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Abstract

Understanding the mechanisms of species coexistence within local assemblages can play a crucial role in conservation of a species. There is little understanding of how large mammalian bovid species from West Africa partition diet resources, and to what extent they may vary their diet and habitat selection seasonally in order to coexist. Here we studied an assemblage of eleven bovid species in Pendjari Biosphere Reserve, West Africa and used faecal stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) to test the impact of body mass diet partitioning at a seasonal scale. We found a significant positive relationship between isotopic niche similarity and body size similarity both in dry (p < 0.001) and wet (p < 0.001) season. Partitioning of carbon isotope niches is at least partly due to interactions amongst species rather than historical effects. Our findings also show numerous patterns in resource partitioning amongst the 11 bovid species studied, suggesting that different species used dietary resources in contrasting ways. In practice, actual resource competition between bovid species is difficult to demonstrate, but there exists much overlap in diet along the stable carbon isotope axis for most of the studied species. However we conclude that in our study area, especially in the wet season, niche breadth and diet overlap remain large. Abundant resources and low herbivore densities mean there is no need for herbivores to specialize, because they do not have to compete over scarce resources.

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... 4). Ungulate diets are influenced by habitats and associated forage availability (Djagoun et al. 2016), and substantial amounts of research has focussed on African ungulate feeding ecology and their associated evolutionary adaptations and diversification as well as their influence on ecosystem processes (du Toit 2003;Djagoun et al. 2016). Research on the relative consumption of graze and browse plant forms in the diets of both grazing and browsing African ungulates, of the same species, indicates variability across temporal and spatial scales. ...
... 4). Ungulate diets are influenced by habitats and associated forage availability (Djagoun et al. 2016), and substantial amounts of research has focussed on African ungulate feeding ecology and their associated evolutionary adaptations and diversification as well as their influence on ecosystem processes (du Toit 2003;Djagoun et al. 2016). Research on the relative consumption of graze and browse plant forms in the diets of both grazing and browsing African ungulates, of the same species, indicates variability across temporal and spatial scales. ...
Chapter
Grazers and browsers are adapted to survive and utilize forage in a wide range of different environments globally. There are major differences in the forage sources they utilize. These differences can be observed from a plant part’s chemical structure up to biome distribution in relation to global climate. As a result there are many differences as well as similarities in the feeding ecology of grazing versus browsing species. In this chapter we discuss these differences in terms of the functional response, how animals search for forage, patch choice, movement dynamics, migratory behaviour as well as habitat selection patterns.
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The South-to-North water diversion impacts on microbial community niche were investigated in the water receiving area. In this paper, the community structure, niche breadth and overlap of the dominant genus were determined to approach the distribution features of microbes and the community changes in Miyun Reservoir. Our results showed that before water transfer, the main bacteria phylum was Proteobacteria, Bacteroidetes, Cyanobacteria, Firmicutes and Actinobacteria. The niche breadth range (OMI value) of dominate bacteria genus was 0.01~0.54, and the tolerance value range was 0.55~4.56. After water transfer, Proteobacteria, Cyanobacteria, Actinobacteria, Bacteroidetes and Verrucomicrobia were the dominate phylum. The niche breadth range of dominate bacteria genus was 0.00~0.38, and the tolerance value range was 0.55~4.56. It indicated that after water diversion, the relative abundance of the Proteobacteria and Verrucomicrobia increased significantly (p<0.05), and the ecological niche of the genus Candidatus Methylacidiphilum, Chitinophagaceae and OM27 clade was significantly differentiated (p<0.05). The niche overlap results suggested that the inter-species niche competition becomes more intense after the water transfer, which reflected the different utilization ability of each bacteria genus in the new aquatic environment of the Miyun Reservoir.
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This study investigated composition and selectivity in diet for waterbuck in the Pendjari National Park in north-western Benin, through the use of micrographic analysis of faecal samples. Three plant species (Panicum anabaptistum, Echinochloa stagnina and Andropogon gayanus) were regularly consumed all year round. Meanwhile, three other species (i.e., Hyparrhenia involucrata, Acroceras amplectens and Oryza barthii) are mostly found in its diet during the beginning of the rainy season. During the dry season, long life grasses (>40%) and tree forage (about 35%) were the most dominant life form in the diet. On the contrary at the beginning of the rainy season, annual species (> 50%) were dominant. In conclusion, the waterbuck has a grazer regime when plant species are abundant and a mixed diet during the dry season. Waterbuck’s food niche breath, defined by Hespenheide [Ecology and Evolution of communities. Harvard Univ. Press, 1975], was lower than 1, implying this antelope does not eat all food categories in a proportional way. Shannon diversity index showed that the diet was more diversified during the rainy season and less diversified at the end of the dry season. Based on [Ecology, 64 (1983), 1297] diet selectivity index, waterbuck exerted a positive selection on the major graminaceous species.
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Although bovids have been studied for decades, debate still exists about their diets. To address this problem, we examined bovid dietary ecology through analysis of stable carbon isotopes. We analyzed tooth enamel, bone collagen, and hair from 312 individual bovids, representing 27 species from southern Africa. Although dietary information from the lit-erature is usually supported by this technique, our results and the literature are sometimes highly divergent. For instance, our results indicate that Taurotragus oryx and Raphicerus campestris eat less grass than is widely believed. Furthermore, contrary to most theoretical expectations, our data indicate no relationship between body size and percentage of mono-cots consumed by southern African Bovidae. Although many researchers have abandoned the idea that bovid soft-tissue anatomy is strongly indicative of diet, we demonstrate a strong relationship between the percentage of grass in a bovid's diet and several hard-tissue craniodental indices.
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Information on overlap in resource use is central to understanding of interspecific exploitation competition and resource partitioning. Despite this, measures of diet overlap among northern ruminants in Fennoscandia is limited to one earlier study (reindeer and sheep). Diet overlap between sympatric moose and roe deer calculated with Schoener’s index was 20.7% and 33.6% during summer (data from one area) and winter (data from two areas), respectively, whereas average diet overlap between moose and red deer was 32.0% during winter (data from four areas). Diet overlap between a coastal island population of red deer and sheep was 59.3% during summer and 63.9% during winter. Summer diet overlap between a sheep and a goat population and a sheep and a reindeer population calculated with data on main types of forage plants was 77.0% and 55.1%, respectively. However, overlap calculated with main plant groups was sometimes considerably higher than when calculated for individual forage species. Neither difference in feeding type nor body mass successfully predicted diet overlap between species pairs (n=9), although there tended to be negative correlation (r p =–0.586, P=0.098) between diet overlap of main plant groups (calculated across studies) and difference in feeding type.
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Ecologists still search for common principles that predict well-known responses of biological diversity to different factors. Such factors include the number of available niches in space, productivity, area, species' body size and habitat fragmentation. Here we show that all these patterns can arise from simple constraints on how organisms acquire resources in space. We use spatial scaling laws to describe how species of different sizes find food in patches of varying size and resource concentration. We then derive a mathematical rule for the minimum similarity in size of species that share these resources. This packing rule yields a theory of species diversity that predicts relations between diversity and productivity more effectively than previous models. Size and diversity patterns for locally coexisting East African grazing mammals and North American savanna plants strongly support these predictions. The theory also predicts relations between diversity and area and between diversity and habitat fragmentation. Thus, spatial scaling laws provide potentially unifying first principles that may explain many important patterns of species diversity.
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Over the past 30 years or so, research effort in behaviour and ecology has progressed from simple documentation of the habits or habitats of differ­ ent species to asking more searching questions about the adaptiveness of the patterns of behaviour observed; moved from documenting simply what occurs, to trying to understand why. Increasingly, studies of behav­ iour or ecology explore the function of particular responses or patterns of behaviour in individuals or populations - looking for the adaptiveness that has led to the adoption of such patterns either at a proximate level (what environmental circumstances have favoured the adoption of some particular strategy or response from within the animal's repertoire at that specific time) or at an evolutionary level (speculating upon what pres­ sures have led to the inclusion of a particular pattern of behaviour within the repertoire in the first place). Many common principles have been established - common to a wide diversity of animal groups, yet showing some precise relationship between a given aspect of behaviour or population dynamics and some particular ecological factor. In particular, tremendous advances have been made in understanding the foraging behaviour of animals - and the 'decision rules' by which they seek and select from the various resources on offer - and patterns of social organization and behaviour: the adap­ tiveness of different social structures, group sizes or reproductive tactics.
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Niche theory suggests differential use of shared resources facilitates coexistence of species in a community. In this study we used the faecal stable isotope analysis with observations along transect lines perpendicular to the Pendjari River. This was to examine seasonal habitat features and diet partitioning between two sympatric bovid species waterbuck (Kobus ellipsiprymnus) and western kob (Kobus kob) in the Pendjari Biosphere Reserve. In support of niche partition hypothesis, diets of western kob and waterbuck diverged significantly along both faecal selection axes (δ¹³C and δ¹⁵N) during the resource-limited period of the dry season as opposed to wet season when there is resource abundance. Western kob and waterbuck resource partitioning does not occur only on the basis of diet segregation but also some habitat variables play an important role in the coexisting system. Findings support the niche partition hypothesis, where morphologically, ecologically and closely related sympatric species segregate at least in one of the niche dimensions to allow coexistence. The two bovid species were observed to diverge largely along distance to water source gradient. The results provided empirical evidence that habitat features acts as an additional dimension over which herbivores partition resources.
Article
Background: Theories of density-dependent habitat selection provide two solutions for co-existence of competing species. The niche compression hypothesis predicts that species reduce their respective niche breadths in response to inter-specific competition. Alternatively, if the species have similar resource preferences, the subordinate species may be forced to expand its niche to incorporate secondary resources. Aim: Determine whether grazing ungulate species partition the resource by compression or expansion of dietary niches. Organisms: Black wildebeest (Connochaetes gnou) and blue wildebeest (C. taurinus). Methods: Stable carbon and nitrogen isotope analysis of faeces. Isotopic niche breadths are compared across allopatric and sympatric wildebeest populations in South African grasslands. Results: Stable carbon and nitrogen isotope niche breadths of the two wildebeest species were virtually identical. In sympatry, however, black wildebeest had a narrower δ13C niche breadth (indicating almost exclusive use of C4 grass), whereas blue wildebeest had a wider δ13C niche breadth (indicating significant contributions from C3 sources). Blue wildebeest also had a wider δ15N niche breadth than sympatric black wildebeest. Moreover, the δ13C niche breadths of sympatric black wildebeest and blue wildebeest were narrower and wider, respectively, than those of allopatric populations of either species. Conclusions: Isotope niche dynamics across allopatric and sympatric populations arise due to the combined effects of competition and habitat heterogeneity on resource use. Although results for black wildebeest resemble niche compression, this hypothesis cannot explain patterns observed in blue wildebeest. Expansion of the blue wildebeest niche, and restricted niche breadth of black wildebeest, is consistent with predictions of a shared preference model in which black wildebeest are the dominant competitor. When competition is operating, differences in the way species use secondary resources can have an important role in structuring grazer assemblages.
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Examined white-tailed deer Odocoileus virginianus ochrourus, Rocky Mountain wapiti Cervus elaphus nelsoni and Shiras moose Alces alces shirasi during consecutive severe and mild winters in NW Montana. The cervids were distributed unevenly among 3 segments of the study area that partitioned elevational and snow-depth gradients, and among vegetation communities. Habitat preferences were predictable on the basis of body size, energy expenditures and nutritional requirements. Cervids were ranked white-tailed deer-wapiti-moose, in order of increasing body size and affinities for open canopy, deep snow, and dense shrubs. Wapiti also favoured grass-dominated communities when snow did not limit foraging options. White-tailed deer and wapiti fed on dwarf evergreen shrubs and grasses, respectively, although deep snow restricted diet selection during the severe winter. Moose were browse specialists, and favoured deciduous shrubs more and coniferous browse less during a mild winter. Interspecific and annual comparisons of niche overlap provided little evidence that resource partitioning resulted from interspecific competition: 1) trophic and ecological overlap between species was greatest during nutritionally restrictive winters; 2) overlap was greater between similar-sized cervids than between species of dissimilar body size; 3) species pairs with the greatest trophic overlap did not exhibit compensatory spatial divergence. Large overlap in resource use, which increased during severe winter periods, suggested possible temporary interspecific competition between white-tailed deer and wapiti and between moose and wapiti. -from Authors
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The prime object of this book is to put into the hands of research workers, and especially of biologists, the means of applying statistical tests accurately to numerical data accumulated in their own laboratories or available in the literature.
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We present a synthesis of diet information for all 78 species of extant African Bovidae (excluding goats and sheep), based on an extensive survey of the literature. We compiled data on food types (percentages of fruits, dicotelydons, and monocotyledons), seasonal and geographic variability, and body mass. Information reported in the literature was evaluated critically to assess its reliability. We performed cluster analyses to identify 6 discrete dietary strategies: frugivores, browsers, generalists, browser-grazer intermediates, variable grazers, and obligate grazers. We identified a positive correlation between an increase in the proportion of monocots in the diet and body mass, and a negative correlation between increases in proportions of dicots and fruits and body mass. We found some degree of correspondence between taxonomic groupings and dietary strategies. Species in the tribes Alcelaphini, Hippotragini, and Reduncini have high proportions of monocots in their diets. Cephalophini, with the exception of Sylvicapra, are frugivores. Tragelaphini and Neotragini, with the exception of Ourebia, have diets that include high proportions of dicots.
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This field guide begins with a checklist. The main part of the volume consists of entries for each species. Each entry provides information on common names, measurements, recognition, geographical distribution (plus map), habitat, diet, behaviour, adaptations and conservation status. Illustrations are also included. Brief notes are also provided on the African environment (physical, climate and vegetation) and palaeoecology (habitats and species). Finally a short section examines African wildlife conservation.
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This article discusses the usefulness of niche overlap and niche overlap measures in studying competition. It is argued that (1) neither niche overlap nor niche overlap measures can be used to estimate the intensity of competition, but (2) niche overlap can be used to determine the relative amounts of inter- and intraspecific competition, while niche overlap measures are not useful in this regard. Before using overlap to estimate the relative intensities of inter- and intraspecific competition, it is necessary to have a model of the consumer-resource interaction, and some knowledge of the parameters in that model. The niche overlap and competition coefficient formulae proposed by Hurlbert (1978) are considered in some detail. Previously proposed niche overlap measures appear to be more useful than Hurlbert"s if one is interested in using the niche overlap measure for purely descriptive purposes.
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We propose a hypothesis for digestive constraints on the browsing and grazing options available to ruminants: that the diet-niche range (maximum and minimum grass intake) of a species is dependent upon its predisposition to stratified rumen contents, based on observations that this characteristic is a critical step towards enhanced fibre digestion and greater fluid throughput. We compare a physiological (heterogeneity of ingesta fluid content) and an anatomical (the intraruminal papillation pattern) measure with dietary evidence for a range of African and temperate species. Both measures are strongly related to the mean percentage of grass in species’ natural diets, as well as to the maximum and minimum levels of grass intake, respectively. The nature of these effects implies a stratification-level threshold, below which a species will not use a grass-based diet, but above which grass consumption can increase exponentially. However, above this threshold, a minimum percentage of grass in the diet is a prerequisite for optimal performance. We argue that this second constraint is crucial, as it depicts how a greater fluid throughput reduces potential for detoxification of plant secondary compounds, and therefore limits the maximum amount of browse a stratifying species will consume.
Article
We tested the reliability of herbivore faecal δ13C and δ15N values for reconstructing diet through review of an extensive database derived from a 3-year study of ungulates in South Africa's Kruger National Park. Faeces are a useful material for stable isotope studies of diet because they record dietary turnover at very short time scales, and because sampling is non-invasive. However, the validity of faecal isotope proxies may be questioned because they represent only undigested food remains. Results from Kruger Park confirm that free-ranging browsers have faecal δ13C consistent with C3 feeding, grazer faeces are C4, and mixed-feeder faeces intermediate. Although the respective ranges do not overlap, there is significant variation in faecal δ13C of browsers and grazers (∼2.0–4.0‰) across space and through time. We demonstrate that most (∼70%) of this variation can be ascribed to corresponding patterns of variation in the δ13C of C3 and C4 plants, respectively, re-enforcing the fidelity of faecal isotope proxies for diet but highlighting a need for mixing models that control for variations in plant δ13C in order to achieve accurate diet reconstructions. Predictions for the effects of climate (rainfall) and ecophysiology on 15N-abundance variations in mammals do not persist in faeces. Rather, faecal δ15N tracks changes in plant δ15N, with further fractionation occurring primarily due to variations in dietary protein (reflected by %N). Controlling for these effects, we show that a dual-isotope multiple source mixing model (Isosource) can extend diet reconstructions for African savanna herbivores beyond simplified C3/C4 distinctions, although further understanding of variations in mammal δ15N are needed for greater confidence in this approach.
Article
Differences in allometric scaling of physiological characters have the appeal to explain species diversification and niche differentiation along a body mass (BM) gradient - because they lead to different combinations of physiological properties, and thus may facilitate different adaptive strategies. An important argument in physiological ecology is built on the allometries of gut fill (assumed to scale to BM(1.0)) and energy requirements/intake (assumed to scale to BM(0.75)) in mammalian herbivores. From the difference in exponents, it has been postulated that the mean retention time (MRT) of digesta should scale to BM(1.0-0.75)=BM(0.25). This has been used to argue that larger animals have an advantage in digestive efficiency and hence can tolerate lower-quality diets. However, empirical data does not support the BM(0.25) scaling of MRT, and the deduction of MRT scaling implies, according to physical principles, no scaling of digestibility; basing assumptions on digestive efficiency on the thus-derived MRT scaling amounts to circular reasoning. An alternative explanation considers a higher scaling exponent for food intake than for metabolism, allowing larger animals to eat more of a lower quality food without having to increase digestive efficiency; to date, this concept has only been explored in ruminants. Here, using data for 77 species in which intake, digestibility and MRT were measured (allowing the calculation of the dry matter gut contents (DMC)), we show that the unexpected shallow scaling of MRT is common in herbivores and may result from deviations of other scaling exponents from expectations. Notably, DMC have a lower scaling exponent than 1.0, and the 95% confidence intervals of the scaling exponents for intake and DMC generally overlap. Differences in the scaling of wet gut contents and dry matter gut contents confirm a previous finding that the dry matter concentration of gut contents decreases with body mass, possibly compensating for the less favorable volume-surface ratio in the guts of larger organisms. These findings suggest that traditional explanations for herbivore niche differentiation along a BM gradient should not be based on allometries of digestive physiology. In contrast, they support the recent interpretation that larger species can tolerate lower-quality diets because their intake has a higher allometric scaling than their basal metabolism, allowing them to eat relatively more of a lower quality food without having to increase digestive efficiency.
Book
Isotopes are forms of an element that differ in the number of neutrons. Isotopes function as natural dyes or colors, generally tracking the circulation of elements. Isotopes trace ecological connections at many levels, from individual microbes to whole landscapes. Isotope colors mix when source materials combine, and in a cyclic process that ecologists can appreciate, the process of isotope fractionation takes the mixed material and regenerates the sources by splitting or fractionating the mixtures. Elements and their isotopes circulate in the biosphere at large, but also in all smaller ecological plant, animal, or soil systems. Chapter 3 reviews this circulation for each of the HCNOS elements, then gives four short reviews that may stimulate you to think about how you could use isotopes in your own ecological research.
Article
Summary • A negative relationship between water availability and the abundance of 15N relative to 14N (expressed as 15N) in the bone collagen of herbivores has been widely reported. However, the relative importance of dietary 15N and animal metabolism in producing this effect remains unclear. • To evaluate the relative importance of these two factors, we examined variation in 15N of both grass foliage and kangaroo (Macropus spp.) bone collagen. We assessed whether the offset between grass and bone collagen 15N was constant with respect to water availability. • An index of water availability (annual actual evapotranspiration/annual potential evapotranspiration) explained a considerable proportion of the variation in both grass 15N (R2 = 0·40) and bone collagen 15N (R2 = 0·57), and the slopes of these negative relationships were similar, with a near-constant 15N offset between grass foliage and bone collagen. • This finding suggests that dietary 15N is the main cause of the negative relationship between kangaroo bone collagen 15N and water availability, with metabolic factors having little discernible effect. Functional Ecology (2006) 20, 1062–1069 doi: 10.1111/j.1365-2435.2006.01186.x
Article
The types of social organisation displayed by the African antelope species have been assigned in this paper to five classes, distinguished largely by the strategies used by the reproductively active males in securing mating rights, and the effects of those strategies on other social castes. The paper attempts to show that these strategies are appropriate to each class because of the effects of other, ecological, aspects of their ways of life. The paper describes different feeding styles among antelope, in terms of selection of food items and coverage of home ranges. It argues that these feeding styles bear a relationship to maximum group size of feeding animals through the influence of dispersion of food items upon group cohesion. The feeding styles also bear a relationship to body size and to habitat choice, both of which influence the antelope species' antipredator behaviour. Thus feeding style is related to anti-predator behaviour which, in many species, influences minimum group size. Group size and the pattern of movement over the annual home range affect the likelihood of females being found in a given place at a given time, and it is this likelihood which, to a large extent, determines the kind of strategy a male must employ to achieve mating rights. The effects of the different strategies employed by males can be seen in such aspects of each species' biology as sexual dimorphism, adult sex ratio, and differential distribution of the sexes.
Article
Comparison of the feeding strategy of buffalo, wildebeest Connochaetes taurinus, Burchell's zebra Equus burchelli and elephant Loxodonta africana was carried out in Lake Manyara Nation Park, Tanzania. Especially during the dry season, elephant are time-limited and, presumably to alleviate a shortage in energy intake, switch from grazing to browsing. Zebra and wildebeest show very high grazing times during the day and have very little resting time during the dry season. If these 2 species are time-limited at that time of the year, it appears to be due to predation risk at night. Buffalo are not time-limited, and show 2 foraging strategies: an option in which they emphasize bulk feeding, and one in which selection is stressed. They appear to be resource-limited. All 4 species show a remarkable correspondence in the proportion of time they spend on food collection. On a yearly basis, amount of time spent on foraging plus moving approximate 80% of their (day) time. Nevertheless, the feeding strategies of these species are different although they inhabit the same environment and face the same sort of shortages. -Authors
Article
Digestion, especially of plant material, is a time-dependent process. In herbivores, an increase in food intake is usually correlated to an acceleration of ingesta passage through the gut, and could hence depress digestive efficiency. Therefore, the nature of the relationship between food intake and ingesta passage (i.e. whether the increase in ingesta passage due to the increase in food intake is mild or drastic) should determine the flexibility of the feeding strategy of herbivore and omnivore species. Using two megaherbivore groups, the elephants and the hippopotamuses, as examples from opposing ends of the range of potential adaptations to this problem, we demonstrate that the species-specific relationship of food intake and ingesta passage can precisely predict feeding ecology and activity budgets. In hippos, the distinct acceleration in ingesta passage due to increased intake limits the additional energy gained from eating more forage, and explains the comparatively low food intake and short feeding times generally observed in these animals. In elephants, increased food intake only leads to a very moderate increase of ingesta passage, thus theoretically allowing to optimize energy gain by eating more, which is in accord with the high food intake and long feeding times observed in these animals. We suggest that the characterization of the intake-passage relationship in herbi- and omnivorous species is of much higher ecological relevance than the determination of a supposedly species-specific “passage time/mean retention time”.
Article
Niche segregation among three small antelopes - red duiker, common duiker and suni - was investigated in a coastal savanna woodland/forest mosaic. It was expected that these similar-sized concentrate selectors would show differentiation in diet choice to decrease competition. Diet composition did not vary significantly among the different vegetation types. For all three antelope species, the number of dietary items was large, with a minimum of 70 different food items per species. Dietary specialization was low, with only 10% of the food items being exclusively used by each of the species. The ranks of food items were positively correlated among species in the wet season, but not in the dry season. Diet breadth significantly decreased in the dry season. The use of exclusive species was significantly larger in the dry season with lowest values recorded for the common duiker. Diet overlap in the wet season was considerable, but significantly decreased in the dry season, the time of food scarcity. The dry season data showed evidence for niche segregation, although this was not based on displacement. As niche segregation in the dry season was coupled to a random apportionment of diet items among antelope species, it cannot be interpreted as the result of competitive displacement.
Article
A review is made of the ruminant digestive system in its morphophysiological variations and adaptations relating to foraging behaviour, digestive physiology, to interactions between plants and ruminants and to geographic and climatic diversity of ruminants' ecological niches. Evidence is provided for evolutionary trends from an extreme selectivity mainly for plant cell contents and dependence upon a fractionated fore- and hindgut fermentation, to an unselective intake of bulk roughage subjected to an efficient plant cell wall fermentation, mainly in the forestomachs. The review is based on detailed comparative morphological studies of all portions of the digestive system of 65 ruminant species from four continents. Their results are related to physiological evidence and to the classification of all extant ruminants into a flexible system of three overlapping morphophysiological feeding types: concentrate selectors (40%), grass and roughage eaters (25%) and intermediate, opportunistic, mixed feeders (35%). Several examples are discussed how ruminants of different feeding types are gaining ecological advantage and it is concluded that ruminants have achieved high levels of digestive efficiency at each evolutionary stage, (including well-documented seasonal adaptations of the digestive system) and that ruminant evolution is still going on. Deductions made from the few domesticated ruminant species may have, in the past, biased scientific evaluation of the free-ranging species' ecology. The main threat to a continuous ruminant evolution and diversity appears to be man's neglect for essential ecological interactions between wild ruminants and their specific habitats, which he alters or destroys.
Article
Variations in nitrogen isotope ratios in terrestrial foodwebs are described, and alternative models for variation in the enrichment between trophic levels are evaluated. Nitrogen isotope ratios in bone collagen have been used to determine trophic levels and differentiate marine from terrestrial resource consumption among prehistoric humans. However, recent research in terrestrial ecosystems has revealed significant variation in nitrogen isotope ratios between habitats, and within trophic levels in the same environment. Foodwebs in hot, arid environments tend to have higher nitrogen isotope ratios than cool, wet ones. Within ecosystems, the stepwise enrichment between trophic levels is often greater in hot, arid environments. Within ecosystems, herbivore species with physiological adaptations to water conservation have higher nitrogen isotope ratios than water-dependent species. The nitrogen isotope ratios of human bones may be affected by climate and physiology and thus cannot be directly compared between different types of ecosystems without first determining the isotopic composition of the local foodweb and the stepwise enrichment between trophic levels.
Article
In order to establish baseline nitrogen isotope data for certain African ecosystems, we have measured the of some 300 marine and terrestrial organisms. The majority of these specimens come from the southwestern Cape, and were chosen to represent a cross-section of the foods important in prehistoric diets in the region. δ15N analyses of 78 Holocene human skeletons from the same area are interpreted in the light of these results. Additional terrestrial animal samples were collected from the northern and eastern Cape and from Botswana and Malawi. They represent a wide range of climatic and environmental zones, from semi-desert to sub-tropical swamps. The patterning in the values for marine organisms is consistent with previously published data; that for terrestrial organisms, however, is more complex than recent studies have indicated. Our data confirm the proposal that animal δ15N values vary with rainfall: high δ15N values for herbivores occur in areas receiving less than 400 mm of rain per annum. We critically examine a recently proposed model explaining this phenomenon, and suggest some additional mechanisms which should be considered. In such arid areas, nitrogen isotope ratios cannot be used as indicators, but may provide some indication of the trophic level of the food consumed. Dietary studies on human populations can only be undertaken with a thorough appreciation of the isotopic ecology of the relevant foodweb.
Article
A major focus in population ecology is understanding factors that limit rare species. We used stable isotope approaches to diet to determine whether remaining rare antelope populations in Kruger National Park (KNP), South Africa experience i) nutritional stress; ii) competition with sympatric bulk grazers; iii) reduced habitat heterogeneity. Rare species consumed near-pure C4 grass-based diets throughout the seasonal cycle, in contrast to field observations that reported significant levels of C3 consumption (browse) by these taxa. This finding, coupled with low faecal %N at the height of the dry season, may indicate nutritional stress, but recent isotopic studies of the same species elsewhere in Africa suggest that field observations overestimated levels of browse consumption. We find little evidence for diet niche overlap between rare antelope with bulk grazing species. This partitioning of resources (interpreted mainly as tall- versus short-grass grazing, respectively), is consistent with reported differences in observed diet, and comparative oral morphology. Last, we find less seasonal diet variations amongst bulk grazers feeding in rare antelope habitats compared with other landscapes. We propose that loss of functional heterogeneity, apparently brought about by high densities of artificial waterholes, limits recovery of diet- and habitat-selective rare antelope populations in KNP.
Article
The gut capacity of mammalian herbivores increases linarly with body weight. This relationship, coupled with the change in basal metabolism with weight, produces an MR/GC ratio (metabolic requirement/gut capacity) that decreases with increasing body size. Since the retention of a food particle within the gut is proportional to this ratio, the extent to which food particles are digested will be related to body size. The fiber fraction of plant material is digested slowly and exclusively by microbial symbiotes. A positive relationship between the fiber content of plant parts and their biomass is used to describe a resource axis on which digestion rate is the scaling variable. In response to this resource axis and metabolic requirements, the fiber content of the diet of herbivores increases with body size. Ruminants are the predominant medium-sized herbivores in East Africa, while nonruminants are mainly small or very large animals. Small herbivores are constrained to rapid passage of ingesta by their high MR/GC ratio and have evolved hindgut fermentation and feed selectively on rapidly digestible (low-fiber) foods. Both responses contribute to loss of nutrients (synthesized by gut microbes) in the feces, and thus contribute to coprophagy in this group. Ruminants must rely almost entirely on the production of microbial volatile fatty acids for energy and postruminal digestion of microbes for other nutrients. With decreasing body size, the increasing rate at which energy must be produced per unit volume of the rumen cannot be matched by a concomitant increase in the fermentation rate of forages. Nonruminants are favored by the more efficient energy transfer of enzymatic digestion in the foregut of the low-fiber foods often required by small animals.-from Authors
Article
Stable isotope analysis has emerged as one of the primary means for examining the structure and dynamics of food webs, and numerous analytical approaches are now commonly used in the field. Techniques range from simple, qualitative inferences based on the isotopic niche, to Bayesian mixing models that can be used to characterize food-web structure at multiple hierarchical levels. We provide a comprehensive review of these techniques, and thus a single reference source to help identify the most useful approaches to apply to a given data set. We structure the review around four general questions: (1) what is the trophic position of an organism in a food web?; (2) which resource pools support consumers?; (3) what additional information does relative position of consumers in isotopic space reveal about food-web structure?; and (4) what is the degree of trophic variability at the intrapopulation level? For each general question, we detail different approaches that have been applied, discussing the strengths and weaknesses of each. We conclude with a set of suggestions that transcend individual analytical approaches, and provide guidance for future applications in the field.
Article
We assess whether interspecific differences in craniodental morphology within a single ruminant feeding guild, the grazers, represent anatomical adaptations to subtle differences in diet. Differences in craniodental anatomy follow a distinct taxonomic pattern that is paralleled by dietary niche differentiation recorded in species' stable carbon (δ13C) and nitrogen isotope (δ15N) compositions, strongly supporting a hypothesis for functional divergence within the grazers. We propose that the evolutionary origin of grazers were multifold; at least two and up to four different types of grazing can be discerned within the 11 taxa studied here alone. However, correspondence between craniodental adaptations and isotopic differences across species are not found when only δ13C data are considered (i.e. morphological differences do not reflect varying proportions of C3 browse to C4 grass consumed). This implies that alternate anatomical adaptations to grazing are not related to differences between variable (part-time browsing) and obligate grazers, as previously predicted. Rather, anatomical differences correlate strongly with changes in δ15N, which we infer to reflect functional responses to changes in diet quality associated with the degree of feeding selectivity and short-, medium-, or tall-grass grazing.
Article
Digestion, especially of plant material, is a time-dependent process. In herbivores, an increase in food intake is usually correlated to an acceleration of ingesta passage through the gut, and could hence depress digestive efficiency. Therefore, the nature of the relationship between food intake and ingesta passage (i.e. whether the increase in ingesta passage due to the increase in food intake is mild or drastic) should determine the flexibility of the feeding strategy of herbivore and omnivore species. Using two megaherbivore groups, the elephants and the hippopotamuses, as examples from opposing ends of the range of potential adaptations to this problem, we demonstrate that the species-specific relationship of food intake and ingesta passage can precisely predict feeding ecology and activity budgets. In hippos, the distinct acceleration in ingesta passage due to increased intake limits the additional energy gained from eating more forage, and explains the comparatively low food intake and short feeding times generally observed in these animals. In elephants, increased food intake only leads to a very moderate increase of ingesta passage, thus theoretically allowing to optimize energy gain by eating more, which is in accord with the high food intake and long feeding times observed in these animals. We suggest that the characterization of the intake-passage relationship in herbi- and omnivorous species is of much higher ecological relevance than the determination of a supposedly species-specific "passage time/mean retention time".