Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    African elephant in a cleft stick : choosing between starving or dying from thirst in arid savanna
    Wato, Yussuf - \ 2016
    Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Ignas Heitkonig; Frank van Langevelde. - Wageningen : Wageningen University - ISBN 9789463430005 - 126
    loxodonta africana - starvation - thirst - savannas - arid zones - animal ecology - mortality - drought - loxodonta africana - uithongering - dorst - savannen - aride klimaatzones - dierecologie - mortaliteit - droogte

    Elephant population studies have become important especially because of the long standing perception that high elephant densities have negative impact on vegetation and other wildlife species. Thus, in areas of high elephant density, managers attempt to re-distribute them or keep their numbers low through provision of water, translocation or culling. These approaches are thought to keep the population within the limits that can be sustained by the ecosystem, termed “the ecological carrying capacity”, a management option hinged on equilibrium theory. Equilibrium systems are considered stable, with resources and the animals that depend on them being at balance with each other. This stability is rarely the case in tropical savannas where the rule appears to be “a flux of nature” rather than “a balance of nature”.

    Tropical savannas, where over half of the African elephant live, are prone to constant environmental fluctuations, especially prolonged droughts, and hence there is a growing understanding that populations of wildlife species and their communities are rarely at equilibrium. Therefore, it is critical to understand how the constant environmental flux in this system affects wildlife populations and the implication for their management. In this thesis, the central focus is to investigate the role of drought occurrences on elephant population dynamics in tropical savannas. To address this question, it is important to have a good understanding of the historical changes of elephant population in relation to drought events and the ecology of elephant in semi-arid savannas - their distribution and density, their movements and behaviour. For the historical data, I analysed the best existing long-term data in Africa of wild elephant population that has been consistently monitored for over 40 years where life histories of over 3000 wild individual elephant are known, at Amboseli National Park in Kenya. In addition, I also analysed geo-referenced elephant mortality data collected daily for 10 years from Tsavo Conservation Area. Further, I analysed 2 years data from 8 GPS collared African elephant to investigate their movement response to seasonal water and forage distribution in Tsavo Ecosystem.

    First, I investigated the temporal effects of drought duration (number of consecutive dry months) and intensity (amount of rainfall) on elephant population structure in Amboseli National Park, Kenya. The result corroborates findings from past studies that calves (<2years) are more susceptible to drought caused mortality and the risk of dying decreased with age. A new finding in this study reveals that the effect of drought induced mortality for the adult elephant is sex and age dependent, with males older than 25 years being less likely to die as compared to females of the same age. This new result is because of the resolution of analysis in this study which focused on the length and severity of drought as opposed to past studies that restricted their analysis to seasonal and inter-annual differences in rainfall pattern. As they grow older and sexually mature, the foraging range of male elephant increase and they begin to take more risks and disperse to unfamiliar habitats to seek for quality forage and mates. Generally, foraging strategies between sexes in many species are more pronounced during periods of food scarcity, and the driving force in the differences appears to be driven by energy need requirements, reproductive status of an individual, body sizes and the social context, all of which differ between sexes.

    In the next study, I investigated the spatial pattern of elephant mortality in relation to drought occurrences in Tsavo National Park using MaxEnt. The results shows that elephant carcasses were aggregated and elephant mortality was negatively correlated with four months cumulative precipitation prior to death, forage availability and distance to water, while local elephant density showed a positive correlation. This finding rules out dehydration as the cause of elephant mortality in Tsavo as the river where the carcasses were aggregated is perennial. Furthermore, forage availability was low close to water sources and did not show a significant difference close to or further away from the river despite high elephant density around the river. Hence, these elephant mortalities may have occurred as a result of starvation.

    I went further to focus on two main limiting resources for elephants, namely forage and water, and their effect on elephant-habitat utilization in semi-arid savannas. I first investigated how water source distribution affect elephants’ seasonal movement patterns. Results indicate that male elephant moved maximally 20 km away from the nearest water source in the dry season while the female elephant foraged to a maximum of about 10 km and only moved further than this distances in the wet season. The strong directionality of elephant movement from a distance of 15km towards water sources (rho > 0.5) as they re-visited their watering source in the dry season suggest that elephant have information on location of the water sources.

    Next, I investigated the factors that determine selection of a foraging site for elephant with a focus on forage nutrients or biomass. Because of their large body size, it is thought that elephant can survive on a less nutritious but high biomass of forage. The results from this study shows that elephant selected foraging site based on forage biomass in dry seasons, whereas they selected areas with higher nutrients in the wet season. Moreover, females selected sites with a higher forage biomass as compared to males. This result may be explained by the difference in social organisation and foraging strategies between the sexes. In the previous studies on human-elephant conflict, for instance, male elephant raided crops more than the mixed herd, perhaps to seek for high quality forage.

    Together, the four studies in this thesis strongly suggest that elephant starve to death in prolonged drought contrary to the past studies that reported that adult elephant are less affected by drought. Even though prolonged droughts usually result in higher elephant mortalities, the resilience of semi-arid savannas may perhaps be as a result of these deaths that release the system from high browsing pressure and give it a window to regenerate. If that is the case, then drought induced elephant mortality may be a better way to regulate elephant numbers than culling. This finding strongly suggests that semi-arid savannas may in fact be a non-equilibrium system sustained by growth and crashes of herbivore populations. Maintaining the system as natural as possible may therefore keep elephant populations in savannas sustained for posterity. The modern day park managers have daunting challenges such as mass elephant deaths in drought, increased human-wildlife conflicts or changes in wildlife use of the landscape which may all be symptoms of wrong management interventions taken in the past or negative impacts of anthropogenic activities that have tipped the natural functioning of a non-equilibrium system. Therefore, park managers should undergo regular trainings on new conservation techniques and they should apply evidence-based science to make informed long term decision.

    The bulldozer herbivore: how animals benefit from elephant modifying an African savanna
    Kohi, E. - \ 2013
    Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Fred de Boer. - S.l. : s.n. - ISBN 9789461735355 - 170
    herbivoren - loxodonta africana - afgrazen - voedingsgewoonten - habitats - diergedrag - dierecologie - savannen - afrika - herbivores - loxodonta africana - browsing - feeding habits - habitats - animal behaviour - animal ecology - savannas - africa

    Herbivore-vegetation interactions are important structuring forces in savanna that modify the availability and quality of forage resources. Elephant for example, are known for their ability to change the vegetation structure through toppling trees, uprooting, snapping, debarking and breaking branches. Controlling the number of elephant is a common response of wildlife managers who think that the increase of elephant will further destroy the habitat and hence cause loss of biodiversity. However, our knowledge on how elephant feeding habits affect other large herbivore species in habit use is limited. Therefore, the question in this thesis is: What is the impact of elephant feeding habits on species diversity of large herbivores in African savanna? To answer this question, it is important to understand the responses of trees when impacted by elephant. What proportion of the browsed biomass is made available after a tree is pushed over or snapped by elephant? How is the forage quality affected? Is the seasonal and intensity of browsing affecting forage availability? Field experiments and field surveys were used to investigate the tree’s response and herbivore species responses to elephant impact. These experiments were (1) simulation of timing and intensity of browsing (hand defoliation) and (2) manipulation of vegetation i.e. simulated pushed over trees, uprooted trees (tree removal) and snapped trees (tree cut at the stem). The field survey involved measuring impacted trees by elephant. Leaf biomass and quality of pushed over, snapped and uprooted trees were measured. The defoliation experiment was conducted in the roan antelope enclosure in Kruger National Park South Africa, and the vegetation manipulation experiment was conducted in the Umbabati Private Nature Reserve, South Africa.

    The results indicate that elephant foraging habits change the distribution of forage, increasing the forage availability at lower feeding heights, which means that accessibility of forage to medium and small herbivores increases. Elephant browsing also improved forage quality and availability in the dry season, which is very important to browsing animals. A high intensity of browsing by elephant in the wet season increased the dry season forage, because the amount of new regrowth (leave compensation) is proportional to the amount of leaves that was removed. Elephant therefore initiate inter and intra-species facilitation processes. Inter-species facilitation occurs when other herbivores species utilize the regrowth stimulated by elephant, whereas intra-species facilitation occurs when the browse resource is exploited by other elephants. The herbivore responses to elephant browsing clearly indicated that facilitation effects occur, especially for certain guilds when selecting their habitat. For example, small predation-sensitive herbivore species (steenbok, impala and common duiker) preferred completely opened up areas, whereas large herbivores were less affected in their habitat preference by elephant impact. Greater kudu selected pushed over and control plots and rarely visited opened up areas. These differential response of herbivores species to elephant impact resulted in a high species richness of large mammals in elephant impacted areas. In conclusion, elephant feeding habits play a major role in structuring the herbivore assemblage/community through modifying the vegetation. Resource heterogeneity increased under the influence of elephant feeding, in particular through increasing the accessibility of leaf biomass at lower feeding heights, increasing green leaf availability in the dry season, and improving the nutrient content in re-growth. Moreover, habitat selection, especially that of small herbivores was positively influenced by elephant impact. With these findings, this study contributes to a better understanding of the role of elephant feeding habits and its cascading effects to other herbivore species.

    Cooperation or competition : dilemma for resource managers in sustainable wildlife utilisation
    Mwakiwa, E. - \ 2011
    Wageningen University. Promotor(en): Herbert Prins; J. Hearne, co-promotor(en): Erwin Bulte; Hans Stigter. - [S.l.] : S.n. - ISBN 9789461730381 - 137
    wildbeheer - particulier eigendom - grondeigendom - modelleren - loxodonta africana - savannen - grondproductiviteit - natuurreservaten - nationale parken - zuid-afrika - wildlife management - private ownership - land ownership - modeling - loxodonta africana - savannas - land productivity - nature reserves - national parks - south africa

    Keywords: analytical modelling; Associated Private Nature Reserves; consumptive use; elephants; Kruger National Park; land productivity; non-consumptive use; waterpoints; Savanna ecosystem model; South Africa.

    Wildlife as part of biodiversity is a global natural resource. However, landowners have some control over the future of wildlife on their land. Wildlife could be managed by the state or private landowners. The survival of the wildlife and their habitats is determined by how these landowners decide to use the land and the renewable resources on it. Some complication come into place given that wildlife usually roam on land held over by more than one owner providing more challenge to its management. In addition, wildlife as a natural resource has multiple uses that generate revenues for the betterment of the landowners. The uses could be consumptive or non-consumptive. Each landowner has multiple objectives which might be conflicting which poses even a greater challenge to the sustainable wildlife management.

    To meet their objectives wildlife managers use management tools. Some of the tools used include constructing or closing of artificial waterpoints, fire management, fencing, and population manipulation through culling/hunting or translocation of animals. However, use of these management tools can lead to unintended or opposite effects if they are not well understood. There are direct and indirect effects of the tools on biodiversity. Landowners could be tempted to excessively use some of the tools in order to achieve their objectives. In addition, most studies have concentrated on either the ecological or economic effects of the wildlife management tools. For the landowner, it is essential that he comprehends both the ecological and economic effects of the wildlife management tools for the sustainable management of wildlife, a contribution of this study.

    The main objective of this study is to assess the ecological and economic implications of some wildlife management tools on the landowners’ welfare. I use simple ecological economic analytical models based on the Pontryagin’s maximum principle to perform the analyses. The Savanna ecosystem model which is a spatially explicit, process-oriented model is also used to further explore the effects of one of the wildlife management tools on landowner’s multiple objectives.

    One of the tools that is analyzed in this thesis is the improvement of land productivity through increasing of vegetation quality. Given that, it is usually not easy to increase the land size in response to increased incentives, some landowners might consider increasing the land productivity. The results show that utilization of wildlife can contribute to wildlife conservation and enhancement of welfare as a result of investment by landowners into habitat quality improvement. However, the use of a wildlife management tool has direct and indirect effects as demonstrated by another framework presented in this thesis on waterpoints. Waterpoints are used by wildlife managers to supplement natural water supplies which in turn support herbivore populations, like elephants. A private oriented landowner may be interested only in maximization of profits or personal benefits either from elephant offtake and/or tourism revenue, thus might ignore the negative effects that could be brought about by elephants to biodiversity. In such case, the game reserve management as the authority entrusted with sustainable management of the game reserve should use economic instruments such as subsidies or payments for the compliant landowners and/or taxes or charges for the non-compliant landowners to encourage compliance with sustainable wildlife management practices.

    The Savanna ecosystem model is used to explore the effects of waterpoints on elephant density (representing an economic objective) and biodiversity (representing an ecological objective). The model is used to analyze the differential impact of waterpoints on the Kruger National Park’s regions under 26 waterpoints manipulation scenarios. The model is also used to analyze elephant impact on vegetation biomass diversity in four regions of Kruger National Park. The results showed that constructing (or closing) extra waterpoints in one region does not necessarily translate into higher (or lower) elephant densities in that region, but the effect depends on the vegetation and other conditions of the region in comparison to neighbouring regions. In one of the regions, the model showed that there is a trade-off between elephant density and vegetation biomass diversity. In another region, elephants’ effect on vegetation biomass diversity follows the intermediate disturbance hypothesis, whilst in other regions the relationship is positive. The intermediate disturbance hypothesis postulates that there would be a higher diversity of vegetation structure at intermediate elephant densities whilst at extreme levels of both low and high disturbance the diversity would be reduced. The model thus suggests that different strategies should be adopted for different regions, e.g., an adaptive management strategy could be used for one of the regions where waterpoints are switched on and off depending on the elephant density.

    Another wildlife management tool that is analyzed is the use of physical barriers like fences. Physical barriers could be utilised by landowners to separate different wildlife uses which might be conflicting. Landowners or game reserve management are often faced with the decision whether to undertake consumptive (hunting) and/or non-consumptive (tourism) use on their properties. A theoretical model is constructed to examine these cases. The results show that that the two uses can be undertaken in the same contiguous area if the consumptive use is not dominating.

    In conclusion, what emerges from this work is that given that the landowner’s welfare is not only affected by his own actions but also his neighbours’ modi operandi, then the landowner should consider all levels of cooperation with his neighbours in order to fully maximize his welfare. This includes cooperation in terms of which management tool(s) he and/or his neighbour should use. The frameworks presented in this thesis could be used by landowners (both state and private) to analyze the effects of their management actions on their welfare.

    Why elephant roam
    Ngene, S.M. - \ 2010
    University of Twente. Promotor(en): Andrew Skidmore; Herbert Prins; H.A.M.J. van Gils. - Enschede : University of Twente Faculty of Geo-Information and Earth Observation ITC - ISBN 9789061642909 - 195
    loxodonta africana - geografische informatiesystemen - remote sensing - zoögeografie - geografische verdeling - beweging - menselijke activiteit - seizoenen - diergedrag - kenya - menselijke invloed - loxodonta africana - geographical information systems - remote sensing - zoogeography - geographical distribution - movement - human activity - seasons - animal behaviour - kenya - human impact
    The expansion of human activities due to the increase in human population outside protected areas is reducing the range of elephant. This range reduction occurs when elephant habitats are cleared for more farms and settlements. This causes fragmentation of the elephant range, which changes the elephant’ distribution, movement patterns, intensity of occupancy, and speed of movement. The objectives of this study were to use GIS and remote sensing to identify the factors that influence the distribution, intensity of occupancy, and speed of movement of Marsabit elephant; to map and describe their wet and dry season range, intensity of occupancy, and speed of movement, as well as seasonal altitudinal movement in the fragmented mosaic of forest and savanna; to research the cost of humans sharing the environment with the elephant in areas adjacent to Marsabit Protected Area.
    Beyond the here and now : herbivore ecology in a spatial-temporal context
    Knegt, H.J. de - \ 2010
    Wageningen University. Promotor(en): Herbert Prins; Andrew Skidmore, co-promotor(en): Frank van Langevelde. - [S.l. : S.n. - ISBN 9789085856283 - 140
    herbivoren - loxodonta africana - ecologie - vegetatie - patronen - habitatselectie - habitats - dierecologie - milieu - afrika - herbivores - loxodonta africana - ecology - vegetation - patterns - habitat selection - habitats - animal ecology - environment - africa
    Ecological phenomena at a certain location often not only depend on the current characteristics of that location itself, but also on characteristics of the landscape surrounding the site or influences from the past. In other words, in order to be able to understand ecological processes here and now, we often need information that is beyond here and now. This thesis investigates the role of such spatial-temporal context on the relationships between species and their environment. The focus is on large mammalian herbivores, an in particular the factors determining the movement and distribution of African elephants (Loxodonta africana) in Kruger National Park (KNP), South Africa.

    This thesis covers four main themes. First, it is shown that spatial-temporal variation in the biotic and abiotic environment creates predictable seasonal and daily cyclic patterns in the distribution of elephants in KNP. Then, herbivores are shown not only to respond to environmental heterogeneity: they also can create distinct spatial patterning in savanna vegetation when foraging initiates a positive plant-herbivore feedback and when the foraging process is spatially explicit. This leads to specific sites being revisited often, and therefore the patterns of site revisitation by elephants in KNP are studied, mainly in relation to surface water availability and vegetation characteristics. Lastly, this thesis focuses on the scale-dependent response of organisms to environmental heterogeneity, showing the consequences of a mismatch in the scale of analysis on statistical inference, and then focusing on finding the appropriate spatial scales to analyse and predict the spatial distribution of elephants in KNP. Together, the chapters presented in this thesis highlight the importance of explicitly considering the scale and context dependency of species-environment relationships, and demonstrate methods to take issues of spatial-temporal scale and context into account. These methods have the potential to increase our understanding of ecological phenomena and therefore may lead to better management of natural resources.

    Effects of elephants on ecosystems and biodiversity
    Kerley, G.I.H. ; Landman, M. ; Kruger, L. ; Owen-Smith, N. ; Balfour, D. ; Boer, W.F. de; Gaylard, A. ; Lindsay, K. ; Slotow, R. - \ 2008
    In: The 2007 scientific assessment of elephant management in South Africa / Mennell, K.G., Scholes, R.J., Pretoria : CSIR - p. 101 - 147.
    loxodonta africana - wildbeheer - wild - zuid-afrika - loxodonta africana - wildlife management - wildlife - south africa
    Scale matters! : a new approach to quantify spatial heterogeneity for predicting the distribution of wildlife
    Murwira, A. - \ 2003
    Wageningen University. Promotor(en): Andrew Skidmore; Herbert Prins. - Wageningen/ Enschede : Wageningen Universiteit - ISBN 9789058089519 - 195
    wild - dierecologie - ruimtelijke verdeling - remote sensing - loxodonta africana - voorspelling - zimbabwe - elephas maximus - wildlife - animal ecology - spatial distribution - remote sensing - loxodonta africana - prediction - zimbabwe - elephas maximus
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