Trophic Niche Breadth Research Articles

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

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

Feeding strategy, dietary overlap and resource partitioning among four mesopredatory catfishes of a tropical estuary.

The feeding strategy, overlap and trophic interactions of four demersal catfishes inhabiting Cochin Estuary, Arius maculatus (n = 67), A. subrostratus (n = 63), A. arius (n = 21) and Mystus gulio (n = 69) were investigated through gut-content analyses. The indices of relative importance revealed that the prey items in their stomachs were dominated by crustaceans except in A. arius where molluscs constituted the major prey item. The highest diet and niche breadth values (3.93, 0.36 respectively) were recorded in A. subrostratus, while the lowest was recorded in A. arius (2.64, 0.23 respectively). Pianka's overlap, calculated through null models constructed by Ecosim 7.0, revealed significant niche overlap between A. maculatus and A. subrostratus (O-0.91, P < 0.001), between A. maculatus and M. gulio (O-0.72, P < 0.05) and between A. subrostratus and M.gulio (O-0.64 P < 0.05). However, no overlap was recorded between A. arius and other species. The trophic niche breadth along with prey specific abundance confirmed that these fishes are highly specific feeders. The present results on trophic level status indicate that these catfishes are mid-level carnivores that can be considered as moderate benthic mesopredators and are specialist feeders unlike most catfishes.

Mechanisms of trophic niche compression: Evidence from landscape disturbance.

Natural and anthropogenic disturbances commonly alter patterns of biodiversity and ecosystem functioning. However, how networks of interacting species respond to these changes remains poorly understood. We described aquatic food webs using invertebrate and fish community composition, functional traits and stable isotopes from twelve agricultural streams along a landscape disturbance gradient. We predicted that excessive deposition of fine inorganic sediment (sedimentation) associated with agricultural activities would negatively influence aquatic trophic diversity (e.g. reduced vertical and horizontal trophic niche breadths). We hypothesized that multiple mechanisms might cause trophic niche 'compression', as indicated by changes in realized trophic roles. Food-web properties based on consumer stable isotope data (δ13 C and δ15 N) showed that increasing sediment disturbance was associated with reduced trophic diversity. In particular, the aquatic invertebrate community occupied a smaller area in isotopic niche space along the sedimentation gradient that was best explained by a narrowing of the invertebrate community δ13 C range. Decreased niche partitioning, driven by increasing habitat homogeneity, environmental filtering and resource scarcity all seemingly lead to greater trophic equivalency caused by the collapse of the autochthonous food-web channel. Bayesian mixing-model analyses supported this contention with invertebrate consumers increasingly reliant on detritus along the sedimentation gradient, and predatory invertebrates relying more on the prey using these basal resources. The narrowing of the fish community δ13 C range along the sedimentation gradient contributed to an apparent 'trophic shift' towards terrestrial carbon, further indicating the loss of the autochthonous food-web channel. On the vertical trophic niche axis, fish became increasingly separated from aquatic invertebrates with an increase in their estimated trophic position. In combination, these responses were most likely mediated through reduced fish densities and a diminished reliance on aquatic prey. Although species losses remain a major threat to ecosystem integrity, the functional roles of biota that persist dictate how food webs and ecosystem functioning respond to environmental change. Sedimentation was associated with nonlinear reductions in trophic diversity which could affect the functioning and stability of aquatic ecosystems. Our study helps explain how multiple mechanisms may radically reshape food-web properties in response to this type of disturbance.

Network-Based Biomonitoring: Exploring Freshwater Food Webs With Stable Isotope Analysis and DNA Metabarcoding

Threatened freshwater ecosystems urgently require improved tools for effective management. Food web analysis is currently under-utilized, yet can be used to generate metrics to support biomonitoring assessments by measuring the stability and robustness of ecosystems. Using a previously developed analysis pipeline, we combined taxonomic outputs from DNA metabarcoding with a text-mining routine to extract trait information directly from the literature. This pipeline allowed us to generate heuristic food webs for sites within the lower Saint John/Wolastoq River and the Grand Lake Meadows (hereafter called the “GLM complex”), Atlantic Canada's largest freshwater wetland. While these food webs are derived from empirical traits and their structure has been shown to discriminate sites both spatially and temporally, the accuracy of their properties have not been assessed against other methods of trophic analysis. We explored two approaches to validate the utility of heuristic food webs. First, we qualitatively compared how well-trophic position derived from heuristic food webs recovered spatial and temporal differences across the GLM complex in comparison to traditional stable isotope approaches. Second, we explored how the trophic position of invertebrates, derived from heuristic food webs, predicted trophic position measured from δ 15N values. In general, both heuristic food webs and stable isotopes were able to detect seasonal changes in maximum trophic position in the GLM complex. Samples from the entire GLM complex demonstrated that prey-averaged trophic position measured from heuristic food webs strongly predicted trophic position inferred from stable isotopes (R 2 = 0.60), and even stronger relationships were observed for some individual models (R 2 = 0.78 for best model). Beyond their areas of congruence, heuristic food web and stable isotope analyses also appear to complement one another, suggesting a surprising degree of independence between community trophic niche width (assessed from stable isotopes) and food web size and complexity (assessed from heuristic food webs). Collectively, these analyses indicate that trait-based networks have properties that correspond to those of actual food webs, supporting the routine adoption of food web metrics for ecosystem biomonitoring.

Multifaceted implications of the competition between native and invasive crayfish: a glimmer of hope for the native’s long-term survival

Biological invasions represent a complex phenomenon driven by multiple factors. In this study, a real-time invasion process between a native (Pontastacus leptodactylus) and an invasive (Faxonius limosus) crayfish species was investigated in the Lower Danube (South-East Europe) through an interdisciplinary approach, by measuring various ecological, genetic, physiological and biometric endpoints. The results revealed that the prolonged competition in old invaded sites of the river (at least a decade) either drove the native species to extinction, or, unexpectedly, allowed its survival as highly fragmented populations. However, for the latter situation, several biological and ecological traits differed in the remnant populations: increased trophic position and elemental imbalance for two major macronutrients (C:N molar ratio), low growth, as strongly contracted trophic niche widths and low overlap degree with the invasive crayfish. The data suggest that the prolonged competition induced potential resource partitioning between species, potentially driving their coexistence, as the development of larger and heavier claws within the native males’ population. On the contrary, in more recently invaded sectors of the Lower Danube (3 years), the trophic niche of the native species was significantly larger compared to old invaded sites and characterised by high level of niche overlap, indicating almost identical diet with the invasive crayfish, but characterised by the lowest trophic position compared to other invasion sectors. The genetic diversity of the native crayfish populations was strongly reduced in the invaded sectors of the river, but without signs of genetic bottleneck, which may be explained by a drift-mutational equilibrium reached as a consequence of diminishing population size. Our findings suggest strong coexistence potential in the future for both species in the Lower Danube.

Preferential assimilation of seagrass detritus by two coexisting Mediterranean sea cucumbers: Holothuria polii and Holothuria tubulosa

Holothuria polii and Holothuria tubulosa are two of the most commercially exploited sea cucumbers of the Mediterranean Sea. As deposit-feeders, they represent an important component of the benthic community. Hence, knowledge of their feeding behaviour is crucial for understanding their function in terms of benthic ecology and sediment dynamics.Using information obtained from stable isotope analysis, the food selectivity/assimilation, temporal variations in diet and trophic niche of H. polii and H. tubulosa were investigated. Analysis of carbon and nitrogen isotopic ratios in body wall tissue showed a preferential assimilation of seagrass detritus among multiple food sources, with a total contribution to the diet ranging from 63% to 74%. The temporal changes in δ13C and δ1⁵N values followed the seagrass isotopic dynamics with depleted values in winter and enriched values in summer. Additionally, δ13C and δ1⁵N measurements were used to outline the species' trophic niche width. The two species coexist, showing an overlap on the δ13C axis and a partial degree of niche segregation on the δ1⁵N axis. Our results provide an overview on the feeding activity of H. polii and H. tubulosa, providing evidence of their crucial role on the seagrass detrital pathways for Mediterranean coastal ecosystems.

Ontogenetic variation in the diet of the anuran community from a semi-arid environment in the southeastern Chihuahuan Desert.

Although ontogeny influences dietary composition and trophic niche breadth in many anurans, its effects on diet have been little analyzed in sympatric species. In this study, we analyzed interspecific and ontogenetic variation in dietary composition and trophic niche width in an anuran community from a semi-arid environment. We found a more profound effect of species identity than body size on dietary composition, with the diet of four species dominated by formicids, that of two others by coleopterans and formicids, and that of the remaining species not dominated by specific prey types. We found ontogenetic changes in dietary composition in three of four species analyzed, in which consumption of some small insects decreased as predator size increased, regardless of species. Additionally, we did not find ontogenetic change in prey number consumed in any of the four species, but prey size increased with increasing predator size in all of them. Most species exhibited a narrow trophic niche, which was even narrower in adults in three of the four species analyzed. Costello’s modified plots revealed a high variation among individuals in termite consumption in Anaxyrus punctatus, and in more prey types in Spea multiplicata. Our results suggest that this community is not size-structured, and that ontogenetic diet shifts are mainly caused by passive sampling toward prey of different sizes. Finally, comparisons with previous data revealed an interpopulation pattern, in which trophic niche width contracts as aridity increases, possibly because of an increase in interspecific competition for trophic resources.

An invasive and a native macrophyte species provide similar feeding habitat for fish

AbstractInvasive macrophytes usually increase the homogenisation of habitats and can affect local communities with negative effects on the food chain. We evaluated experimentally the composition, density, richness and diversity of the invertebrates in the invasive macrophyte Hydrilla verticillata and assessed the potential effects of this macrophyte on the diet and foraging efficiency of small native fishes. The native macrophyte Egeria najas was used as control, since it has very similar physical structure and physical complexity to H. verticillata. Macrophytes of both species were maintained separately in aquaria with the fishes, and the invertebrates richness and abundance associated with plants and within fish stomach were evaluated. No significant difference was found in the richness and diversity of invertebrates attached to macrophytes; however, the two macrophytes differed in regard to invertebrate composition, and the density was significantly higher in H. verticillata. The fish foraging efficiency was high in both macrophytes, and the difference between them was not significant. The fish diet did not differ significantly between the native and the invasive macrophyte in respect to invertebrate composition, abundance and richness, and trophic niche breadth. We found no evidence that H. verticillata negatively affects the density of associated invertebrates, and as a consequence, fish diet and foraging efficiency. Our results indicate that the replacement of E. najas by a similar biomass of H. verticillata does not affect the feeding behaviour of associated fish species.

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

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

Sargassumblooms in the Caribbean alter the trophic structure of the sea urchinDiadema antillarum

The arrival of large masses of drifting Sargassum since 2011 has caused changes in the natural dynamics of Caribbean coastal ecosystems. In the summer of 2015, unprecedented and massive mats of S. fluitans and S. natans have been observed throughout the Mexican Caribbean including exceptional accumulations ashore. This study uses stable isotopes to assess the impact of Sargassum blooms on the trophic dynamics of the Diadema antillarum sea urchin, a keystone herbivore on many Caribbean reefs. Bayesian models were used to estimate the variations in the relative proportions of carbon and nitrogen of assimilated algal resources. At three lagoon reef sites, the niche breadth of D. antillarum was analysed and compared under massive influx of drifting Sargassum spp. vs. no influx of Sargassum blooms. The effects of the leachates generated by the decomposition of Sargassum led to hypoxic conditions on these reefs and reduced the taxonomic diversity of macroalgal food sources available to D. antillarum. Our trophic data support the hypothesis that processes of assimilation of carbon and nitrogen were modified under Sargassum effect. Isotopic signatures of macroalgae associated with the reef sites exhibited significantly lower values of δ15N altering the natural herbivory of D. antillarum. The Stable Isotopes Analysis in R (SIAR) indicated that, under the influence of Sargassum blooms, certain algal resources (Dictyota, Halimeda and Udotea) were more assimilated due to a reduction in available algal resources. Despite being an abundant available resource, pelagic Sargassum was a negligible contributor to sea urchin diet. The Stable Isotope Bayesian Ellipses in R (SIBER) analysis displayed differences between sites, and suggests a reduction in trophic niche breadth, particularly in a protected reef lagoon. Our findings reveal that Sargassum blooms caused changes in trophic characteristics of D. antillarum with a negative impact by hypoxic conditions. These dynamics, coupled with the increase in organic matter in an oligotrophic system could lead to reduce coral reef ecosystem function.

Ecological specialization is associated with high conservation concern in skates (Chondrichthyes, Rajiformes)

AbstractIdentifying the ecological traits of threatened species may help to identify species vulnerable to exploitation and habitat loss, predict future declines in abundance and provide the basis for their conservation. We assessed the relationship of dietary and habitat niche breadth on conservation status of skate species (Chondrichthyes, Rajiformes). We hypothesized that skate species with a narrow niche breadth have a higher conservation concern than skate species with wide niche breadth. Conservation status (IUCN), dietary and depth range data on 57 skate species were collected. Generalized linear mixed effect models were fitted with taxonomic level (genera nested within family) included as a random effect term in each model. In each model, body size of skate species was included as a variable because this life history trait is a known predictor of vulnerability. A model selection approach to test the level of support for alternative models was applied. Our results support the hypothesis that a narrow niche breadth is related to high vulnerability. Skate species with high probability of being of conservation concern have a narrow trophic niche breadth and a large body size. We conclude that dietary niche breadth together with body size may be an important trait to identify potentially vulnerable skate species. Conservation biology faces the challenge of identifying what species are vulnerable to anthropogenic stressors and to determine why this is so. The predictive value of our results may allow to know a priori which species should receive prioritary attention.

Trophic niche of medium-form and dwarf-form of purple flying squid Sthenoeuthis oualaniensis in the central and western South China Sea

To explore the characteristics of carbon and nitrogen stable isotope and trophic niche between two forms (medium-form and dwarf-form) of the purple flying squid Sthenoteuthis ouala-niensis, we collected samples from the central and western South China Sea in August 2017 to analyze the values of carbon and nitrogen stable isotope and the changes of trophic level for different mantle lengths. We further compared the trophic niche differences of the two forms populations. The results showed that for the medium-form, the δ13C value ranged from -19.54‰ to -18.10‰ and the δ15N value ranged from 7.79‰ to 9.45‰. The average trophic level of medium-form was 2.90 and ranged from 2.72 to 3.21. For the dwarf-form, the δ13C value ranged from -19.69‰ to -18.43‰, and the δ15N value ranged from 8.02‰ to 8.99‰. The average trophic level of the dwarf-form was 2.91 and ranged from 2.79 to 3.08. There were significant differences of δ15N but no differences of δ13C values between the medium-form and dwarf-form of purple flying squid. The mantle length had a significant impact on δ13C and δ15N, with the value of δ15N increasing with the mantle length. The trophic niche breadth and the trophic level of the medium-form purple flying squid were more diverse than those of dwarf-form.

Convictfish on the move: variation in growth and trophic niche space along a latitudinal gradient

Abstract The range expansion of tropical fish into temperate waters is increasing markedly in response to climate change. Range-expanding fish encounter novel diets and environments, but we know little about how these conditions facilitate or hinder distribution shifts. Here, we quantified relative growth rate, morphometric condition and trophic niche of juvenile Acanthurus triostegus, a dominant range-expanding tropical surgeonfish, at four locations across 10° of latitude off eastern Australia. We related these metrics to differences in temperature and nutritional quality of dominant seaweeds and the epilithic algal matrix. Temperate food sources were richer in nitrogen than tropical diets. Stable isotope analysis (δ13 carbon and δ15 nitrogen) of fish muscle revealed a large trophic niche breadth at the highest latitude indicating a generalist foraging strategy, and more nitrogen-enriched isotopic signatures compared to tropical regions. Fish length was strongly correlated to δ13C in all regions, suggesting an ontogenetic shift in diet independent of latitude. Despite temperature differences of 4°C, fish growth and body condition were similar across tropical and temperate regions. These results suggest that more nutritious temperate diets may compensate for the effects of cooler water temperatures. Neither summer water temperatures nor dietary factors appear to limit the success of juvenile tropical vagrants as they continue to expand their range along eastern Australia.

Non-linear relationship between body size of terrestrial carnivores and their trophic niche breadth and overlap

Studying food partitioning of mammalian predators is important for understanding trophic structures and interactions between coexisting carnivore species. This is particularly pertinent in the light of expanding ranges of populations of generalist species whose habitat and diet overlap with more specialized species. Here, we tested the resource partitioning hypothesis in terrestrial carnivores, predicting that trophic niche breadth and overlap relate positively to body mass. We used dietary data from 18 terrestrial carnivore taxa in four families (Canidae, Mustelidae, Felidae and Ursidae; body mass 0.1–173.6kg) in three regions in Central and Eastern Europe, i.e. deciduous forest and forest-steppe region (DFR), temperate deciduous and mixed forest region (MFR) and transitory mixed forest regions (TFR). We ranked carnivores along an axis of trophic niche (breadth and overlap), and analysed the relationship between trophic niche and body mass (or pair-wise difference in body mass). A hierarchical cluster analysis of diet composition divided carnivores into four ecological groups: wild ungulate predators; small-mammal predators; amphibians and small mammal predators and omnivores. The relationship between body mass of predators and both trophic niche breadth and trophic niche overlap were hump-shaped. The trophic niche breadth to body mass ratio was significantly lower in DFR than in TFR and trophic niche overlap was significantly higher in DFR than in MFR and TFR. The predominant food resource is small mammals whose abundance is related to local agricultural and forestry management practices. Modifications of management techniques can affect population dynamics and community composition of carnivore species, especially in the case of small-mammal predators.

Food habits of Rhinella proboscidea (Anura: Bufonidae) in terra firme forests of central Amazonia

Food habits of Rhinella proboscidea (Anura: Bufonidae) in terra frme forests of central Amazonia. Anuran species are considered generalist and opportunist feeders. However, some species have dietary specializations. Here we describe the diet composition of Rhinella proboscidea based on the stomach content of 29 individuals captured in terra frme forests in Manaus and São Sebastião do Uatumã, state of Amazonas, Brazil. Each prey item was measured and identifed to Order, Suborder or Family; ants were identifed to Genus. We determined and tested for differences in the trophic niche breadth and the relationships between the frog size and the volume of the largest prey item. We recorded 1614 prey items of 44 taxa. Hymenoptera was the most abundant Order followed by Isoptera, Acari, Coleoptera, Orthoptera, Araneae, Hemiptera, Dermaptera, Diptera, and Collembola. Formicidae comprised 46.56% of the all stomach items and was represented by six subfamilies and 22 genera. Additionally, we found 80 nematodes in a total of 18 frogs. There was a signifcant difference in the trophic niche breadths of the study areas, and a positive relationship between the toad size and volume of the largest prey item consumed. Rhinella proboscidea feeds on a variety of invertebrates, with ants, termites, and mites being the most abundant; this suggests that the toad is an active forager. The most common subfamily was Myrmicinae primarily represented by Crematogaster and Atta. Differences in trophic niche breadths of the study areas may be related to seasonal differences in the diet composition or local factors.

The role of detritivory as a feeding tactic in a harsh environment \u2013 a case study of weatherfish (Misgurnus fossilis)

The weatherfish (Misgurnus fossilis) is a species that is tolerant of unfavourable environmental conditions and can survive low dissolved oxygen concentrations and high water temperatures. Although this species occurs across almost the whole of Europe, and is protected in many countries, relatively little is known regarding its ecology. To determine the diet of weatherfish, 120 individuals from an artificial drainage canal in central Poland were collected in two seasons (spring and late summer) with contrasting abiotic condition (oxygen concentration, water temperature and transparency). Analysis of gut fullness showed that weatherfish consumed a greater quantity of food in spring (0.92 ± 0.90) compared with summer (0.20 ± 0.26). Contrary to other cobitid taxa, weatherfish fed actively during daytime in both seasons. An estimate of the importance of each dietary component indicated that the most important food categories were chironomids, copepods, Asellus aquaticus and detritus. SIMPER analysis indicated that these four categories together constituted over 65.8% of cumulative dissimilarity in the diet between seasons. Additionally, trophic niche breadth differed significantly between seasons. The study demonstrated that the weatherfish is an opportunistic feeder, consuming large quantities of detritus despite possessing a gut morphology that is atypical of a detritivore. The quantity of detritus in the gut of weatherfish was positively associated with fish total length and varied seasonally, with a greater quantity of detritus in the diet in late summer. These results demonstrate the importance of detritus as a source of energy, particularly during periods of scarcity of alternative prey categories.

Two is better than one: combining gut content and stable isotope analyses to infer trophic interactions between native and invasive species

Two complementary approaches are commonly used for analysing trophic interactions that allow inferences about consumed and assimilated resources: gut content (GCA) and stable isotope (SIA) analyses. We used these methods to assess the trophic ecology of a native (Pontastacus leptodactylus) and an invasive species (Faxonius limosus) of crayfish in the Lower Danube (Romania) by calculating five frequently used metrics (i.e. trophic position, omnivory index, elemental imbalance for C:N ratio, trophic niche width and overlap). The SIA approach indicated significantly different trophic niche widths between the crayfish species and potential resource partitioning that triggered lower niche overlap, aspects not depicted by GCA. The latter approach suggested higher omnivory indices and elemental imbalance for macronutrients, potentially because of high incidences of basal resources with low nitrogen content in the foreguts of both species. Although, as indicated by GCA, the two species seem to feed largely on the same resources, SIA suggested that the ingested food items were assimilated with differing efficiencies. These findings are of importance for studies of invasion biology, where the replacement of native species by invasive taxa is underpinned by mechanisms that should be explored by using the most appropriate approach.

Beta diversity and specialization in plant–pollinator networks along an elevational gradient

AbstractAimTo assess whether the reduced nutritional resources available for pollinators due to plant community simplification along an elevational plant‐diversity gradient changes pollinator niche breadth and richness. Additionally, we evaluated how body size and proboscis length of pollinators shifted along the gradient, and whether these changes were related to pollinator niche breadth.LocationAn elevational gradient (2,350–3,520 m a.s.l.) on the oceanic high‐mountain strato‐volcano of El Teide (Tenerife, Canary Islands).TaxonFlowering plant and pollinator species.MethodsWe compared quantitative plant–pollinator networks along the plant‐diversity gradient. We calculated a set of niche‐based topological metrics that capture the degree of specialization, niche breadth and niche overlap. Furthermore, we obtained β‐diversity measures and the proportion of replacement and richness components.ResultsThere was an overall decline in species richness of pollinators with increasing elevation. This decline was mainly driven by the loss of species along the elevational gradient, which conformed a nested subset pattern. The whole network showed less specialization, greater connectance and lower modularity towards the summit. At high elevations, pollinators were more generalized and less selective in their flower choice, showing a greater trophic niche breadth compared to pollinators at lower elevations. Mean body size of pollinators increased with elevation, and species body size and proboscis length were positively associated with the number of plant species visited.Main conclusionsOverall, results indicated that the elevational gradient filters pollinator species, probably according to their thermal tolerance and ability to exploit a wide range of trophic resources. The finding that pollinators become more generalized and opportunistic at higher elevations is a novel result, which may have implications for new research into how ecological networks vary over environmental gradients. From an applied perspective, our results highlight the importance of considering the spatial variation of species assemblages when aiming to construct functionally reliable interaction networks along environmental gradients.

Seasonal, geographical, and habitat effects on the diet of a recovering predator population: the European pine marten (Martes martes) in Ireland

Human activity is increasingly altering the natural world. Yet the natural adaptability of most mammal species remains unknown. Seasonal and spatial influences on the diet of temperate carnivores tending towards omnivory are, particularly, poorly understood. The pine marten is one such species which in Ireland and Britain is of additional interest due to the recent recovery in its range and abundance from near collapse. We investigated diet of the pine marten on regional, national, and continental scales and with regard to seasonal and habitat variation. Habitat effects on diet were examined with regard to samples from deciduous woodland, coniferous forestry plantations, heath-coniferous matrices, and mixed habitats. Finally, we discuss the implications of dietary variation in the ecological role of the European pine marten in Ireland and elsewhere and consider how these may be affected by further environmental change. The diet of the pine marten differed significantly amongst all studies across its range, although it maintains the same approximate trophic niche breadth throughout. This plasticity may explain its recovery in an environment where resources are scarce, and underscores its status as an opportunistic species which is likely to be robust to environmental and habitat changes in the future.

Biological traits, phylogeny and human footprint signatures on the geographical range size of passerines (OrderPasseriformes) worldwide

AbstractAimMany hypotheses exist to explain the astonishing variation in geographical range size across species, but these have rarely been tested under a unifying framework that simultaneously considers direct and indirect effects of ecological niche processes and evolutionary dynamics. Here, we jointly evaluate ecological and evolutionary hypotheses that might account for global interspecific patterns of range size in the most species‐rich avian order: Passeriformes (perching birds).LocationGlobal.Time periodCurrent.Major taxa studiedOrder Passeriformes.MethodsWe used phylogenetic path analysis to test for the relationship between eight variables and range size. Our list of predictors included a set of niche‐related variables (both Grinellian and Eltonian), species‐specific morphological and life‐history traits (body size, dispersal ability and fertility), extrinsic (human footprint) and evolutionary factors (time since divergence from the closest extant relative).ResultsWe found that Grinellian (climatic) and Eltonian (trophic) niche breadth are crucial to account for the observed patterns, followed by reproductive effort (as measured by clutch size). We also found a negative relationship between native range size and human footprint. The significant and positive relationship between niche breadth, either Grinnellian or Eltonian, and range size was consistent across all species, irrespective of their migratory/resident status or taxonomic grouping (Passeri versus Tyranni).Main conclusionsGlobally, the range sizes of passerine species are associated with the Grinellian niche, meaning that species with broader environmental tolerances exhibit larger geographical ranges. These findings give further empirical support to the positive niche breadth–range size relationship as a general pattern in ecology.