Ecomorphological Studies Research Articles

Lizard Locomotion: How Morphology Meets Ecology

Biological evolution often leads, through natural selection, to an optimal fit between 'design' and ecology. However, the adaptation process may be impeded or slowed down by several constraints or trade-offs between conflicting functions. This is frequently observed by ecomorphological studies focusing on lower taxonomic levels: form-function relationships get blurred because subtle adaptive traits remain hidden or simply do not exist. Therefore, a rigorous analytic approach is required, (ideally) assessing the links between the four stages of the adaptive process simultaneously (i.e., from genetic variation to variation in design, to variation in performance, to differential fitness), taking into consideration all potential factors hindering the normal progression of this process. Lizard locomotion is a good model for such an analysis. Locomotion is essential in many ecologically relevant functions (feeding, predator avoidance, etc.). It consists of several components (speed, acceleration, endurance, manoeuvrability, etc.) and modes (level running, climbing, etc.) with conflicting demands, leading to potential trade-offs. Moreover, several of its components proved to be heritable and obvious relations between habitat use and locomotor design are often absent (e.g., in lacertid lizards). Two cases, focusing on the potential trade-off between climbing and level-running, are presented to illustrate the subtle interplay between variation in ecology, performance and design in lizard locomotion. (1) For two gekkotans (a climber and a ground dwelling species) the moments exerted by several important leg muscles appear to be tuned to their primary mode of locomotion. (2) In two sibling lacertid species, the inverse trade-off between climbing and running, put forward on the basis of observed substrate use, does not exist. Instead, a drastic difference in running performance, likely related to different running styles, emerged. The latter case illustrates the potential use of 'integrated, dynamic design traits' as an intermediate stage between variation in design and performance.

Comparative three-dimensional kinematics of the hindlimb for high-speed bipedal and quadrupedal locomotion of lizards

Although lizards have been model organisms for testing locomotor performance and in ecomorphological studies, the limb movements of lizards during high-speed locomotion are poorly understood. Thus, we quantified the three-dimensional kinematics of the hindlimb, body and tail for five morphologically distinct species of lizard during steady-speed locomotion near maximum sprinting speed (2-5 m s-1). The kinematics of different species had little multivariate overlap. More than half of the strides of all species had digitigrade foot posture, but the frequency of using digitigrade foot posture varied among species. The combination of digitigrade foot posture and large foot size of the lizards contributed substantially to the high values of hip height. For each species, different suites of kinematic variables distinguished bipedal from quadrupedal strides. Interspecific morphological variation did not correspond globally to variation in kinematics, although lizard species with elongated hindlimbs took longer strides than species with shorter hindlimbs. The Froude numbers and relative stride lengths of all lizards running near maximal speeds were large compared with those reported previously for other vertebrates.

Habitat selection as a major resource partitioning mechanism between the two sympatric sibling bat species Myotis myotis and Myotis blythii

1. Ecomorphological studies have described local bat communities as densely‐packed species assemblages arising from non‐deterministic processes. Together with the observation that insectivorous bats readily exploit patchy, often unlimited trophic resources, this has even led to the claim that partitioning of niche space may be absent. However, the paucity of data on resource exploitation per se among bat guilds rarely allows these assertions to be verified. In particular, the mechanisms allowing the co‐existence of similar species have proved difficult to determine. 2. As a subset of an insectivorous guild, the vespertilionid bats Myotis myotis and M. blythii offer an opportunity to examine this question. Genetically closely‐related, they are morphologically almost identical. Yet, as established by faecal analysis, they exploit distinct trophic niches, preying upon ground‐ and grass‐dwelling prey taxa, respectively. The distinct habitat requirements of their basic prey suggest that ecological segregation may stem primarily from a differential allocation of foraging space. 3. The present study tests the hypothesis that sympatric M. myotis and M. blythii segregate spatially to an extent which prevents competitive interference. I performed radio‐tracking on Swiss sympatric populations. Using multivariate analyses and randomized contingency table procedures, I looked for (i) habitat overlap and overall inter‐specific differences in habitat choice, and (ii) the habitat preferences exhibited by individuals when foraging within their own feeding areas. 4. Primary foraging habitats were largely species‐specific. Not only were they spatially segregated, but they also differed structurally. All habitats selected by M. myotis offered a high accessibility to ground‐dwelling prey (freshly‐cut meadows, mown grass in intensively cultivated orchards, forests without undergrowth), whereas grassland predominated in all habitats of M. blythii (steppe, unmown meadows, pastures). This corroborates the predictions drawn from dietary niches. 5. This study shows that refined mechanisms of resource partitioning, not predictable by the study of morphological characters or echolocation alone, may still account for the organization of parts of insectivorous bat guilds. It also supports the view that habitat selection may prove to be a major mode of resource allocation amongst similar insectivorous bats, particularly for species exploiting limited food supplies.

Ecomorphological study of large canids from the lower Pleistocene of southeastern Spain

An ecomorphological analysis of the skeletal remains of large canids, Canis (Xenocyon) falconeri and Canis etruscus (Mammalia, Carnivora, Canidae), preserved in an assemblage of large mammals from the lower Pleistocene site at Venta Micena (Guadix–Baza Basin, Orce, Granada, southeastern Spain) is reported. Mean body mass of adult individuals was estimated to be around 10 kg for C. etruscus and approximately 28 kg for C. falconeri using multiple regression. A comparative study of tooth measurements in modem canids, using principal components and discriminant function analysis, infers quite different ecomorphological adaptations and feeding behavior for both fossil species. The craniodental morphology of C. falconeri is similar to that shown by extant hypercarnivorous canids whose diet include more than 70% of vertebrate meat, whereas C. etruscus shows a cranial morphology similar to those of modem omnivorous species, thus indicating a dietary niche in which vertebrate meat represented less than 70% of its diet, with other feeding resources making up the balance. These results suggest that there was a marked ecological segregation between both sympatric species of large canids. The find of a complete skull of C. falconeri showing bilateral asymmetry and marked dental anomalies could suggest high levels of genetic homozygosis in the population which inhabited this region during early Pleistocene times, possibly as a consequence of isolation and the low number of individuals. This may have subsequently led to the extinction of C. falconeri in the Western fringe of Europe. The survival of this pathological individual to adulthood indicates that this species may have developed cooperative behavior similar to that of modem African wild dogs.

Size patterns among competitors: ecological character displacement and character release in mammals, with special reference to island populations

Morphological relationship among sympatric animal species have often been seen as indirect evidence for competition. Many early ecomorphological studies revealed patterns that were taken as indicating character displacement and character release, driven by competition or lack thereof. These patterns may result from a coevolutionary morphological response or from species sorting according to size. Thus, the relationship between morphology and competition may be crucial for understanding both the morphological evolution of animals and the role of competition in structuring communities. Some earlier research perceived as indicating morphological relationships conditioned by interaction of species was conducted on mammals, particularly carnivores. Subsequent criticism in the ecological literature demonstrated that many of the perceived patterns could not be statistically confirmed, thus calling into question this line of evidence for competition. More recent ecological literature relies on strong statistical analyses and careful consideration both of guild composition and of which morphological traits should be examined. This literature, resting largely on mammals, includes several cases that suggest a coevolutionary morphological response to interspecific competition. These studies have focused on the thropic apparatus directly related to food procurement by mammals — the teeth. Island mammals often show striking morphological patterns, some of which have been interpreted as resulting from release from competition with mainland species that have not reached islands. However, few of these patterns were critically evaluated to demonstrate their support for the hypothesis of character release. Despite several decades of interest and research, many questions regarding competitively induced morphological patterns remain unresolved and require further research. Mammals are especially promising subjects for such researh.

Modulation of attack behavior and its effect on feeding performance in a trophic generalist fish,

This study examines the ability of a temperate marine fish, Hexagrammos decagrammus, to modulate its prey capture behavior in response to differences in prey type. This species has an extremely broad diet, feeding on prey which demonstrate very different anti-capture behaviors. Video-taped attacks on three shrimp species, one crab and pieces of shrimp were analyzed to determine the relative contributions of suction-feeding and ram-feeding behaviors to prey capture. The prey capture behaviors used by the predator were related to differences in escape behavior among the three shrimp species. H. decagrammus used behaviors characteristic of other ram-feeding predators when feeding on the two most elusive shrimp species: high attack velocity, attack initiated at a greater distance from the prey, and greater movement of the predator relative to the prey. Strikes at crabs and pieces of shrimp elicited strikes more typical of other suction-feeding predators, with lower attack velocities, shorter initial predator­prey distances and greater relative movement of the prey towards the predator. Attacks on the least elusive shrimp species showed elements of both ram and suction feeding. Modulation of attack velocity increased capture success on elusive prey, supporting the hypothesis that diet diversity is associated with the presence of a repertoire of feeding behaviors. These data suggest that functional differences in prey anti-capture behavior, as well as the functional versatility of the predator, must be addressed in ecomorphological studies that try to correlate predator morphology with diet.

The role of ecomorphological studies in the comparative biology of fishes

The role of ecomorphological studies in the comparative biology of fishes

Evolution of foraging ecology in Fennoscandian tits (Parusspp.)

Species belonging to the same genus exploit similar resources in a similar manner. Despite their general similarities in behaviour, they differ in morphology, and these differences are often interpreted as adaptations for use of different resources. Here we report on the relation between morphology, habitat selection and feeding ecology in seven tit species (Parus spp.) in Fennoscandia. A problem previously disregarded in most ecomorphological studies is that members of a guild with closely related species share their common ancestry. This historical legacy causes similarity in ecology and morphology. We have used phylogenetic information with proper comparative methods to reveal the evolutionary associations. Our field data represented the winter, when tits commonly form mixed-species flocks and exploit non-renewable and limited food resources. Our rigorous analysis confirmed the previous suggestions that the smallest tit species tend to forage in the exterior tree parts whereas the heavier species use the inner parts. Another ecomorphological pattern is that tits inhabiting coniferous habitats have more slender bills than those inhabiting deciduous habitats. After removing the effects of historical legacy, we found strong support for adaptive interpretations of among-species variation in habitat selection and foraging site selection. Ecological variation along either of these two niche axes is associated with predictable morphological variation.

On Characterizing Foraging Versatility, Illustrated by Using Birds

Versatility in foraging behavior is a crucial component of several areas of behavioral and ecological research, including optimal foraging, ecomorphological studies, resource partitioning, and comparisons of guild structures. Unfortunately, the methods by which foraging versatility has been characterized in the past (e.g., Shannon-Wiener and inverse Simpson diversity indices) produce inconsistent results depending upon the degree to which workers split or lump categories of foraging manoeuvres. I refer to this problem as aliasing, by analogy to a similar difficulty that arises in signal processing in electrical engineering (...) A method is presented here to afford some protection against aliasing by using a new versatility index that explicitly accounts for dissimilarities between foraging classes

Ecomorphological pattern in Bermuda birds: The influence of competition and implications for nature preserves

Previous ecomorphological studies of introduced land birds on oceanic islands have revealed several patterns consistent with the hypothesis that interspecific competition influenced the assembly process of that community. We extend one of these analyses to Bermuda, which differs from the previous islands in its size, latitude and isolation from the mainland. We tested for the presence of morphological overdispersion in surviving introduced passeriforms. Despite a possible predominance of random events in the assembly process due to Bermuda's small size and the presence of migrant species, the surviving passeriforms were morphologically overdispersed. The presence of this pattern supports the hypothesis that the assembly of the Bermuda passeriform community has been influenced by interspecific competition. This marks the third distinct community of island land birds in which this competitive pattern has been identified. This is particularly interesting because certain attributes of Bermuda and its avifauna make it more equivalent to communities in mainland refuges than avian assemblages on islands studied previously. This suggests that interspecific competition may have important effects on the structure of refuge communities.

The ecomorphology of Bornean tree frogs (family Rhacophoridae)

Ecomorphological studies generally assume a causal relationship between morphology and ecology mediated by performance. That assumption was tested in a community of Bornean tree frogs of the family Rhacophoridae. Biomechanical models allow a priori predictions about expected intra- and interspecific correlations among toepad area, hind-limb length, body mass, sticking ability, jumping distance, microhabitat, vertical height and substrate. Both intra- and interspecifically, size and shape variables showed patterns of association with ecology predicted on the basis of maintaining relative as well as absolute levels of performance. Unexpectedly, the form-function relationship between toepad area and sticking ability differed intra- and interspecifically. These findings indicate the need for more empirical work examining morphology-performance relationships and their use in ecology.

Predation, seed size partitioning and the evolution of body size in seed-eating finches

I compare the relationship between bill size (depth) and body size among different taxa of seed-eating finches to test the hypothesis (Schluter, 1988a) that in habitats where seed-eating finches are vulnerable to predators, finches have larger bodies relative to their bill size. In support of this hypothesis, ground-foraging finches on continents (Emberizidae, Passeridae, Fringillidae), where predators are more common, have larger bodies relative to their bill sizes than do ground-foraging finches on islands (Emberizidae, Fringillidae). Ground-feeding finches on continents may also be more vulnerable to predators than tree- and shrub-foraging finches. As predicted, in North America, ground-feeding finches (Emberizinae) have larger bodies relative to their bill size than do tree- and shrub-foraging finches (Carduelinae). As a consequence of increased body size relative to bill size, both the range of possible bill sizes and potential seed sizes that can be eaten are reduced. Moreover, increased metabolic demands caused by larger body size may lessen the ability to specialize on a few seed types. These two factors reduce the potential for seed size partitioning. Consequently, vulnerability to predators may limit, and is inversely correlated with, seed size partitioning in seed-eating finch communities. The extent to which predation has influenced other bird communities may be considerable, and the patterns found by Schluter (1988a) and in this study indicate that future ecomorphological studies, especially on species that spend much of the day foraging, might profit by considering predator vulnerability as well as foraging behaviour.

Ecomorphology, Performance Capability, and Scaling of West Indian Anolis Lizards: An Evolutionary Analysis

Studies of ecomorphology–the relationship among species between morphology and ecology–contain two implicit and rarely tested hypotheses: (1) that morphological differences among species result in differences in performance capability at ecologically relevant tasks, which, in turn, produce differences in behavior and ecology; and (2) that morphology, performance capability, ecology and behavior have evolved synchronously. I tested these hypotheses using the Anolis lizards of Jamaica and Puerto Rico. I measured morphological and performance variables on recently caught lizards. Movement, display rate and microhabitat measurements were made on lizards observed in the field. Body size explained most of the variation in morphology and performance ability, but was not correlated with the ecological or behavioral variables. When the effect of body size is removed from the morphological and performance variables, the ecomorphological hypotheses were confirmed. Species that were similar morphologically were also similar in performance ability, ecology, and behavior. Evolutionary changes in morphology, performance, and ecology and behavior (ecobehavior) were correlated. The morphology–ecobehavior comparison revealed that: long—legged, heavy—bodied lizards jump farther in nature, jump and display more often, walk less often, and use wide perches that are distant from the nearest available perches; and that species with many subdigital lamellae perch lower, use narrower supports, and walk more frequently. Inclusion of performance parameters revealed a relationship, in agreement with biomechanical models, between body proportions and running and jumping capability; in turn, performance capability related to locomotor patterns and microhabitat use. Despite the relationship between lamellae number and ecobehavioral variables, clinging performance did not contribute to the correlations with either morphology or ecology.

Versatility and specialization in labrid fishes: ecomorphological implications.

The term "specialized" has been used to describe species that possess unique functional attributes and/or a narrow, stereotyped range of attributes, but there are few comparative functional analyses of specialists and generalists. If species with functional morphological specializations are capable of functioning over a broad range, the link between morphology and ecology may be relaxed under certain environmental conditions. In this study, high-speed films of jaw movements during prey capture were compared statistically for three coexisting coral reef fish species in the family Labridae, one trophic specialist and two trophic generalists. The trophic specialist possessed a unique functional feature related to the movement of the hyoid in the floor of the mouth, while the trophic generalists were not observed to possess any functional specializations. All three species showed functional versatility in that they were able to adjust their prey capture mechanism in response to the evasive potential of the prey. The functional versatility of trophic specialists has implications for ecomorphological studies, since species characterized as possessing unique functional or morphological features may demonstrate marked flexibility in ecological variables such as diet or foraging behavior, decreasing the likelihood of identifying correlations between morphology and ecology.

From Biologische Anatomie To Ecomorphology

Morphologists have been slow in realizing that the basic principles of Darwin's theory of evolution by natural selection meant that understanding the evolution of anatomical features must to be based on an analysis of how these structures interact with demands of the external environment on the organisms. An early, although largely forgotten, beginning can be found in Hans Boker's two volume work Vergleichendc Biologische Anatomic der Wirbeltiere. The real start of ecomorphology came only after the modern synthesis of evolutionary theory (1937-48) and the foundations of an experimental functional morphology in the 1950's. However, vertebrate ecomorphology had its origins in the 1960's within ecology, with little to no input from morphology. Ecology, ethology and descriptive plus functional morphology formed the major foundations for the new ecomorphology which has as its chief goals: (a) assessment of the adaptiveness of morphological features, and their comparison within taxa and communities; (b) explanation of the evolutionary history of features and groups of organisms; (c) understanding the composition of evolutionary communities and the diversity within taxonomic groups; and lastly (d) contribution to evolutionary theory associated with adaptation, macroevolution, and evolution of ecological systems. Ecomorphology is not synonymous with evolutionary morphology, but is a subdiscipline of the latter field. Proper ecomorphological study requires both laboratory and field work as it depends on thorough descriptive and functional morphology and a full understanding of the ecology of the organisms. These studies are best done as teamwork involving morphologists, ethologists and ecologists with extensive feed-back between the two groups during the course of any ecomorphological study.

Stochasticity in Stream Fish Communities: An Alternative Interpretation

Stochasticity in Stream Fish Communities: An Alternative Interpretation