Degree Of Dietary Overlap Research Articles

Stable isotope ecology and interspecific dietary overlap among dolphins in the Northeast Atlantic

Dolphins are mobile apex marine predators. Over the past three decades, warm-water adapted dolphin species (short-beaked common and striped) have expanded their ranges northward and become increasingly abundant in British waters. Meanwhile, cold-water adapted dolphins (white-beaked and Atlantic white-sided) abundance trends are decreasing, with evidence of the distribution of white-beaked dolphins shifting from southern to northern British waters. These trends are particularly evident in Scottish waters and ocean warming may be a contributing factor. This mobility increases the likelihood of interspecific dietary overlap for prey among dolphin species previously separated by latitude and thermal gradients. Foraging success is critical to both individual animal health and overall population resilience. However, the degree of dietary overlap and plasticity among these species in the Northeast Atlantic is unknown. Here, we characterise recent (2015-2021) interspecific isotopic niche and niche overlap among six small and medium-sized delphinid species co-occurring in Scottish waters, using skin stable isotope composition (δ13C and δ15N), combined with stomach content records and prey δ13C and δ15N compiled from the literature. Cold-water adapted white-beaked dolphin have a smaller core isotopic niche and lower dietary plasticity than the generalist short-beaked common dolphin. Striped dolphin isotopic niche displayed no interspecific overlap, however short-beaked common dolphin isotopic niche overlapped with white-beaked dolphin by 30% and Atlantic white-sided dolphin by 7%. Increasing abundance of short-beaked common dolphin in British waters could create competition for cold-water adapted dolphin species as a significant portion of their diets comprise the same size Gadiformes and high energy density pelagic schooling fish. These priority prey species are also a valuable component of the local and global fishing industry. Competition for prey from both ecological and anthropogenic sources should be considered when assessing cumulative stressors acting on cold-water adapted dolphin populations with projected decline in available habitat as ocean temperatures continue to rise.

How influential is the role of oligotrophication on the integrity of fish assemblages in the littoral zone?

Food web theory predicts that one of the consequences of oligotrophication is the decline in fisheries following the establishment of nutrient-deficient conditions and low biogenic production. However, emerging evidence suggests that more complex trophic interactions, induced by plankton composition, dietary diversification, temporal and spatial heterogeneity, variations in fish age and size structure can lead to ecosystem responses that deviate from theoretical predictions; especially in the shallow littoral zone. In this study, two end-to-end modelling strategies are used to characterize potential food web structural shifts and overall ecosystem productivity in response to oligotrophication. Our modelling strategy draws upon empirical and theoretical evidence from the Bay of Quinte, a semi-enclosed embayment in northeastern Lake Ontario that has been subjected to phosphorus (P) abatement strategies in the 1970s. We first show that the role of food abundance has been a primary factor shaping fish production, but the fish community gradually responded to the reduced availability of pelagic staples of their diet by displaying greater reliance upon alternative sources, including benthic and other autochthonous (or even allochthonous) food items. Our analysis further suggests that degree of diet overlap between competing trophic guilds can significantly modulate realized biomass levels. The composition of the autotrophic community is another major confounding factor that can induce significant variations from the predicted food web productivity patterns in response to oligotrophication. Overall, our analysis suggests that the proposed reduction of the ambient total phosphorus levels may not necessarily trigger a significant decline in fish biomass in the Bay of Quinte.

The role of spatial and temporal variations in habitat uses and food habits of larvae in persistent occurrence of multiple odonate species in Mizorogaike Pond, Kyoto, Japan

Larvae of many odonate species commonly appear within the same freshwater ecosystem. However, it remains unknown whether there is a dietary separation among the larvae of different species. In this study, we collected different species of odonate larvae in different seasons at various sites on the floating mat of Mizorogaike Pond in Kyoto, Japan, and examined the abundance and gut contents of the dominant species. Our analyses showed that habitat and seasonal abundance of the odonate larvae did not significantly overlap between most pairs of the dominant species. Moreover, the degree of dietary overlap was not related to larval biomass in microhabitats. These results suggest that, although larval food habits were similar among species, the existence of various vegetation types on the floating mat allowed many odonate species to inhabit Mizorogaike Pond.

New insights on the trophic ecology of blue (Prionace glauca) and shortfin mako sharks (Isurus oxyrinchus) from the oceanic eastern South Pacific

ABSTRACTThe blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus) are two large and highly migratory sharks distributed in most oceans. Although they are often caught in the south Pacific Ocean long-line fisheries, their trophic ecology is poorly understood. Stable isotopes with Bayesian mixing and dependence concentration models were performed to determine the diet and trophic differences between the two species in the South-eastern Pacific Ocean. According to the mixing models, fishes are the most important prey of these sharks. Dolphin calves and remains were found in the stomachs of both species, which represents a novel finding in trophic ecology of South Pacific sharks. Intra-specific differences were found in P. glauca, but not in specimens of I. oxyrinchus. The two sharks showed a high degree of diet overlap (73%), primarily over mackerel and dolphin carcasses. Our results indicate that blue and shortfin mako sharks have a generalist feeding strategy in the eastern Pacific Ocean, with a strong preference for teleost fishes and also for dolphin carcasses. Therefore, trophic studies are useful to understand energy flow through the food web, and the trophic position of key species.

Superposición de la dieta del pez león Pterois volitans (Teleostei: Scorpaenidae) con la de peces nativos de nivel trófico similar en Cuba

The spread of the Indo-Pacific lionfish has been one of the most rapid marine fish invasions in the history of the tropical and subtropical western Atlantic, and populations of this species pose a threat to native fishes feeding at similar trophic levels due to competition for food. To determine dietary overlap, 899 lionfish and 377 native fishes of the families Haemulidae, Holocentridae, Serranidae and Lutjanidae were caught in three Cuban localities, and their stomach contents were analyzed based on the number of items, frequency, volume and index of relative importance. Diet composition was similar in the studied localities; Lutjanidae, Serranidae and lionfish mainly fed on fish while Haemulidae and Holocentridae primarily consumed small benthic invertebrates. Mantel correlations showed that the consumption of fish and crustaceans did not increase as lionfish increased in size. The degree of dietary overlap between lionfish and some native fishes depends on locality, ecological zone and the characteristics of each family, confirming the opportunistic nature of the invader. It is likely that native fishes are not affected by competition with lionfish for food because they feed on the mostabundant and available organisms; therefore, food availability is not a limiting factor for these groups.

Trophic relationships in fish assemblages of Neotropical floodplain lakes: selectivity and feeding overlap mediated by food availability

ABSTRACT. The relationships between the degree of dietary overlap and food availability, and implications for food selectivity of fish species were evaluated at floodplain lakes on the upper Paraná River floodplain, Brazil. The hypothesis tested were: i) species become less selective in lakes with high availability of food resources; and ii) species (interspecific) or individual (intraspecific) present higher food overlap in conditions of high availability of food resources. In general, with the results was observed that species become less selective when the environment provided higher availability of food resources. Interspecific overlap did not show a pattern when evaluating availability of food resources in the lakes. However, intraspecific overlap tended to be more accentuated in conditions of high availability of resource food.

What is the destiny of a threatened fish, Ptychobarbus chungtienensis, now that non-native weatherfishes have been introduced into Bita Lake, Shangri-La?

Biological invasion is a pervasive negative force of global change, especially in its effects on sensitive freshwater ecosystems. Even protected areas are usually not immune. Ptychobarbus chungtienensis is a threatened freshwater fish now almost confined to Bita Lake, in the Shangri-La region of Yunnan province, China. Its existence is threatened by the introduction of non-native weatherfishes (Misgurnus anguillicaudatus and Paramisgurnus dabryanus) by an unusual method known as 'prayer animal release'. Periodic surveys revealed the ratio of invasive weatherfishes to P. chungtienensis has been increasing since the former species was first recorded from the lake in August, 2009. Ptychobarbus chungtienensis shows low genetic diversity in the relict Lake Bita population. Weatherfishes, however, have highly successful survival strategies. The degree of dietary overlap between the species is alarming and perhaps critical if food is found to be a limiting factor.

Differences in time and space use between two sympatric Acrocephalus warblers with similar diets

ABSTRACTCapsule: We found high diet overlap and different uses of space and time between Moustached Warblers Acrocephalus melanopogon and Reed Warblers Acrocephalus scirpaceus breeding in sympatry at a marshland in Spain.Aims: To study the degree of diet overlap between both species, their space use on a local scale and their breeding phenologies.Methods: We studied the breeding phenologies of the two species by standardized ringing activity. Spatial distribution was investigated by point counts. We determined diet composition from emetic samples and we collected invertebrates by standardized sweep-netting to estimate food availability.Results: Diet and prey selection were similar among species. Conversely, spatial overlap was relatively small (<50%) and breeding phenologies were not synchronized. Both food availability and the overall abundance of the two species increased throughout the breeding season.Conclusion: The two species are potential competitors for food and the observed differences in spatial and temporal niches may represent a way to lower competition for trophic resources: Moustached Warblers could reduce competition by breeding early, while Reed Warblers could avoid settling in areas occupied by the other species.

Feeding ecology of dominant fish species from beach seine discards (Praia de Mira, Central Portugal)

Event Abstract Back to Event Feeding ecology of dominant fish species from beach seine discards (Praia de Mira, Central Portugal) Pedro Seabra1*, Inês Louro1, Pedro Neves1, Rui P. Vieira2, 3 and Marina R. Cunha2* 1 Universidade de Aveiro, Departamento de Biologia, Portugal 2 Universidade de Aveiro, Departamento de Biologia & CESAM, Portugal 3 University of Southampton, Ocean and Earth Sciences, United Kingdom Beach seine fishery (Arte Xávega) has a great tradition in Portugal and it is an activity with high socio-economic implications for small fishing communities. However, this fishery is characterised by the significant bycatch and discards of numerous species. In this study, we investigated the feeding habits of two dominant fish species from beach seine discards of Praia de Mira. The stomach contents of Chelidonichthys lucernus (TL = 12.7 - 18.5cm) and Trisopterus luscus (TL = 9.7 - 13.1cm), collected in September 2015, were analysed. Decapod crustaceans (mainly Crangon crangon) constitute the main food items of C. lucernus, while T. luscus also includes a large number of amphipods in their diet. Secondary prey of both species includes other small crustaceans (e.g. Brachyura and Cumacea), teleost fish larvae and small mollusks. Niche breadth and overlap were estimated using indexes of Levins and Pianka, respectively, showing a high level of specialization but also some degree of diet overlap between these two species; the occurrence of items in a reduced state of digestion suggests that C. lucernus is an opportunistic feeder. All the analysed specimens are juveniles and no empty stomachs were found, revealing the importance off shallow waters off Praia de Mira as feeding areas. Acknowledgements Thanks are due, for the financial support to CESAM (UID/AMB/50017), to FCT/MEC through national funds, and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. R.P. Vieira is supported by a doctoral grant from the Portuguese Science Foundation (SFRH/BD/84030/2012). Keywords: Discards, Beach seine, trophic ecology, Fishes, feeding habits Conference: IMMR | International Meeting on Marine Research 2016, Peniche, Portugal, 14 Jul - 15 Jul, 2016. Presentation Type: Poster presentation Topic: Fisheries and Management Citation: Seabra P, Louro I, Neves P, Vieira RP and Cunha MR (2016). Feeding ecology of dominant fish species from beach seine discards (Praia de Mira, Central Portugal). Front. Mar. Sci. Conference Abstract: IMMR | International Meeting on Marine Research 2016. doi: 10.3389/conf.FMARS.2016.04.00021 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Jun 2016; Published Online: 13 Jul 2016. * Correspondence: Mr. Pedro Seabra, Universidade de Aveiro, Departamento de Biologia, Aveiro, 3810-193 Aveiro, Portugal, ppedro@ua.pt Dr. Marina R Cunha, Universidade de Aveiro, Departamento de Biologia & CESAM, Aveiro, 3810-193 Aveiro, Portugal, marina.cunha@ua.pt Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Pedro Seabra Inês Louro Pedro Neves Rui P Vieira Marina R Cunha Google Pedro Seabra Inês Louro Pedro Neves Rui P Vieira Marina R Cunha Google Scholar Pedro Seabra Inês Louro Pedro Neves Rui P Vieira Marina R Cunha PubMed Pedro Seabra Inês Louro Pedro Neves Rui P Vieira Marina R Cunha Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Feeding ecology of common demersal elasmobranch species in the Pacific coast of Costa Rica inferred from stable isotope and stomach content analyses

Knowledge of the feeding ecology and trophic interactions of marine species is essential to understanding food web dynamics and developing ecosystem-based management approaches. Given that many top predatory fishes have experienced large population declines from coastal ecosystems, it is critical to understand the role of smaller, mesopredators in coastal food webs. This study used stomach content (SCA) and stable isotope analyses (SIA) of muscle tissue (δ13C, δ15N) to examine the feeding ecology of four common demersal elasmobranchs (Mustelus henlei, Raja velezi, Zapteryx xyster and Torpedo peruana) from the Pacific coast of Costa Rica, Central America. Specifically, we investigated: (i) size- and sex-related changes in diet; (ii) dietary changes between seasons; (iii) dietary changes across depth and latitudinal gradients; and (iv) the degree of diet overlap among species. SCA showed that M. henlei, R. velezi and Z. xyster were feeding on a wide range of teleost and decapod species, whereas teleosts dominated the diet of T. peruana. Torpedo peruana had a lower prey diversity and dietary breath than the other species. Interestingly, SIA revealed a significantly larger isotopic niche breath in Z. xyster, indicating that SIA can provide a broader perspective of diet than SCA. Both SCA and SIA showed relatively low dietary overlap among species, except between R. velezi and Z. xyster which have a similar size, mouth morphology and potentially feeding behaviour. Latitude and size were identified as important drivers of the feeding ecology of elasmobranchs; however, their effect varied considerably among species and was often influenced by other factors such as sex and depth. Season had little influence on elasmobranch diet, but our data suggested that isotopic baseline values differ between geographic regions due to differences in local biogeochemical processes and/or prey availability, and possibly in response to seasonal nutrient fluctuations. This may also indicate that some of these elasmobranchs tend to use more localized habitats along the coast. The present study increased our understanding of the feeding ecology of common demersal elasmobranch species. Moreover, trophic information of elasmobranchs provided an important baseline record to understanding how trawling fisheries may impact demersal ecosystems in Costa Rica and the Central American region.

Diet composition of an invasive population of Lithobates catesbeianus (American Bullfrog) from Argentina

The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high and probably has an impact on their prey. Freshwater crabs are the main items in the diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region’s freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles.

English

Understanding of dietary requirements of different wildlife populations is critical in wildlife habitat conservation especially in Sub-Saharan Africa where wildlife contributes much to the National GDP of many countries. This study was conducted to determine the seasonal (wet/dry) diet profiles of Thomson&rsquo;s and Grant&rsquo;s gazelles (Gazella Thomson and Gazella granti) in the Athi-Kapiti savannah ecosystem of south-central Kenya. Diet composition was determined using the micro histological faecal analysis technique. Plant species in the diets were categorized into grasses, forbs and browse. Botanical compositions for diet selection by the two gazelles were generally influenced by season. Forage classes were significantly (P&lt;0.05) associated with the two gazelles. Grant&rsquo;s gazelle was a mixed feeder in the wet season and a browser in the dry season, whereas Thomson&rsquo;s gazelle was a grazer during wet season and a browser in the dry season. The two gazelles had diverse diets in the wet season with Thomson&rsquo;s gazelle having diverse diets in both seasons than Grant&rsquo;s gazelle. The degree of dietary overlap between the two gazelles was highest during the dry season with a significant (P&lt;0.05) Spearman&rsquo;s rank-order correlation coefficient; Rn&nbsp;= 0.92. The results indicate that the two species are competitors during the dry season and complimentary feeders during the wet season. This implies that Wildlife Managers manning the conservation areas in the region need to consider the optimal stocking rates of the two gazelles during the dry season. The shift in dietary diversifications between the two species should be investigated further. The degrees of dietary overlap within the forage and forbs classes were highest throughout the two seasons. Therefore, key browse plants such as the Acacia spp, Grewia spp. and&nbsp;Balanities glabra&nbsp;and forbs such as&nbsp;Hibiscus parvifolius&nbsp;should be spared during bush control activities. &nbsp; Key words:&nbsp;Grant&rsquo;s gazelle, Thomson&rsquo;s gazelle, herbivore diet, conservation management, Kenya.

The role of exotic ladybeetles in the decline of native ladybeetle populations: evidence from long-term monitoring

Ladybeetles (Coleoptera: Coccinellidae) are ubiquitous predators which play an important role in suppressing pest insects. In North America, the coccinellid community is increasingly dominated by exotic species, and the abundance of some native species has declined dramatically since the 1980s. Several hypotheses have been proposed to describe the mechanism of invasion coupled with native species declines, e.g. vacant niche exploitation, intraguild predation, competitive exploitation and habitat compression. We analyze a 24-year dataset of coccinellid community structure in southwestern Michigan to elucidate the most likely mechanism(s) of native coccinellid decline and implications for their conservation. Correlation analyses indicated that impact of exotic species on native coccinellids varies with their degree of interaction. Although several native species were observed to be in numerical decline, only Adalia bipunctata and Coleomegilla maculata had declines that were statistically significant. The magnitude of decline in these two species varied with the degree of dietary overlap with invaders, thus their decline is most likely driven by competitive exploitation. Habitat use patterns by some native species (A. bipunctata and Coccinella trifasciata) changed during years when the exotic Harmonia axyridis reached high numbers, lending support to the habitat compression hypothesis, where native species survive in ancestral (i.e. natural or semi-natural) habitats when invaders dominate cultivated habitats. Coccinellid communities occurring in semi-natural forested habitats were unique in both composition and variability from those occurring in cultivated habitats. Such semi-natural habitats can act as refuges for native coccinellids and may play a role in maintaining the functional resilience of coccinellid communities.

The feeding habits of the eyespot skate Atlantoraja cyclophora (Elasmobranchii: Rajiformes) in southeastern Brazil

The stomach contents of the eyespot skate, Atlantoraja cyclophora (Regan, 1903), were examined with the goal to provide information about the diet of the species. Samples were collected off the southern coast of Rio de Janeiro, Brazil, near Ilha Grande, between January 2006 and August 2007, at a depth of about 60 m. The diet was analyzed by sex, maturity stages and quarterly to verify differences in the importance of food items. The latter were analyzed by: frequency of occurrence, percentage of weight and in the Alimentary Index. The trophic niche width was determined to assess the degree of specialization in the diet. Additionally, the degree of dietary overlap between males and females; juveniles and adults and periods of the year were defined. A total of 59 individuals of A. cyclophora were captured. Females and adults were more abundant. The quarters with the highest concentrations of individuals were in the summer of the Southern Hemisphere: Jan-Feb-Mar 06 and Jan-Feb-Mar 07. Prey items were classed into five main groups: Crustacea, Teleosts, Elasmobranchs, Polychaeta, and Nematoda. The most important groups in the diet of the eyespot skate were Crustacea and Teleosts. The crab Achelous spinicarpus (Stimpson, 1871) was the most important item. The value of the niche width was small, indicating that a few food items are important. The comparison of the diet between males and females and juveniles and adults indicates a significant overlap between the sexes and stages of maturity; and according to quarters, the importance of prey groups differed (crustaceans were more important in the quarters of the summer and teleost in Jul-Aug-Sep and Oct-Nov-Dec 06), indicating seasonal differences in diet composition. Three groups with similar diets were formed in the cluster analysis: (Jan-Feb-Mar 06 and 07); (Apr-May-Jun 06 and Jul-Aug-Sep 07); (Jul-Aug-Sep 06 and Oct-Nov-Dec 06).

Ontogenetic dietary shifts and feeding ecology of the rasptail skate Raja velezi and the brown smoothhound shark Mustelus henlei along the Pacific coast of Costa Rica, Central America

Stomachs from 511 Raja velezi and 340 Mustelus henlei captured as by-catch in the commercial trawling fishery (2010-2012) were analysed to examine diet composition, ontogenetic shifts and degree of dietary overlap between species life stages in the Pacific Ocean of Costa Rica. Shrimps were the most important prey categories in the diet of R. velezi, while teleosts and cephalopods dominated the diet of M. henlei. Diet comparisons between different stages of R. velezi and M. henlei revealed clear ontogenetic dietary shifts: crustaceans (mainly shrimps, crabs and stomatopods) dominated the diet of immature individuals, and adults had a higher proportion of teleosts. The results suggest that R. velezi is an epibenthic predator that specializes in shrimps during early life stages, and to a lesser extent, teleosts as it matures, while M. henlei is an opportunistic predator with a highly diverse diet consisting of teleosts, cephalopods, shrimps and stomatopods. This study also found little evidence of dietary overlap between species or life stages and suggests that intra- and interspecific competition between R. velezi and M. henlei may be reduced by: (1) diet specialization in immature stages of R. velezi, (2) ontogenetic dietary shifts between immature and mature individuals, (3) prey-size selectivity in larger individuals of R. velezi and (4) differences in depth utilization in overlapping geographical regions.

Macrobenthic prey availability and the potential for food competition between 0 year group Pleuronectes platessa and Limanda limanda

This study describes the feeding habits of plaice Pleuronectes platessa and dab Limanda limanda during early juvenile development and relates differences between nursery grounds and sampling years to spatial and temporal variabilities in macrobenthic prey availability. The main prey taxa of both species were copepods, bivalves, amphipods, polychaetes and oligochaetes and size-related variation in diet was found. Despite considerable similarity in the prey items, differences in food composition between the two species were observed and spatial variability in diet confirmed their opportunistic feeding behaviour. A high degree of dietary overlap was found in June and decreased steadily throughout the season. The prey composition in the guts of both species largely reflected the composition of the main macrobenthic taxa in the sediment. The overall data suggest that resources were not limiting in the littoral sandy nursery areas in the west of Ireland and no indications were found that exploitative competitive forces upon the benthic prey assemblages occurred between P. platessa and L. limanda. Feeding success, Fulton's K condition and dietary overlap, however, showed spatial and temporal variations, and were probably affected by the availability and density of macrobenthic prey.

Adaptive Dynamics of Competition for Nutritionally Complementary Resources: Character Convergence, Displacement, and Parallelism

Consumers acquire essential nutrients by ingesting the tissues of resource species. When these tissues contain essential nutrients in a suboptimal ratio, consumers may benefit from ingesting a mixture of nutritionally complementary resource species. We investigate the joint ecological and evolutionary consequences of competition for complementary resources, using an adaptive dynamics model of two consumers and two resources that differ in their relative content of two essential nutrients. In the absence of competition, a nutritionally balanced diet rarely maximizes fitness because of the dynamic feedbacks between uptake rate and resource density, whereas in sympatry, nutritionally balanced diets maximize fitness because competing consumers with different nutritional requirements tend to equalize the relative abundances of the two resources. Adaptation from allopatric to sympatric fitness optima can generate character convergence, divergence, and parallel shifts, depending not on the degree of diet overlap but on the match between resource nutrient content and consumer nutrient requirements. Contrary to previous verbal arguments that suggest that character convergence leads to neutral stability, coadaptation of competing consumers always leads to stable coexistence. Furthermore, we show that incorporating costs of consuming or excreting excess nonlimiting nutrients selects for nutritionally balanced diets and so promotes character convergence. This article demonstrates that resource-use overlap has little bearing on coexistence when resources are nutritionally complementary, and it highlights the importance of using mathematical models to infer the stability of ecoevolutionary dynamics.

Dietary Overlap Among Two Introduced and One Native Sympatric Carnivore Species, the Raccoon, the Masked Palm Civet, and the Raccoon Dog, in Chiba Prefecture, Japan

To assess the degree of competition for food items between non-natives and natives, dietary overlap among three carnivore species living sympatrically in the area of Isumi City, southeastern Chiba Prefecture, central Japan, was analyzed by examining the gut contents of 221 animals collected from spring through summer 2006. The animals comprised two introduced species, the raccoon Procyon lotor and the masked palm civet Paguma larvata, and a native species, the raccoon dog Nyctereutes procyonoides. All three species were found to eat berries and seeds, amphibians and arthropods. The raccoons ate more crustaceans, the masked palm civets ate more mollusks, and the raccoon dogs ate more human meal scraps than the other two species. The food diversity of raccoons was lowest in both spring and summer. The dietary overlap was highest between raccoon dogs and masked palm civets. The degree of dietary overlap among the three species increased from spring to summer. These results suggest that overlap of food items is high and the degree of food resource segregation is low among the three species.

Seasonal Variation in Guild Structure of the Puget Sound Demersal Fish Community

Identification of food web linkages is a major aim in ecology because it provides basic information on trophic flows and the potential for interspecific interactions. In addition, policy and restoration measures mandated to conform to ecosystem-based management principals can benefit from information on temporal and spatial variability in community-level interactions. Here, we analyzed guild structure of the demersal fish assemblage in Puget Sound, WA, a temperate estuarine system on the US west coast. Using diet information from 2,401 stomachs collected across three seasons (fall, winter, and summer), we identified guild membership for 21 fish species, examined seasonal guild switching, and tested for seasonal shifts in predation and for differences in the degree of diet overlap at the assemblage level. We accounted for ontogenetic variation in diet by dividing species into large (L) and small (S) size classes when appropriate. Using cluster analysis and a permutation approach, we identified seven significant guilds that were typified by predation on benthic invertebrates, pelagic invertebrates, and piscivory. Of the 18 species with more than one season of diet information, six switched guilds (Pacific sanddab L, sturgeon poacher, Pacific tomcod S, speckled sanddab, rex sole, and rock sole S). At the assemblage level, we tested for seasonal differences in prey use between seasons by performing an analysis of similarities based on Bray–Curtis diet similarities and found no significant difference. However, diet overlap was significantly higher in the summer than the fall and winter (with summer > fall > winter) indicating that diets within the assemblage converged in the summer. These results indicate that analyses of guild structure and diet overlap can reveal seasonal variation in community trophic structure and highlight intra-annual food web variation in the Puget Sound demersal fish community.

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

ABSTRACTUnderstanding coexistence between sympatric felines with similar body sizes, such as jaguarsPanthera oncaand pumasPuma 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.