Ecomorphological Approach Research Articles

Trophic ecology of terapontid fishes (Pisces: Terapontidae): the role of morphology and ontogeny

With the covariation between fish form and function of long-standing interest to fish biologists, ecomorphological research provides a framework for assessing the interaction between the morphology of an organism and their ecology. Whereas ecomorphological studies of Australian fishes are rare, the terapontid grunters are an ideal candidate for study because of their diversity of dietary habits. We examined the morphological correlates of the diet of 21 species of northern Australia’s terapontids and their constituent ontogenetic trophic units. Preliminary analyses focusing on morphology identified the role of allometric growth – in characters such as intestinal length, maxilla length and mouth width – as driving considerable ontogenetic divergence in interspecific morphological trajectories. A significant relationship was identified between diet and morphology across species, although morphology explained only half of the observed dietary variation. Body size, and its relationship to allometric development of several morphological parameters, appears to constrain the trophic habits expressed by many terapontids at different life-history stages. Many of the diet–morphology relationships evident within the Terapontidae parallel those seen in other studies, providing substantial corroboration for the ecomorphological approach. This demonstrates that selective pressures have driven morphology in terapontids to converge morphologically with other ecologically comparable fishes across the globe.

Inferring habitat and feeding behaviour of early Miocene notoungulates from Patagonia

Cassini, G.H., Mendoza, M., Vizcaíno, S.F. & Bargo, M.S. 2011: Inferring habitat and feeding behaviour of early Miocene notoungulates from Patagonia. Lethaia, Vol. 44, pp. 153–165. Notoungulates, native fossil mammals of South America, have been usually studied from a taxonomic point of view, whereas their palaeobiology has been largely neglected. For example, morpho-functional or eco-morphological approaches have not been rigorously applied to the masticatory apparatus to propose hypothesis on dietary habits. In this study, we generate inferences about habitat and feeding preferences in five Santacrucian genera of notoungulates of the orders Typotheria and Toxodontia using novel computer techniques of knowledge discovery. The Santacrucian (Santa Cruz Formation, late-early Miocene) fauna is particularly appropriate for this kind of studies due to its taxonomic richness, diversity, amount of specimens recorded and the quality of preservation. Over 100 extant species of ungulates, distributed among 13 families of artiodactyls and perissodactyls, were used as reference samples to reveal the relationships between craniodental morphology and ecological patterns. The results suggest that all Santacrucian notoungulates present morphologies characteristic of open habitats’ extant ungulates. Although the Toxodontia exhibits the same morphological pattern of living mixed-feeders and grazers, the Typotheria shows exaggerated traits of specialized grazer ungulates. □Craniodental morphology, ecomorphology, fossil ungulates, knowledge discovery, South America.

Mandible morphology, dental microwear, and diet of the extinct giant rats Canariomys (Rodentia: Murinae) of the Canary Islands (Spain)

An ecomorphological approach of mandible shape through Fourier analyses combined with a paleodietary analysis of dental microwear patterns is used to reconstruct the diet of the extinct endemic Canariomys bravoi Crusafont, Pairo & Petter, 1964 and Canariomys tamarani Lopez-Martinez & Lopez-Jurado, 1987. These two large rodents, respectively, lived on Tenerife and Gran Canaria, the central islands of the Canarian Archipelago. Mandible shape and dental microwear respectively inform us on the volume of vegetal matter and on the presence of grass in the diet. Both Canariomys, which are of similar size, possess relatively similar mandible outlines and microwear patterns. For each species, a diet based on plant materials except grass is the most likely. Such results chime with the similar environments offered by the islands in which the species lived. On the contrary, molar morphology suggests different feeding habits of the two Canariomys. Thus, this suggests a case of mosaic evolution between teeth and mandibles, as well as the likely sensitivity of mandible shape to a combination of ecological and allometric factors. These new data obtained from the fossil record underline the propensity of island endemic mammals to yield surprising examples of phenotypic evolution.

Habitat partitioning, habits and convergence among coastal nektonic fish species from the São Sebastião Channel, southeastern Brazil

Based on a fish survey and preliminary underwater observations, 17 "morphotypes" were identified that characterize the morphological diversity found within 27 nektonic fish species sampled at São Sebastião Channel. Such "morphotypes" were studied using an ecomorphological approach, with the intention to investigate similarities and differences in shape and habits. Underwater field observations were also performed, to verify if the lifestyle of these species, such as vertical occupation of the water column and the habitat use, are in accordance with their distribution in the morphospace. The results, complemented with data from scientific literature on the taxonomy and phylogenies of these species, allowed discussing some of the typical cases of convergent and divergent evolution. Some of the ecomorphological clusters had no phylogenetic support although this is probably due to the environmental conditions in which theirs members have evolved. The body shape and fins positions of a fish clearly influence its ecological performance and habitat use, corroborating the ecomorphological hypothesis on the intimate link between phenotype and ecology.

Wing shape variation in the medium ground finch (Geospiza fortis): an ecomorphological approach

Wing design in birds is subject to a suite of interacting selective pressures. As different performance traits are favoured in different ecological settings, a tight link is generally expected between variation in wing morphology and variation in ecological parameters. In the present study, we document aspects of variation in wing morphology in the medium ground finch (Geospiza fortis) on Isla Santa Cruz in the Galapagos. We compare variation in body size, simple morphometric traits (body mass, last primary length, wing length, wing chord, and wing area) and functional traits (wing loading, aspect ratio and wing pointedness) across years, among populations, and between sexes. Functional traits are found to covary across years with differences in climatic conditions, and to covary among populations with differences in habitat structure. In dry years and arid locations, wing aspect ratios are highest and wings are more pointed, consistent with a need for a low cost of transport. In wet years and cluttered habitats, wing loading is lowest and wings are more rounded, suggesting enhanced capabilities for manoeuvrability. Sexes differ in wing loading, with males having lower wing loadings than females. Superior manoeverability might be favoured in males for efficient territory maintenance. Lastly, in contrast to functional traits, we found little consistent inter-annual or inter-site variation in simple morphometric traits. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 129–138.

Tracing the ecophysiology of ungulates and predator–prey relationships in an early Pleistocene large mammal community

Research into the reconstruction of ancient communities in terms of dietary regimes, habitat preferences and ecological interactions of species has focused predominantly on biogeochemistry or ecomorphology alone and not in combination. The Venta Micena site (Orce, Guadix–Baza basin, SE Spain) has an early Pleistocene vertebrate assemblage with exceptional biomolecular preservation. Collagen was successfully extracted from 77 bone samples of 18 species of large mammals, which allowed analyses of carbon- and nitrogen-isotopes. δ 13C, δ 15N and δ 18O ratios combined with ecomorphological indexes provide interesting clues on the autecology and palaeophysiology of extinct species, which help in deciphering aspects of community trophic structure and predator–prey interactions. Specifically, morphometric ratios (e.g., hypsodonty index and relative length of the lower premolar tooth row; [Palmqvist, P., Gröcke, D.R., Arribas, A., Fariña, R. 2003. Paleoecological reconstruction of a lower Pleistocene large mammals community using biogeochemical ( δ 13C, δ 15N, δ 18O, Sr:Zn) and ecomorphological approaches. Paleobiology 29, 204–228.]) allow classifying the ungulates among grazers ( Equus altidens, Bison sp., Praeovibos sp., Hemitragus albus, Hippopotamus antiquus, and Mammuthus meridionalis), mized-feeders ( Soergelia minor and Pseudodama sp.) and browsers ( Stephanorhinus sp. and Praemegaceros cf. verticornis). However, δ 13C values reveal that these ungulates consumed exclusively C 3 plants and significant differences in isotopic values between perissodactyls (monogastric, hindgut fermenters) and ruminants (foregut fermenters) must reflect physiological differences related to their rates of methane production and digestive efficiency. δ 18O ratios allow the interpretation of the dietary water source of these species, suggesting that fallow deer Pseudodama sp., goat H. albus and ovibovine S. minor obtained a significant fraction of their metabolic water from the vegetation consumed. Carnivore species have higher δ 15N values than herbivores, which records the isotopic enrichment expected with an increase in trophic level. However, the unexpectedly high δ 15N values of hippo H. antiquus and muskoxen Praeovibos sp. suggest that these ungulates predominantly consumed aquatic plants and lichens, respectively. Inferences on predator–prey relationships within this ancient community, derived from the dual linear mixing model, indicate resource partitioning among sympatric predators, suggesting that sabre-tooth Megantereon whitei and jaguar Panthera cf. gombaszoegensis were ambushers of forest environments while sabre-tooth Homotherium latidens and wild dog Lycaon lycaonoides were coursing predators in open habitat . The giant, short-faced hyena Pachycrocuta brevirostris scavenged the prey of these hypercarnivores.

Diet-morphology relationship in a fish assemblage from a medium-sized river of French Guiana: the effect of species taxonomic proximity

We investigated the global relationship between diet and morphology for 42 fish species from a medium-sized river in French Guiana and checked the influence of the species taxonomic proximity on the implication of individual morphological traits in that relation. The 42 species were classified in eight trophic guilds based on analysis of more than 4000 stomach contents. Taxonomic proximity between species was accounted for by an autoregressive model applied to original data of diet and morphology. Original and taxonomic-free data were then submitted to a Canonical Correspondence Analysis in order to detect the relationship between diet and morphology. We compared the results obtained by analyzing the original data and the corrected data. The results confirm the existence of a significant global relationship between diet and morphology. However, morphological traits responsible for that relation were different when considering the taxonomic-free data. Particularly the well known relationship between gut length and detritivory was not observed on the taxonomic free analysis. It is concluded that controlling for phylogeny is essential to the detection of relationships between diet and morphology. It is also concluded that, despite the robustness of some relationships between morphology and diet, many diets cannot be inferred by a ecomorphological approach.

Probability of competition between introduced and native rodents in Madagascar: An estimation based on morphological traits

An ecomorphological approach was used to estimate the probability of interspecific competition between introduced and native rodents in Madagascar. Comparison of body size, body construction, and craniodental characters leads to the conclusion that there is a high probability of competition between introduced Rattus rattus and the following native taxa: all species of Nesomys, larger semiarboreal Eliurus species (e.g. E. tanala, E. webbi), and especially Gymnuromys roberti. The competitive relationships between introduced rodents and the remaining species of the Nesomyinae have a low probability or are improbable, except possibly for Mus musculus and the so far poorly studied Monticolomys koopmani and Voalavo species.

Comparative trophic morphology in eight species of damselfishes (Pomacentridae)

Damselfishes show significant biodiversity in the coral reefs. To better understand such diversity, an ecomorphological approach was investigated in the trophic morphology of eight species of Pomacentridae (Chromis acares, C. margaritifer, Dascyllus aruanus, D. flavicaudus, Pomacentrus pavo, Plectroglyphidodon johnstonianus, Pl. lacrymatus and Stegastes nigricans) belonging to different trophic guilds (zooplankton, algal, coral polyp feeders and omnivores). Geometric morphometrics were used to quantify size and shape variations in four skeletal units: (1) neurocranium, (2) suspensorium and opercle, (3) mandible and (4) premaxilla. This method allowed us to reveal shape and size differences correlated to functional diversity both within and between trophic guilds. Among zooplanktivores, C. margaritifer, D. aruanus and D. flavicaudus have a high and long supraoccipital crest, short mandibles forming a small mouth and high suspensoria and opercles. These three species can be considered to be suction feeders. In the same guild, C. acares shows opposite characteristics (long and thin mandibles, lengthened neurocranium and suspensorium) and can be considered as a ram feeder. Among herbivores and corallivores, the two species of Plectroglyphidodon and S. nigricans can be considered as grazers. Differences in skeletal shape are mainly related to improving the robustness of some skeletal parts (broad hyomandibular, short and high mandibles). The shapes of P. pavo, which feeds largely on algae, strongly differ from that of the other three grazers exhibiting similar morphological characteristics to C. acares (e.g., long and shallow suspensorium, lengthened neurocranium). This highlights likely differences concerning cutting or scraping method. Finally, no strong correlations exist between size and shapes in the eight studied species. Size difference among species having a very similar shape could be viewed as a factor optimizing resource partitioning.

Morphological diversity among fishes in a Great Plains river drainage

Longitudinal succession of stream fish faunas is commonly related to increasing stream size and stability. However, effects of succession on assemblage morphology are seldom quantified. We used an ecomorphological approach to determine differences in faunal structure among distinct stream types of the Cheyenne River drainage in South Dakota, USA. During May–October 2004 we collected fishes monthly from five streams. We examined 28 morphological traits of the dominant fish species and compared morphological structure among faunas using univariate analysis of variance (ANOVA) tests and multivariate ordination and distance calculation techniques. Species richness and composition varied between smaller creeks and larger rivers. Morphological diversity increased with richness, but richer assemblages were also more tightly packed in morphospace, partly because of increased cyprinid richness. Some morphological differences were predicted by variation in mean discharge and discharge flashiness (flow stability). Fishes of more stable or larger river stations characteristically had smaller heads and mouths and longer intestines. Larger mean standard length was also associated with less flashy flow regimes and higher mean discharge. All assemblages were hyperdispersed in morphological space, consistent with the harsh zoogeographical history of the region and suggesting the presence of open niches. Increasing species and morphological diversity despite increasing discharge flashiness suggests higher niche diversity in Great Plains rivers compared to adjacent creeks.

Dietary resource partitioning in ruminant communities of Miocene wetland and karst palaeoenvironments in Southern Germany

Ruminants made up a major component in Early and Middle Miocene European land mammal faunas. Hypotheses are tested which concern the diversity of feeding niches in Miocene ruminants and their resource partitioning. Because teeth are the basis of taxonomic work in the biota investigated here, the tooth-based mesowear method of dietary evaluation is applied. Dental wear equilibria as evaluated using mesowear analysis represent an immediate taxon-independent habitat interface, which bridges extant and Neogene communities. Two adjacent palaeoenvironments have been selected as models for testing our hypotheses, because ruminants are well recorded, the temporal window represents a long lasting and stable period before the onset of a global and regional environmental change that led to an increase of grass-dominated environments and because both environments represent fundamentally different habitat conditions but are spatially connected and represent the same climatic zone (i.e., the Molasse Basin wetland and the adjacent karstified Jurassic limestone plateau in Southern Germany). The ruminant communities of both biomes are brachydont throughout and a prevalence of browsing ruminants is found in both biomes, which is in accordance with isotope data. Both habitats, however, did also support strategies equalling those of extant mixed feeders. Among these mixed feeders, there are more grass-dominated mixed feeders in the karst habitat than there are in the wetland. The ruminant communities are thus found to apparently support a range of feeding traits, not evidenced by other ecomorphological approaches such as tooth crown height evaluation nor taxonomic uniformitarianism. The presence of these feeding types suggests that niche segregation in Lower and Middle Miocene brachydont ruminants was already fairly pronounced and reflects the hypothesised niche availability in the two palaeobiomes. The comparatively dry karstified landscape of the Jurassic limestone plateau is reflected by a higher diversity in abrasive feeders compared to the Molasse Basin wetland. As a second approach, two cervid species that co-occur in both biomes, Lagomeryx parvulus and L. pumilio have been tested in terms of differences in the abrasiveness of their diet in the two biomes. L. pumilio has a large dietary spectrum, and in the karst biome, it shows a signal equalling that of extant grass-dominated mixed feeders, while in the wetland biome it behaves as a browser as many other taxa also do. L. parvulus is shown to have a much less pronounced flexibility, as its diet consists of browse in both biomes. The coincidence of both, community structure and interspecific variability in dietary traits of the Lagomeryx species is a strong argument to consider the central hypothesis as supported, that drier environments result in more abrasion dominated dietary signals of flexible feeders, and that there is a general relationship between habitat structure, food availability, the abrasiveness of the forage, and tooth wear. The dietary variability of a species therefore seems to be a highly indicative characteristic in any ecological analysis of extant and fossil biomes and the presented approach adds rarely gained information on certain fossil members of a palaeocommunity and their potential role in the ecosystem.

Morphological and Ecological Correlates of Coexistence in Malaysian Fruit Bats (Chiroptera: Pteropodidae)

Niche theory predicts that coexisting species should differ ecologically, morphologically, or behaviorally in ways that minimize competition. We used an ecomorphological approach to determine how coexisting species in the Old World fruit bat genus, Cynopterus, assort in morphological and ecological space. The study was conducted in peninsular Malaysia where 4 species of Cynopterus are broadly sympatric. Interspecific separation in resource use was estimated along 3 main axes: habitat, based on abundance across a habitat gradient at 2 sites; trophic niche, inferred from a suite of cranial and postcranial characters; and locomotory behavior and efficiency, inferred from wing morphology. Habitat associations, overall size, and the size and shape of the trophic apparatus were all important in separating 2 or more species, whereas interspecific differences in wing morphology were minor. In combination, the results of this study suggest that relatively minor separation among Cynopterus species pairs along single axes of resource use is sufficient to counteract overlap on other axes, and permit the coexistence of potential competitors.

Novos métodos no estudo da estratificação vertical de marsupiais neotropicais

NEW METHODS FOR THE STUDY OF VERTICAL STRATIFICATION OF NEOTROPICAL OPOSSUMS. New methods have been developed for the study of vertical stratification on small neotropical mammals, alternative to traditional methods using live traps. We reviewed three such alternative methods to study vertical stratification of didelphid marsupials in tropical forests: performance tests in an ecomorphological approach, spool-and-line, and artificial nests. The history of each method was reviewed, discussing their advantages and pitfalls, and presenting examples of the unique results reac,hed. More accurate tests of hypothesis about assemblage structure and population demography can be obtained by combination of traditional and alternative methods, which complement each other, minimizing their limitations. Key-words: Ecomorphology, Spool-and-line, Artificial Nests, Didelphidae, Techniques.

Predicting and testing resource partitioning in a tropical fish assemblage of zooplanktivorous ‘barbs’: an ecomorphological approach

Morphometrics on 25 critical feeding structures predicted conspicuous specializations in Barbus tanapelagius (pursuit hunting for zooplankton), Labeobarbus brevicephalus (surface dwelling pump‐filter‐feeder on zooplankton) and Barbus pleurogramma (particulate feeding on tough, benthic food), whereas for Barbus humilis intermediate values predicted few constraints and specializations in feeding. These potential niches, set by fish size and structural constraints, were tested by comparing gut contents collected during a 24 months sampling programme on Lake Tana, Ethiopia. Zooplankton dominated the diet of B. tanapelagius (75% of gut volume) and L. brevicephalus (39%). The guts of B. pleurogramma and juveniles of the large labeobarbs showed an array of benthic food types, whereas B. humilis had the widest food niche, both zooplankton (40% of gut volume) and benthic invertebrates. Although the pelagic species showed the largest spatial overlap, their size, feeding modes and utilization of zooplankters differed: L. brevicephalus preyed predominantly on the larger zooplankton (Daphnia sp.) and B. tanapelagius also on smaller species (e.g. Bosmina sp. and cyclopoid copepods). The spatial segregation between B. tanapelagius (pelagic) and the juvenile labeobarbs (littoral) indicated the possibility for a small pelagic barb fishery without negative effects on the labeobarb stocks. The ecomorphological approach using the ‘Food‐Fish Model’ appeared to predict competitive positions and resource partitioning appropriately, and is of major importance to evaluate food web interactions.

Morphological assembly mechanisms in Neotropical bat assemblages and ensembles within a landscape

Empirical studies on bat assemblages have shown that richness is not appreciably influenced by local processes such as ecological interactions. However, most of these studies have been done in large areas that include high heterogeneity, and they analyse all bat species within such areas, and thus they may be not reflecting local but supra-community conditions. We followed an ecomorphological approach to assess how bat assemblages of species from the families Phyllostomidae and Mormoopidae, and ensembles of frugivorous bats, are assembled in local habitats within a single landscape. We measured the volume of the space defined by wing morphology and quantified the average distance between species within such a volume. Then, we related these measures to local richness. Such relationships were contrasted against relationships with random assemblages to test for statistical differences. At the ensemble level of organization, we found that the frugivorous bat morphological assembly mechanism is different from random patterns, and it corresponds to the volume-increasing model. On the other hand, bat assembly mechanisms may be ubiquitous at the assemblage level, because groups of species coexisting in a local habitat and delimited only by phylogeny include more than one ecological group with no potential to interact. Assembling processes are crucial to an understanding of species diversity in local communities, and ecomorphological analyses are very promising tools that may help in their study.

ECOMORPHOLOGY OF PARASITE ATTACHMENT: EXPERIMENTS WITH FEATHER LICE

The host specificity of some parasites can be reinforced by morphological specialization for attachment to mobile hosts. For example, ectoparasites with adaptations for attaching to hosts of a particular size might not be able to remain attached to larger or smaller hosts. This hypothesis is suggested by the positive correlation documented between the body sizes of many parasites and their hosts. We adopted an ecomorphological approach to test the attachment hypothesis. We tested the ability of host-specific feather lice (Phthiraptera: Ischnocera) to attach to 6 novel species of pigeons and doves that vary in size by nearly 2 orders of magnitude. Surprisingly, Rock Pigeon lice (Columbicola columbae) remained attached equally well to all 6 novel host species. We tested the relative importance of 3 factors that could facilitate louse attachment: whole-body insertion, tarsal claw use, and mandible use. Insertion, per se, was not necessary for attachment. However, insertion on coarse feathers of large hosts allowed lice to access feather barbules with their mandibles. Mandible use was a key component of attachment regardless of feather size. Attachment constraints do not appear to reinforce host specificity in this system.

African Climbing Mice (Dendromus, Muroidea) and Palaearctic Birch Mice (Sicista, Dipodoidea): An Example of Parallel Evolution Among Rodents

Despite belonging to two different superfamilies (Dipodoidea and Muroidea), African climbing mice (Dendromus) and Palaearctic birch mice (Sicista) have remarkable similarity in their overall appearance. An ecomorphological approach was used for the quantitative estimation of the similarity and the revealing of its biological meaning. Body proportions, craniodental characters and habits were compared in four species of Dendromus (D. insignis, D. melanotis, D. mesomelas, D. mystacalis) and all recent species of Sicista. The results show that both genera include species adapted to (1) climbing grasses and twigs, (2) long jumps, which serve as a mean of escape from predators, (3) predominantly nocturnal activity, and (4) the mostly granivorous-insectivorous diet. These ecological strategies are accompanied by a set of morphological adaptations, which is common for both genera. They are: small size, a very long tail, elongated limbs, including forefeet, which are adapted for grasping stems and twigs. Parallel evolution of these adaptations is suggested. On the other hand, the level of specialisation varies within and between these groups. In general, Dendromus have more advanced locomotor adaptations, while most species of Sicista have more specialised dentition.

COEXISTENCE OF PECCARIES AND FERAL HOGS IN THE BRAZILIAN PANTANAL WETLAND: AN ECOMORPHOLOGICAL VIEW

Niche partitioning among sympatric populations of white-lipped peccary (Tayassu pecari), collared peccary (Pecari tajacu), and feral hog (Sus scrofa) is evaluated using an ecomorphological approach. Masticatory apparatus and head-elevation lever system of the 3 species are compared by skull measures related to moment arms of associated muscles. Forcerates based on the equation of static equilibrium are proposed as a basis of comparison between species-specific cranial designs related to mastication and digging ability. Morphofunctional data suggest that feral hogs have a powerful bite and are able to feed on seeds of different degrees of resistance. With an optimized lever system of head elevation, feral hogs are more efficient than peccaries at rooting. These facts, along with the capacity of feral hogs to explore a wide range of habitats, support the view that the species acts as a potential competitor of native peccaries.

Speciation of endemic Lake Tana barbs (Cyprinidae, Ethiopia) driven by trophic resource partitioning; a molecular and ecomorphological approach

A unique species flock of large barbs (Barbus spp.) from Lake Tana is presented, from the level of fish stocks to molecules. Evidence is given for the species status of 14 morphotypes of large barbs. They distinctly differ in: (1) head and body morphometrics, (2) food preferences, (3) distribution patterns, (4) maximal body size, (5) spawning area and period, and (6) molecular genetic characters. Most types show early morphological divergence at small size. Major Histocompatibility Complex (MHC) genes, encoding cell membrane proteins involved in defence against pathogens, were found to be diagnostic for the species' genetic identity. A strong selective pressure on particular amino acid positions in the MHC protein sequence most probably arose in response to different pathogen loads from the newly invaded ecological niches after formation of Lake Tana, ca. two million years ago.

Functional morphology of the feeding apparatus of ten species of Pacific butterflyfishes (Perciformes, Chaetodontidae): an ecomorphological approach

The functional morphology of the feeding apparatus and the feeding ecology of an assemblage of ten species of butterflyfishes was investigated using a comparative ecomorphological approach. Behavioral observations in situ and in vivo, morphological measurements of fresh-killed specimens, scanning electron microscopy, and kinematic modeling were utilized. The fishes show varying degrees of morphological and behavioral specialization and generalization. The more specialized species group according to how they feed, rather than what they feed on. The feeding guild concept is therefore not very instructive in understanding the functional significance of the feeding apparatus. Many of the morphologically specialized butterflyfishes demonstrate evolutionary convergence in feeding morphology. Whereas the more morphologically specialized species do generally have more ecologically specialized diets, these data do not particularly support the ecomorphological hypothesis in that similar diets do not correspond to similar morphologies.