Correlation of relative muzzle width and relative incisor width with dietary preference in ungulates

Qualitative observations suggest that grazing ungulates have relatively broader muzzles than browsing ones, and that grazers have incisors that are all of a similar size, as opposed to the large central and smaller lateral incisors seen in browsers. These differences may be correlated respectively with the need for grazing ungulates to maintain a large daily intake, or for browsing ungulates to forage selectively in a stand of vegetation. Quantitative examination of relative muzzle width and incisor width ratio in 95 species of living ungulates, correlated with seven different types of dietary preferences, substantiated these observations, although phylogenetic history may exhort a strong influence on morphological proportions. For example, equids have relatively narrower muzzles than grazing ruminants despite their less selective mode of feeding. The narrowest relative muzzle widths are not found in regular browsers, but in high level browsers and in mixed feeders in open habitats. Incisor width ratio can distinguish grazers from browsers, but can not be used to discriminate mixed feeders from other feeding types, and grazers appear to have incisors that are relatively broader overall than those of other dietary types, in correlation with their relatively broader muzzles.     

Phylogenetic analysis of stomach adaptation in digestive strategies in African ruminants

The stomach morphology of 28 species of artiodactyls that differ in feeding style (browser, mixed feeder, grazer) was analysed using a multivariate approach and phylogenetic correction in order to test whether stomach morphology was correlated with feeding style when body mass was controlled for. A total of 25 morphological traits of the stomach were used in the analysis. After the effects of body mass and phylogeny on stomach morphology were taken into account, there was no significant grouping of species according to feeding style. When information about the feeding style of each species was included in the analysis, the set of morphological traits separated the mixed feeders from the other two feeding styles, but grazers and browsers had similar morphological features. Most of the variance in stomach morphology was explained by body mass and a lesser proportion by phylogeny. The main morphological features that have previously been proposed as being adaptations in grazing species, namely, lengthening of the retention time of ingesta to achieve an increase in their fibre digestion capability by means of a larger relative stomach capacity, a greater subdivision of chambers and smaller openings, are not supported by the findings of this study. Thus, there is no consistent evidence to support a significant adaptive effect of stomach morphology to different diets in the Artiodactyla.     

The functional relationship between feeding type and jaw and cranial morphology in ungulates

The relationship between jaw and skull morphology and feeding type (grazer, mixed feeder, browser, frugivorous, omnivorous) was analysed in 94 species of extant ungulates. A total of 21 morphological traits of the jaw and skull (17 and 4, respectively) were analysed using analysis of covariance, with body mass as covariate. To take into account the phylogenetic effect, simulations were generated under the Brownian motion model of character evolution. Analysis of covariance was applied to these simulations and the simulated F-ratios were used to assess the signification of the F-ratios for the real values of the traits. The feeding types had a weak effect on ungulate cranial and jaw morphology in comparison with the phylogenetic effect, since, before phylogeny correction, the analysis of covariance showed statistically significant differences associated with feeding type in 15 out of the 21 traits analysed. After controlling for phylogeny, only 2 significant traits remained, the length of the coronoid process and the occipital height. Omnivorous species had shorter coronoid processes than grazers or mixed feeders, and the occipital height was greater in the omnivorous species than in the grazers, mixed feeders or browsers. The coronoid process is involved in the generation of bite force, being the effective moment arm of the temporalis muscle, and occipital height is positively related to the force exerted by the temporalis muscle. This result matches the hypothesis that species with a toughness diet should show higher bite force (“toughness” describes the resistance of a material to being mechanically broken down). When the omnivorous species were excluded from the analysis, no differences in jaw and skull morphology were detected between the rest of the feeding types. Received: 1 September 1998 / Accepted: 2 November 1998     

The effect of season, sex and feeding style on home range area versus body mass scaling in temperate ruminants

Sex-specific estimates of the summer and winter home range area of 19 species of temperate ruminants were collated from the literature. It was predicted that there should be a shallower slope for the home range area against body mass relationship during winter than during summer, as large ruminants can meet more of their energy requirements from the fat reserves deposited during summer than small ruminants. Consequently, relatively large species do not need to range as widely during winter. There was a significant positive relationship between body mass and summer and winter home range area in both females and males. This relationship remained significant when analysed within feeding styles (browser, mixed feeder, grazer), except in mixed feeders in winter. As predicted, slope estimates were significantly lower during winter (b=0.59) than during summer (b=1.28), both before and after controlling for phylogeny. After controlling for phylogeny, browsers had a steeper slope (summer: b=1.48; winter: b=1.07) of the home range area against body mass relationship than did mixed feeders (summer: b=0.75; winter: b=-0.11) or grazers (summer: b=1.10; winter: b=0.34). There was no effect of sex after body mass was controlled for. The effect of season, sex and feeding style on the home range area versus body mass relationship in temperate ruminants is discussed.     

Adaptation of ruminants to browse and grass diets: are anatomical-based browser-grazer interpretations valid?

As a result of pioneering work of Hofmann (1973, 1989), nutritional ecologists classify ruminants into three feeding-type categories: browsers (concentrate feeders), grazers, and intermediate or mixed feeders. Hofmann proposed that these feeding types result from evolutionary adaptations in the anatomy of the digestive system and that one consequence is shorter retention of the digesta in the rumen of browsers, and thus a decreased efficiency of fiber digestion relative to that of grazers. We examined the hypotheses that (1) fiber digestion of browsers is lower than that of grazers, (2) salivary gland size is larger in all browsers than in grazers, (3) the browser's larger salivary glands produce larger volumes of thin serous saliva than those of grazers, and (4) thus, browsers have higher liquid passage rates than do grazers. We found that the extent of fiber digestion is not significantly different between browsers and grazers, although fiber digestion is positively related to herbivore size. In general, salivary gland size is approximately 4 times larger in browsers than grazers, but some browsers (e.g., greater kudu) have small, grazer-sized salivary glands. Resting (non-feeding or ruminating) saliva flow rates of mule deer (browser) and domestic sheep and cattle (grazers) were not significantly different from each other. Finally, ruminal liquid flow rates were not different between feeding types. We conclude that many of Hofmann's nutritional and physiological interpretations of anatomical differences amongst ruminants are not supportable.     

The relationship between ecological segregation and sexual body size dimorphism in large herbivores

Ecological segregation (sexual differences in diet or habitat use) in large herbivores has been intimately linked to sexual body size dimorphism, and may affect both performance and survival of the sexes. However, no one has tested comparatively whether segregation occurs at a higher frequency among more dimorphic species. To test this comparatively, data on sex-specific diet, habitat use and body size of 40 species of large herbivores were extracted from the literature. The frequency of ecological segregation was higher among more dimorphic herbivores; however, this was only significant for browsers. This provides the first evidence that segregation is more common among more dimorphic species. The comparative evidence supported the nutritional-needs hypothesis over the incisor breadth hypothesis, as there was no difference in frequency of segregation between seasons with high and low resource levels, and since segregation was also evident among browsers. Whether the absence of a correlation between ecological segregation and level of sexual body size dimorphism for intermediate feeders and grazers is due to biological differences relative to browsers or to the fact that the monomorphic species included in the analysis were all browsers is discussed. Received: 18 August 1999 / Accepted: 31 January 2000     

The evolution of phylogenetic differences in the efficiency of digestion in ruminants

This study investigates, for the first time (to our knowledge) for any animal group, the evolution of phylogenetic differences in fibre digestibility across a wide range of feeds that differ in potential fibre digestibility (fibre to lignin ratio) in ruminants. Data, collated from the literature, were analysed using a linear mixed model that allows for different sources of random variability, covariates and fixed effects, as well as controlling for phylogenetic relatedness. This approach overcomes the problem of defining boundaries to separate different ruminant feeding styles (browsers, mixed feeders and grazers) by using two covariates that describe the browser-grazer continuum (proportion of grass and proportion of browse in the natural diet of a species). The results indicate that closely related species are more likely to have similar values of fibre digestibility than species that are more distant in the phylogenetic tree. Body mass did not have any significant effect on fibre digestibility. Fibre digestibility is estimated to increase with the proportion of grass and to decrease with the proportion of browse in the natural diet that characterizes the species. We applied an evolutionary model to infer rates of evolution and ancestral states of fibre digestibility; the model indicates that the rate of evolution of fibre digestibility accelerated across time. We suggest that this could be caused by a combination of increasing competition among ruminant species and adaptation to diets rich in fibre, both related to climatically driven environmental changes in the past few million years.     

THE SHAPE OF CONTENTION: ADAPTATION,HISTORY, AND CONTINGENCY IN UNGULATE MANDIBLES

Mandibles and teeth of ungulates have been extensively studied to discern the functional significance of their design. Grazing ungulates have deeper mandibles, longer coronoid processes, flatter incisor arcades, and more hypsodont molars in comparison to browsers. If the functional significance of both mandible and teeth shapes is well‐established, it remains uncertain to what extent mandible shapes are really adapted to grazing, meaning that they evolved either to serve their current biological function or just as a structural requirement to accommodate higher crowned molars. Here, we address this question by studying the contribution of phylogeny, hypsodonty, and body size to mandibular shape variation. The mandible shape appeared to be significantly influenced by hypsodonty but not by body size. Interestingly, hypsodonty‐related changes influenced the tooth row in artiodactyls and perissodactyls significantly but in the opposite directions, which is ultimately related to their different digestive strategies. Yet, we obtained a strong phylogenetic effect in perissodactyls, suggesting that their mandible shape should be strongly inherited. The strength of this effect was not significant within artiodactyls (where hypsodonty explained much more variance in mandible shape). Digestive strategy is deemed to interplay with hypsodonty to produce different paths of adaptation to particular diets in ungulates.     

Comparing ungulate dietary proxies using discriminant function analysis

A variety of tooth‐wear and morphological dietary proxies have been proposed for ungulates. In turn, they have been applied to fossil specimens with the purpose of reconstructing the diets of extinct taxa. Although these dietary proxies have been used in isolation and in combination, a consistent set of statistical analyses has never been applied to all of the available datasets. The purpose of this study is to determine how well the most commonly used dietary proxies classify ungulates as browsers, grazers, and mixed feeders individually and in combination. Discriminant function analysis is applied to individual dietary proxies (hypsodonty, mesowear, microwear, and several cranial dietary proxies) and to combinations thereof to compare rates of successful dietary classification. In general, the tooth‐wear dietary proxies (mesowear and microwear) perform better than morphological dietary proxies, though none are strong proxies in isolation. The success rates of the cranial dietary proxies are not increased substantially when ruminants and bovids are analyzed separately, and significance among the three dietary guilds is reduced when controlling for phylogenetic relatedness. The combination of hypsodonty, mesowear, and microwear is found to have a high rate of successful dietary classification, but a combination of all commonly used proxies increases the success rate to 100%. In most cases, mixed feeders bear the greatest resemblance to browsers suggesting that a morphology intermediate to browsers and grazers may represent a fitness valley resulting from the inability to exploit both browse and graze efficiently. These results are important for future paleoecological studies and should be used as a guide for determining which dietary proxies are appropriate to the research question. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Geometric morphometrics of mandibles for dietary differentiation of Bovidae (Mammalia: Artiodactyla)

The mammalian family Bovidae has been widely studied in ecomorphological research, with important applications to paleoecological and paleohabitat reconstructions. Most studies of bovid craniomandibular features in relation to diet have used linear measurements. In this study, we conduct landmark-based geometric-morphometric analyses to evaluate whether different dietary groups can be distinguished by mandibular morphology. Our analysis includes data for 100 species of extant bovids, covering all bovid tribes and 2 dietary classifications. For the first classification with 3 feeding categories, we found that browsers (including frugivores), mixed feeders, and grazers are moderately well separated using mandibular shape. A finer dietary classification (frugivore, browser, browser–grazer intermediate, generalist, variable grazer, and obligate grazer) proved to be more useful for differentiating dietary extremes (frugivores and obligate grazers) but performed equally or less well for other groups. Notably, frugivorous bovids, which belong in tribe Cephalophini, have a distinct mandibular shape that is readily distinguished from all other dietary groups, yielding a 100% correct classification rate from jackknife cross-validation. The main differences in mandibular shape found among dietary groups are related to the functional needs of species during forage prehension and mastication. Compared with browsers, both frugivores and grazers have mandibles that are adapted for higher biomechanical demand of chewing. Additionally, frugivore mandibles are adapted for selective cropping. Our results call for more work on the feeding ecology and functional morphology of frugivores and offer an approach for reconstructing the diet of extinct bovids.     

Paleoenvironment of Dryopithecus brancoi at Rudabánya, Hungary: evidence from dental meso- and micro-wear analyses of large vegetarian mammals

The environment of the hominoid Dryopithecus brancoi at Rudabánya (Late Miocene of Hungary) is reconstructed here using the dietary traits of fossil ruminants and equids. Two independent approaches, dental micro- and meso-wear analyses, are applied to a sample of 73 specimens representing three ruminants: Miotragocerus sp. (Bovidae), Lucentia aff. pierensis (Cervidae), Micromeryx flourensianus (Moschidae), and one equid, Hippotherium intrans (Equidae). The combination of meso- and micro-wear signatures provides both long- and short-term dietary signals, and through comparisons with extant species, the feeding styles of the fossil species are reconstructed. Both approaches categorize the cervid as an intermediate feeder engaged in both browsing and grazing. The bovid Miotragocerus sp. is depicted as a traditional browser. Although the dental meso-wear pattern of the moschid has affinities with intermediate feeders, its dental micro-wear pattern also indicates significant intake of fruits and seeds. Hippotherium intrans was not a grazer and its dental micro-wear pattern significantly differs from that of living browsers, which may suggest that the fossil equid was engaged both in grazing and browsing. However, the lack of extant equids which are pure browsers prevents any definitive judgment on the feeding habits of Hippotherium. Based on these dietary findings, the Rudabánya paleoenvironment is reconstructed as a dense forest. The presence of two intermediate feeders indicates some clearings within this forest; however the absence of grazers suggests that these clearings were most likely confined. To demonstrate the ecological diversity among the late Miocene hominoids in Europe, the diet and habitat of Dryopithecus brancoi and Ouranopithecus macedoniensis (Greece) are compared.     

Dental fast track: Prenatal enamel growth,incisor eruption,and weaning in human infants

Correlation between the timing of permanent first molar eruption and weaning age in extant primates has provided a way to infer a life history event in fossil species, but recent debate has questioned whether the same link is present in human infants. Deciduous incisors erupt at an age when breast milk can be supplemented with additional foods (mixed feeding), and weaning is typically complete before permanent first molars erupt. Here, I use histological methods to calculate the prenatal rate by which enamel increases in thickness and height on human deciduous incisors, canines, and molars (n = 125). Growth trajectories for each tooth type are related to the trimesters and assessed against the eruption sequence and final crown height. Analyses show that central incisors initiate early in the second trimester with significantly faster secretion rates relative to canines and second molars, which initiate closer to birth. Even though initial extension rates were correlated with crown height and scaled with positive allometry within each tooth class, the relatively short incisors still increased in height at a significantly faster rate than the taller canines and molars. The incisor prenatal “fast track” produces a greater proportion of the crown before birth than all other tooth types. This growth mechanism likely facilitates early incisor eruption at a time when the mixed feeding of infants can be initiated as part of the weaning process. Findings provide a basis from which to explore new links between developmental trends along the tooth row and mixed feeding age in other primates. Am J Phys Anthropol 156:407–421, 2015. © 2014 Wiley Periodicals, Inc.     

Quantifying rapid spatial and temporal variations of CO<Subscript>2</Subscript> fluxes from small,lowland freshwater ponds

In Lake Tanganyika, several lineages of cichlids have diversified into 200 species. Tribe Tropheini contains the greatest richness of herbivorous species that are classified into four ecomorphs: grazers, browsers, suckers, and pickers. All of these ecomorphs coexist on littoral rocky shores. To reveal the differences among species within ecomorphs, we analysed fish shape and functional morphology related to feeding habits, using geometric morphometrics, and measured intestine length. Furthermore, we tested the relationship between genetic and morphological distances. As a result, diversities of functional morphology among ecomorphs, and among species within ecomorphs, were revealed. In grazers, morphological diversity was greatest in jaws and the opening direction of mouth, suggesting that these species have adapted to feed on various substrata. In browsers, intestine length varied among species, indicating that this ecomorph consists of species with various specializations in herbivory. Morphological divergence was found only in the mandible and occlusal facet in grazers. No clear relation was found between morphological and phylogenetic distances in browsers, which are a polyphyletic group, indicating that their traits were acquired by convergence in multiple lineages. Our data suggest that the observed morphological variation among species enable sympatric species to separate their feeding niches.     

The functional significance of the browser-grazer dichotomy in African ruminants

The allometric relationships for the fermentation rate of dry matter, the total energy concentration of volatile fatty acids (VFAs), the energy supplied from VFA production and the mass of the digesta contents within the rumen or caecum and proximal colon (hindgut) were used to test whether the digestive strategies of grazing and browsing African ruminants differ. The wet and dry mass of the contents of the rumen and hindgut were allometrically related to body mass (BM). These relationships did not differ between browsing and grazing ruminants. The fermentation rates in the rumen were strongly allometric and the intercepts of the relationships did not differ between browsers and grazers. The fermentation rates in the hindgut were not allometrically related to BM and did not differ between ruminants with different feeding habits. Likewise, the total energy concentration of the VFAs in the rumen and hindgut showed no allometric scaling and did not differ between browsing and grazing ruminants. The energy supplied by VFA production in both the rumen and hindgut of African ruminants scaled at around 0.8 with BM. Only in the case of the energy supplied by VFAs in the rumen were there significantly different intercepts for browsing and grazing ruminants. The energy supplied by VFA production in the rumen was inadequate to meet the energy requirements for maintenance of browsers and small grazers. The retention time of digesta in the alimentary tract was positively related to BM although there was no difference in the allometric relationships for grazers and browsers. The results of these analyses suggest that, after controlling for the effects of body mass, there is little difference in digestive strategy between African ruminants with different morphological adaptations of the gut.     

Drought‐response strategies of savanna herbivores

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Tooth wear in captive wild ruminant species differs from that of free-ranging conspecifics

The mesowear method evaluates the wear patterns of herbivore cheek teeth by visually evaluating the facet development of the occlusal surfaces. It thus allows classification of most herbivorous ungulates into browsers, grazers or intermediate feeders, due to the fact that in grazers, tooth wear is characterized by a comparatively high degree of abrasion, most probably due to the presence of silicacious phytoliths in grasses, a higher amount of dust and grit adhering to their forage, or both. It has been suggested that excessive tooth wear could be a particularly limiting factor in the husbandry of captive large browsing species, and major tooth wear was demonstrated in captive as compared to free-ranging giraffe. If this increased tooth wear in captivity was an effect of feeding type and diets fed, then it would be expected that other browsing species are affected in a similar manner. In order to test this hypothesis, we investigated the dental mesowear pattern in captive individuals of 19 ruminant species and compared the results to data on free-ranging animals. Compared to free-ranging populations, captive browsers show a significantly more abrasion-dominated tooth wear signal. The reverse applies to captive grazers, which tend to show a less abrasion-dominated wear in captivity. Captive ruminants were generally more homogenous in their wear signature than free-ranging ruminants. If grit contamination in the natural habitat is a major cause of dental wear in grazers, then diets in captivity, although similar in botanical composition, most likely contain less abrasives due to feeding hygiene. If dental wear is one of the major factors limiting longevity, then captive grazers should achieve longer lifespans than both captive browsers and free-ranging grazers. In particular with respect to browsers, the results suggest that captive feeding regimes could be improved.     

Extinctions of herbivorous mammals in the late Pleistocene of Australia in relation to their feeding ecology: No evidence for environmental change as cause of extinction

Abstract There has been debate over the cause of the extinction of ‘megafauna’ species during the late Pleistocene of Australia. One view is that environmental change, either natural or human‐induced, was the main factor in the extinctions. Some support for this comes from the observation that, among herbivores, most of the species that went extinct were apparently browsers rather than grazers. Browsers would presumably have been more dependent on shrubland and woodland habitats than grazers, and it has been argued that such habitats might have contracted in response to aridity or changed fire regimes in the late Pleistocene. Here, we test this idea by comparing extinction rates of browsers and grazers in the late Pleistocene, controlling for body mass in both groups. We show that in both browsers and grazers the probability of extinction was very strongly related to body mass, and the body mass at which extinction became likely was similar in the two groups. It is true that more browsers than grazers went extinct, but this is largely because most very large herbivores in the late Pleistocene were browsers, not because large browsers were more likely to go extinct than similarly sized grazers. This result provides evidence against some forms of environmental change as a cause of the extinctions.     

Higher masseter muscle mass in grazing than in browsing ruminants

Using cranioskeletal measurements, several studies have generated evidence that grazing ruminants have a more pronounced mastication apparatus, in terms of muscle insertion areas and protuberances, than browsing ruminants, with the resulting hypothesis that grazers should have larger, heavier chewing muscles than browsers. However, the only investigation of this so far [Axmacher and Hofmann (J Zool 215:463-473, 1988)] did not find differences between ruminant feeding types in the masseter muscle mass of 22 species. Here, we expand the dataset to 48 ruminant species. Regardless of phylogenetic control in the statistical treatment, there was a significant positive correlation of body mass and masseter mass, and also a significant association between percent grass in the natural diet and masseter mass. The results support the concept that ruminant species that ingest more grass have relatively larger masseter muscles, possibly indicating an increased requirement to overcome the resistance of grass forage. The comparative chewing resistance of different forage classes may represent a rewarding field of ecophysiological research.     

Effects of grass and browse consumption on the winter mass dynamics of elk

Much of the research into herbivore ecology and evolution has focused on patterns and mechanisms of niche partitioning in the diets of specialized grazers and browsers, but the significance of the balance of grazing and browsing within intermediate feeders present unique questions that have received less attention. We explored the nutritional effects of varying the balance of grass and browse in the winter diets of elk (Cervus elaphus). We compiled published data from three similar studies that monitored the mass dynamics of captive elk fed diets of pure grass, pure browse or 1 of 14 mixed diets in winter feeding trials. Elk lost mass (up to 22% of initial body weight) in 29 of 33 feeding trials, similar to wild elk in winter. We used regression models of mass dynamics, considering the linear, quadratic or logarithmic effects of the proportion of the diet that was grass (≈1 − proportion of the diet that was browse) and the additive and interactive effects of nitrogen intake. Diet composition had strong effects on mass dynamics, and all models explained ≥73% of the variation (adjusted r ²) in mass dynamics. Nitrogen intake had uniformly positive effects on mass balance, and increasing grass intake caused improved maintenance of body mass up to a point, but further increases in the proportion of grass in the diet had neutral or negative effects on body mass. Overall, the data suggest that elk are adapted to consuming mixed diets. Nonetheless, data on the foraging behavior and diet selection of wild elk in many populations show that elk often consume grass-dominated diets and sometimes consume browse-dominated diets, but rarely consume mixed diets. Physiological adaptations to mixed diets may place unique spatio-temporal constraints on diet selection in intermediate feeders and impose large penalties for a sub-optimal balance of grazing and browsing.     

A comparison of food habits of two sympatric ruminants of Mt. Yatsugatake,central Japan: sika deer and Japanese serow

Comparison of food habits of sympatric animals provides understanding of interspecific relations. Previous studies of food habits of the two ruminants of Japan, sika deer (Cervus nippon) and Japanese serows (Capricornis crispus), have shown that sika deer are variable, and they are gazers in northern Japan, but browsers in southern Japan, whereas Japanese serows are browsers. However, these studies described the food habits of each species separately, and no study has compared the food habits of these species living in sympatry. Therefore, we examined these species on Mt. Yatsugatake, central Japan, using microhistological analyses and nutritional analyses of feces. Sasa nipponica, a dwarf bamboo, predominated in the fecal composition of sika deer, whereas both S. nipponica and dicotyledonous plants were found in the feces of Japanese serows. Crude protein levels of serow feces were higher than those of deer. The particle sizes of plant fragments in serow feces were smaller than those in deer feces, suggesting that serow fed more selectively on digestible plants than deer did. These results support the suggestions of previous studies conducted in different habitats and show that sika deer are less selective grazers, and Japanese serows are more selective browsers. Thus, food differences are likely explained by the feeding ecophysiology of the animals and not habitat differences.