Browsing

Distribution by Scientific Domains

Kinds of Browsing

  • deer browsing


  • Selected Abstracts


    Browsing in a heterogeneons savanna

    ECOGRAPHY, Issue 5 2000
    C. Skarpe
    Large herbivores generally depend on and interact with a food resource that is heterogeneous at different spatial scales. Plants allocate resources to rapid growth or to defence mechanisms depending on the availability of resources relative to loss of resources from herbivory. Herbivores select food and feeding habitats in order to maximize intake rate of nutrients and digestible energy, while avoiding chemical and structural deterrents. To optimize foraging, herbivores select habitats and food items in a hierarchical way, and different attracting and deterring factors may govern selection at different scales. We studied the impact of twig biting by a guild of indigenous browsers in three vegetation types in a semi-arid savanna in Botswana. The heaviest browsing pressure was in the vegetation type richest in preferred plant species, although that type was also richest in defended species. There were large differences in relative utilization between plant species, and ranking of species was roughly similar in the different vegetation types. Browsing pressure varied between species from almost 0-30%. Overall, spinescent trees were less browsed than non-spinescent ones, and evergreen species were less browsed than deciduous ones. In two of the three vegetation types there was a negative correlation between browsing pressure on a species and its frequency. There was a high incidence of rebrowsing, and once a tree had been browsed, the probability that it would be browsed again increased. The results largely agree with predictions based on the resource availability hypothesis, the scarcity accessibility hypothesis and recent theories on the significance of plant defences and on plant's response to browsing and the subsequent response by herbivores on the plant's responses. [source]


    Browsing, Bouncing, Murdering, and Mooring

    JOURNAL OF ARCHITECTURAL EDUCATION, Issue 1 2005
    Negotiating the Relationship Between Inhabitation, Representation
    This paper presents the theoretical context and results of an advanced research seminar, Visualizing Information in Space, Time, and Motion, that explores the production of space with respect to the spatial inhabitation of our built environment, strategies of representation, and the research, analysis, synthesis, and construction of notation communicating perceived aspects of space, time, and motion. [source]


    The intraruminal papillation gradient in wild ruminants of different feeding types: Implications for rumen physiology

    JOURNAL OF MORPHOLOGY, Issue 8 2009
    Marcus Clauss
    Abstract Browsing and grazing ruminants are thought to differ in the degree their rumen contents are stratified,which may be due to different characteristics of their respective forages, to particular adaptations of the animals, or both. However, this stratification is difficult to measure in live animals. The papillation of the rumen has been suggested as an anatomical proxy for stratification,with even papillation indicating homogenous contents, and uneven papillation (with few and small dorsal and ventral papillae, and prominent papillae in the atrium ruminis) stratified contents. Using the surface enlargement factor (SEF, indicating how basal mucosa surface is increased by papillae) of over 55 ruminant species, we demonstrate that differences between the SEFdorsal or SEFventral and the SEFatrium are significantly related to the percentage of grass in the natural diet. The more a species is adapted to grass, the more distinct this difference, with extreme grazers having unpapillated dorsal and ventral mucosa. The relative SEFdorsal as anatomical proxy for stratification, and the difference in particle and fluid retention in the rumen as physiological proxy for stratification, are highly correlated in species (n = 9) for which both kind of data are available. The results support the concept that the stratification of rumen contents varies among ruminants, with more homogenous contents in the more browsing and more stratified contents in the more grazing species. J. Morphol., 2009. © 2009 Wiley-Liss, Inc. [source]


    Latent demand and the browsing shopper

    MANAGERIAL AND DECISION ECONOMICS, Issue 3-4 2000
    Peter E Earl
    This article explores ways of making sense of unplanned purchases on shopping expeditions without seeing shopping as lacking any systematic foundations or reflecting some kind of pathology. The analysis employs both introspection and inputs from cognitive science and focuses on shifts from planned search to browsing in response to promotional cues encountered whilst navigating malls that are designed to promote browsing behaviour. Browsing is examined both in terms of its socio-psychological foundations and with respect to a variety of kinds of latent demand. The economic psychology of attention is examined as are a variety of factors that bring browsing processes to a close. The paper concludes with a discussion of the significance of the analysis in terms of the path dependence of economic systems. Copyright © 2000 John Wiley & Sons, Ltd. [source]


    Vegetation Control Treatments to Favor Naturally Regenerated Betula alleghaniensis Saplings Following Seed-Tree Cut: Sapling Monitoring Two Years after Treatment

    RESTORATION ECOLOGY, Issue 4 2007
    Daniel Bouffard
    Abstract Control of competing vegetation is recommended to ensure successful Yellow birch (Betula alleghaniensis Britton) regeneration within juvenile stands that do not sustain high enough sapling densities of this species. Four contrasting vegetation control treatments were tested to determine their effect on the growth and vigor of eight-year-old B. alleghaniensis saplings regenerating after final cutting of a shelterwood seed cut. Vegetation control treatments were TC (total circular removal), PC (circular removal of codominant competing vegetation), TS (total semicircular removal on 180° section), and NC (no vegetation control). Two years after treatment application, diameter growth significantly improved in response to vegetation control treatments, whereas sapling height growth did not. This pattern of biomass allocation was directly related to sapling etiolation, which increased with decreasing severity of vegetation removal. As a result, application of vegetation control, especially TC and PC treatments, was valuable in reducing signs of stress in saplings. However, increasing the severity of vegetation removal also made saplings more conspicuous to herbivores, which increased browsing, especially in the TC and PC treatments. Browsing was sufficient in some plots of the TC and PC treatments to overcome the vigor and diameter growth enhancements observed when browsing was negligible. In contrast to the TC and PC treatments, the TS treatment kept browsing very low while largely removing competition. The results suggest that B. alleghaniensis saplings established after final cutting of a shelterwood seed cut do take advantage of vegetation control treatments, but the decision to apply these treatments must include consideration of local herbivore population densities. [source]


    The Ecology of Browsing and Grazing

    AUSTRAL ECOLOGY, Issue 2 2010
    BEN MOORE
    No abstract is available for this article. [source]


    Integrating Web-Based Documents, Shared Knowledge Bases, and Information Retrieval for User Help

    COMPUTATIONAL INTELLIGENCE, Issue 1 2000
    Doug Skuce
    We describe a prototype system, IKARUS, with which we investigated the potential of integrating web-based documents, shared knowledge bases, and information retrieval for improving knowledge storage and retrieval. As an example, we discuss how to implement both a user manual and an online help system as one system. The following technologies are combined: a web-based design, a frame-based knowledge engine, use of an advanced full-text search engine, and simple techniques to control terminology. We have combined graphical browsing with several unusual forms of text retrieval,for example, to the sentence and paragraph level. [source]


    Browsing in a heterogeneons savanna

    ECOGRAPHY, Issue 5 2000
    C. Skarpe
    Large herbivores generally depend on and interact with a food resource that is heterogeneous at different spatial scales. Plants allocate resources to rapid growth or to defence mechanisms depending on the availability of resources relative to loss of resources from herbivory. Herbivores select food and feeding habitats in order to maximize intake rate of nutrients and digestible energy, while avoiding chemical and structural deterrents. To optimize foraging, herbivores select habitats and food items in a hierarchical way, and different attracting and deterring factors may govern selection at different scales. We studied the impact of twig biting by a guild of indigenous browsers in three vegetation types in a semi-arid savanna in Botswana. The heaviest browsing pressure was in the vegetation type richest in preferred plant species, although that type was also richest in defended species. There were large differences in relative utilization between plant species, and ranking of species was roughly similar in the different vegetation types. Browsing pressure varied between species from almost 0-30%. Overall, spinescent trees were less browsed than non-spinescent ones, and evergreen species were less browsed than deciduous ones. In two of the three vegetation types there was a negative correlation between browsing pressure on a species and its frequency. There was a high incidence of rebrowsing, and once a tree had been browsed, the probability that it would be browsed again increased. The results largely agree with predictions based on the resource availability hypothesis, the scarcity accessibility hypothesis and recent theories on the significance of plant defences and on plant's response to browsing and the subsequent response by herbivores on the plant's responses. [source]


    Wolves, trophic cascades, and rivers in the Olympic National Park, USA

    ECOHYDROLOGY, Issue 2 2008
    Robert L. Beschta
    Abstract Gray wolves (Canis lupus) were extirpated in the early 1900s from the Olympic Peninsula of northwestern Washington. Thus, we studied potential cascading effects of wolf removal by undertaking a retrospective study of Roosevelt elk (Cervus elaphus) populations, riparian forests, and river channel morphology. For three riparian sites within the western portion of Olympic National Park, the age structure of black cottonwood and bigleaf maple indicated a pattern of significantly decreased recruitment (growth of seedlings/sprouts into tall saplings and trees) associated with intensive elk browsing in the decades following the loss of wolves. At a riparian site outside the park, which represented a refugium from elk browsing, cottonwood recruitment has been ongoing during the 20th century, indicating that climate and flow regimes, in the absence of intensive herbivory, have not limited the establishment and growth of this deciduous woody species. Using 1994 orthophotos, we also measured channel dimensions and planform morphology of 8-km-long river reaches at each vegetation sampling site and an additional reach outside the park. Channels inside the park versus those outside the park had greater percent braiding (37 vs 2%) and larger ratios of active channel width/wetted width (3·0 vs 1·5 m/m). Results for western Olympic National Park were consistent with a truncated trophic cascade hypothesis whereby ungulate browsing following the extirpation of wolves caused significant long-term impacts to riparian plant communities which, in turn, allowed increased riverbank erosion and channel widening to occur. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    The importance of ecological research for ecosystem management: The case of browsing by swamp wallabies (Wallabia bicolor) in commercially harvested native forests

    ECOLOGICAL MANAGEMENT & RESTORATION, Issue 1 2004
    Julian Di Stefano
    Summary Ecosystem management often proceeds within the context of sub-optimal relationships between ecologists and ecosystem managers, and management outcomes could be improved with greater collaboration between members of these disciplines. This paper identifies an ecosystem management problem resulting from the interaction between timber harvesting and browsing wallabies, and this case study is used to exemplify how ecological data and expertise can contribute to the process of ecosystem management. It is argued that appropriate use of existing ecological data, establishment of strategic new research and the implementation of management actions as experimental hypothesis tests can facilitate achievement of management objectives, but greater collaboration between ecologists and managers is required before this can occur. Reasons for sub-optimal relationships are outlined, and the potential for structural change within large State-run ecosystem management agencies to improve interactions between managers and ecologists is discussed. [source]


    Importance of rhizodeposition in the coupling of plant and microbial productivity

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2003
    Eric Paterson
    Summary Plant roots influence the biological, chemical and physical properties of rhizosphere soil. These effects are a consequence of their growth, their activity and the exudation of organic compounds from them. In natural ecosystems, the linkages between inputs of carbon from plants and microbial activity driven by these inputs are central to our understanding of nutrient cycling in soil and the productivity of these systems. This coupling of plant and microbial productivity is also of increasing importance in agriculture, where the shift towards low-input systems increases the dependence of plant production on nutrient cycling, as opposed to fertilizers. This review considers the processes by which plants can influence the cycling of nutrients in soil, and in particular the importance of organic inputs from roots in driving microbially mediated transformations of N. This coupling of plant inputs to the functioning of the microbial community is beneficial for acquisition of N by plants, particularly in low-input systems. This occurs through stimulation of microbes that produce exoenzymes that degrade organic matter, and by promoting cycling of N immobilized in the microbial biomass via predation by protozoa. Also, plants increase the cycling of N by changes in exudation in response to nitrogen supply around roots, and in response to browsing by herbivores. Plants can release compounds in exudates that directly affect the expression of genes in microbes, and this may be an important way of controlling their function to the benefit of the plant. [source]


    Mortality in seedling populations of Silver Birch: genotypic variation and herbivore effects

    FUNCTIONAL ECOLOGY, Issue 5 2003
    K. Prittinen
    Summary 1Variation among mature plants reflects mortality that has occurred during the seedling phase. Our earlier studies have shown variation in resistance to insect and vole herbivory among Silver Birch genotypes that represent variation in a naturally regenerated birch stand. The aim of this study was to examine whether seedling mortality varied among these genotypes, and whether insect and field vole herbivory affected mortality. The 20 genotypes studied competed with each other in dense stands, which were randomly assigned to insect and vole exposure and fertilization treatments. 2Insect herbivory and fertilization increased mortality significantly (by 98 and 68%, respectively). The fertilization effect was probably due to accelerated self-thinning among fast-growing seedlings. Although vole browsing removed considerable biomass, it did not affect seedling mortality. 3Mortality was context-dependent. The genotypes differed both in their overall mortality and in their response to insect herbivory. However, the effect of insects on a genotype depended more on its success in competition than on its resistance: even small amounts of feeding were detrimental to short, shaded seedlings, while taller seedlings in the canopy were affected less, although they were eaten more. 4It is concluded that moderate levels of insect herbivory can increase seedling mortality considerably. Furthermore, herbivory can change the genetic structure of birch populations through selective mortality, which in dense stands is dependent on competitive traits. [source]


    Experimental evidence that deer browsing reduces habitat suitability for breeding Common Nightingales Luscinia megarhynchos

    IBIS, Issue 2 2010
    CHAS A. HOLT
    The ecological impacts of increasing populations of deer (Cervidae) in Europe and North America are becoming more widespread and pronounced. Within Britain, it has been suggested that declines in several woodland bird species, particularly those dependent on dense understorey vegetation, may be at least partly due to these effects. Here we present experimental evidence of the effects of deer browsing on the fine-scale habitat selection and habitat use by a bird species in Europe. The study was conducted in a wood in eastern England where a decrease in Common Nightingale Luscinia megarhynchos numbers has coincided with a large increase in deer numbers. Eight woodland plots were cut to produce young coppice regrowth (a favoured habitat for Nightingales). Deer were excluded from half of each plot using steel fences, thus creating eight experimental pairs of exclosures (unbrowsed) and controls (browsed). Radiotelemetry and territory mapping of male Nightingales showed strong selection of exclosures. The density of territories was 15 times greater in the exclosures than in grazed controls. Selection for exclosures was significant for the minimum convex polygon, 95% kernel and 50% core home-ranges used by seven radiotracked males. Tracked birds spent 69% of their time in the 6% of the study area protected from deer. Intensified browsing by deer influenced local settlement patterns of Nightingales, supporting the conclusion that increased deer populations are likely to have contributed to declines of Nightingales in Britain, and potentially those of other bird species dependent on dense understorey. [source]


    The birth of the housing consumer in the United States, 1918,1960

    INTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 5 2009
    Richard Harris
    Abstract Between 1918 and 1960, those Americans who were able to buy a home learned to think and act as housing consumers. By 1960, the typical couple purchased a finished dwelling from a speculative builder instead of hiring the services of a contractor. Builders now produced for an anonymous market. They learned how to sell, and buyers learned to expect, a comprehensive and standardized package of services that included long-term financing. Such financing required, and buttressed, a Fordist regime of mass production and consumption, and was promoted after 1934 by a new federal agency. It stabilized the economy by pushing families to make long-range spending plans, while shaping their pattern of monthly expenditures. Increasingly, Americans came to think of homes as commodities, as investments and as means of self-expression. They enacted these assumptions by browsing through model homes, by making elaborate financial calculations, by borrowing and by taking on home repair and improvement projects. These changes were promoted by the real estate industry and the state, and were soon accepted for the comfort and convenience they offered. [source]


    Feedback effects of chronic browsing on life-history traits of a large herbivore

    JOURNAL OF ANIMAL ECOLOGY, Issue 4 2008
    M. Anouk Simard
    Summary 1Increasing ungulate populations are affecting vegetation negatively in many areas, but few studies have assessed the long-term effects of overbrowsing on individual life-history traits of ungulates. 2Using an insular population of white-tailed deer (Odocoileus virginianus Zimmermann; Anticosti, Québec, Canada) introduced in 1896, and whose density has remained high since the first evidence of severe browsing in the 1930s, we investigated potential feedbacks of long-term and heavy browsing on deer life-history traits. 3We assessed whether chronic browsing contributed to a decline of the quality of deer diet in early autumn during the last 25 years, and evaluated the impacts of reduced diet quality on deer body condition and reproduction. 4Rumen nitrogen content declined 22% between two time periods, 1977,79 and 2002,04, indicating a reduction in diet quality. 5After accounting for the effects of year within the time period, age and date of harvest in autumn, peak body mass of both sexes declined between the two time periods. At the end of November, males were on average 12% heavier and adult does 6% heavier in 1977,79 than in 2002,04. Hind foot length did not vary between time periods. 6The probability of conception increased 15% between the two time periods, but litter size at ovulation declined 7%, resulting in a similar total number of ovulations in 2002,04 and in 1977,79. 7Our results suggest that following a decline in diet quality, white-tailed deer females modified their life-history strategies to maintain reproduction at the expense of growth. 8Deer appear to tolerate drastic reductions in diet quality by modifying their life history traits, such as body mass and reproduction, before a reduction in density is observed. Such modifications may contribute to maintain high population density of large herbivores following population irruption. [source]


    Mechanisms of functional response and resource exploitation in browsing roe deer

    JOURNAL OF ANIMAL ECOLOGY, Issue 5 2002
    Andrew W. Illius
    Summary 1The functional responses of roe deer were examined using 11 plant species. A technique to discriminate between encounter- and handling-limited processes was used, and it can be concluded that the functional response applicable to patch browsing by roe deer is governed not by the rate of encounter but by the rate of oral processing. 2The large differences between plant species were due to variations in both parameters of the functional response: h , the time lost in biting, and Rmax , the maximum processing rate. Removing the thorns from three of the species affected these parameters differently, according to the size and density of thorns. 3Animals took larger bites from larger patches (branches), and bite mass declined as patch exploitation progressed, implying that animals were selecting the larger items to eat first. It was demonstrated experimentally that depletion of the larger bites does occur first, and it was concluded that prey selection is an important component of herbivore foraging behaviour. 4The gain curves for deer feeding on the different plant species are calculated as being virtually linear. Patch depression did not, in general, occur because increasing bite rate compensated for declining bite mass. Our mechanistic approach is contrasted with other approaches to describing the gain curve in the literature. 5A priori and empirical grounds are presented for rejecting the hypothesis that resource exploitation by browsing mammals is governed by optimal patch use. Diet optimization, involving a trade-off between diet quality and quantity, offers a better explanation of herbivore foraging behaviour. [source]


    Assessing impacts of large herbivores on shrubs: tests of scaling factors for utilization rates from shoot-level measurements

    JOURNAL OF APPLIED ECOLOGY, Issue 1 2007
    DANIELLE M. BILYEU
    Summary 1Accurate methods for estimating the intensity of browsing by herbivores are fundamental to understanding the ecology of shrub communities. Quantifying browse utilization on shrubs at large scales is difficult because shrubs have complex, spatially variable growth forms. Most existing methods estimate browsing rate at the scale of linear current-year shoots or twigs. How such fine-scale estimates relate to the proportion of current-year growth consumed from whole plants or plots is often unknown. The relationship is likely to be complex because herbivores selectively browse more productive plants and plant parts. 2Using a clipping experiment designed to mimic elk Cervus elaphus browsing, we quantified how utilization estimates at the scale of individual current-year shoots of two willow species, Salix bebbiana and Salix geyeriana, relate to actual mass removed at the scale of rooted stems. Three approaches to scaling were examined: (i) taking an average, (ii) multiplying by the proportion of shoots clipped and (iii) multiplying by a novel scaling factor that weights utilization by productivity. To address how to scale-up from stems to plots, we applied the most accurate stem-level method to elk-browsed willow and compared plot-level estimates by two scaling approaches. 3In scaling from shoots to stems, the novel scaling factor was most successful and resulted in accurate estimates for up to c. 45% of current annual growth clipped. In scaling from the stem to the plot, elk preference for more productive stems caused a simple average of stem-level utilization to differ from a productivity-weighted average by 15%. 4Synthesis and applications. In order to reflect accurately the proportion of biomass consumed at a whole-plant level, fine-scale estimates of utilization should be weighted by an estimate of pre-browse productivity, as this is mathematically equivalent to summing pre-browse and post-browse mass before calculating the proportion consumed. In developing methods to estimate utilization at plot scales, an important consideration is the choice of sampling unit, which should be both amenable to unbiased sampling and tractable in terms of measuring productivity. [source]


    Adaptive restoration of sand-mined areas for biological conservation

    JOURNAL OF APPLIED ECOLOGY, Issue 1 2005
    JASON CUMMINGS
    Summary 1Adaptive management approaches to ecological restoration are current best practice. The usefulness of such an approach was tested in this study by implementing repeated experiments that examined restoration options for derelict sand mine sites dominated by Imperata cylindrica. Reclamation of degraded land that is dominated by I. cylindrica is a common problem throughout the tropics. 2Initially, the hypothesized barrier to regeneration was limited seedling establishment because of I. cylindrica competition. After burning the grassland, woody weed control and planting of seedlings were implemented in factorial combination. 3Seedling survival 28 months after planting averaged 26%, with < 1% of all seedlings establishing to a height > 1 m. The hypothesis that a transition barrier comprising solely biotic interactions restricted regeneration of native woody cover was rejected after seedlings and natural regeneration failed to thrive in this experiment. 4A revised hypothesis, that the transition barrier comprised a combination of abiotic limitations (soil deficiencies) and biotic interactions (Wallabia bicolor browsing and I. cylindrica competition), was developed. A second experiment tested this hypothesis by removing W. bicolor (fencing), slashing the I. cylindrica, adding organic mulch and planting a mixture of native pioneer and secondary successional woody species in factorial combination. 5Seedling survival was 61% in the second experiment and mulching significantly enhanced the survival and growth of all planted species. Planting alone reduced the regeneration of I. cylindrica after slashing. Native woody cover establishment was maximized by planting seedlings in mulched treatments. 6Synthesis and applications. Taken together, these experiments support the hypothesis that there is a barrier restricting regeneration of native woody cover, and the barrier probably comprises both abiotic and biotic components. By adopting an adaptive management approach to the ecological restoration of sites, significant insights into their management requirements have been gained, supporting the current best practice restoration framework. Insights gained through monitoring and adaptation will be used to update the reserve plan of management, enhancing restoration of this severely degraded area and promoting connectivity of native woody cover within the conservation estate. [source]


    Assessing spatial variation in browsing history by means of fraying scars

    JOURNAL OF BIOGEOGRAPHY, Issue 6 2004
    Bruno Vila
    Abstract Aim, We used fraying scars to understand spatial variation in browsing history. Information on browsing history is an essential background in studies on the long-term effect of deer browsing on the flora and fauna and of its variation in space. Location, We focused on two small neighbouring islands of Haida Gwaii (British Columbia, Canada), Reef Island and South-Skedans Island, colonized by introduced black-tailed deer (Odocoileus hemionus sitkensis). Methods, We searched for sites where trees with fraying scars were clustered. We studied the trees that deer selected (species, size) and the characteristics of scars (number, position, size). Using a cross-dating procedure, we dated fraying scars with dendrochronology, obtaining an accurate estimate of the year the scar was formed. Results, On Reef Island, Thuja plicata was the tree species chosen for fraying. On South-Skedans Island, where Thuja plicata is missing, deer chose Salix sp. and Alnus rubra. Deer chose only trees with a circumference of less than 50 cm. About two to three fraying scars were recorded per tree. All of them extended between 30,40 and 70,80 cm from the ground and were between 5 and 6 cm in width. On Reef Island, 95% of the scars were formed during the last 50 years. On South-Skedans Island, 95% were formed over the last 10 years. Age distribution of scars showed a constant increase of the number of scars over time. It indicated that deer had colonized Reef Island 53 years prior to this study but were absent or rare on South-Skedans Island until 13 years prior to this study. Main conclusions, These results indicate different colonization dates and thus different length of browsing histories for the islands studied and provide the historical background necessary to analyse the involvement of deer in the current differences in the flora and fauna observed between islands. [source]


    Acacia species turnover in space and time in an African savanna

    JOURNAL OF BIOGEOGRAPHY, Issue 1 2001
    William J. Bond
    Aim Patterns of species turnover along environmental gradients are better studied than their causes. Competitive interactions, or physiological tolerance are most often cited as determinants of turnover. Here we investigate differential tree species response to disturbance by fire and mammal browsing as causes of changing dominance of species within and among sites along an altitudinal gradient. Methods We documented the distribution of two Acacia species using maps and sample transects. We explored possible causes of species turnover by studying differences between the species in tolerance to grass competition using pot experiments, to browsers by observing patterns of shoot damage, and to fire by comparing the size structure of populations burnt at different frequencies and intensities. Results Acacia karroo woodlands were rare and occur at higher elevations than the much more common A. nilotica woodlands. Woodland composition seems set to change in future since the pattern of dominance was reversed in juvenile stages. A. karroo juveniles were very widespread and far more abundant than A. nilotica juveniles. A. karroo juveniles were most abundant in tall fire-prone grasslands and were rare on grazing lawns whereas A. nilotica showed the reverse pattern. In the pot experiments, growth of both species was suppressed by grasses but there were no significant differences in response between the two species. Juveniles of A. karroo were more heavily browsed than those of A. nilotica. However juveniles of A. nilotica were less tolerant of frequent intense burns than juvenile A. karroo. Main conclusions Disturbance gradients, from high fire frequency and low herbivore density at high altitudes, to lower fire frequency and higher herbivore density at low altitudes, are responsible for the shift in community structure along the spatial gradient. Differential responses to browsing and fire may also explain temporal turnover from A. nilotica in the past to A. karroo in the present. Changes in the area burnt annually, and in faunal composition, suggest a landscape-scale shift from grazing-dominated short-grass landscapes in the 1960s, favouring A. nilotica, to fire-dominated tall grasslands in the 1990s favouring A. karroo. We suggest that species turnover due to differential responses along disturbance gradients may be much more widespread than the current paucity of studies suggests. [source]


    Effects of simulated browsing on growth and leaf chemical properties in Colophospermum mopane saplings

    AFRICAN JOURNAL OF ECOLOGY, Issue 1 2010
    Edward M. Kohi
    Abstract Browsing intensity influences a plant's response to herbivory. Plants face a trade-off between investment in the production of secondary compounds and investment in growth. To elucidate this trade-off, we simulated four browsing intensities (0%, 50%, 75% and 100%) on mopane saplings, Colophospermum mopane (J. Kirk ex Benth.) J.Léonard, in a greenhouse experiment. This showed that, with increasing defoliation intensity, plants change their investment strategy. At intermediate levels of defoliation (50%), mopane saplings increased the synthesis of condensed tannins, so that tannin concentrations followed a hump-shaped relation with defoliation intensity, with significantly higher tannin concentration at intermediate defoliation levels. When defoliated heavily (75% and 100%), tannin concentrations dropped, and plants were carbon stressed as indicated by a reduced growth rate of the stem diameter, and leaf production and mean individual leaf mass were reduced. This suggests that, at intermediate defoliation intensity, the strategy of the plants is towards induced chemical defences. With increasing defoliation, the relative costs of the secondary metabolite synthesis become too high, and therefore, the plants change their growing strategy. Hence, browsers should be able to benefit from earlier browsing by either adopting a low or a relatively high browsing pressure. Résumé La réponse d'une plante à sa consommation dépend de l'intensité de ce phénomène. Les plantes sont confrontées à un compromis entre un investissement dans la production de composants secondaires et un investissement dans leur croissance. Pour élucider ce compromis, nous avons simulé quatre intensités de consommation (0%, 50%, 75% et 100%) sur des jeunes mopanes, Colophospermum mopane (J. Kirk ex Benth.) J.Leonard, lors d'expériences sous serre. Ceci a montré que, lorsque la défoliation s'intensifie, les plantes changent leur stratégie d'investissement. À des niveaux de défoliation intermédiaires (50%), les jeunes plants de mopanes augmentaient la synthèse de tanins condensés, de sorte que les concentrations en tanins suivaient une courbe en cloche (hump-shaped) selon l'intensité de la défoliation; elles étaient significativement plus élevées aux niveaux de défoliation intermédiaires. Lorsque les plantes sont fortement défoliées (75% et 100%), leurs concentrations en tanins chutent, et elles sont en stress carbone comme le montre le taux de croissance réduit du diamètre du tronc; la production de feuilles et la masse moyenne de feuilles par individu sont aussi réduites. Cela suggère que, quand l'intensité de défoliation est intermédiaire, la stratégie des plants va vers une défense chimique induite. Lorsque la défoliation augmente, le coût relatif de la synthèse du métabolite secondaire devient trop élevé et le plant change de stratégie de croissance. Donc, les herbivores qui les consomment devraient pouvoir bénéficier d'une consommation antérieure en adoptant une pression de consommation faible ou relativement élevée. [source]


    Impact of the black rhinoceros (Diceros bicornis minor) on a local population of Euphorbia bothae in the Great Fish River Reserve, South Africa

    AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
    Bodina L. Luske
    Abstract In the Great Fish River Reserve, South Africa, black rhinoceros (Diceros bicornis minor) feed extensively on a local population of Euphorbia bothae. Maintaining the endangered black rhinoceros and the protected E. bothae population are both conservation priorities of the reserve. Therefore, the sustainability of this plant,animal interaction was investigated by comparing population characteristics, browsing incidence and intensity within the reserve and in an adjacent exclosure without access to rhino. Fixed-point photographs showed that over a 2-month period 36.6% of 213 monitored plants were browsed, with an average biomass loss of 13%, and 1% were destroyed. Of 26 plants re-photographed after approximately 3 years, 70% showed a decrease in biomass, averaging 37.8% over this period. In this time span, 19% of the monitored plants died. Small plants (<45 cm) were over-represented in the rhino-browsed area, whereas the fraction of reproductively active plants and overall plant density were found to be lower than in the adjacent exclosure. No evidence of short-term compensatory growth in response to browsing was found for E. bothae. This study indicates that, with the current population size, rhinos are overexploiting the E. bothae population and special measures should be taken to prevent local extinction. Résumé Dans la Great Fish River Reserve, en Afrique du Sud, le rhinocéros noir (Diceros bicornis minor) se nourrit en très grande partie d'une population locale d'Euphorbia bothae. Le maintien du rhino noir en danger et de la population protégée d'E. bothae sont deux priorités de la réserve en matière de conservation. C'est pourquoi on a investigué la durabilité de cette interaction plante-animal en comparant les caractéristiques des populations, l'incidence et l'intensité de la consommation du rhino dans la réserve et dans un enclos adjacent d'où les rhinos sont exclus. Des photographies prises d'un point fixe ont montré que, sur une période de deux mois, 36.6% des 213 plantes suivies avaient été broutées, avec une perte moyenne de biomasse de 13%, et un pour cent avait été détruit. Des 26 plantes qui avaient été rephotographiées après environ trois ans, 70% montraient une diminution de la biomasse, qui était de 37.8% en moyenne pour cette période. Pendant ce laps de temps, 19% des plantes suivies sont mortes. Les petites plantes (<45 cm) étaient surreprésentées dans la zone broutée par les rhinos, alors que la fraction des plantes actives au point de vue reproduction et la densité générale des plantes se sont avérées plus faibles que dans l'enclos adjacent. On n'a pu mettre en évidence aucune croissance compensatoire d'E. bothaeà court terme en réponse au broutage des rhinos. Cette étude indique que, vu la taille actuelle de leur population, les rhinos surexploitent la population d'E. bothae et qu'il faut prendre des mesures spéciales pour empêcher l'extinction locale de cette dernière. [source]


    Natural regeneration and population dynamics of the tree Afzelia quanzensis in woodlands in Southern Africa

    AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
    Karin Gerhardt
    Abstract The logging of tree species of high commercial value is increasing throughout the African continent, yet the ecology of these species is generally poorly known. We studied the regeneration pattern and size class distribution of Afzelia quanzensis populations in northern South Africa over a 5-year period. Recruitment was low as the annual seedling mortality was >65%. Seedlings were located under the canopy and were affected by drought and browsing. The adults were scattered or were in a clump-dispersed pattern, which would result in higher recruitment of offspring near parents. Individuals of 0,10 cm diameter at breast height (DBH) were few, while there were 32 trees ha,1 at >10 cm DBH with an annual mortality of 0.8%. Annual diameter increments varied between 0.06 and 0.28 cm. It appears that the transition from the sapling into the juvenile stage could be a bottleneck in the regeneration of the species. A longer study, including more rainfall cycles, may reveal other patterns as dry and wet years have different impacts on dynamics. Résumé La coupe d'espèces d'arbres de grande valeur commerciale augmente dans tout le continent africain, pourtant l'écologie de ces espèces est généralement mal connue. Nous avons étudié le schéma de régénération et la distribution des classes d'âge des populations d'Afzelia quanzensis dans le nord de l'Afrique du Sud pendant cinq ans. Le recrutement était faible car la mortalité annuelle des jeunes plants était de plus de 65%. Les jeunes plans se trouvaient sous la canopée et étaient affectés par la sécheresse et par le broutage des animaux. Les adultes étaient dispersés ou se trouvaient en un schéma en bosquet, qui résulte en un plus fort recrutement de la progéniture près des parents. Les individus de 0,10 cm DBH étaient rares, alors qu'il y avait32 arbres ha,1à >10 cm DBH, avec une mortalité annuelle de 0,8%. L'incrément annuel du diamètre variait entre 0,06 et 0,28 cm. Il semble que la transition entre le stade de jeune arbre et celui de juvénile pourrait bien constituer un étranglement dans la régénération de l'espèce. Une étude plus longue, comprenant plus de cycles de pluies, pourrait révéler un autre schéma étant donné que les années sèches et humides ont des impacts différents sur cette dynamique. [source]


    Effects of moisture, nitrogen, grass competition and simulated browsing on the survival and growth of Acacia karroo seedlings

    AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
    Keletso Mopipi
    Abstract The effects of irrigation, nitrogen fertilization, grass competition and clipping were investigated for one growing season at the research farm of the University of Fort Hare in the Eastern Cape Province of South Africa. The aim of the experiment was to assess the short-term performance of Acacia karroo seedlings under different environmental conditions and the implications of such factors on the long-term recruitment of plant species in savanna rangelands. There were no significant treatment effects on the survival of A. karroo seedlings. Using stem length and basal diameter as growth parameters, it was observed that irrigation enhanced both variables, while nitrogen fertilization did not have any significant effects. Clipping, grass competition and their interaction greatly suppressed the growth of the seedlings. Clipping increased the mean stem length when they were irrigated and fertilized. Control and fertilized plants had the highest stem length in the absence of grass competition, while grass competition combined with clipping resulted in the lowest stem length in both irrigated and nonirrigated plants. It was concluded that in the presence of grass competition, controlled browsing could be a viable solution to the problem of bush encroachment in savanna rangelands. Résumé Les effets de l'irrigation, d'une fertilisation à l'azote, de la compétition avec l'herbe et de la taille ont étéétudiés pendant une saison de croissance dans la ferme expérimentale de l'Université de Fort Hare, dans la Province du Cap oriental, en Afrique du Sud. Le but de l'expérience était d'évaluer les performances à court terme de jeunes plants d'Acacia karroo dans différentes conditions expérimentales, et les implications de ces facteurs sur le recrutement à long terme d'espèces végétales dans des pâturages de savane. Il n'y a pas eu d'effet significatif des traitements sur la survie des plants d'A. karroo. En utilisant la longueur des troncs et le diamètre de la base comme indicateurs de croissance, on a observé que l'irrigation augmentait les deux variables, alors que la fertilisation à l'azote n'avait aucun effet significatif. La taille, la compétition avec l'herbe et leur interaction supprimait fortement la croissance des jeunes plants. La taille augmentait la longueur moyenne des troncs lorsqu'ils étaient irrigués et fertilisés. Les plants témoins et les plants fertilisés avaient les troncs les plus longs en absence de toute compétition avec des herbes, alors que cette dernière, combinée avec la taille, aboutissait à la longueur la plus petite des troncs, chez les plants irrigués ou non. On en a conclu qu'en cas de compétition avec des herbes, un pâturage contrôlé pourrait être une solution viable au problème de l'envahissement des broussailles dans les pâturages de savane. [source]


    Browsing impact of large herbivores on Acacia xanthophloea Benth in Lake Nakuru National Park, Kenya

    AFRICAN JOURNAL OF ECOLOGY, Issue 2 2009
    N. Dharani
    Abstract Significant differences (P<0.05) were found in growth of plant height, canopy cover and stem diameter of Acacia xanthophloea trees in fenced plot as compared with unfenced plot both in the wet and in the dry seasons. Finding of this study showed that although heavy browsing reduced the height and canopy of trees, it did not kill any trees and seedling regeneration took place simultaneously. Despite the presence of large herbivores that impact some considerable browsing pressure results indicate that the A. xanthophloea habitat type would continue to remain in balance in the presence of recruitment of seedlings and saplings. The conditions at the time of study indicate that the browsing on A. xanthophloea was not significant and was not serious enough to warrant management intervention at present. Résumé Des différences significatives (P<0,05) ont été relevées dans la croissance en hauteur, le couvert de la canopée et le diamètre des tiges d'Acacia xanthophloea dans des parcelles clôturées, comparées à des parcelles non clôturées, en saison sèche comme en saison des pluies. Les résultats de cette étude ont montré que, même si un pâturage intense réduisait la hauteur et la canopée des arbres, il n'en tuait aucun et que la régénération des jeunes plants se faisait simultanément. Malgré la présence de grands herbivores qui exercent une pression considérable, les résultats indiquent que le type d'habitat àA. xanthophloea resterait équilibré grâce au recrutement de jeunes plants et de repousses. Les conditions prévalant au moment de l'étude indiquaient que la consommation d'A. xanthophloea n'était pas significative et qu'elle n'était pas assez grave pour justifier pour le moment une intervention en matière de gestion. [source]


    Interactions between large African browsers and thorny Acacia on a wildlife ranch in Kenya

    AFRICAN JOURNAL OF ECOLOGY, Issue 4 2006
    Antoni V. Milewski
    Abstract Some plants respond to browsing with compensatory regrowth of plant tissues and with increased thorn growth. Associations between browsers and their preferred forage were examined through wandering quarter vegetation sampling and observational studies in an effort to understand how some plants respond to browsing by large African herbivores. Acacia seyal (n = 2680) A. drepanolobium (n = 1850), and Balanites glabra (n = 960) were three species of frequently browsed indigenous plants examined on Game Ranching Ltd. in Kenya. There were several statistically significant associations revealed. Individual A. seyal exposed to intensive browser utilization were observed to lose shoot tips, produce long thorns, and have relatively few flowers and fruits. Browser utilization was associated with increased lateral branching in A. drepanolobium and with an increased occurrence of short, thickened spines in B. glabra. Thorns, spines and flowers were measurable indicators of relative browser utilization, and may be useful features to monitor in the management of large African mammals and their prickly forage Résumé Certaines plantes réagissent au pâturage par une repousse du tissu végétal et une croissance accrue d'épines. Les associations entre les animaux et leur nourriture favorite ont été examinées grâce à des échantillonnages de la végétation par quadrats aléatoires, et par des observations spécifiques afin de comprendre comment certaines plantes répondent au broutage par de grands mammifères africains. Acacia seyal (n = 2680), A. drepanolobium (n = 1850) et Balanites glabra (n = 960) sont trois espèces de plantes indigènes fréquemment consommées àGame Ranching Ltd, au Kenya. On y révèle plusieurs associations statistiquement significatives. On y a observé des A. seyal exposés à une consommation intensive perdre l'extrémité des pousses, produire de longues épines et relativement peu de fleurs et de fruits. La consommation par les herbivores était associée à une production accrue de branches latérales chez A. drepanolobium et à la présence accrue de piquants courts et épais chez Balanites glabra. Les piquants, les épines et les fleurs étaient des indicateurs mesurables de la consommation relative par des herbivores, et peuvent être des caractéristiques utiles à surveiller dans le cadre de la gestion des grands mammifères africains et de leur alimentation épineuse. [source]


    Structure and composition of Acacia xanthophloea woodland in Lake Nakuru National Park, Kenya

    AFRICAN JOURNAL OF ECOLOGY, Issue 4 2006
    N. Dharani
    Abstract The woody vegetation of Lake Nakuru National Park occurs along rivers, lakeshores and flood plains. Four different sites within the Acacia xanthophloea woodlands were selected for the study. Vegetation structure was not significantly different in the four woodlands used for the study, but these sites differed in the relative density of Acacia trees. Regeneration of A. xanthophloea differed in each site, with the highest regeneration rates found in the nonfenced plots where browsing took place. Résumé La végétation ligneuse du Parc National de Nakuru se trouve le long des cours d'eau, sur les berges du lac et dans les plaines inondables. Nous avons sélectionné quatre sites dans les zones arborées àAcacia xanthophloea. La structure da la végétation n'était pas significativement différente dans les quatre forêts sélectionnées pour l'étude, mais ces sites différaient quant à la densité relative d'acacias. La régénération des Acacia xanthophloea différait sur chaque site, et le taux de régénération était le plus élevé dans les plots non clôturés fréquentés par les herbivores. [source]


    Landscape monitoring of semi-arid rangelands in the Kenyan Rift Valley

    AFRICAN JOURNAL OF ECOLOGY, Issue 4 2000
    A. D. Q. Agnew
    A sampling system was devised and used from 1992 to 1996 in annual grassland and open woodland of the south-west Kenyan Rift Valley. The monitoring was designed to detect vegetation changes consequent on the attempted removal of the tsetse vectors of trypanosomiasis in cattle during a simultaneous trapping programme. The sampled sites covered most vegetation-landscape types, and have led to a better understanding of processes within some. Although fluctuations in pastoralist use and occupancy have been observed, no change in vegetation can be attributed to increased grazing or browsing. Although there is high climatic variability some vegetation types seemed stable over the period studied, and some trends appear to be predictable. Resume On a conçu un système d'échantillonnage qui fut utilisé de 1992 à 1996 dans les prairies annuelles et dans les forêts ouvertes du sud-ouest de la Rift Valley, au Kenya. La surveillance était conçue de façon à détecter les changements de végétation qui résultaient des tentatives d'éradication des mouches tsé-tsé, vecteurs de la trypanosomiase chez le bétail, au cours d'un programme de piégeage. Les sites d'échantillonnages couvraient des paysages correspondant à la plupart des types de végétation et ont conduit à une meilleure compréhension du processus dans certains d'entre eux. Bien qu'on ait observé des fluctuations dans l'occupation et l'utilisation pastorales, on ne peut attribuer aucun changement de végétation à une augmentation du pâturage. Bien que le climat soit très variable, certains types de végétations semblent être restés stables pendant la durée de l'étude et l'on semble pouvoir prédire certaines tendances. [source]


    Impulsive donation decisions during online browsing of charity websites

    JOURNAL OF CONSUMER BEHAVIOUR, Issue 2-3 2009
    Roger Bennett
    Although online fundraising by charitable organisations is now commonplace, many aspects of effective online fundraising remain unexamined. In particular, little is known about the nature and determinants of impulsive donation decisions taken by browsers of charity websites. This empirical study attempted to help fill this important gap in current knowledge about online fundraising via an investigation of the antecedents of impulsive online giving to a hospice organisation in the south of England. Two hundred and thirty-nine donors who stated that their gifts had been made impulsively and 223 donors whose online gifts were reported as having been pre-planned completed a questionnaire that explored, inter alia, a person's socio-demographic characteristics, level of impulsiveness and attitude towards impulsive behaviour, charity donation history, prior knowledge of hospice issues, subjective norms and personal involvement with charity giving. The main determinants of impulsive donations were identified and the profiles of various types of impulsive giver were established. Relevant matters were investigated in the contexts of two types of web page design: emotive and informative. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    The intraruminal papillation gradient in wild ruminants of different feeding types: Implications for rumen physiology

    JOURNAL OF MORPHOLOGY, Issue 8 2009
    Marcus Clauss
    Abstract Browsing and grazing ruminants are thought to differ in the degree their rumen contents are stratified,which may be due to different characteristics of their respective forages, to particular adaptations of the animals, or both. However, this stratification is difficult to measure in live animals. The papillation of the rumen has been suggested as an anatomical proxy for stratification,with even papillation indicating homogenous contents, and uneven papillation (with few and small dorsal and ventral papillae, and prominent papillae in the atrium ruminis) stratified contents. Using the surface enlargement factor (SEF, indicating how basal mucosa surface is increased by papillae) of over 55 ruminant species, we demonstrate that differences between the SEFdorsal or SEFventral and the SEFatrium are significantly related to the percentage of grass in the natural diet. The more a species is adapted to grass, the more distinct this difference, with extreme grazers having unpapillated dorsal and ventral mucosa. The relative SEFdorsal as anatomical proxy for stratification, and the difference in particle and fluid retention in the rumen as physiological proxy for stratification, are highly correlated in species (n = 9) for which both kind of data are available. The results support the concept that the stratification of rumen contents varies among ruminants, with more homogenous contents in the more browsing and more stratified contents in the more grazing species. J. Morphol., 2009. © 2009 Wiley-Liss, Inc. [source]