Trophic Traits Research Articles

Structure and function of nematode assemblages in contaminated sediments: what can we learn from the Mar Piccolo of Taranto (Ionian Sea)?

Free-living nematodes were investigated in the Mar Piccolo of Taranto (Ionian Sea), a semi-enclosed basin of strategic importance for its complex productive infrastructure but in need of remediation due to the alarming amounts of heavy metals and synthetic organic contaminants in the sediments. Abundance, genera composition, biodiversity and trophic traits of nematodes were related to the gradual transition from marine to more brackish conditions and to the varying levels of contaminants in different sub-areas of the basin. Nematodes were more abundant and diverse at the most marine site while low numbers and diversity characterized the most contaminated station. Going towards the innermost part of the basin, gradually increasing values of abundance and biodiversity were observed although the assemblage was susceptible to the organic enrichment caused by mussel farms. The use of nematodes as ecological indicators mirrored the response of the assemblage to the main patterns acting in the basin (High/Good scores at the most marine site and Poor/Bad scores at the most contaminated station), giving a clear indication of environmental quality to stakeholders/authority that can contribute to address remediation actions in contaminated sediments.

Do long‐distance migratory birds track their niche through seasons?

AbstractAimSeasonal migration by animals is an extensively studied, global phenomenon. Yet, we still lack a general understanding whether migrants track their niche between summer and winter ranges (following fixed environmental conditions throughout the year) and which mechanisms influence this behaviour. Here, we assessed the degree of seasonal niche tracking in Holarctic long‐distance migratory birds (n = 717; excluding very rare species) and evaluate the influence of biogeographic (regional and range characteristics) and ecological (trophic) factors on tracking.LocationGlobal.TaxonBirds.MethodsWe calculated seasonal niche overlap by means of ordination, and estimated the degree of niche tracking using similarity tests. Niche tracking was evaluated for two different environmental predictor sets: climate and vegetation productivity (reflecting resource selection) versus climate and land cover (reflecting habitat choice). Multivariate phylogenetic regression was used to evaluate effects of biogeographic and ecological traits on niche tracking.ResultsWe found significant niche tracking in 65–95% of species with a higher proportion of species significantly tracking climate and land cover compared to climate and vegetation productivity. Traits explained 12–18% of the variance in niche tracking with strong regional differences, a negative effect of migration distance and positive effects of range size on niche tracking. The effects of niche breadth and trophic traits were less pronounced and varied between environmental predictor sets.Main conclusionsOur results indicate that at coarse spatial resolution, long‐distance migratory species tend to track their niche and select largely similar environments through seasons. Stronger niche tracking of land cover could reflect conservatism in habitat selection across seasons, for example for foraging and roosting. This conservatism towards land cover should be considered when making predictions to future environments. A better understanding of the factors that constrain seasonal range limits will be critical for predicting how migration patterns could respond to future environmental changes.

Similar levels of trophic and functional diversity within damselfish assemblages across Indo‐Pacific coral reefs

Abstract Understanding the forces that influence the dynamics of communities is a key challenge to undertake in changing environments. Despite recent advances in coral reef community ecology, a more comprehensive knowledge about processes (niche‐related traits and phylogenies) driving the composition of reef fish community is needed. Here, we conducted a quantitative comparison of these processes in damselfish assemblages that belong to three distinct Indo‐Pacific coral reefs differing in taxonomic composition, morphology and degree of human disturbance. We compiled a dataset of eight categorical variables to estimate functional diversity of damselfish assemblages and a second one of stable isotope ratios to evaluate isotopic diversity, a proxy of trophic diversity. Both datasets represent the eco‐functional diversity and provide insights into niche‐related traits. Indices were then computed to grasp complementary facets of this diversity: the size of multidimensional space (richness), the partitioning of niches (divergence) and the regularity in the distribution of niches (evenness) within each space. We also tested whether functional and trophic traits displayed some evolutionary niche conservatism. We found that functional richness was influenced by the number of species and functional entities (unique combination of trait values), and that the portions of the functional spaces filled by assemblages mainly overlapped. Functional divergence and evenness indices were similarly high. For trophic diversity, the isotopic richness remained equivalent, while the two other indices were of high values and did not significantly differ. Both functional and trophic traits did not display any phylogenetic conservatism. We demonstrated consistent levels of eco‐functional diversity in Indo‐Pacific coral reef damselfishes. Each assemblage hosted species whose niches were highly differentiated and evenly distributed in eco‐functional spaces of similar sizes, albeit the extent of functional space varied with the species richness. Assemblages also tended to share similar functional attributes. The inconsistent phylogenetic structures of eco‐functional traits and the similarity in diversity indices suggest that the assemblage composition of damselfishes is mainly driven by niche‐related processes rather than by phylogenetic relatedness. Our work helps to determine which mechanisms shape coral reef fish biodiversity and more particularly assemblages issued from replicated events of ecological radiation. A plain language summary is available for this article.

Trophic traits of Grammostola vachoni, a tarantula (Araneae : Theraphosidae) from Argentina

This is the first study about trophic traits of Grammostola vachoni, a threatened theraphosid spider endemic to the mountain systems of central Argentina. Four prey types were used in experiments: crickets, cockroaches, beetle larvae and adult beetles. Grammostola vachoni was observed to eat at a rate of about once every 11 days, with the mean total number of prey consumed per spider during the experimental period being 2.7. Latency to the first attack was similar for crickets, cockroaches and beetle larvae, but was shorter for adult beetles. Feeding time was significantly longer for crickets and beetle larvae. Mass gain was significantly different among prey types. Feeding effectiveness and ingestion rate were significantly higher for crickets. A significant positive correlation for feeding effectiveness and ingestion rate with prey mass and the initial spider mass was also found.

How Fishes Can Help Us Answer Important Questions about the Ecological Consequences of Evolution

Much of the recent progress in the study of eco-evolutionary dynamics has occurred in fish models. In this review, I focus specifically on the mechanisms by which fish evolution affects ecological processes, highlighting outstanding questions and new frontiers. Fish evolution can alter the ecology of individuals by changing traits that underlie resource use or interactions with other species. Fish eco-evolutionary studies have focused on the ecological consequences of two kinds of effect traits (trophic traits and nutrient recycling traits), but questions remain about the relative influences of genetic and environmental factors. Other fish traits might also have large ecological effects, but we lack frameworks for identifying them, and it remains difficult to link the traits to their ecological consequences. The effect of fish evolution also depends on changes in fish populations, which might vary because of genetic or by environmental factors. Such changes can have dramatic impacts on the expression of e...

A trophic interaction framework for identifying the invasive capacity of novel organisms

Abstract The likelihood and impacts of invasions by novel organisms (e.g. non‐native species, genetically modified organisms) on the composition and functioning of receiving biological communities hinges on their capacity to exploit resources and/or avoid predation relative to resident counterparts. While assessment of invasion risk based on the comparison of functional responses (per‐capita consumption rate as a function of resource density) of novel species with native analogues has been gaining popularity, it may be undermined if alternative prey and potential predators are not represented realistically. Here, we propose a conceptual framework that enables rigorous identification of trophic traits conducive to invasion success by novel organisms—irrespective of their trophic position—and their likely ecological impacts, given their arrival and establishment. We focus on consumption here, but our framework can also be used for autotrophic energy acquisition, and extended to non‐trophic and indirect interactions. The framework enables a structured and prioritized selection of subsets of trophic links for invasion risk assessment. It is based on foraging theory and advances in comparative functional responses in invasion ecology. It can even be used in the absence of a resident comparator organism and when resources or predators are only partly known. Our approach enhances the predictive power of species screening, and thus advances prevention and management of invasions under a common framework for all types of novel organisms.

Nuevas perspectivas en la diversidad funcional de ambientes marinos

Marine ecosystems are under anthropogenic pressures degrading both biodiversity and functional diversity. Functional diversity studies identify species functions through trait analysis, and are a robust alternative to the classical taxonomic approach. Although trophic traits are considered predominantly when analyzing functional diversity on marine ecosystem studies, there are other functional traits related to the species functions in the ecosystem. To critically understand the use of existing functional diversity indexes, we analyze them and their trait selection processes. The functional diversity approach improves our understanding of ecosystems and can help us slow and reduce the global-scale biodiversity loss by developing effective frameworks for monitoring and protection. We present some study questions and suggestions about how research should be oriented through functional analysis.

Seasonal succession in zooplankton feeding traits reveals trophic trait coupling

AbstractThe seasonal forcing of pelagic communities invokes a succession of the dominant phytoplankton and zooplankton species. Here, we characterize the seasonal succession of the plankton traits and their interactions using observations and model simulations of the plankton community in the western English Channel. We focus on activity traits that characterize the defensive and feeding abilities of zooplankton and distinguish between low risk, low return ambush feeders and high risk, high return feeding‐current feeders. While the phytoplankton succession depends on traits related to nutrient acquisition and photosynthesis, it also depends on grazing which couples feeding and motility traits across trophic guilds. Despite interannual variations in the species dominating the protist plankton community, the seasonal trait distribution reveals robust and repeatable seasonal patterns, changing between non‐motile cells flourishing in spring and motile community dominating during summer. The zooplankton community is dominated by active feeding‐current feeders with peak biomass in the late spring declining during summer. The model reveals how zooplankton grazing reinforces protist plankton seasonal succession and shows how the physical environment controls the vertical structure of plankton communities, where ambush feeders exhibit a preference for greater depths during summer. We characterize the seasonal succession as trophic trait coupling and conjecture that this coupling leads to a trophic trait cascade where successive trophic levels alternate in their expression of activity traits further up in the food chain.

The genetic architecture of novel trophic specialists: larger effect sizes are associated with exceptional oral jaw diversification in a pupfish adaptive radiation.

The genetic architecture of adaptation is fundamental to understanding the mechanisms and constraints governing diversification. However, most case studies focus on loss of complex traits or parallel speciation in similar environments. It is still unclear how the genetic architecture of these local adaptive processes compares to the architecture of evolutionary transitions contributing to morphological and ecological novelty. Here, we identify quantitative trait loci (QTL) between two trophic specialists in an excellent case study for examining the origins of ecological novelty: a sympatric radiation of pupfishes endemic to San Salvador Island, Bahamas, containing a large-jawed scale-eater and a short-jawed molluscivore with a skeletal nasal protrusion. These specialized niches and trophic traits are unique among over 2000 related species. Measurements of the fitness landscape on San Salvador demonstrate multiple fitness peaks and a larger fitness valley isolating the scale-eater from the putative ancestral intermediate phenotype of the generalist, suggesting that more large-effect QTL should contribute to its unique phenotype. We evaluated this prediction using an F2 intercross between these specialists. We present the first linkage map for pupfishes and detect significant QTL for sex and eight skeletal traits. Large-effect QTL contributed more to enlarged scale-eater jaws than the molluscivore nasal protrusion, consistent with predictions from the adaptive landscape. The microevolutionary genetic architecture of large-effect QTL for oral jaws parallels the exceptional diversification rates of oral jaws within the San Salvador radiation observed over macroevolutionary timescales and may have facilitated exceptional trophic novelty in this system.

Global meta-analysis of native and nonindigenous trophic traits in aquatic ecosystems.

Ecologists have recently devoted their attention to the study of species traits and their role in the establishment and spread of nonindigenous species (NIS). However, research efforts have mostly focused on studies of terrestrial taxa, with lesser attention being dedicated to aquatic species. Aquatic habitats comprise of interconnected waterways, as well as exclusive introduction vectors that allow unparalleled artificial transport of species and their propagules. Consequently, species traits that commonly facilitate biological invasions in terrestrial systems may not be as represented in aquatic environments. We provide a global meta-analysis of studies conducted in both marine and freshwater habitats. We selected studies that conducted experiments with native and NIS under common environmental conditions to allow detailed comparisons among species traits. In addition, we explored whether different factors such as species relatedness, functional feeding groups, latitude, climate, and experimental conditions could be linked to predictive traits. Our results show that species with traits that enhance consumption and growth have a substantially increased probability of establishing and spreading when entering novel ecosystems. Moreover, traits associated with predatory avoidance were more prevalent in NIS and therefore favour invasive species in aquatic habitats. When we analysed NIS interacting with taxonomically distinctive native taxa, we found that consumption and growth were particularly important traits. This suggests that particular attention should be paid to newly introduced species for which there are no close relatives in the local biota. Finally, we found a bias towards studies conducted in temperate regions, and thus, more studies in other climatic regions are needed. We conclude that studies aiming at predicting future range shifts should consider trophic traits of aquatic NIS as these traits are indicative of multiple interacting mechanisms involved in promoting species invasions.

Seasonality and trophic diversity in molluscan assemblages from the Bay of Tunis (southern Mediterranean Sea)

Soft bottom molluscan assemblages from the Bay of Tunis have been studied in order to analyse their seasonality and trophic diversity in relation to environmental variables. A total of 147 species of molluscs was identified, with gastropods displaying the highest species richness and bivalves the highest abundances, and including five non-indigenous species such as the dominant ectoparasite Polycerella emertoni. Carnivorous and scavenger gastropods were among the most frequent species, reflecting a diverse benthic community. Seasonal changes were significant, being more acute at 3-4 m than at 10-15 m depth, and were driven mainly by seawater temperature and percentage of organic matter in the sediment. The high affluence of tourists in summer was coincident with high decreases in species richness and abundance of molluscs, together with a strong siltation of the sediment. Nevertheless, most trophic groups remained and the trophic diversity was relatively high. Significant relationships were found between the index of trophic diversity and Shannon-Wiener diversity and evenness indices, suggesting that the identity of the species with its particular trophic trait, together with the good distribution of the individuals among the species (density) would be the drivers for the maintenance of the molluscan food web under environmental stress. The abundance of P. emertoni altered the trophic structure of the molluscan assemblage, with the ectoparasite trophic group reaching an unusual punctual higher dominance. Soft bottom molluscan assemblages of the Bay of Tunis should be taken into account in monitoring programs for anthropogenic impacts and non-indigenous species trends throughout the Mediterranean basin.

Population divergence in fish elemental phenotypes associated with trophic phenotypes and lake trophic state.

Studies of ecological stoichiometry typically emphasize the role of interspecific variation in body elemental content and the effects of species or family identity. Recent work suggests substantial variation in body stoichiometry can also exist within species. The importance of this variation will depend on insights into its origins and consequences at various ecological scales, including the distribution of elemental phenotypes across landscapes and their role in nutrient recycling. We investigated whether trophic divergence can produce predictable patterns of elemental phenotypes among populations of an invasive fish, the white perch (Morone americana), and whether elemental phenotypes predict nutrient excretion. White perch populations exhibited a gradient of trophic phenotypes associated with landscape-scale variation in lake trophic state. Perch body chemistry varied considerably among lakes (from 0.09 for % C to 0.31-fold for % P) casting doubt on theassumption of homogenous elemental phenotypes. This variation was correlated with divergence in fish body shape and other trophic traits. Elemental phenotypes covaried (r (2) up to 0.84) with lake trophic state. This covariation likely arose in contemporary time since many of these perch populations were introduced in the last century and the trophic state in many of the lakes has changed in the past few decades. Nutrient excretion varied extensively among populations, but was not readily related to fish body chemistry or lake trophic state. This suggests that predictable patterns of fish body composition can arise quickly through trophic specialization to lake conditions, but such elemental phenotypes may not translate to altered nutrient recycling by fish.

Seasonal variability in the structure and functional diversity of psammic rotifer communities: role of environmental parameters

Data on the variability in structure and functioning of interstitial rotifer assemblages are rare; however, this knowledge is essential for understanding their role in the interstitial food web. In the present study, we characterized psammic rotifer communities in terms of dominance structure, trophic traits, taxonomic and functional diversity at a seasonal scale in freshwater lakes across Estonia and coastal beaches of the Baltic Sea. A total of 42 rotifer species were found from the coastal beaches and 66 species from the lakes. Functional indices did not exhibit smaller seasonal variability and neither did they respond better to changes in the environment compared to taxonomic indices. However, there were differences how environmental variables affected these two broad groups of response variables. The taxonomy-based indices of rotifer communities were primarily driven by seasonal temperature regime, sediment characteristics and anthropogenic stressors, whereas the trait-based indices were a function of ecosystem types (freshwater or brackish water). The functional indices of the psammic rotifer communities strongly distinguished between freshwater and brackish habitats indicating that rotifers have different functional roles in food webs in fresh and brackish water environments.

Native richness and species level trophic traits predict establishment of alien freshwater fishes

Community level ecological traits are thought to affect invasibility as more diverse communities with complex trophic interactions may be associated with greater biotic resistance. Elucidation of the nature of this relationship is often hampered by difficulties in characterising food webs, particularly where field data are lacking. We attempted to overcome this by coupling food web modelling with information-theoretic analysis of the modelled webs. In addition, we also investigated the possibility that species level trends in trophic traits of established aliens might reflect exploitation of empty niches. We constructed hypothetical food webs of 26 natural and artificial lentic habitats from a data set consisting of 370 fish species representing 71 families. Using these food webs, we investigated associations at the community level between food web traits and network topology and number of alien fish species using an information-theoretic approach based on a set of competing a priori hypotheses. At the species level, we similarly tested for trends in trophic traits of established alien fishes using the information-theoretic approach in addition to nMDS of diet data. We found that native species richness in a community was the most important determinant of the number of alien fish taxa, displaying an inverse relationship. Our data also show that alien fish generally feed lower down the food web. Our findings suggest that the biotic resistance hypothesis, though scale dependent, can result in observable effects in animal communities. Moreover, we also found that the ability to exploit low energy yield food sources could favour the establishment of alien species via avoidance of resistive forces from native taxa.

Trophic niche partitioning between two Rock Nuthatches (Sitta tephronota&Sitta neumayer) in a contact zone in Iran

AbstractTwo sympatric nuthatch species,Sitta tephronotaandS. neumayer, provided the exemplar case of character displacement when the term was coined. The two species are quite similar morphologically but have diverged from one another in sympatry, presumably because of competition‐driven selection favoring the partitioning of food resources. However, actual diet partitioning has never been shown. Here, we report the dietary composition of the two species by analyzing items recovered from the gastrointestinal tract. We found thatS. tephronatafed predominantly on Coleopterans, Hemipterans and Orthopterans with the most important seed plants taken beingAmygdalus lycioides, Ficus caricaand Fabaceae, whereas,S. neumayerfed mainly on Coleopterans, Hemipterans and Lepidopteran, withA. lycioides, Fabaceae andTritium aestivumas the most important plants taken. To determine whether the two species partition prey into different sizes, we examined two mostly abundant insect preys (Hemipterans and Coleopterans) and measured head length for Hemipterans and mandible size for Coleopterans as proxies for prey body size. We found a significant relationship between bird body size and prey size, asS. tephronata, which is larger, captured larger bugs and beetles. We also measured the ability of each species to crack seeds of different hardness, finding thatS. tephronatatakes larger and harder seeds thanS. neumayer. Analyses of trophic niche breadth and overlap showed (1) that trophic niche breadth forS. neumayerwas wider than that forS. tephronata;(2) overall trophic niche overlap was considerably high but (3) overlap in the size of the most frequently consumed insects was low, suggesting that the species may be partitioning resources by prey size. We conclude that the relative body size of consumed prey is an important axis of niche partitioning and may have driven character displacement in associated trophic traits, allowing the stable coexistence of the two species.

The functional organisation of the mesopedobionts community of sod pinewood soils on arena of the river Dnepr

We revealed the functional groups of the animals of sod pinewood soils (arena of the river Dnepr in the "Dneprovsko-Orelsky" Nature Reserve) on the basis of cluster analysis of the RLQ-axes received as result of interaction of matrix of community, matrix of edaphic parameters and matrix of ecomorphs of soil animals. The quantitative account of soil mesofauna has allowed us to establish that the community of animals inhabiting sod pinewood soils is represented by 20 species at a density of 68.9 ± 14.6 ind./m2, 8 forms were identified at the level of genus, family or order. Two species were represented by their larval and imago phases (Anatolica eremita (Steven, 1829) and Calathus ambiguus (Paykull, 1790)). A count of animals conducted in an alternative way has allowed us to expand the list to 38 species or forms at species level. The level of abundance and diversity for sod pinewood soils on the arena is not high compared with other types of soils of the arena of the river Dnepr. This result shows that the community has a simplified ecological structure. The prevailing ecological structure of the community can be characterised as steppe, xerophilous, oligotrophocoenomorphic. Anecic animals are absent from the topomorphic structure and saprophagous animals absent from the trophic structure. Only additional collection by alternative methods has allowed us to establish the presence in the community of saprophagous and anecic animals. The latter ecological group is represented by the extremely mobile vertebrate species Pelobates fuscus. The foromorphic structure of the community differs by its great variety. In this structure various strategies of animals’ movement through the soil are proportionately represented. On the one hand, we see various ways of movement of herpetobiont animals, mainly insect imagoes, which as a whole differ in their considerable migratory potential. This circumstance staticizes the historical reasons for the formation of the studied community. On the other hand, in the community there are various strategies of movement in the soil that allow us to assume or determine the reasons or causes of structurization of an ecological niche. Environmental factors are described by two groups of indicators, edaphic properties and values of phytoindicator scales. The mesopedobionts community structure is presented as a classical matrix of species/sampling points. The ecology of communities is principally focused not on taxonomic features but on biological properties (traits) of species. Such features can act on ecomorphs of soil animals. The direct functional analysis of relationship of biological properties of species with variables of environment by means of data on the abundance of species demands association of three matrixes of data. Such problem can be tackled by means of the RLQ-analysis. A key aspect of structurization of communities of soil mesofauna is differentiation in trophic traits. The organisation of a community of soil animals in an ecological space set by axes RLQ can be displayed in the form of a natural variation of RLQ-axes in geographical space. Everything in the RLQ is represented, as follows from the mathematical nature of this generalisation, an independent aspect of the coordinated variation of structure of a community of soil animals, properties of environment and ecomorphic features of mesopedobionts.

Environmental constraints structuring fish assemblages in riffles: evidences from a tropical stream

ABSTRACT Riffles are unique habitats regarding to assemblage structure. However, understanding how these assemblages respond to environmental variations in small spatial extents, as within a stream, is a challenge. We assess whether the quantitative structure and the trophic composition of fish assemblages vary predictably among stream riffles. We predict that the variation of environmental conditions will explain species abundance and trophic composition, with the latter presenting higher predictive power, since species would be filtered according to their traits (e.g. diet). Moreover, we expect that the low among-riffle dispersal limitation within a stream and the strong habitat filtering would result in lower importance of spatial variables in the structure of riffle fish assemblages. We tested these predictions by studying 18 riffles of a stream in the Central Brazil. Environmental variables, but not spatial ones, were the most important in explaining the variation in assemblages structure. Environmental variables explained a greater portion of the trophic structure variation (R2=0.62) than of abundance (R2=0.37), indicating that the variation on the trophic traits at community level are more predictable. These results also indicate that these assemblages are subject to environmental control, highlighting the importance of riffle characteristics in driving ecological processes within streams.

Evolution and function of fossoriality in the Carnivora: implications for group-living

The societies of group-living carnivores that neither hunt nor interact cooperatively may arise due to ecological drivers and/or constraints. In this study we evaluate whether group-living may be intrinsically associated with fossoriality; a link that is well supported in other taxa, but hitherto under-evaluated in the Carnivora. We make two over-arching predictions: i) that fossoriality will be associated with carnivoran sociality; and ii) that this association will be most evident in those species making extended use of subterranean dens. From a meta-analysis of key behavioural, ecological, ontological, and trophic traits, we demonstrate that three quarters of carnivore species exhibit some reliance on underground dens. Congruence between life-history traits and metrics of fossoriality evidenced that: 1) there are phylogenetic, and morphological constraints on wholly fossorial life-histories; 2) fossoriality correlated positively with the extent of offspring altriciality, linked to the use of natal dens; 3) burrow use increased with latitude; and 4) insectivorous carnivores were more fossorial than predatory carnivores. Corroborating work in the Rodentia, fossorial traits associated strongly with carnivoran group-living tendencies, where species utilising subterranean natal dens are 2.5 times more likely to form groups than those that do not. Furthermore, using comparative analyses, we evidence support for an evolutionary relationship between diet, fossoriality and sociality. We propose that fossorial dens act as a safe haven, promoting fitness benefits, territorial inheritance and cooperative breeding. We conclude that, among smaller (<15kg) den-using carnivores, and especially for omnivorous/ insectivorous species for which food resource dispersion is favorable, continued cohabitation at natal dens can promote cohabitation among adults; that is, philopatric benefits leading to (not necessarily cooperative) spatial groups.

Sexual dimorphism in a trophically polymorphic cichlid fish?

Sexual dimorphism in ecologically relevant traits is ubiquitous in animals. However, other types of intraspecific phenotypic divergence, such as trophic polymorphism, are less common. Because linkage to sex should often lead to balancing selection, understanding the association between sex and phenotypic divergence could help explain why particular species show high morphological variability. To determine if sexual dimorphism could be helping to maintain ecomorphological variation in a classic case of intraspecific trophic polymorphism, we examined the association between sex and morphological divergence in the cichlid Herichthys minckleyi. Although H. minckleyi with enlarged molariform teeth on their pharyngeal jaws have been reported to more commonly be male, we did not find an association between sex and pharyngeal morphotype. Sex was associated with divergence in body size (as measured through standard length). But, sex was not associated with any of the other trophic traits examined. However, pharyngeal morphotype did show an association with gut length, gape, and tooth number. Sexual dimorphism is not playing a central role in enhancing trophic diversity within H. minckleyi.

Environmental context and trophic trait plasticity in a key species, the tellinid clam Macoma balthica L.

Species show varying levels of plasticity regarding morphology, physiology and behaviour in relation to their immediate environment, and several trait characteristics are habitat-dependent. Determining when and how the environmental context changes trait expression is of key importance for understanding the role of individual species for ecosystem functioning. The tellinid clam Macoma balthica can vary its feeding behaviour, shifting between deposit- and suspension-feeding. In order to study the context-dependency of this trophic plasticity in adult clams, we conducted an experiment assessing food uptake by using stable isotope signatures (δ13C and δ15N). We transplanted individuals between and within two shallow bays differing in exposure (exposed–sheltered) and sediment characteristics. Our results show that isotope signatures of clams differed between the two habitats and that clams in the exposed site showed stable isotope values linked to a diet of suspended particulate organic material, while values of individuals in the sheltered site corresponded to an uptake of sediment-bound organic material. Clams transplanted between these two environmental settings were gradually showing differing isotopic signatures from clams at their original habitat, over time mirroring the changes in clams in the site to which they were transferred. The shift in carbon and nitrogen stable isotopes of the clams provides insights into the context-dependent intraspecific feeding plasticity of this zoobenthic key species. The causes for this shift were coupled to contrasts in the hydrodynamic and biotic setting, implying that feeding plasticity may explain adaptation of organisms to changes in their surroundings.