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Journal Article•DOI•

Vigilance Behaviour in Grazing African Antelopes

R. Underwood1•
01 Jan 1982-Behaviour (Brill)-Vol. 79, Iss: 2, pp 81-107
TL;DR: Time spent looking varied with position within the group; this effect was strongest in closed habitats, where central animals tended to scan least and feed most, and within species, animals inclosed habitats, those with dense vegetation, tended to spend more time in looking than did animals in the open.
Abstract: African antelope may devote a large proportion of their foraging time to looking around. The factors affecting such vigilance behaviour are examined for grazing antelope, five species being studied in detail. The proportion of time spent looking decreased as species body weight increased. Within species, animals in closed habitats, those with dense vegetation, tended to spend more time in looking than did animals in the open. There was some evidence that vigilance, presumably for predators, was shared by group members, but in one species, impala, vigilance apparently increased with group size and with proximity to neighbours. Time spent looking varied with position within the group; this effect was strongest in closed habitats, where central animals tended to scan least and feed most. Vigilance increased as feeding success decreased, partly due to mutual interference between looking and feeding. The possible social, foraging and predator-detection values of vigilance are discussed. A simple model is introduced to help explain the effects of cover and to facilitate further discussion.
Citations
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Monograph•DOI•
27 Jun 2002
TL;DR: An adaptive resource ecology: foundation and prospects References Index.
Abstract: The adaptation of herbivore behaviour to seasonal and locational variations in vegetation quantity and quality is inadequately modelled by conventional methods. Norman Owen-Smith innovatively links the principles of adaptive behaviour to their consequences for population dynamics and community ecology, through the application of a metaphysiological modelling approach. The main focus is on large mammalian herbivores occupying seasonally variable environments such as those characterised by African savannahs, but applications to temperate zone ungulates are also included. Issues of habitat suitability, species coexistence, and population stability or instability are similarly investigated. The modelling approach accommodates various sources of environmental variability, in space and time, in a simple conceptual way and has the potential to be applied to other consumer-resource systems. This text highlights the crucial importance of adaptive consumer responses to environmental variability and is aimed particularly at academic researchers and graduate students in the field of ecology.

239 citations

Journal Article•DOI•
Neil B. Metcalfe1•
TL;DR: Turnstones, Arenaria interpres, and purple sandpipers, Calidris maritima, show very similar increases in the level of vigilance with decreasing visibility, but achieve these increases by different means: turnstones lengthen the duration of each vigilant scan, while purple Sandpipers scan more often.

238 citations


Cites background from "Vigilance Behaviour in Grazing Afri..."

  • ...However Underwood (1982) showed that antelopes increased their vigilance when in habitats he categorized as closed (i.e. with reduced visibility)....

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Journal Article•DOI•
TL;DR: Remote video cameras revealed both grazing and browsing fishes avoided high density patches, preferring relatively open areas with low macroalgal cover, which may provide a positive feedback leading to the growth and persistence of Macroalgal stands; increasing the stability of phase shifts to macroalgae.
Abstract: Coral reefs globally are in decline, with some reefs undergoing phase shifts from coral-dominance to degraded states dominated by large fleshy macroalgae. These shifts have been underpinned by the overharvesting of herbivorous fishes and represent a fundamental change in the physical structure of these reefs. Although the physical structure provided by corals is regarded as a key feature that facilitates herbivore activity, the influence of the physical structure of macroalgal stands is largely unknown. Using transplanted Sargassum, the largest coral reef macroalga, we created habitat patches of predetermined macroalgal density (0.25–6.23 kg m−2). Remote video cameras revealed both grazing and browsing fishes avoided high density patches, preferring relatively open areas with low macroalgal cover. This behaviour may provide a positive feedback leading to the growth and persistence of macroalgal stands; increasing the stability of phase shifts to macroalgae.

226 citations


Cites background from "Vigilance Behaviour in Grazing Afri..."

  • ...Alternatively, consumers may avoid complex habitats if their ability to detect predators is reduced (Underwood 1982; Riginos & Grace 2008) or the physical structure obstructs their movements, limiting access to preferred food resources (van de Koppel et al. 1996)....

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  • ...Alternatively, consumers may avoid complex habitats if their ability to detect predators is reduced (Underwood 1982; Riginos & Grace 2008) or the physical structure obstructs their movements, limiting access to preferred food resources (van de Koppel et al....

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Journal Article•DOI•
01 Aug 2008-Ecology
TL;DR: It is suggested that, for all but the largest species, top-down behavioral effects of predator avoidance on herbivores are mediated by tree density, which appears to have cascading effects on the herbaceous vegetation.
Abstract: Herbivores choose their habitats both to maximize forage intake and to minimize their risk of predation. For African savanna herbivores, the available habitats range in woody cover from open areas with few trees to dense, almost-closed woodlands. This variation in woody cover or density can have a number of consequences for herbaceous species composition, cover, and productivity, as well as for ease of predator detection and avoidance. Here, we consider two alternative possibilities: first, that tree density affects the herbaceous vegetation, with concomitant "bottom-up" effects on herbivore habitat preferences; or, second, that tree density affects predator visibility, mediating "top-down" effects of predators on herbivore habitat preferences. We sampled sites spanning a 10-fold range of tree densities in an Acacia drepanolobium-dominated savanna in Laikipia, Kenya, for variation in (1) herbaceous cover, composition, and species richness; (2) wild and domestic herbivore use; and (3) degree of visibility obstruction by the tree layer. We then used structural equation modeling to consider the potential influences that tree density may have on herbivores and herbaceous community properties. Tree density was associated with substantial variation in herbaceous species composition and richness. Cattle exhibited a fairly uniform use of the landscape, whereas wild herbivores, with the exception of elephants, exhibited a strong preference for areas of low tree density. Model results suggest that this was not a response to variation in herbaceous-community characteristics, but rather a response to the greater visibility associated with more open places. Elephants, in contrast, preferred areas with higher densities of trees, apparently because of greater forage availability. These results suggest that, for all but the largest species, top-down behavioral effects of predator avoidance on herbivores are mediated by tree density. This, in turn, appears to have cascading effects on the herbaceous vegetation. These results shed light on one of the major features of the "landscape of fear" in which African savanna herbivores exist.

224 citations


Cites background from "Vigilance Behaviour in Grazing Afri..."

  • ...In the Serengeti, Underwood (1982) found that wildebeest, impala, topi, and reedbuck all exhibited greater predator vigilance and, consequently, less forage intake, in areas with more woody vegetation....

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  • ...Because smaller herbivores are more susceptible to predation (Sinclair et al. 2003, Radloff and du Toit 2004) and exhibit greater anti-predator vigilance (Underwood 1982, Berger and Cunningham 1988), we would expect smaller-bodied species to prefer open areas more than larger-bodied species do....

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Journal Article•DOI•
Jens Krause1•
TL;DR: A general overview of position-related fitness differences in group-living animals is given for the first time and it is suggested that edge positions achieve a higher net-energy pay-off and should therefore be preferred by individuals with low energy reserves.
Abstract: 1. A general overview of position-related fitness differences in group-living animals is given for the first time. 2. Differential fitness returns in groups are often related to competition for resources among group members due to resource limitation. If resources are very scarce, then competition may finally lead to the disbandment of groups. The encounter-dilution effect predicts that grouping confers a benefit if the conspicuousness of large groups does not outweigh the dilution effect and each predator or parasite attacks only one (or a few) prey per encounter (Uetz & Hieber, 1993). While the encounter-dilution effect limits the number of predators and parasites a group is faced with at a given time, marginal predation and communal defence are probably the most important factors for position-related differences in predation risk. 3. Limitation of resources increases competition between groups members and should widen the gap between fitness returns of dominant and subordinate group members. In some group-living animals such as schooling fish, however, predator pressure has apparently selected for uniformity in morphology and behaviour which presumably restricts the potential for resource competition (Magurran & Seghers, 1991). 4. A general problem of assessing individual fitness returns in that different short-term strategies may achieve the same long term goals (Magurran, 1993). The use of feeding rates and predation risks as currencies for fitness returns over short time periods is therefore questionable and can only be a first step. So far, hardly any information is available on long-term effects of differences in positioning behaviour. 5. Food availability and food intake rates tend to be higher in edge positions, whereas energy expenditure does not differ significantly with group position in non-roosting mobile groups. This suggests that edge positions achieve a higher net-energy pay-off and should therefore be preferred by individuals with low energy reserves. 6. Differential predation risks are well documented for stationary and colony-breeding species, but there is a lack of data for mobile, non-breeding species. The reason for the latter is that predation is rarely observed (in the field) and often difficult to relate to group position in fast-moving species such as flocks of birds. Further studies, especially in the field, are needed. 7. Vigilance rates and attack rates do not necessarily give a true reflection of mortality risk. Vigilance is not exclusively related to predation and can be confounded by competition effects and hunger. Attack rates are difficult to translate into per capita risks if hardly any mortality is observed and therefore little information is available about the ratio of successful attacks/total attacks. 8. Most of the literature up to date consists of descriptive studies. There is a need for experimental work that investigate (a) the influence of predator attack mode on differential predation risks; (b) the influence of internal states (such as hunger) on the tradeoff between predation risk and foraging behaviour and its consequences for the positioning behaviour in groups; (c) the 'egalitarian' nature of groups with respect to group position. Do all individuals continuously rotate positions? Or do dominant individuals monopolize certain positions?, and (d) that separate the effects of nutritional state, vigilance and food availability on feeding rates in different group positions. 9. Reproductive success is often related to group position in breeding colonies and lekking animal species. Females probably prefer the safer territories in the group centre, but more empirical data are required to test this hypothesis. 10. Position-related differences in parasitism rate between group members are well documented with per capita rate of parasitism being lower in the centre of groups than at the periphery.(ABSTRACT TRUNCATED AT 400 WORDS)

219 citations

References
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Journal Article•DOI•
Jeanne Altmann1•
TL;DR: Seven major types of sampling for observational studies of social behavior have been found in the literature and the major strengths and weaknesses of each method are pointed out.
Abstract: Seven major types of sampling for observational studies of social behavior have been found in the literature. These methods differ considerably in their suitability for providing unbiased data of various kinds. Below is a summary of the major recommended uses of each technique: In this paper, I have tried to point out the major strengths and weaknesses of each sampling method. Some methods are intrinsically biased with respect to many variables, others to fewer. In choosing a sampling method the main question is whether the procedure results in a biased sample of the variables under study. A method can produce a biased sample directly, as a result of intrinsic bias with respect to a study variable, or secondarily due to some degree of dependence (correlation) between the study variable and a directly-biased variable. In order to choose a sampling technique, the observer needs to consider carefully the characteristics of behavior and social interactions that are relevant to the study population and the research questions at hand. In most studies one will not have adequate empirical knowledge of the dependencies between relevant variables. Under the circumstances, the observer should avoid intrinsic biases to whatever extent possible, in particular those that direcly affect the variables under study. Finally, it will often be possible to use more than one sampling method in a study. Such samples can be taken successively or, under favorable conditions, even concurrently. For example, we have found it possible to take Instantaneous Samples of the identities and distances of nearest neighbors of a focal individual at five or ten minute intervals during Focal-Animal (behavior) Samples on that individual. Often during Focal-Animal Sampling one can also record All Occurrences of Some Behaviors, for the whole social group, for categories of conspicuous behavior, such as predation, intergroup contact, drinking, and so on. The extent to which concurrent multiple sampling is feasible will depend very much on the behavior categories and rate of occurrence, the observational conditions, etc. Where feasible, such multiple sampling can greatly aid in the efficient use of research time.

12,470 citations

Journal Article•DOI•
TL;DR: An antithesis to the view that gregarious behaviour is evolved through benefits to the population or species is presented, and simply defined models are used to show that even in non-gregarious species selection is likely to favour individuals who stay close to others.

3,343 citations


Additional excerpts

  • ...The 'selfish herd' (HAMILTON, 1971)...

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Journal Article•DOI•
TL;DR: The paper describes different feeding styles among antelope, in terms of selection of food items and coverage of home ranges, and argues that these feeding styles bear a relationship to maximum group size of feeding animals through the influence of dispersion ofFood items upon group cohesion.
Abstract: 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.

2,088 citations


"Vigilance Behaviour in Grazing Afri..." refers background in this paper

  • ...Such habitat differences may have influenced the evolution of social and anti-predator behaviour in antelope (GEIST, 1974; JARMAN, 1974; ESTES, 1974) and may also affect both predator and prey behaviour on a day to day basis (SCHALLER, 1972; KRUUK, 1972; CURIO, 1976; EDMUNDS, 1974)....

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  • ...If scanning reduces predation, it may take up less of the large animals' time either because both the number and the range of potential predators are smaller (JARMAN, 1974; GEIST, 1974), or because these antelope, being found in large groups, either are (a) less easy for a predator to find, (b) share vigilance with other group members (CARACAO et al....

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  • ...The smaller and, according to JARMAN (1974), the more selective species are those which show significant correlations between the rate of looking and indices of feeding success, supporting the possibility that scanning forms a part of foraging behaviour....

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Journal Article•DOI•

1,193 citations

Book•
21 Sep 1976
TL;DR: This chapter discusses hunting for Prey, the Diversity of Hunting Methods, and the Motivation Underlying Feeding Responses of Predator-Prey Interactions.
Abstract: 1 Internal Factors.- A. Hunger: Expression through Overt behavior.- I. Predatory Schedules.- 1. Patterns of Satiation.- 2. Feast and Famine.- II. Hunger and Diel Rhythms.- III. The Ramification of Hunger Effects.- 1. Capture-eliciting Prey Stimuli.- 2. Search behavior.- IV. The Motivation Underlying Feeding Responses.- 1. Hunger Thresholds of Feeding Response Components.- 2. The Complexity of Predatory Motivation.- V. The Diversity of Foraging Tactics.- VI. Feeding Components Affected and not Affected by Hunger.- B. The Control of Feeding Responses by Factors Other than Hunger.- I. The Readiness to Hunt.- II. Prey Storing.- III. Providing Food for Dependent Family Members.- C. The Problem of Specific Hungers.- I. Switching of Prey.- II. The Prey-density Predation Curve.- III. Swamping the Appetite of Predators.- D. Daily and Annual Rhythms in Predator-Prey Interactions.- I. Daily Rhythm of Predation.- II. Daily Activity Patterns of the Prey.- III. Annual Rhythm of Predation.- 2 Searching for Prey.- A. Path of Searching and Scanning Movements.- B. Area-concentrated Search.- I. Short-term Area Concentration.- 1. Living Scattered and Area-concentrated Search.- 2. The Nature of the Path Changes.- 3. Search Behavior after the Disappearance of Prey.- II. Long-term Area Concentration.- III. One-prey : One-place Association.- C. Object-concentrated Search.- I. Existence and Properties of "Searching Image".- 1. Ecological Evidence.- 2. Experimental Evidence.- II. Social Facilitation of Searching Image Formation.- III. Searching Image and "Training Bias".- IV. Searching Image and Profitability of Hunting.- 1. Ecological Evidence for Profitability of Hunting.- 2. Experimental Evidence for Profitability of Hunting.- V. Prey-specific Expectation.- VI. Ecological Implications of Searching Image.- 3 Prey Recognition.- A. The Stimulus-specificity of Prey Capture.- I. Capture-eliciting Prey Stimuli.- II. Capture-inhibiting Prey Stimuli.- B. One-prey : One-response Relationships.- C. The Assessment of the Circumstances of a Hunt.- D. Prey Recognition by Prey-related Signals.- E. Prey Stimulus Summation.- F. Novelty Versus Familiarity.- I. The Rejection of Novel Prey.- II. Familiarization with Prey and Its Consequences.- G. The Multi-channel Hypothesis of Prey Recognition.- 4 Prey Selection.- A. Preying upon the Weak and the Sick.- B. Preying upon the Odd and the Conspicuous.- C. The Mechanics of Prey Selection.- D. Evolutionary Implications.- 5 Hunting for Prey.- A. Modes of Hunting.- I. Hunting by Speculation.- II. Stalking and Ambushing.- 1. Stalking.- 2. Ambushing.- III. Prey Attack under Disguise.- IV. Pursuit of the Prey.- 1. Changes of Velocity of Attack (Pursuit).- 2. Interception of the Flight Path.- 3. Counteradaptations of the Prey.- V. Exhausting Dangerous Prey.- VI. Insinuation.- VII. Scavenging and Cleptoparasitism.- 1. Modes and Extent.- 2. Cleptoparasitism and Competition.- 3. Counter-measures of the Robbed.- VIII. Tool-use.- IX. Mutilation.- B. The Diversity of Hunting Methods.- I. Prey-specific Methods.- II. Situation-specific Methods.- III. Mechanisms and Causes of Predatory Versatility.- 1. General.- 2. Individual Predatory Repertories.- 3. The Persistence of Individual Traits.- 4. Predatory Specialization and Structural Modification.- 5. Predatory Versatility in Relation to Prey Availability.- C. Behavioral Aspects of Hunting Success.- I. A Comparison of Hunting Success across Predator Species.- II. Variables Influencing Hunting Success within Predator Species.- III. Aspects of Communal Hunting.- 1. Modes and Properties of Communal Hunting.- 2. Factors Conducive to Communal Hunting.- 3. Benefits of Communal Hunting.- References.- Scientific Names of Animals and Plants.

919 citations


"Vigilance Behaviour in Grazing Afri..." refers background in this paper

  • ...Such habitat differences may have influenced the evolution of social and anti-predator behaviour in antelope (GEIST, 1974; JARMAN, 1974; ESTES, 1974) and may also affect both predator and prey behaviour on a day to day basis (SCHALLER, 1972; KRUUK, 1972; CURIO, 1976; EDMUNDS, 1974)....

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