periods of depleted preferred foods.     

Moorea BIOCODE barcode library as a tool for understanding predator–prey interactions: insights into the diet of common predatory coral reef fishes

Identifying species involved in consumer–resource interactions is one of the main limitations in the construction of food webs. DNA barcoding of prey items in predator guts provides a valuable tool for characterizing trophic interactions, but the method relies on the availability of reference sequences to which prey sequences can be matched. In this study, we demonstrate that the COI sequence library of the Moorea BIOCODE project, an ecosystem-level barcode initiative, enables the identification of a large proportion of semi-digested fish, crustacean and mollusks found in the guts of three Hawkfish and two Squirrelfish species. While most prey remains lacked diagnostic morphological characters, 94% of the prey found in 67 fishes had >98% sequence similarity with BIOCODE reference sequences. Using this species-level prey identification, we demonstrate how DNA barcoding can provide insights into resource partitioning, predator feeding behaviors and the consequences of predation on ecosystem function.     

枸杞岛岩礁生境主要鱼类的食物组成及食物竞争

基于2009年3月-2010年2月枸杞岛沿岸岩礁生境渔业资源调查数据,对岩礁生境中的3种定居性鱼类（褐菖鲉、大泷六线鱼和斑头六线鱼）和3种非定居性鱼类（花鲈、黄姑鱼和小黄鱼）的食物组成及食物关系进行了研究.结果表明： 麦秆虫、钩虾、褐菖鲉幼鱼、鳀鱼和中国毛虾等是6种鱼类的主要饵料生物,且饵料组成随季节而变化.3种定居性鱼类中,大泷六线鱼和斑头六线鱼在秋季食物竞争激烈;3种非定居性鱼类中,黄姑鱼和小黄鱼在夏季食物竞争激烈;非定居性鱼类和定居性鱼类之间,黄姑鱼分别与褐菖鲉（秋季）和大泷六线鱼（冬季）食物竞争激烈.黄姑鱼是引起岩礁生境中6种主要鱼类食物竞争的关键鱼种.枸杞岛岩礁生境中6种主要鱼类的摄食活动对褐菖鲉幼鱼的资源量有一定影响.     

Seasonal food habits of corsac and red foxes in Mongolia and the potential for competition

Competition often occurs between sympatric species that exploit similar ecological niches. Among canids, competition may be reduced by partitioning resources such as food, time, and habitat, but the mechanisms of coexistence remain poorly understood, particularly among fox species. We described the food habits of two foxes that live sympatrically across northern and central Asia, the corsac fox (Vulpes corsac) and red fox (V. vulpes), by analyzing scats collected during a field study in Mongolia. We analyzed 829 corsac and 995 red fox scats collected from April 2005 to August 2007 and tested the extent to which food partitioning occurred. The diets of both species consisted mainly of insects followed by rodents, but also included birds, reptiles, large mammal remains (carrion), plant material (including fruits and seeds), and garbage. Despite high overlap in the proportion of food items consumed, differences existed between species in overall diet with corsacs more frequently consuming beetles, but proportionally fewer crickets and large mammal remains than red foxes. We detected interspecific differences during the pup rearing and dispersal seasons, when prey was abundant, but not during the breeding season, when prey was scarce and diet overlap highest. Each species’ diet also differed seasonally and exhibited moderate overall breadth. Corsacs consumed proportionally more beetles and rodents during pup rearing and crickets during dispersal relative to other seasons, whereas red foxes consumed proportionally more crickets during pup rearing and dispersal and more rodents and large mammals during pup rearing and breeding relative to other seasons. Our results suggest that partitioning of food resources during most of the year facilitates coexistence, and that the potential for competition is highest during winter months.     

Does sympatry affect trophic resource use in congeneric tidepool fishes? A tale of two gobies Favonigobius lentiginosus and Favonigobius exquisitus

The feeding ecology of two sympatric gobies, Favonigobius lentiginosus and Favonigobius exquisitus, which inhabit soft substrate pools was studied in Moreton Bay, Australia. Favonigobius spp. and sediment cores were collected from three locations within the bay and fish gut contents were analysed to explore potential competition and ontogenetic dietary shifts. The most abundant prey at all sites was nematodes at 6.33 ± 0.38 cm(-3) at Dunwich, 33.58 ± 0.26 cm(-3) at Manly and 6.36 ± 0.849 cm(-3) (mean ± S.E.) at Godwin Beach. Nevertheless, they were not a dominant component of the diets. Volumetric percent contribution of prey showed that copepods and decapod shrimps dominated F. lentiginosus diets at Dunwich (7.8 and 6.6%, respectively) and Godwin Beach (6.5 and 14.3%, respectively) and the diets of F. exquisitus at Manly (9.2 and 9.5%, respectively) and Godwin Beach (10.4 and 11.8%, respectively). Schoener's index of dietary overlap between the two species, when sympatric, was 0.85 indicating a high similarity. An ontogenetic shift towards larger prey items occurred as Favonigobius spp. reached larger sizes. Gut fullness indices showed significant differences between time of day (two-way ANOVA, P < 0.01) and species (two-way ANOVA, P < 0.05) but Bonferroni's multiple comparison test showed that the only significant difference was between F. lentiginosus at Dunwich and F. exquisitus at Godwin Beach at 1800 hours. Food resource competition and temporal resource partitioning did not appear to be a limiting factor between F. lentiginosus and F. exquisitus despite cohabitation in such restricted environments.     

Evidence of resource partitioning between humpback and minke whales around the western Antarctic Peninsula

For closely related sympatric species to coexist, they must differ to some degree in their ecological requirements or niches ( e.g. , diets) to avoid interspecific competition. Baleen whales in the Antarctic feed primarily on krill, and the large sympatric prewhaling community suggests resource partitioning among these species or a nonlimiting prey resource. In order to examine ecological differences between sympatric humpback and minke whales around the Western Antarctic Peninsula, we made measurements of the physical environment, observations of whale distribution, and concurrent acoustic measurements of krill aggregations. Mantel's tests and classification and regression tree models indicate both similarities and differences in the spatial associations between humpback and minke whales, environmental features, and prey. The data suggest (1) similarities (proximity to shore) and differences (prey abundance versus deep water temperatures) in horizontal spatial distribution patterns, (2) unambiguous vertical resource partitioning with minke whales associating with deeper krill aggregations across a range of spatial scales, and (3) that interference competition between these two species is unlikely. These results add to the paucity of ecological knowledge relating baleen whales and their prey in the Antarctic and should be considered in conservation and management efforts for Southern Ocean cetaceans and ecosystems.     

The feeding relationships of the larger fish species in a Scottish sea loch

Patterns within a fish assemblage have been examined from catches obtained over a period of 17 months using fixed nets and rod and line sampling. A total of 19 species were caught with summer samples dominated by dab and saithe and winter samples by whiting. Cod were caught regularly throughout the year. Catches at the study site of dab and whiting occurred mainly at night but for cod and saithe catches occurred throughout the day. There was no indication ofa crepuscular or tidal rhythm for any species. Differences between our own observations and those from other published studies lead us to conclude that no species-specific generalizations about feeding periodicities can be made. Feeding patterns are more likely to be determined by site-specific features of particular habitats and their associated prey and predator assemblages.
Examination of stomach contents data using a variety of methods indicates that conclusions are highly dependent on the form of the resource matrix used. However, our analyses indicate that during summer cod and dab feed on a much narrower range of prey than saithe and that there is significant overlap in their diets if a resource matrix based on percentage occurrence of prey species is used. Nevertheless, most diet overlap values for the species examined were low (between 0.1 and 0.2) suggesting that competition for food is unlikely. To date, no experiments have been performed to test the hypothesis that cod and dab compete for food.     

Food Habits and Livestock Depredation of Sympatric Jaguars and Pumas in the Iguaçu National Park Area, South Brazil

Understanding coexistence between sympatric felines with similar body sizes, such as jaguars Panthera onca and pumas Puma concolor , requires knowledge of the way these predators consume and partition food resources. Yet the importance of livestock predation on jaguar and puma coexistence is poorly known. I investigated food habits and patterns of livestock depredation of jaguar and pumas in the Iguaçu National Park (INP) in southern Brazil. From 1997 to 2001, I collected scats opportunistically on trails and roads in INP and visited ranches on the border of INP. I found that jaguars relied mostly on large and medium-sized wild prey species, while pumas concentrated on medium-sized prey species. Livestock was the fifth most frequent prey found in jaguar scats but the most important one in terms of biomass consumed. Jaguar and puma diets differed significantly when all prey items were compared and also when livestock was excluded from the jaguar diet. Jaguar predation on livestock was considerably higher than predation by pumas. However, predation was not substantial relative to availability of livestock, and cattle likely constitute an alternative source of prey for jaguars. Degree of diet overlap between jaguar and puma in INP suggests that coexistence was likely driven by exploitative competition through some degree of food partitioning. My results highlight the importance of more actions toward increasing numbers of large ungulates to preserve the population of jaguars in INP.     

Ontogenetic niche shifts and resource partitioning in a subarctic piscivore fish guild

The feeding ecology of three piscivorous fish species (perch (Perca fluviatilis), pike (Esox lucius) and burbot (Lota lota)), was studied in the subarctic Pasvik watercourse (69 °N), northern Norway and Russia. All three species primarily occupied the benthic habitats in the watercourse. Perch and burbot exhibited distinct ontogenetic niche shifts in food resource use, perch changing from a dominance of zooplankton to zoobenthos to fish, and burbot from zoobenthos to fish. Fish prey dominated the diet of all the investigated size-classes of pike, but small-sized pike (<20 cm) were not represented in the sample. Fish prey size was positively related to predator size in all three species. Whitefish (Coregonus lavaretus) was the dominant prey of pike and large-sized burbot and perch. Nine-spined sticklebacks (Pungitius pungitius) was also an important prey and appeared to be a dietary stepping-stone enhancing the transition from invertebrate feeding to consumption of large-sized whitefish prey for all three predators. A cluster analysis separated the different size groups of the three predator species into five functional feeding groups, most of them containing two or all three species. Within these feeding groups, and especially among the piscivorous size-classes, there was a strong and significant interspecific overlap in prey selection, and the dietary similarities between the species were in general much larger than the intraspecific similarities between ontogenetic stages. All three piscivorous species are important top predators in the aquatic food web of the watercourse, and their ontogenetic diet shifts and resource partitioning patterns generate a substantial food web complexity in this subarctic ecosystem.