Article

The Return of the Giants: Ecological Effects of an Increasing Elephant Population

September 2004
AMBIO A Journal of the Human Environment 33(6):276-82

DOI:10.1579/0044-7447-33.6.276

Source
PubMed

Authors:

Per Arild Aarrestad

Norwegian Institute for Nature Research

Harry P. Andreassen

Hedmark University College

Sd Sd

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Northern Botswana and adjacent areas, have the world's largest population of African elephant (Loxodonta africana). However, a 100 years ago elephants were rare following excessive hunting. Simultaneously, ungulate populations were severely reduced by decease. The ecological effects of the reduction in large herbivores must have been substantial, but are little known. Today, however, ecosystem changes following the increase in elephant numbers cause considerable concern in Botswana. This was the background for the "BONIC" project, investigating the interactions between the increasing elephant population and other ecosystem components and processes. Results confirm that the ecosystem is changing following the increase in elephant and ungulate populations, and, presumably, developing towards a situation resembling that before the reduction of large herbivores. We see no ecological reasons to artificially change elephant numbers. There are, however, economic and social reasons to control elephants, and their range in northern Botswana may have to be artificially restricted.

Long‐term high densities of African elephants clear the understorey and promote a new stable savanna woodland community

Article

Full-text available

Dec 2021

Questions Species defined as ecosystem engineers (e.g. elephant) are able to strongly shape their habitat. In African savannas, elephants have often been shown to reduce woody plant abundance and diversity. However, recent studies highlight more complex elephant-induced effects on vegetation. Here, we assessed if long-term high elephant densities (>2.km⁻²) in a large open landscape resulted in the depletion of savanna woodland woody communities or if it led to a new alternative equilibrium. Location Woodland savanna of Hwange National Park, Zimbabwe. Elephant densities at the study site have remained high for the past two decades (>2.km⁻²). Methods We measured long-term (>15 years) elephant utilization of woody plant communities and their effects on vegetation structure, species composition and functional traits (e.g. N leaf concentration, specific leaf area) in twelve vegetation plots. Results We observed opportunistic foraging behaviour by elephants with only a slight temporal shift in species composition, mainly explained by changes in rare species. Further, we did not observe any modification in mean functional trait values, overall height and stem diameters of the woody plant communities. However, we found differential changes in woody plant abundance according to the height layer (decrease in the number of tall plants (>200 cm) and increase in the number of short plants (<50 cm)) and a strong reduction in crown diameter for plants in the 50-200 cm height class. Conclusion Our study strongly suggests that long-term high elephant densities have led to a stable state in savanna woodland vegetation in terms of plant community composition and their functional traits. However, high elephant densities did affect vegetation structure, which would have several important indirect effects on this ecosystem (e.g., predator-prey interactions). We hope that this study stimulates more work on the long-term effects of ecosystem engineers in large and open ecosystems.

The management dilemma: Removing elephants to save large trees

Article

Full-text available

Aug 2019

The loss of large trees ( 5 m in height) in Africa’s protected areas is often attributed to the impact by savanna elephants (Loxodonta africana). Concerns have been raised over large tree mortality levels in protected areas such as South Africa’s Kruger National Park (KNP) and in the past, the need to manage its elephant population in order to preserve large trees and biodiversity as a whole. Our review aims to synthesise and discuss the complexities of managing elephants’ effects on the landscape to ensure the survival of large trees, as well as the application purposes of the various lethal and non-lethal elephant mitigation strategies. We further critically evaluate past management strategies, which have solely focused on controlling elephant numbers to protect large trees. Past mitigation strategies focused on managing elephant impact by directly reducing elephant numbers. However, maintaining elephant numbers at a pre-determined carrying capacity level did not prevent the loss of large trees. Research on large tree survival in African savannas has continually exposed the complexity of the situation, as large tree survival is influenced at various demographic stages. In some cases, a coalescence of historical factors may have resulted in what could be perceived as an aesthetically appealing savanna for managers and tourists alike. Furthermore, the past high density of surface water within the KNP homogenised elephant impact on large trees by increasing the encounter rate between elephants and large trees. Our review evaluates how current mitigation strategies have shifted from purely managing elephant numbers to managing elephant distribution across impact gradients, thereby promoting heterogeneity within the system. Additionally, we discuss each mitigation strategy’s occurrence at various landscape scales and its advantages and disadvantages when used to manage impact of elephant on large trees. Conservation implications: A variety of options exist to manage the effects that elephants have on large trees. These options range from large-scale landscape manipulation solutions to small-scale individual tree protection methods. Interactions between elephants and large trees are complex, however, and conservation managers need to consider the advantages and disadvantages of each mitigation strategy to protect large trees.

Elephant herbivory of knob‐thorn ( Senegalia nigrescens ) and ivory palm ( Hyphaene petersiana ) in Bwabwata National Park, Caprivi, Namibia: The role of ivory palm as a biotic refuge

Article

Aug 2019

African elephants have major impacts on vegetation, particularly at high densities. Knob‐thorns ( Senegalia nigrescens ) are typically ring‐barked by elephant, and high levels of mortality are common at high elephant densities. Our study aimed to test whether ivory palm clusters ( Hyphaene petersiana ) form a biotic refuge for knob‐thorn against elephant herbivory. We measured the density, damage and mortality of knob‐thorns in sites differing according to ivory palm presence and elephant density, and thus, the probability of knob‐thorn encounter by elephants. The site with palms and low elephant density, had a high density of knob‐thorns, but lower proportions of damaged and dead trees, than sites without palms but with similar or higher elephant density. In the former, knob‐thorns were associated with palm clusters, particularly saplings and young adults. In this site, low proportions of damaged and dead knob‐thorns were recorded in palm clusters, compared with outside clusters, and to those in the other sites. Our study also showed that juvenile palms which protected knob‐thorns, suffered low mortality in contrast to subadult palms. We have no evidence but implicate elephants and suggest that in palm clusters, subadult palms are more accessible to elephants than knob‐thorns because of the different methods of utilisation.

Elephant‐mediated compositional changes in riparian canopy trees over more than two decades in northern Botswana

Article

Full-text available

Apr 2018

Questions How has the composition and diversity of canopy tree species in a riparian woodland changed over time? How are the compositional changes related to impact of elephants? Does the composition of juvenile plants indicate that the woodland retains the potential to recover its former composition? Location Northern Botswana adjoining the Linyanti River. Methods We assessed the species composition of the riparian woodland in 2007/2008 along belt transects, recording living and dead individuals in different size classes plus signs of elephant damage and the presence of juvenile plants. We related this current composition to the composition recorded in a previous survey in 1991/1992 and reconstructed the earlier composition by combining living and dead trees recorded in 1991/1992. We established the association between mortality and impact agent, severity, year and size class using model selection statistics. Changes in species diversity were assessed using the Shannon diversity index. Results The composition of canopy trees changed from the initial dominance of two Acacia spp. towards the current situation with these two species forming <5% of the woodland canopy. Dead trees were strongly associated with severe damage inflicted by elephants, including bark stripping and felling. As the acacia trees declined, elephant impacts shifted onto other canopy tree species. The woodland canopy became progressively more open because recruitment from juvenile and sapling stages to replace trees that had died was also suppressed. Nevertheless, the tree species that had decreased in abundance in the canopy remained abundant as juvenile plants. Conclusion Substantial changes in woodland composition can occur in the presence of high elephant concentrations because of the selective damage that elephants impose on particular tree species and size classes. The loss of functionally important species may not be reflected by changes in compositional diversity measures.

Seasonal Variation in Home Range Sizes and Daily Distance to Ephemeral Surface Water for African Savannah Elephant (Loxodonta africana) in Eastern Okavango Panhandle, Northern Botswana

Article

Full-text available

Jan 2025

African elephants (Loxodonta africana) are megaherbivores of the African savannas requiring extensive ranges that can provide critical resources for their survival and reproduction at different spatiotemporal scales. We studied seasonal differences in home range sizes and daily distance to the nearest surface water sources by five male and 10 female African elephants in the eastern Okavango Panhandle in northern Botswana between 2014 and 2017. We hypothesized that (i) elephant home ranges would be larger in the wet than in the dry season (because critical resources tend to be less localized in the wet than in the dry season), (ii) the daily distance of the elephants to the nearest ephemeral surface water sources would be larger in the dry than in the wet season because many of the ephemeral water sources would be dry in the dry season and elephants would start moving towards permanent water sources such as rivers, and lastly (iii) that the differences in elephant home ranges and daily distance to water would differ between sexes. Our results showed that elephant home ranges were larger in the wet than in the dry season, and that they differed between sexes with female elephants having smaller home ranges in the late wet season. The mean daily distance to the nearest ephemeral surface water sources was larger in the dry than in the wet season. There was an inverse relationship between elephants' daily distance to permanent surface water and to ephemeral water sources. The findings indicate the need for large conservation areas and functional connectivity between landscapes to enable the highly mobile savanna elephants to access critical seasonal resources such as water and forage in semi‐arid savannas. Such landscapes are critical, especially in the face of climate change, when high air temperatures and droughts may exacerbate forage and water shortage and intensify human–elephant interactions in surrounding agroecosystems.

Understanding human-elephant interactions across time is key to illuminate pathways toward coexistence

Article

Full-text available

Sep 2024
ECOL SOC

Lauren Redmore

Research on human-elephant interactions (HEI) seeks to better understand relationships between people and elephants with the goal of reducing unwanted interactions for the long-term survival of elephants in social-ecological systems. Many examinations of HEI often rely on a short temporal scale of several seasons to several years, often because of limited data availability across time. These examinations offer limited understanding of processes that influence HEI and mutual adaptations of people and elephants. In this synthesis, I present an ethnographic case study from the Okavango Delta, Botswana, where human and elephant populations have increased in the past 20 years. I use bricolage, a practice of using available materials at hand, to weave together diverse historical and current scholarship and primary data to understand dynamics of HEI and coadaptation across three different periods (pre-colonial, colonial, and post-independence). I show that people and elephants were coadapted in the pre-colonial period when people were highly mobile and hunted elephants with rudimentary technologies in ways that supported human development across southern Africa with minimal impact on elephants. European colonization brought sweeping changes, including through the introduction of guns and the development of the ivory trade that led to massive declines in elephant populations. Development policies that were magnified in the years following independence, including the establishment of land policies that settled communities, additionally disrupted the formally fluid nature of HEI. Simultaneously, wildlife conservation policies that coincided with dramatic increases in elephant populations shape how people perceive HEI and elephants as a predominant environmental force today. I argue that the incorporation of wider historical contexts, where necessary through the practice of bricolage, reveals coadaptation across time and offers understanding of possibilities of coexistence where people and elephants thrive alongside each other.

A Systematic review of the success and unintended consequences of management interventions on African elephants

Article

Full-text available

Dec 2022
PACHYDERM

With elephant numbers increasing in some parts of their range, and related conservation concerns including elephants’ impact on vegetation and human–elephant conflict, management interventions have been used to artificially reduce elephant numbers, to stabilize populations locally and regionally, or to affect their spatial distribution. Interventions may have environmental, demographic, or social impacts, often unintended. We evaluated elephant management interventions, including both direct (contraception, vasectomy, translocation, hunting, culling) and indirect interventions (fencing, range expansion, corridors, water provision, and fire management). The study draws on evidence from across the range of African and Asian elephants, but with a focus on South Africa, through a systematic literature review using Science Direct, Web of Science, Scopus, Google Scholar, and Google from 2007 onwards, i.e. covering the period since the publication of the 2008 Assessment of South African Elephant Management. We focus on the effects of management on elephants, and present information on success of each method, as well as its demographic effects. We also identified unintended consequences of the interventions, such as increased human–elephant conflict, irruptive growth rates, social disruption, inbreeding depression, truncation of migratory routes, excessive vegetation damage, and breakdown in social structure. Culling and trophy hunting had the most unintended consequences, and evoked the most negative sentiments among tourists. There was a large disparity in the research effort directed towards different interventions, and we highlight gaps where additional research is needed. Elephant management can be contentious, with polarized views, and the broader social and economic elements need consideration. Disservices such as human–elephant conflict need to be reduced, and increased attention paid to animal welfare, and the broader expectations of society in this regard. Despite the review not being restricted, our study is informed mainly by research carried out in South Africa, drawing in large part on the base created by the 2008 assessment, as well as the norms and standards for management interventions formalized in South African regulations. Furthermore, the aim of the review was to produce information that could be used to update current approaches to elephant management in South Africa. The review draws on publications outside South Africa where they are available, as knowledge gained elsewhere is crucial for improving management decisions. We believe that our study has wider application for use throughout the African savannah elephant range. Du fait du nombre d’éléphants en augmentation dans certains territoires et des inquiétudes relatives à leur conservation — dont les répercussions sur la végétation et les conflits humains-éléphants — des interventions de gestion ont été mises en place afin de réduire artificiellement les populations et les stabiliser localement et régionalement, ou pour agir sur leur répartition dans ces espaces. Des impacts environnementaux, démographiques ou sociaux, souvent imprévus, peuvent découler de ces opérations. Nous avons évalué ces interventions de gestion, qu’elles soient directes (contraception, vasectomie, transferts, chasse, abattage) ou indirectes (clôtures, agrandissement des aires de répartition, couloirs biologiques, approvisionnement en eau ou gestion des incendies). L’étude s’appuie sur des données provenant de l’ensemble des aires de répartition des éléphants d'Afrique et d'Asie avec un gros plan sur les individus sud-africains, grâce à une analyse systématique de la littérature sur le sujet en utilisant Science Direct, Web of Science, Scopus, Google Scholar et Google à partir de 2007, soit toute la période depuis le 2008 Assessment of South African Elephant Management (Évaluation de la gestion de l’éléphant sud-africain en 2008). Nous avons ciblé les effets immédiats de ces interventions sur les éléphants et nous présentons ici les réussites de chaque méthode, ainsi que leur impact sur la démographie. Nous avons également identifié les conséquences involontaires de ces initiatives, telles que l’augmentation des conflits humains-éléphants, des croissances soudaines de certaines populations, des perturbations sociales, dépression consanguine, routes migratoires tronquées, dommages excessifs dans la végétation et dégradation des structures sociales. L’abattage et la chasse au trophée ont causé les retombées les plus inattendues et ont suscité les sentiments les plus négatifs parmi les touristes. D’importantes disparités ont été constatées dans l’effort de recherche consacré aux différentes interventions et nous soulignons les lacunes lorsque de plus amples informations sont nécessaires. La gestion des éléphants peut être controversée et soulever des points de vue opposés, et les composantes sociales et économiques plus générales doivent être prises en compte. Il convient de réduire les torts causés par les conflits humain-éléphant et d’accorder une plus grande attention au bien-être des animaux et aux attentes de la société à cet égard. Bien que le rapport ne soit pas restrictif, notre étude se base principalement sur les recherches menées en Afrique du Sud, plus précisément sur les éléments rassemblés lors de l’évaluation de 2008, ainsi que sur les normes et critères des interventions de gestion formalisés dans la réglementation sud-africaine. De plus, l’objectif du rapport était de produire des informations pouvant être utilisées pour une nouvelle approche de la gestion de l’éléphant en Afrique du Sud. Le compte-rendu fait appel à certaines publications autres que sud-africaines lorsqu’elles étaient disponibles, car indépendamment de leur origine, les données sont essentielles pour renseigner les décisions dans le domaine de la gestion. Nous considérons que notre étude sera utile dans toutes les aires de répartition de l’éléphant de savane.

Bat Functional Diversity along the Chobe River Floodplain, Botswana

Article

Jun 2023

The hard lives of trees in African savanna—Even without elephants

Article

Jan 2023

The ongoing loss of large trees and densification of shrubs are two prevalent processes that take place in African savannas, with profound consequences for their structure and function. We evaluated herbivore impacts on savanna woody communities using a long‐term exclosure experiment in the Kruger National Park, South Africa, with three treatments: the exclusion of large mammals only (i.e. elephant and giraffe), exclusion of all herbivores larger than a hare, and areas open to all herbivores. We asked three questions: (1) How did variable exclusion of herbivores affect woody density and structure across the catena (i.e. riparian, sodic and crest vegetation)? (2) Did the exclusion of herbivores result in unique woody species composition? (3) Did herbivore exclusion result in a higher proportion of palatable species? After 17 years, we found that herbivores mainly affected the heights and densities of existing species, rather than leading to turnover of woody species assemblages. Although densities of individuals increased in the full exclosure (350 ha−1), the change was more moderate than expected. By contrast, mixed mega‐and meso‐herbivores decreased the number of trees and shrubs (decreases of 780 ha−1) via a variety of physical impacts. Meso‐herbivores alone, on the other hand, had less impact on individual density (i.e. no change), but limited average height growth and canopy dimensions in certain habitat types. Where elephants are present, they are effective at reducing the density of woody stems to the point of counteracting woody encroachment, but at the same time are actively preventing the persistence of large trees (>5 m) as well as preventing trees from recruiting to larger size classes. However, the lack of massive recruitment and woody cover increases with elephant exclusion, especially for more preferred species, suggests that factors beyond elephants, such as dispersal limitation, seed predation, and drought, are also acting upon species. We evaluated herbivore impacts on savanna woody vegetation using a long‐term exclosure experiment (17 years) in the Kruger National Park, South Africa, with three treatments: the exclusion of large mammals only (i.e. elephant and giraffe), exclusion of all herbivores, and areas open to all herbivores. Elephants (and giraffe) reduced the density of woody stems to the point of counteracting woody encroachment, and at the same time prevented trees from recruiting into larger size classes. However, removing elephants resulted in non‐linear vegetation responses; partly because smaller herbivores also have pronounced impacts on vegetation dynamics, as well as other factors, such as dispersal limitation, seed predation, and drought, acting upon species.

The effect of Loxodonta africana (African elephant) damages to vegetation on bird diversity with reference to provision of water

Thesis

Full-text available

Feb 2016

Ettore Fedele

Elephants (Loxodonta africana) are mega-herbivores and key-stone species of African savanna ecosystems with a large capability of altering their habitats. As the human population in Africa continues to grow and wild animals are forced into smaller protected areas at much higher densities, experts have suggested that damaging effects on ecosystems will follow. With elephants being a major asset for tourism revenue, reserve managers have actively manipulated the landscape and created artificial water sources in order to increase wildlife viewing. It has been suggested that the creation of additional water sources may have a range of detrimental effects on ecosystem heterogeneity, with large-herbivores exerting greater pressures on water surrounding vegetation. The aim of this project was to examine how this could change elephant foraging behaviour and the knock-on effects on floral and faunal biodiversity in Struwig Eco Reserve (part of the Kruger National Park) in South Africa. Floral community species richness, diversity and damage (using a ) were surveyed every day in June and July 2015. Birds were used as an indicator of faunal diversity and were surveyed each morning for two and a half hours after dawn. It was found that elephants have an impact on vegetation as no significant difference was found in Species Diversity levels with reference to proximity to water, as would be expected in a semi-arid environment. Botanical surveys identified plants on Struwig which appeared to increase their susceptibility to damage by elephants. In addition it was found that the highest functional diversity amongst bird species was recorded furthest from the water source. This suggests that in this study area biodiversity is higher further away from water, where the impacts from elephants are lower. This is in contrast to the widely accepted theory that in semi-arid habitats biodiversity is higher near water sources. In conclusion this research suggests that elephant populations do influence woody vegetation diversity, especially when close to a permanent water source. This leads to knock-on effects on other species, as suggested by looking at diversity of birds which are an important indicator group.

Long-term field studies of elephants: understanding the ecology and conservation of a long-lived ecosystem engineer

Article

Full-text available

May 2018

Hervé Fritz

Elephants may live for > 60 years, so it is obvious that long-term studies are necessary if we are to understand their life histories. Here, I review long-term population studies, most based on individual elephants, to show the wealth of detailed mechanisms that such studies can reveal. This review is biased toward African savanna elephants, a reflection of existing long-term studies on elephants worldwide. Besides life histories, there are 2 aspects of elephant biology that are illuminated by long-term field studies (not necessarily those based on individual elephants). First is knowledge of spatial dynamics of populations that occur in response to environmental change (climatic or anthropogenic), such as density dependence that is associated with the distribution of surface water or responses to specific management decisions, and second is the effects these ecosystem engineers have on habitats, landscapes, other species, and ultimately on ecosystems. I also argue that these long-term data are crucial to inform conservation policies and associated management actions, such as changes in water-pumping strategies, landscape management, and control of elephant populations.

PREDICTING HABITAT SUITABILITY FOR VACHELLIA STUHLMANNII (TAUB.) AND VACHELLIA TORTILIS (FORSKK.) IN SEMI-ARID AFRICAN SAVANNA USING MAXENT

Article

Full-text available

Sep 2024

Sellina Ennie Nkosi

Nkosi: Predicting habitat suitability for Vachellia stuhlmannii (Taub.) and Vachellia tortilis (Forskk.) in semi-arid African savanna using MaxEnt-4463-APPLIED ECOLOGY AND ENVIRONMENTAL RESEARCH 22(5):4463-4480. Abstract. Habitat suitability of Vachellia stuhlmannii and Vachellia tortilis was evaluated using MaxEnt. Location data was collected, and nineteen bioclimatic variables data downloaded from the WorldClim database. Soils were analysed to investigate their influence on habitat suitability of the two species. MaxEnt effectively predicted current habitat suitability with an average test Area Under Curve value of 0.936 for V. stuhlmannii and 0.689 for V. tortilis. Key influential variables were BIO-1 (Annual mean temperature) with 71.7% highest gain for V. stuhlmannii and BIO-17 (Precipitation of driest quarter) with 65.3% highest gain for V. tortilis. However, BIO-14 (Precipitation of driest month) exhibited limited influence in predicting habitat suitability. V. stuhlmannii is estimated to cover an area of ~3 255.8 hectares, while V. tortilis is estimated to cover ~11 180.7 hectares. Both species predominantly occur on Prismacutanic/pedocutanic B-horizons. V. tortilis also thrive on Glenrosa and Mispah soils, which are crucial for diverse plant and animal life. These findings have practical implications for conservation efforts aimed at protecting these species. Identifying suitable habitats and preserving soil types is crucial as soil affects microclimate conditions and influences moisture retention. Overall, this study provides insights for the conservation of V. stuhlmannii and V. tortilis in the semi-arid African savanna.

Mapping plant communities of the Karoo National Park, South Africa, using Sentinel-2 and topo-morphological data-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Article

Full-text available

Aug 2024
S AFR J BOT

Aims: This study aimed at classifying, mapping and describing the plant communities of the Karoo National Park using floristic surveys in conjunction with Sentinel-2 and topo-morphological data. Study area: Karoo National Park, Western Cape, South Africa. Methods: The vegetation of the Karoo National Park was delineated into homogenous physiognomic-physio-graphic units using Sentinel-2 images. A total of 128 survey plots (100 m 2 each) were surveyed within the different homogeneous units during the period 2016 to 2020. Within each survey plot, all rooted species were identified and their cover abundance estimated. Each plot was photographed and its geolocation recorded. The floristic data were captured using the Braun Blanquet Personal Computer suite and exported to the JUICE Software programme. A modified TWINSPAN classification was done to derive a first tabled synopsis of the plant communities. The different plant communities were subsequently classified and described according to their diagnostic and dominant species gleaned from the synoptic table. Species richness was determined by counting the number of different species per plant community while the ShannonÀWiener Index and Rich-GiniÀSimpson Index of diversity (D) were used to derive indices of species diversity per plant community. Results: 12 major communities and two sub-communities that are distinctly linked to various abiotic factors were identified, described and mapped. The higher-lying rocky steep midslopes as well as the valley bottom-land areas had the highest diversity and species richness. Conclusions: This study proves the efficacy of using Sentinel-2 and topo-morphological data in classification, description and mapping vegetation of extensive natural areas. The vegetation map and classification of plant communities provide a baseline to inform management decisions.

Are hippos Africa's most influential megaherbivore? A review of ecosystem engineering by the semi-aquatic common hippopotamus

Article

Apr 2023
BIOL REV

Megaherbivores perform vital ecosystem engineering roles, and have their last remaining stronghold in Africa. Of Africa's remaining megaherbivores, the common hippopotamus (Hippopotamus amphibius) has received the least scientific and conservation attention, despite how influential their ecosystem engineering activities appear to be. Given the potentially crucial ecosystem engineering influence of hippos, as well as mounting conservation concerns threatening their long-term persistence, a review of the evidence for hippos being ecosystem engineers, and the effects of their engineering, is both timely and necessary. In this review, we assess, (i) aspects of hippo biology that underlie their unique ecosystem engineering potential; (ii) evaluate hippo ecological impacts in terrestrial and aquatic environments; (iii) compare the ecosystem engineering influence of hippos to other extant African megaherbivores; (iv) evaluate factors most critical to hippo conservation and ecosystem engineering; and (v) highlight future research directions and challenges that may yield new insights into the ecological role of hippos, and of megaherbivores more broadly. We find that a variety of key life-history traits determine the hippo's unique influence, including their semi-aquatic lifestyle, large body size, specialised gut anatomy, muzzle structure, small and partially webbed feet, and highly gregarious nature. On land, hippos create grazing lawns that contain distinct plant communities and alter fire spatial extent, which shapes woody plant demographics and might assist in maintaining fire-sensitive riverine vegetation. In water, hippos deposit nutrient-rich dung, stimulating aquatic food chains and altering water chemistry and quality, impacting a host of different organisms. Hippo trampling and wallowing alters geomorphological processes, widening riverbanks, creating new river channels, and forming gullies along well-utilised hippo paths. Taken together, we propose that these myriad impacts combine to make hippos Africa's most influential megaherbivore, specifically because of the high diversity and intensity of their ecological impacts compared with other megaherbivores, and because of their unique capacity to transfer nutrients across ecosystem boundaries, enriching both terrestrial and aquatic ecosystems. Nonetheless, water pollution and extraction for agriculture and industry, erratic rainfall patterns and human-hippo conflict, threaten hippo ecosystem engineering and persistence. Therefore, we encourage greater consideration of the unique role of hippos as ecosystem engineers when considering the functional importance of megafauna in African ecosystems, and increased attention to declining hippo habitat and populations, which if unchecked could change the way in which many African ecosystems function.

Assessing the Impact of Wildlife on Vegetation Cover Change, Northeast Namibia, Based on MODIS Satellite Imagery (2002–2021)

Article

Full-text available

May 2022
SENSORS-BASEL

Human–wildlife conflict in the Zambezi region of northeast Namibia is well documented, but the impact of wildlife (e.g., elephants) on vegetation cover change has not been adequately addressed. Here, we assessed human–wildlife interaction and impact on vegetation cover change. We analyzed the 250 m MODIS and ERA5 0.25° × 0.25° drone and GPS-collar datasets. We used Time Series Segmented Residual Trends (TSS-RESTREND), Mann–Kendall Test Statistics, Sen’s Slope, ensemble, Kernel Density Estimation (KDE), and Pearson correlation methods. Our results revealed (i) widespread vegetation browning along elephant migration routes and within National Parks, (ii) Pearson correlation (p-value = 5.5 × 10−8) showed that vegetation browning areas do not sustain high population densities of elephants. Currently, the Zambezi has about 12,008 elephants while these numbers were 1468, 7950, and 5242 in 1989, 1994, and 2005, respectively, (iii) settlements and artificial barriers have a negative impact on wildlife movement, driving vegetation browning, and (iv) vegetation greening was found mostly within communal areas where intensive farming and cattle grazing is a common practice. The findings of this study will serve as a reference for policy and decision makers. Future studies should consider integrating higher resolution multi-platform datasets for detailed micro analysis and mapping of vegetation cover change.

Elephant browsing impacts in a Zambezian Baikiaea woodland with a high density of pumped waterholes

Article

Full-text available

Oct 2021

Foraging by African savanna elephant (Loxodonta africana) and other herbivores tends to result in a piosphere effect around water sources, with increasing pressure on vegetation as distance to water decreases. This study aimed to investigate the impacts of pumped waterholes on woody vegetation in the southern portion of Zimbabwe’s Zambezi National Park, a Baikiaea woodland ecosystem characterised by high elephant densities. The recent rehabilitation and addition of pumped waterholes has resulted in a dense waterhole network in the park, prompting concerns around potential negative impacts on vegetation. Sampling plots were located at different distances from four pumped waterholes in Baikiaea plurijuga and Terminalia sericea woodlands. Elephant browsing levels and vegetation structure were assessed across three plant height classes (0.2 - < 1 m; 1 - < 3 m and ≥ 3 m). Elephant dung counts were also conducted to provide a relative measure of elephant occupancy. A decline in elephant browsing with distance to waterholes was evident in both woodland types, though browsing was consistently higher in the Terminalia woodland. Structural impacts of elevated elephant browsing around waterholes were limited in the Baikiaea woodland. However, substantial reductions in the basal area and canopy volume of trees were evident closer to waterholes in the Terminalia woodland, with widespread conversion of woodland to shrubland. Elephant dung decreased with distance from waterholes in both woodland types, confirming that elephant occupancy was higher closer to waterholes. Overall, clear effects of pumped waterholes were evident. The ecological integrity of the Terminalia woodland in particular appears to be under threat, especially as the current surface water regime places most of it within 3 km of waterholes. The cessation of pumping at some waterholes was thus recommended, to achieve a more heterogenous browsing regime in the area.

Naïve plant communities and individuals may initially suffer in the face of reintroduced megafauna: An experimental exploration of rewilding from an African savanna rangeland

Article

Full-text available

Apr 2021
PLOS ONE

Excluding large native mammals is an inverse test of rewilding. A 25-year exclosure experiment in an African savanna rangeland offers insight into the potentials and pitfalls of the rewilding endeavor as they relate to the native plant community. A broad theme that has emerged from this research is that entire plant communities, as well as individual plants, adjust to the absence of herbivores in ways that can ill-prepare them for the return of these herbivores. Three lines of evidence suggest that these “naïve” individuals, populations, and communities are likely to initially suffer from herbivore rewilding. First, plots protected from wild herbivores for the past 25 years have developed rich diversity of woody plants that are absent from unfenced plots, and presumably would disappear upon rewilding. Second, individuals of the dominant tree in this system, Acacia drepanolobium, greatly reduce their defences in the absence of browsers, and the sudden arrival of these herbivores (in this case, through a temporary fence break), resulted in far greater elephant damage than for their conspecifics in adjacent plots that had been continually exposed to herbivory. Third, the removal of herbivores favoured the most palatable grass species, and a large number of rarer species, which presumably would be at risk from herbivore re-introduction. In summary, the native communities that we observe in defaunated landscapes may be very different from their pre-defaunation states, and we are likely to see some large changes to these plant communities upon rewilding with large herbivores, including potential reductions in plant diversity. Lastly, our experimental manipulation of cattle represents an additional test of the role of livestock in rewilding. Cattle are in many ways ecologically dissimilar to wildlife (in particular their greater densities), but in other ways they may serve as ecological surrogates for wildlife, which could buffer ecosystems from some of the ecological costs of rewilding. More fundamentally, African savannah ecosystems represent a challenge to traditional Western definitions of “wilderness” as ecosystems free of human impacts. We support the suggestion that as we “rewild” our biodiversity landscapes, we redefine “wildness” in the 21st Century to be inclusive of (low impact, and sometimes traditional) human practices that are compatible with the sustainability of native (and re-introduced) biodiversity.

Assessment of elephant diets in Omo Forest Reserve, South-Western Nigeria

Thesis

Full-text available

Mar 2021

Esther C Chinweuba

The elephant is the largest land-dwelling mammal that feeds on a variety of plant species. The details regarding elephant food and preference remain unknown in Nigeria. This study was carried out to assess elephant diet, and determine the feeding preference among plant parts and the relationship between the availability of plants species and preference by elephants in Omo Forest Reserve, Ogun State, Nigeria during the dry season. Five line transects were laid each in elephant Sanctuary and farmland. Five plots of 20 × 20 m were obtained in each transect making a total of 50 sample plots and were used to collect data on plant species, plant parts, frequency, and DBH. A micro-histological analysis of elephant dung was carried out in the laboratory to determine micro-fragments of plants in the elephant diet. Feeding score, Importance value index (IVI), preference index (PI), Simpson‘s diversity, Chi-square analysis and Pearson correlation were employed for data analysis. Twenty-nine plant species belonging to twenty-three taxonomic families were consumed by elephants. The plant species eaten by elephants include twenty species of trees, five species of climbers, three species of herbs and one species of shrub. Elephants feed on leaves, bark, fruits/or seed, stem and tubers. The preference index (PI) showed fifteen food plant species that were highly preferred by the elephant in the study area. The micro histological analysis showed ten species of plant in elephant dungs assessed. The results present useful information on elephant diet which could ensure the conservation of elephant habitat, hence the continuity of elephant in Nigeria. All illegal activities carried out in the Sanctuary that threatens elephant food and habitat need great attention from the government and local authorities. Further study on nutrient analysis of the plant species should be done. Keywords: Elephant diet, browse, feeding preference, habitat, conservation

Feasibility of reintroducing grassland megaherbivores, the greater one-horned rhinoceros, and swamp buffalo within their historic global range

Article

Full-text available

Feb 2021

Reintroduction of endangered species is an effective and increasingly important conservation strategy once threats have been addressed. The greater one-horned rhinoceros and swamp buffalo have declined through historic hunting and habitat loss. We identify and evaluate available habitat across their historic range (India, Nepal, and Bhutan) for reintroducing viable populations. We used Species Distribution Models in Maxent to identify potential habitats and evaluated model-identified sites through field visits, interviews of wildlife managers, literature, and population-habitat viability analysis. We prioritize sites based on size, quality, protection, management effectiveness, biotic pressures, and potential of conflict with communities. Our results suggest that populations greater than 50 for rhinoceros and 100 for buffalo were less susceptible to extinction, and could withstand some poaching, especially if supplemented or managed as a metapopulation. We note some reluctance by managers to reintroduce rhinoceros due to high costs associated with subsequent protection. Our analysis subsequently prioritised Corbett and Valmiki, for rhino reintroduction and transboundary complexes of Chitwan-Parsa-Valmiki and Dudhwa-Pilibhit-Shuklaphanta-Bardia for buffalo reintroductions. Establishing new safety-nets and supplementing existing populations of these megaherbivores would ensure their continued survival and harness their beneficial effect on ecosystems and conspecifics like pygmy hog, hispid hare, swamp deer, hog deer, and Bengal florican.

2 12.1 Introduction: The Relevance of Growth Rates Patterns and Determinants of Woody Plant Growth in Savannas, in "Savanna Woody Plants and Large Herbivores"

Chapter

Full-text available

Nov 2019

This chapter reviews the theory and data relating to the growth rates of woody plants in savanna ecosystems. What is the relevance of these growth rates? Understanding growth rates of savanna trees and shrubs is critical for understanding the current struc ture and functioning of savanna ecosystems, determining causes of recent changes, and predicting changes that will occur in response to global change impacts over the coming decades. Growth rates are a key component of theories that aim to explain the coexist ence of woody plants and grasses in savannas (Sankaran et al. 2004), while differences in growth rates may be a key factor explaining the coexistence of many woody species. Growth rates are key parameters in many models of the structure or functioning of savanna ecosystems (Table 12.1), and are integral to many ecosystem services provided by savannas. Differences in growth rates between savanna and forest species may also be important for determining the boundary between these respective ecosystems (Chapter 1). Woody plants comprise the majority of the biomass of many savannas, and it is their growth that primarily regulates the exchanges of carbon, water, and energy among savanna ecosystems, the atmosphere, and the hydrosphere. Tropical savannas are responsible for approximately 15% of global carbon storage, with net primary produc tivity that, on average, matches that of tropical forests (Grace et al. 2006). Temperate savannas contribute an additional but unknown amount. The growth of woody plants is responsible for about half of this contribution, with grasses contributing the remainder, although the relative contribution of the two groups varies greatly according to woody plant abundance (Menaut and Cesar 1979; Scholes and Walker 1993; Hughes et al. 2006; Lloyd et al. 2008). The growth, and regrowth, of the stems of woody plants provides fuelwood and charcoal for millions of people (Chapter 6), while the growth, and

Patterns and Determinants of Woody Plant Growth in Savannas

Chapter

Full-text available

Aug 2019

This chapter reviews the theory and data relating to the growth rates of woody plants in savanna ecosystems. Growth rates are a key component of theories that aim to explain the coexistence of woody plants and grasses in savannas, while differences in growth rates may be a key factor explaining the coexistence of many woody species. Woody plants comprise the majority of the biomass of many savannas, and it is their growth that primarily regulates the exchanges of carbon, water, and energy among savanna ecosystems, the atmosphere, and the hydrosphere. The growth of woody plants is responsible for about half of this contribution, with grasses contributing the remainder, although the relative contribution of the two groups varies greatly according to woody plant abundance. Common patterns of growth rates, within sites and species, would provide useful insights regarding determinants of growth rates and allow for more accurate modeling of the growth of woody plants in savannas.

Soil diversity and major soil processes in the Kalahari basin, Botswana

Article

Full-text available

Jul 2019

The study area of the Chobe Enclave (northern Botswana) is defined as mostly covered by Arenosols in available maps. However, recent explorations of the area showed that soils are more diverse than expected. This is because of complex interactions between current alluvial deposition processes, paleo-environmental effects (ancient alluvial deposition, ancient wind-blown sand deposits) and ongoing hydrological effects and colluvial effects on topographic gradients. An in-depth exploration of both soils and vegetation in the area was conducted with the aim (i) to survey the soil diversity at the Chobe Enclave, (ii) to study soil dynamics and identify the key factors of this diversity, and (iii) to create a soil map based on the analysis of the soil-vegetation relationship. For this purpose, thirty-six soil profiles were extensively described according to the World Reference Base for soil resources. In order to better classify these soils, physicochemical parameters, such as pHH2O, exchangeable cations, and particle size distributions, were measured for a specific set of soils (n = 16), representative of their diversity. To assess Soil Organic Matter (SOM) dynamics, samples were studied using Rock Eval pyrolysis. Results show a high soil diversity and heterogeneity with the presence of (i) Arenosols, as expected, but also of (ii) organic-rich soils, such as Chernozems, Phaeozems, and Kastanozems, (iii) salty/sodic soils, such as Solonchaks and Solonetz, and finally (iv) calcium-rich soils, such as Calcisols. Analyses of the different actors driving the soil diversity emphasized the importance of the surficial geology, composed of different sand deposits (red sands/white sands), carbonate and diatomite beds, as well as ancient salt deposits, in which high proportions of exchangeable Na⁺ were found, associated with high pHH2O (up to 11.3). In addition, as a parameter, the topography creates a complex hydrological system in the Chobe Enclave and therefore, induces a notable soil moisture gradient. Moreover, this study stressed the key role of termites: not only do they modify physicochemical patterns of soils, but they also decay and incorporate large quantities of fresh plant materials into soils. Finally, the analysis of Organic Matter (OM) showed that the Soil Organic Carbon (SOC) is composed essentially by recalcitrant Organic Carbon (OC) substances, such as charcoal, a common carbon type of tropical soils.

Simulated elephant-induced habitat changes can create dynamic landscapes of fear

Article

Jul 2019
BIOL CONSERV

Landscapes of fear have become widely studied in the northern hemisphere, but are still largely understudied in the more complex, diverse carnivore-prey communities of Africa. Habitat changes brought about by a mega-herbivore, the African elephant (Loxodonta africana), can modify the perceived landscape of fear by predation vulnerable prey species (impala Aepyceros melampus and warthog Phacochoerus africanus) in contrast with non-prey species (white rhinoceros Ceratotherium simum). We hypothesized that by opening up woody vegetation, elephants may modify perceived risk at a landscape-scale, but also at a fine scale by depositing escape impediments in the form of coarse woody debris. We experimentally tested this in Hluhluwe-iMfolozi Park, South Africa, by simulating elephant-induced habitat changes on patch scale (opening up woody vegetation) and within-patch scale (deposition of coarse woody debris) and monitoring the herbivore visitation using camera traps. We compared visitation on the edge of grazing lawns (in proximity of dense vegetation) and the centre (open, highly visible patches), either with or without coarse woody debris and with or without fresh predator scat. We found that mesoherbivore prey species showed contrasting responses, with warthog avoiding plots close to dense vegetation and plots with coarse woody debris. Impala reduced their visitation to dense vegetation patches only during risky times, at night, especially in the presence of predator scat, but did not clearly avoid plots with coarse woody debris. Our study indicates that, in African savannas, the perceived landscape of fear is a highly dynamic phenomenon varying in both space and time and being species-specific. Elephant induced habitat changes may shape landscapes of fear in complex and contrasting ways.

Processes involved in the functioning of large mammal communities : the role of the African elephant in the ecology of predator-prey relationships

Thesis

Full-text available

Apr 2018

Nicolas Ferry

Species can indirectly affect other species and their interactions. The trophic interaction between a predator and its prey can be modified by the presence of a third species either through chain interactions (e.g. successive predation link) either through interaction modification. However, these indirect received few attentions in theorical modelling of food web, and fewer studies tried to explore this phenomenon at the scale of natural complex communities of large mammals. The role of the elephants as modifier of lion’s trophic interaction is explored in the semi-arid woodland savannah ecosystem of Hwange National Park, Zimbabwe. African elephants, as key competitor (male body mass ~ 4000 kg with aggressive behaviour) shape the behaviour of herbivores at waterholes results do not allow to state on the elephant mediation of lion trophic interaction at waterholes. In addition, elephants seem to facilitate the availability of food resources for impalas, possibly by increasing regrowth of shoots by breaking twigs and stem, as these last select habitats used by elephants. However, not effect of facilitation or competition were observed for the other herbivores, which lead to think that elephants do not influence lion trophic interaction in that way. Finally, by altering the physical environment (i.e. engineer species) the elephants affect the visibility and ambush sites for lions in the woody vegetation and ultimately seem to influence the lion kill site selection. This study suggests that indirect effects may act at the community level even if their observation and quantification are difficult in natural communities. Moreover, it supports the observation that it is important to take into account these indirect effects in order to have a thorough understanding and have a better ability to predict the consequences that disruptions may have on the structure and functioning of communities

Synthesizing the effects of large, wild herbivore exclusion on ecosystem function

Article

Full-text available

Jun 2019
FUNCT ECOL

Wild large herbivores are declining worldwide. Despite extensive use of exclosure experiments to investigate herbivore impacts, there is little consensus on the effects of wild large herbivores on ecosystem function. Of the ecosystem functions likely impacted, we reviewed the five most‐studied in exclosure experiments: ecosystem resilience/resistance to disturbance, nutrient cycling, carbon cycling, plant regeneration, and primary productivity. Experimental data on large wild herbivores' effects on ecosystem functions were predominately derived from temperate grasslands (50% grasslands, 75% temperate zones). Additionally, data were from experiments that may not be of adequate size (median size 400 m² despite excluding all experiments below 25 m²) or duration (median duration 6 years) to capture ecosystem‐scale responses to these low‐density and wide‐ranging taxa. Wild herbivore removal frequently impacted ecosystem functions; for example, net carbon uptake increased by three times in some instances. However, the magnitude and direction of effects, even within a single function, were highly variable. A focus on carbon cycling highlighted challenges in interpreting effects on a single function. While the effect of large herbivore exclusion on carbon cycling was slightly positive when its components (e.g. pools vs. fluxes of carbon) were aggregated, effects on individual components were variable and sometimes opposed. Given modern declines in large wild herbivores, it is critical to understand their effects on ecosystem function. However, this synthesis highlights strong variability in direction, magnitude, and modifiers of these effects. Some variation is likely due to disparity in what components are used to describe a given function. For example, for the carbon cycle we identified eight distinctly meaningful components, which are not easily combined yet are potentially misrepresentative of the larger cycle when considered alone. However, much of the observed difference in responses likely reflects real ecological variability across complex systems. To move towards a general predictive framework we must identify where variation in effect is due to methodological differences and where due to ecosystem context. Two critical steps forward are (a) additional quantitative synthetic analyses of large herbivores' effects on individual functions, and (b) improved, increased systematic exclosure research focusing on effects of large herbivores' exclusion on functions. A free Plain Language Summary can be found within the Supporting Information of this article.

Elephant-induced landscape heterogeneity change around artificial waterholes in a protected savanna woodland ecosystem

Article

Oct 2018

In protected areas, establishment of artificial waterholes has been hypothesised to result in increased elephant (Loxodonta africana) densities around these waterholes which would in turn result in changes in landscape heterogeneity. To test this hypothesis this study first tested the relationship between waterhole distribution from remotely sensed waterholes and elephant density in Hwange National Park (HNP), Zimbabwe. The study tested using the coefficient of variation of the Normalised Difference Vegetation Index (NDVI CoV) the short-term effects of varying elephant densities on vegetation heterogeneity change at the landscape scale. This study also tested the relation between artificial waterholes and surrounding landscape configuration and composition change and in addition assessed the potential influence of spatial variability in rainfall on landscape configuration and composition dynamics. Results indicate that elephant density increases in response to the increase in concentration of late dry season waterholes. Results indicate that there is no relationship between elephant density and vegetation heterogeneity change at the seasonal scale (short-term). This could be attributable to differences in sensitivity and response of different vegetation types to elephant browsing even the variable foraging preferences of elephants at the landscape scale regardless of elephant occupation. Findings of this study imply that in the long term, maintenance of artificial waterholes results in a decrease in woody vegetation structural heterogeneity through conversion of woodlands to coppiced bushland in areas with high artificial waterhole density. Findings of this study also show that landscape heterogeneity change is not significantly related to the existing north-east to south-west gradient of decreasing rainfall in HNP.

Animal diversity declines with broad-scale homogenization of canopy cover in African savannas

Article

Oct 2018
BIOL CONSERV

Complexity in African savannas: Direct, indirect, and cascading effects of animal densities, rainfall and vegetation availability

Article

Full-text available

May 2018
PLOS ONE

Savanna ecosystems are popular subjects for interaction studies. Multiple studies have been done on the impact of elephants on vegetation, the impact of grass and browse availability on animal densities or on competition between herbivore species. Previous studies showed that elephant densities are frequently negatively correlated with densities of tall trees, and that browse and grass availability are correlated with browser and grazer density respectively. Additionally, a competition effect between browse and grass availability has been reported. These relationships are usually analysed by testing direct relationships between e.g., herbivore densities and food availability, without addressing competition effects or other indirect effects. In this study, multiple interactions in a savanna system have been analysed simultaneously using Partial Least Square-Path Modelling (PLS-PM) using mammal and vegetation data from three different wildlife reserves in southern KwaZulu-Natal. The results showed that the processes that three separate models for the three areas provided the best understanding of the importance of the different interactions. These models suggest that elephants had a negative impact on trees, but also on grass availability. The impact is stronger when elephants are not able to migrate during the dry season. Browsers and grazers were correlated with browse and grass availability, but competition between browse and grass was not detected. This study shows that due to the complexity of the interactions in an ecosystem and differences in environmental factors, these interactions are best studied per area. PLS-PM can be a useful tool for estimating direct, indirect, and cascading effects of changing animal densities in conservation areas.

The Influence of Area Enclosure on the Conservation of Plant Species in an Urban Ecosystem

Chapter

Dec 2024

Area exclosures are used to minimise degradation of plant populations which are threatened by overexploitation. This study assessed the influence of a national botanical garden (area exclosure) on plant diversity and population structure. This was done by sampling in area exclosure and adjacent communal areas. Data were collected from a total of 60 (10 m × 10 m) randomly selected plots. Diameter at breast height (DBH) was measured and percentage canopy cover was estimated for all plant species. Species diversity and evenness were calculated for each site. Plant communities were classified using cluster analysis. Student t-test was used to compare diversity and evenness between the sites. Plant species composition was compared using multi-response permutation procedures. Species richness was higher in area exclosure (21) than in communal areas (12). Species diversity was significantly (p < 0.05) higher in area exclosure than in communal area. The total density was higher in area exclosure than in the communal area. The overall structure in area exclosure was healthy while the communal area showed unhealthy pattern. There were three distinct (p < 0.05) woody plant communities being Vachellia tortilis–Grewia flavescens (communal), Senegalia erubescens–Rhigozum brevispinosum (exclosure), and Dichrostachys cinerea–Combretum hereroense (exclosure). Area exclosures should be increased in Botswana to conserve woody plants.

Modern African ecosystems as landscape-scale analogues for reconstructing woody cover and early hominin environments

Article

Nov 2024
J HUM EVOL

Local extirpation of woody species in Colophospermum mopane woodland under chronic utilisation by elephants

Article

Jul 2024

The hypothesis that certain woody species may be prone to local extirpation under chronic elephant utilisation was examined for Colophospermum mopane open woodland, for an area within the foraging range of elephants from permanent water. Elephant density increased from nearly absent in the 1970s to >3 elephants km ⁻² , with 0.62 adult bulls km ⁻² , by 2022. Study components of vegetation impact included a long‐term elephant exclosure, a fence‐line contrast with an adjacent communal area, comparison with an adjacent wildlife reserve carrying a fifth of the elephant density and the use of historical studies of the vegetation. A history of elephant utilisation resulted in woodland becoming hedged through pollarding of tree stems by elephants. Impacted woodland was characterised by a slightly lower tree density, reduced average height of trees, altered shrub composition and lower species richness. The dominant C. mopane and sub‐dominant species had persisted. However, about 14 species were potentially trending towards local extirpation on account of very high levels of adult mortality, but had persisted because of a low level of seedling recruitment. Fleshy fruits were a shared attribute among most extirpation‐trending species, which, together with a reduction in woody species richness that affects browsers, has ramifications for trophic flows.

Megaherbivores

Chapter

Jan 2024

Norman Owen-Smith

Structure and Regeneration Status of Woody Seed Oil Species in Northern Botswana

Article

Full-text available

Nov 2023

Concerns about energy security and environmental risks have sparked interest in edible and non-edible seed oils as potential renewable feedstocks for biodiesel production. A study was conducted to investigate the population structure and regeneration status of woody seed oil species in the districts of Chobe and Ngamiland. The population structure and regeneration condition of woody seed oil species were studied in 20 × 20 m (400 m ² ) quadrats spaced 50 m apart along a parallel line transect. Data on the identity of all woody species, the number of all live individuals, and the diameter at breast height (DBH) of individuals with DBH > 2 cm of each woody species were collected in each quadrat. The diversity ( Hʹ ) and evenness ( Jʹ ) of woody seed oil species were 1.53, 1.42 and 0.71, and 0.85, 0.73 and 0.51 in Parakarungu, Seronga and Shorobe, respectively. Ximenia caffra was the dominant woody seed oil plant in Shorobe and Seronga, and exhibited an inverted J -shaped curve with continuous diameter classes distribution. Trichilia emetica was only found in Parakarungu, where it was the second dominant species and demonstrated excellent recruitment and regeneration. In Shorobe and Seronga, Croton megalobotrys was the second most dominant species. It had low recruitment, which was most likely due to herbivory and predation on seeds and seedlings. The least prevalent species ( Sclerocarya birrea, Schinziophyton rautanenii and Guibourtia coleosperma ) had no representation in the intermediate diameter-classes, which might be attributed to the selective removal in these diameter-classes. The examination of the population structure of woody seed oil species indicated variations in patterns of diameter-class distribution, indicating differences in the population dynamics of the species across the study areas. The least dominant species experienced hindered recruitment and regeneration due to herbivory and anthropogenic influences.

The effects of floods, droughts and elephants on riparian tree mortality in a semi-arid savanna

Article

Oct 2023
FOREST ECOL MANAG

Limited impact of elephants on trees and shrubs in semi-arid thicket vegetation in southern Africa

Article

Full-text available

Sep 2023
PLANT ECOL

When wide ranging, herbivorous species such as African elephants (Loxodonta africana) are confined and their population densities increase, the vegetation may be negatively affected. Any changes to vegetation structure and complexity may then result in a series of ecological cascades on other plant and animal species that rely on the vegetation for survival. We assessed the composition and structure of the woody and succulent plants within the locally endemic Albany Thicket Biome at five protected areas (reserves) with elephants in the Eastern Cape province, South Africa in 2006 and 2016. We show that when elephant populations in this region are actively managed, wholesale negative impacts on woody thicket plant physiognomy are not observed. In fact, the only statistically detectable change over time, presumably due to elephants, was the toppling of larger, single-stemmed trees. We believe that because the Albany Thicket Biome evolved in the presence of large, top-down browsers such as elephants, the generally negative effects that have been observed of elephants on vegetation in savanna systems are not evident. However, the reserves with elephants in the Eastern Cape are all relatively small (< 400 km2) and fenced which prevents elephant dispersal. Thus, continued monitoring of elephant browsing effects is crucial for the future conservation of this unique biome.

Grouping behavior of African forest elephants (Loxodonta cyclotis): A significant habitat exploitation strategy in Mount Cameroon National Park, Southwest region, Cameroon

Article

Aug 2023

Wildlife grouping behavior is a significant survival strategy beneficial to all the group members. Migration to healthy food locations, defense from predators, mating, and social organization are some of the products of a well-established and organized grouping behavior of wildlife species such as elephants. Hence, the main objective of this study was to explore the grouping behavior of elephants on some ecological parameters in Mount Cameroon national park. Research data was collected within a period of four months by monitoring and observing elephant groups and their activities within their feeding ecology. Data collection was done during the first 15 days of each month and analyzed by Chi-square and correlation statistical models. In the study, elephant-group activity recorded a significance, X2 = 29.89 df = 8 p = 0.000, X2 = 12.95 df = 8 p < 0.05, and X2 = 11.801 df = 4 p = 0.019 on photo-period, atmospheric conditions, and habitat types respectively. The elephant groups also recorded a significant agreement, r = 0.061 p = 0.008, X2 = 17.35 df = 16 p < 0.05, and X2 = 27.62 df = 12 p = 0.006 on landscape, crop-farm, and crop-farm size estimate respectively. Additionally, elephant group activity recorded a significance, X2 = 18.39 df = 8 p = 0.018, r = 0.107 p < 0.05, X2 = 9.12 df = 8 p < 0.05, and X2 = 13.85 df = 8 p < 0.05 on farm destruction rate, farm destruction distance from human homes, elephant trails, and the crop-raided villages respectively. Group formation of elephants in the park is however reduced to smaller sizes probably due to the killing of elephants for human safety, a situation that could scare and cause some of the elephants to migrate to distant areas.

Restoring the functions of grazed ecosystems

Chapter

May 2006

Iain James Gordon

Most large herbivores require some type of management within their habitats. Some populations of large herbivores are at the brink of extinction, some are under discussion for reintroduction, whilst others already occur in dense populations causing conflicts with other land use. Large herbivores are the major drivers for forming the shape and function of terrestrial ecosystems. This 2006 book addresses the scientifically based action plans to manage both the large herbivore populations and their habitats worldwide. It covers the processes by which large herbivores not only affect their environment (e.g. grazing) but are affected by it (e.g. nutrient cycling) and the management strategies required. Also discussed are new modeling techniques, which help assess integration processes in a landscape context, as well as assessing the consequences of new developments in the processes of conservation. This book will be essential reading for all involved in the management of both large herbivores and natural resources.

Themes and future directions in herbivore‐ecosystem interactions and conservation

Chapter

May 2006

Looking into the world’s largest elephant population in search of ligninolytic microorganisms for biorefineries: a mini-review

Article

Full-text available

Jun 2022
Biotechnol Biofuels

Gastrointestinal tracts (GIT) of herbivores are lignin-rich environments with the potential to find ligninolytic microorganisms. The occurrence of the microorganisms in herbivore GIT is a well-documented mutualistic relationship where the former benefits from the provision of nutrients and the latter benefits from the microorganism-assisted digestion of their recalcitrant lignin diets. Elephants are one of the largest herbivores that rely on the microbial anaerobic fermentation of their bulky recalcitrant low-quality forage lignocellulosic diet given their inability to break down major components of plant cells. Tapping the potential of these mutualistic associations in the biggest population of elephants in the whole world found in Botswana is attractive in the valorisation of the bulky recalcitrant lignin waste stream generated from the pulp and paper, biofuel, and agro-industries. Despite the massive potential as a feedstock for industrial fermentations, few microorganisms have been commercialised. This review focuses on the potential of microbiota from the gastrointestinal tract and excreta of the worlds’ largest population of elephants of Botswana as a potential source of extremophilic ligninolytic microorganisms. The review further discusses the recalcitrance of lignin, achievements, limitations, and challenges with its biological depolymerisation. Methods of isolation of microorganisms from elephant dung and their improvement as industrial strains are further highlighted.

Structure and composition of woody vegetation along the Zambezi river floodplain and seasonal water pans in Mana Pools National Park, Zimbabwe

Article

May 2022

This study aimed at investigating woody vegetation structure and composition in relation to surface water availability in Mana Pools National Park (MPNP). Two study sites, namely the Zambezi River floodplain and seasonal water pans were selected. Sampling plots were systematically placed along transects from water pans at 100 m, 200 m and 500 m and thirty (30) different sampling plots of size 600 m2 were used. Statistical analysis was done using STATISTICA 7. A total of 192 woody plants from 18 woody species were recorded. More woody tree species (n = 13) were recorded around seasonal water pans as compared to the Zambezi River zone (n = 5). Results obtained from Kruskal Wallis H test showed no significant difference in height, basal area and tree density along a distance gradient from the Zambezi River to the interior (inland). Stem density and diversity showed a significant difference along a distance gradient from the Zambezi River to the interior (p < 0.05). Woody species density and diversity increased as a function of distance from the Zambezi River channel, with species diversity higher around seasonal water pans. A comparison obtained from the Mann Whitney U test between the two sampling sites showed significant difference in all structural variables. Findings of this study showed that the woodlands along the Zambezi River were more degraded as compared to those around seasonal water pans. It is an indication that the concentration of herbivores is impacting woodlands along the Zambezi River. Management should consider establishing artificial water pans around the park to minimise herbivore pressure along the Zambezi River.

Surface water distribution challenges and elephant impacts on woody species in Mana Pools National Park, Zimbabwe

Article

Apr 2022

This study assessed the relationship between surface water distribution and elephant impacts on the Zambezi River flood plain, Mana Pools National Park woody species ecosystem. Water availability and forage are major requirements for African elephant distribution within an ecosystem landscape in Zimbabwe. Surface water unavailability reduce elephant home range to around peripheries of water bodies and this is intensifying the destruction of wood species around these water bodies. The study adopted a mixed methods research design which combined qualitative and quantitative methods. Field data were collected between 10 January 2017 and 14 February 2019. Questionnaires, interviews and field observations were the major tools used to collect data in Mana Pools National Park. Data were analysed using the Statistical Package for Social Sciences version 20.0. Inferential statistics were employed to determine the relationship between elephant activity and damage of woody species. Chi square test results revealed that there is a significant relationship (P < 0.05; P = 0.001) between elephant activity and woody species damage. This means that woody species damage in the Mana Pools National Park Zambezi Valley flood plain can be attributed to elephant activity. This study recommends that Government and Zimbabwe Parks and Wildlife Management Authourity (ZPWMA) should formulate effective elephant population analysis through periodic surveys in order to continuously update the national data base of elephant population trends in areas such as Mana Pools National Park.

The effect of insects on elephant‐induced tree damage within a small, fenced reserve in South Africa

Article

Mar 2022

African savanna elephants ( Loxodonta africana ) have been recognised as ecosystem engineers, where their feeding habits have been shown to alter landscapes. Within small, fenced reserves, studies exploring elephant damage on trees and their recovery have overlooked secondary damages that could be contributing to tree mortality. The aim of this study is to assess the significance of both elephant damage and secondary damage, and the subsequent tree recovery. We identified secondary damage as insects and considered wood borers and termites in this study. This was conducted in in the small fenced Karongwe Private Game Reserve, South Africa. We analysed the level of damage, recovery and insect presence using vegetation transects, where all trees ≥2 m in height were surveyed ( n = 1278 trees). Forty tree species were recorded, with 5 species accounting for 77% of the data set and used for further analysis. Termites were found to be more likely to colonise damaged trees without signs of recovery. However, wood borers were more likely to colonise damaged trees showing signs of recovery. Termites and wood borer presence on damaged trees was not dependent on tree height. We suggest carefully considering management approaches for elephant‐induced termite and wood borer damage on trees.

Oh, What a Tangled Web … Complex Networks in Ecology

Chapter

Jul 2020

Networks are inherent in all complex systems. Patterns of interactions influence system behaviour. Many kinds of large scale patterns emerge from local interactions, including critical collapse. Ecosystems are really interconnected networks of many kinds, so changed conditions in one network can affect the entire ecosystem. One example of this was the reintroduction of wolves into Yellowstone National Park, which initiated a trophic cascade that transformed the landscape.

Savannen und Trockenwälder

Chapter

Jan 2019

Unter Savannen und Trockenwäldern werden hier die tropischen und subtropischen Gehölz- und Graslandformationen zusammengefasst, die deutliche Trockenperioden im Jahresverlauf aufweisen und im Wesentlichen den Übergang zwischen den immerfeuchten Tropen und den Wüstengebieten im Bereich der Wendekreise bilden. Temperate und mediterrane Grasländer und Gehölze, die im englischen Sprachraum teilweise zu den Savannen gestellt werden (z. B. die Eichen-„Savannen“ Kaliforniens oder am Ostrand der Great Plains), werden hier nicht eingeschlossen.

Mesobrowser Abundance and Effects on Woody Plants in Savannas

Chapter

Aug 2019

This chapter focuses on the direct effects of the mesobrowsers on woody plants in savannas, focusing on the class of mammalian ungulates and macropodids that range in size from approximately 5kg to 1000kg, but which are mostly <500 kg. It first reviews the distribution and abundance of mesobrowsers in savannas around the world. The chapter then reviews long‐term studies of the effects of mesobrowsers on woody plant growth and community dynamics, most of which have been conducted in African savannas. It makes readers to understand ecosystem‐level characteristics that allow or prevent mesobrowser regulation of woody plant recruitment and growth rates, as both native and domestic mesobrowser abundance are influenced by human activities and management. Furthermore, debates surrounding elephant management in African savannas often center on how elephants are affecting woody plants, but knowledge of mesobrowser effects is essential to determine whether elephant management will achieve desired outcomes for savanna vegetation.

Characteristics of banded mongoose (Mungos mungo) den sites across the human-wildlife interface in Northern Botswana

Article

Apr 2019

Denning behavior is a critical life history attribute for many mammalian species and can be impacted by urbanization, affecting species’ reproductive success and survival in these landscapes. One significant factor that is influenced by this behavior is the spread of disease. Banded mongooses (Mungos mungo) in Northern Botswana are often infected with a novel Mycobacterium tuberculosis complex pathogen, M. mungi, that is transmitted through olfactory communication networks that allow the pathogen to move through the population by both direct and environmental transmission routes. We have studied characteristics of active banded mongoose den sites across 24 troops and 308 den sites in Northern Botswana (348 den nights from 2008 to 2010 and 281 den nights from 2016–2017). Dens were located across the human-wildlife interface (national park, lodge, urban, residential, and undeveloped). Cluster analysis and Classification and Regression Tree (CART) analysis of the den sites identified differences in den site characteristics across the land area designations. Habitat was the most important factor for den sites located at lodges, associated with the presence of gallery forest and teak woodlands. Distance to the nearest tar road was the most important variable separating the dens in the National Park from those in human-transformed landscapes. Den type was the most predictive of den sites located in human-modified environments. Sites that had the longest use were dominantly anthropogenic in nature (94% ± 6%, n = 67, used in 2008–2010 and 2016–2017). Natural dens, in contrast, appeared to be more vulnerable to destruction, shortening the period of structural soundness and use. Although banded mongoose are territorial, den use by troops other than the resident troop was observed, but only for anthropogenic dens sites (6%, n = 308). These space-sharing behaviors can significantly impact pathogen transmission dynamics and disease spread. Anthropogenic landscapes can have a critical influence on animal behavior and space use, potentially influencing infectious disease exposure and transmission potential.

A synopsis of field and remote sensing based methods for studying African elephant (Loxodonta Africana) impact on woody vegetation in Africa

Article

Full-text available

Mar 2019

African elephants (Loxodonta africana) negatively influence woody vegetation, causing structural changes to ecosystems. Field-based survey methods used to monitor elephant impact, while valuable, are costly and time-consuming to execute. By applying distance-sampling techniques such as remote sensing technology, inaccessible areas can be surveyed. This overview provides insight into methods used by scientists to determine the impact of elephants on woody vegetation in sub-Saharan Africa. Data were sourced from a variety of research databases. Findings indicate that 87% (n = 92) of the reviewed studies used field-based methods and 13% (n = 14) used remote sensing-based methods. We explore the national affiliations of the lead and the last authors of the reviewed studies and the scientific journals that published them. Field-based is the dominant method used in the majority of published studies on elephant impact. The majority of these studies were published in European and American journals, instead of African journals, which are less represented. However, the majority of the lead and last authors’ affiliations for both field-based and remote sensing based methods are affiliated with African institutions. We conclude that there is a need to improve the integration of remote sensing techniques into conservation and other ecological fields.

Demographic Bottlenecks and Savanna Tree Abundance

Chapter

Mar 2017

Centring on South Africa's Hluhluwe-iMfolozi Park, this book synthesizes a century of insights from the ecology and conservation management of one of Africa's oldest protected wildlife areas. The park provides important lessons for conservation management, as it has maintained conservation values rivalling those of much larger parks sometimes through, and sometimes despite, strong management interventions, including the rescue of the white rhino from extinction. In addition, the book highlights the ecological science produced in the park, much of which has become widely influential, including the megaherbivore concept, new functional approaches to understanding biomes, and new understandings about the role of consumers in shaping ecosystems. The volume is ideal for researchers and policymakers interested in the conservation of relatively small, isolated and protected areas.

Megaherbivores

Chapter

Jan 2013

Norman Owen‐Smith

Megaherbivores were abundant and diverse worldwide until the end of the Pleistocene. They represent a distinct adaptive syndrome in: (1) dietary tolerance; (2) invulnerability to predation as adults; (3) population regulation; (4) dominance of large herbivore biomass; and (5) impacts on vegetation. Their demise probably contributed to cascading extinctions among other species. Surviving populations of elephants and rhinos remain vulnerable to human overkill but when effectively protected can threaten the persistence of other species as well as human livelihoods.

Range size and drivers of African elephant ( Loxodonta africana ) space use on Karongwe Private Game Reserve, South Africa

Article

Feb 2018

Katherine D. Orrick

Mathematical models can identify different drivers and/or habitat preferences depending on the size and area of the analysis. Important criteria for survival, such as water access, may be seen at various spatial ranges while features such as human disturbance may only impact wildlife at a coarse scale. This study analyses the impact of roads surrounding Karongwe Private Game Reserve, South Africa, on a herd of African elephants ( Loxodonta africana ) over 6 years at three separate spatial ranges—coarse (the entire available area), home (95% isopleth) and core (50% isopleth). The purpose was to determine which anthropogenic (eastern and western public roads) and natural features (rivers, dams and vegetation) elephants avoided and preferred within each range. Coarse‐scale analysis indicates a clear avoidance by elephants for all public roads. Home and core range analyses showed a seasonal avoidance of roads by the breeding herd but not by bulls. Results indicate the importance in interpreting data at various ranges to improve identifying wildlife movement drivers.

Options for the management of elephants in northern Botswana

Article

Full-text available

Dec 1996
PACHYDERM

Reviews the recent history and status of what can perhaps be considerd the largest population in Africa, the elephant population in northern Botswana which since 1983 has been managed through a policy of non-interference. The population of approximately 70,000 is contained in a range of about 80,000 sq kms which includes 18,247 sq kms of protected areas, Chobe and Nxai Pan NPs and Moremi GR. The elephant distribution during the dry season is restricted by the availability of surface water. Up to 75% of the population may be confined to 10,000 to 12,000 sq kms mostly within 30 km of the permanent water sources of the Kwando-Linyanti and Chobe Rivers. The impact the animals have exerted and continue to exert on their immediate habitat in the dry season has been a source of much concern, but decisions regarding effective management options are yet to made. The problems associated with the high population and alternative management strategies are outlined. It is suggested that a combination of actions should be coinsidered and implemented.

Trends of the elephant population in northern Botswana from aerial survey data

Article

Full-text available

Jul 1998
PACHYDERM

Summarizes methods and results of aerial surveys since 1973, and presents a history of the elephant population in Botswana with estimates of recent trends provided by survey data. Aerial surveys of northern Botswana's elephants have been taking place since the early 1970s. While it is not possible to use all of the data from the surveys, they provide evidence to suggest that since 1987 the population of elephants in northern Botswana has increased to the present level of about 80,000 animals at a rate of around 6% per annum. Their range, which has expanded south and westward, changes seasonally, but is largely outside protected areas.

Elephants, woodlands and biodiversity in Southern Africa

Article

Full-text available

May 1997

When elephant densities exceed approximately 0.5 per km2, savanna woodlands are generally converted to shrublands or grasslands. The impact of such elephant-mediated habitat change on biodiversity in African game reserves has seldom been measured. We examined species richness of woody plants, birds, bats, mantises and ants in reserves where elephants had destroyed the miombo woodland and in adjacent but intact miombo woodlands outside the reserves. Species richness of woodland birds and ants was significantly lower where elephants had removed the tree canopy. Our findings may have important policy implications for conserving biodiversity in many African reserves in the face of rapidly growing elephant populations (approximately 5% per annum). The problem is further compounded by international public pressures against reducing elephant densities within game reserves while, outside these protected areas, savanna woodlands and their associated faunas are being lost to agriculture. Where then will refugia for habitat-sensitive species exist if not within the region's largest protected areas?.

Elephants and Fire as Causes of Multiple Stable States in the Serengeti-Mara Woodlands

Article

Full-text available

Oct 1990

(1) Multiple stable states in ecosystems have been proposed on theoretical grounds, and examples have been offered, but direct tests of the predictions are lacking. A boundary between states exists if: (i) a system when disturbed from one state to another does not return to its original state once the cause of the disturbance returns to its original value; and (ii) a second factor takes over and holds the system in the new state. We examine these predictions for two stable states in the woodlands of the Serengeti-Mara ecosystem in East Africa. (2) Woodlands in natural areas of savannah Africa have declined over the past 30 years. Three general hypotheses have been proposed: (i) expanding human populations have concentrated elephants into protected areas, elephants then caused the decline of woodlands but man-induced fires prevented regeneration (two stable states); (ii) fires caused the decline and also prevented recovery (one stable state); (iii) fires caused the decline while elephants inhibited recovery through density-dependent mortality of seedlings (two stable states). (3) Two time periods, the 1960s when woodlands changed fastest and the 1980s when grasslands prevailed, produced four specific hypotheses. (i) `The 1960s elephant hypothesis' and (ii) `the 1960s fire hypothesis' hold that elephants and fire, respectively, caused woodland change. (iii) The `1980s elephant hypothesis' and `the 1980s fire hypothesis' hold that these factors, respectively, prevented woodland recovery. (4) From experiment and observation of seedling recruitment, mortality due to combinations of burning rates, elephant browsing, wildebeest trampling, and antelope browsing was estimated and used to model tree population dynamics; predictions for rates of decline and increase were compared with independent estimates from aerial photographs. (5) Maximum rates of elephant and antelope browsing could not have caused the observed decline of woodlands in the 1960s. The most conservative burning rates in the 1960s, without elephants, could have caused a decline consistent with the 1960s fire hypothesis. (6) The combined impact of fire and browsing most closely matched the observed rate of woodland loss. (7) Wildebeest grazing in the 1980s reduced dry grass and minimized fire incidence. The model predicted that fire mortality and wildebeest grazing could not maintain the present grassland state. (8) The present high elephant density was sufficient to prevent an increase in the woodlands consistent with the 1980s elephant hypothesis. Wildebeest trampling and other browsers ensures that the vegetation is currently stable in a grassland state. (9) Thus, an external perturbation, such as fire, was necessary to change the vegetation from woodland to grassland. Elephants were unable to cause such a change. Once the grassland was formed, however, elephants were able to hold it in that state. These results are consistent with the third general hypothesis that there are two stable states of woodland and grassland, the latter maintained by herbivores. (10) Simulation of conditions in the 1890s suggests that the rinderpest epidemic combined with elephant hunting could have caused the woodland regeneration observed before the 1950s. Therefore, (i) savannah woodlands may regenerate in pulses as evenaged stands, and (ii) there may have been more grassland in Africa before 1890. This longer time-scale view of the dynamics of vegetation has implications for the conservation of elephants and their habitats.

Distance Sampling: Estimating Abundance of Biological Populations

Book

Full-text available

Jan 1993

This book is available for purchase, The 1993 version is available on the page at http://distancesampling.org/downloads/distancebook1993/index.html

Sex differences in feeding-patch choice in a megaherbivore: Elephants in Chobe National Park, Botswana

Article

Full-text available

Dec 1999

Sigbjørn Stokke

Differences in diet and patch choices of African elephants (Loxodonta africana) according to sex and herd structure were examined during the dry season in a dystrophic savanna-woodland ecosystem in northern Botswana. The study revealed that female elephants with dependent young fed more selectively than the very large adult males, as indicated by the large number of woody plant species utilised, in order to minimise fibre intake, at both the woody plant species level and the feeding-patch level. Adult females fed on more woody plant species per unit area in patches containing higher numbers of such plants than adult males. Family units also browsed on more woody plant species per unit area and in total than adult males. Finally, family units discriminated between patches in their surroundings and selected patches offering the highest density of palatable species, whereas males were apparently ignorant of the distribution of resources in their environment and browsed in patches containing the same amount and combination of species as surrounding areas. This suggests that body size is a paramount factor mediating dietary differences between the sexes in African elephants at both the feeding-patch and the woody plant species level. These findings are consistent with the sexual dimorphism - body size hypothesis, which states that an increase in body size leads to a relaxation of the requirement for selectivity in feeding.

Article

Full-text available

Feb 2000
ECOGRAPHY

Differences in feeding patterns of the African elephant were examined by sex and age during the dry season in a dystrophic savanna-woodland ecosystem in northern Botswana. Adult males had the least diverse diet in terms of woody plant species, but they consumed more plant parts than family units. The diameter of stems of food plants broken or bitten off was also greater for adult males than for females and subadult males. Adult males spent more time foraging on each woody plant than did females. The number of woody plant species and individuals present were higher at feeding sites of family units than at feeding sites of adult males, indicating that family units positioned themselves at feeding sites with higher species diversity than those of males. We argue that the most likely explanation for these differences is related to the pronounced sexual size dimorphism exhibited by elephants, resulting in sex differences in browsing patterns due to the allometric relationships that govern the tolerance of herbivores for variation in diet quality. From our results this Body Size Hypothesis is accepted rather than the alternative Scramble Competition Hypothesis, which predicts that adult male elephants consume lower quality browse because they are displaced from preferred browse as an outcome of scramble competition with adult females and their offspring. If the feeding patterns of adult male elephants were affected by intersexual scramble competition, we would expect adult males to browse at a higher level in the canopy than the smaller-bodied females and their offspring. No evidence was found for this, although adult females were found to browse at a higher level in the canopy when feeding in close proximity to subadults and juveniles than when feeding alone. Sex differences in elephant browsing patterns are, we propose, of relevance to understanding and managing elephant impacts on African woodlands.

Ungulate Effects on The Functional Species Composition of Plant Communities: Herbivore Selectivity and Plant Tolerance

Article

Full-text available

Oct 1998
J WILDLIFE MANAGE

Large mammalian herbivores not only depend on plant communities for their existence but cause major changes in plant community composition and structure. These changes have direct consequences for ecosystem processes, but recent studies of ungulate-ecosystem relations show widely divergent ungulate effects in different ecosystems. We reviewed studies of ungulate effects on plant community composition to gain insight into potential mechanisms of ungulate-induced changes in both community composition and ecosystem processes. Our analysis of these studies is based on the premise that the effect ungulates exert on plant communities depends on the balance between (1) feeding selectivity of herbivores (i.e., degree to which different plant species or ecotypes experience different levels of tissue loss), and (2) differences among plant species in their ability to recover from tissue loss. A large number of studies clearly show that selective ungulate herbivory leads to the dominance of unpalatable, chemically defended plant species in communities. However, many studies have also demonstrated that intensive long-term herbivory does not lead to the invasion of unpalatable species into the community, and can even increase the dominance of highly palatable species. Our review indicates that high levels of nutrient inputs or recycling and an intermittent temporal pattern of herbivory (often due to migration) are key factors increasing the regrowth capacity of palatable species and hence maintaining their dominance in plant communities supporting abundant herbivores. Key factors limiting ungulate foraging selectivity, again limiting herbivore-induced dominance of slow-growing, unpalatable species, include herding behavior, early growing season and postfire herbivory, asynchronous phenology of palatable versus unpalatable species, and low relative abundance of unpalatable species. Our review indicates differences among ecosystems in the role played by ungulate herbivory result from the relative strength of these factors enhancing plant tolerance to herbivory and limiting foraging selectivity. Anthropogenic changes in these factors (e.g., alteration of migration patterns) therefore have the potential to significantly alter the effects of ungulates on plant communities and ecosystem processes.

Sexual segregation in habitat use by elephants in Chobe National Park, Botswana

Article

Full-text available

Nov 2002
AFR J ECOL

We report on a study conducted on free-ranging Africa elephants in the woodlands of northern Botswana. We compared bull groups and family units with regard to (1) their patterns of habitat use and (2) their ranging distances from perennial water sources. During the dry season, adult males frequented more habitat types than family units, whereas family units used a wider diversity of habitats than bulls during the wet season. Bulls roamed widely (>10 km) from perennial drinking water in the dry season, when family units congregated within 3.5 km of the rivers. During the wet season, when ephemeral pans were abundant, all elephant groups were found at intermediate distances (5 km) from the rivers. The spacing of elephants in the dry season is consistent with sexual segregation but we reject the hypothesis that this is a outcome of indirect competition for food, because our concurrent studies on elephant feeding ecology found no evidence for intraspecific competition. Instead, we propose that most adult male elephants space themselves to avoid conflict with musth bulls and roam widely in the dry season between discretely distributed feeding 'hotspots'. The small proportion of males that are in musth remain close to family units to maximize mating opportunities, and family units are unable to range far from water in the dry season. This is due to (1) comparatively high rates of water turn-over among juveniles and lactating cows and (2) the reduced mobility of neonates.

Megaherbivores influence trophic guilds structure in African ungulate communities

Article

Full-text available

May 2002

We used a data set of ungulate censuses from 31 natural ecosystems from East and Southern Africa to test two hypotheses: (1) megaherbivores should dominate ungulate communities in ecosystems with high rainfall and low soil nutrient status because of their ability to survive on poor quality food resources, and (2) the abundance of megaherbivores affects the abundance of the mesoherbivores, distinguishing the different feeding guilds: mesograzers, mesobrowsers and mesomixed feeders. Two axes of a multivariate analysis (77% of the variance) discriminated the sites well, the first separating sites dominated by megaherbivores from those dominated by mesoherbivores, and the second representing a gradient between mesograzers and mesobrowsers. Our analysis shows (1) that megaherbivores can be considered to be a separate trophic guild and (2) that mesograzers and mesobrowsers respond differently to variation in their trophic environments. The metabolic biomass density of megaherbivores increased with annual rainfall, but was not related to soil nutrient status, and as predicted, megaherbivores comprised a larger proportion of the biomass of ungulate communities in ecosystems with high rainfall and low nutrient soils. The metabolic biomass density of mesoherbivores increased with rainfall and soil nutrient status. Within the mesoherbivores, the metabolic biomass density of mesograzers showed the same trend, and seemed unaffected by megaherbivores. Conversely, mesobrowsers and mesomixed feeders appeared to be unaffected by rainfall or soil nutrient status, but mesomixed feeders declined when megaherbivores were abundant. This suggests that megaherbivores may compete with the mesomixed-feeder species for food or they may alter the vegetation communities unfavourably. A similar analysis using elephants alone instead of megaherbivores as a group showed that both mesobrowsers and mesomixed feeders were affected significantly by elephant, which is consistent with the fact that most of the effect of megaherbivores on browse resources or woodland habitat is due to elephants. This study shows that the different trophic guilds within African ungulate communities react differently to environmental factors (rain and soil), and that megaherbivores, and particularly elephants, appear to compete with mesomixed feeders and mesobrowsers. These results are relevant for the understanding of the functioning of African ungulate communities and call for further testing with longitudinal data.

Detrended Correspondence Analysis – An Improved Ordination Technique

Article

Full-text available

Oct 1980

Detrended correspondence analysis (DCA) is an improvement upon the reciprocal averaging (RA) ordination technique. RA has two main faults: the second axis is often an arch or horseshoe distortion of the first axis, and distances in the ordination space do not have a consistent meaning in terms of compositional change (in particular, distances at the ends of the first RA axis are compressed relative to the middle). DCA corrects these two faults. Tests with simulated and field data show DCA superior to RA and to nonmetric multidimensional sealing in giving clear, interpretable results. DCA has several advantages. (a) Its performance is the best of the ordination techniques tested, and both species and sample ordinations are produced simultaneously. (b) The axes are scaled in standard deviation units with a definite meaning, (c) As implemented in a FORTRAN program called DECORANA, computing time rises only linearly with the amount of data analyzed, and only positive entries in the data matrix are stored in memory, so very large data sets present no difficulty. However, DCA has limitations, making it best to remove extreme outliers and discontinuities prior to analysis. DCA consistently gives the most interpretable ordination results, but as always the interpretation of results remains a matter of ecological insight and is improved by field experience and by integration of supplementary environmental data for the vegetation sample sites.

The importance of herbivore interactions for the dynamics of African savanna woodlands: a hypothesis

Article

Full-text available

Sep 1998
J TROP ECOL

Current hypotheses to explain dynamic transitions between savanna grasslands and woodlands in Africa focus on grazing by elephant or the influence of fire. Using a simple mathematical model, this paper argues that interactions between small herbivores such as impala or buffalo and large herbivores such as elephant or giraffe may provide a plausible alternative hypothesis. The interplay of competition and facilitation between these types of herbivores could explain transitions between grassland and woodland and vice versa. A review of the literat- ure is presented in support of this hypothesis.

Herbivore population crashes and woodland structure in East Africa.

Article

Full-text available

A Hunter's Wanderings in Africa

Article

Feb 1974

A detailed vegetation study on the Chobe river in north-east Botswana

Article

Jan 1975

C.D. Simpson

Ecological guidelines for waterpoints in extensive protected areas

Article

Dec 1996
S AFR J WILDL RES

N. Owen-Smith

Augmenting natural water supplies by providing artificial waterpoints is an intervention commonly adopted by managers of national parks and other large protected areas. Contrasting policies are currently being followed in three of the premier national parks in southern Africa. Some empirical guidelines for waterpoint provision are suggested by case histories of these and other wildlife reserves. A geometric model, based on the rotation of water-dependent herbivores between wet season and dry/season ranges, is outlined to indicate the appropriate spacing between perennial waterpoints. The aim is to apportion vegetation impacts evenly between these ranges, and allow plants a period of recovery from severe grazing pressure. The model suggests that a much wider spacing between perennial water sources is advisable than is currently operative in most conservation areas. Seasonal waterpoints reduce the period of concentration near perennial water, but prolong use of vegetation in the wet season range. Excessive waterpoints (1) favour water-dependent ungulates and elephants at the expense of rarer ungulates, (2) increase predator impacts on prey populations, (3) widen vegetation degradation, (4) worsen animal mortality during droughts, (5) decrease ecosystem stability, and (6) lead to a loss of biodiversity.

The African Buffalo: A Study of Resource Limitation of Population

Article

Jul 1978

Elephants as Agents of Habitat and Landscape Change in East Africa

Article

Jan 1970

R. M. Laws

The preferred habitats of the African bush elephant, Loxodonta africana, are forestedge, woodland, bushland and wooded or bushed grassland. Increasing amounts of grass in the elephants' diet are correlated with conversion of wood habitats towards grassland, and with increasing elephant mobility, poorer physical condition, and progressively increasing natural regulatory processes leading to decrease in numbers. Elephant occur in discrete unit populations. Each population shows a series of highly contagious instantaneous distributions which, when averaged over a period of time, probably tend, in a uniform habitat, to approach a random or regular distribution. High densities or disturbance by man lead to increase in mean group size and more uneven distribution. The effect on woody vegetation is greater and more lasting than on grass or herbs and usually radiates outwards from the initial centre of damage. The typical cycle begins with destruction of the understory, followed by ringbarking of adult trees, and is accelerated by fire. Several case studies involving forest, moist and dry woodlands, and dry bushland are described which fit this pattern. /// Предпочитаемые местообитания Африканских слонов Loxodonta africana - опушки леса, лесистые местности, кустарник и открытые участки с деревьями или кустами. Увеличение относительного количества травы в диете слонов коррелирует со сменой лесных местообитаний открытыми, увеличением подвижности слонов, ухудшением физических условий и усилением действия естественных регулирующих процессов, ведущих к снижению поголовья. Слоны встречаются отдельными разрозненными популяциями. Каждая популяция образует ряд временных, вступающих в контакт группировок, которые при анализе в среднем за определенный промежуток времени очевидно имеют тенденцию к однородным местообитаниям, и их распределение приближается к рандомическому распределению. Высокая плотность и влияние деятельности человека приводит к увеличению стад слонов и еще более неравномерному распределению. Повреждения древесной растительности более сильные и длительные, чем травянистой. Обычно эти повреждения распространяются вширь от одного исходного очага. Типичный цикл смены местообитаний начинается с уничтожения подстилки и обгрызания коры на деревьях. Эта деятельность усугубляется пожарами. Приведены некоторые случаи исследований во влажных и сухих лесах и сухих кустарниках, которые подтверждают эту схему.

In Ecology, Change Brings Stability

Article

Nov 1986

ROGER LEWIN

Vegetation changes during a 36-year period in northern Chobe National Park, Botswana

Article

Sep 2002

Changes in vegetation cover in northern Chobe National Park (Botswana) were assessed using aerial photographs from 1962, 1985 and 1998, with subsequent ground proofing. In addition, cumulative browsing by elephants and the occurrence of fire scars were recorded on random vegetation sites within shrubland (n = 20) and mixed woodland (n = 20). Coverage of woodland vegetation decreased from 60% to 30% between 1962 and 1998, while shrubland vegetation increased from 5% to 33% during the same period. During the study period, woodland has gradually retreated away from the river front. While riparian forest covered a continuous area along the riverfront in 1962, only fragments were left in 1998. We found a significant decrease in browse use with increasing distance to the Chobe river for Combretum apiculatum, Combretum elaeagnoides, Combretum mossambicense and other woody plants combined (all P < 0.0001). The occurrence of fire (P < 0.0001) and basal area (P < 0.0001) were positively related to distance to the river. Elephant browsing occurred on >70% of available stems within 2 km from the river, while less than 20% of the trees had fire scars in the same zone. Beyond 7 km from the river, elephant browsing was reduced to >50% of available stems, while more than 50% of the trees had fire scars. The density of any of the shrubs was not related to distance to the river neither within shrubland (all P > 0.05) nor within mixed woodlands (all P > 0.05).

Elephant decline: downward trends in African elephant distribution and numbers (Part II)

Article

Dec 1989
Int J Environ Stud

East African ivory exports prove that elephant mortality rose between 1925 and 1975, confirming Kingdon's reported declines from contracting range. Exports rose even when ivory values fell or were low. No correlation exists between variations about the means of ivory price or production trends. Apparently price does not drive production. Other large mammals and forests which do not produce ivory decline in concert with elephants, calling for a general explanation. Competitive exclusion (of which economics are part) is suggested and conservation failures are attributed to not meeting the costs of keeping areas free from human competition.

Elephant decline: Downward trends in African elephant distribution and numbers. Part I

Article

Sep 1989
Int J Environ Stud

Humans and elephants are complete competitors. Biological theory maintains that such species cannot co‐exist on the same range and that increase in one will exclude the other. Measurements of human increase, elephant decline and ivory production are in keeping with this hypothesis.

The African Elephant Database

Article

Apr 2001
ORYX

Effects of browsing by elephants on the Combretum/Terminalia woodland at the Nazinga Game Ranch, Burkina Faso, West Africa

Article

Dec 1991
BIOL CONSERV

Elephant-woodland interactions at the Nazinga Game Ranch in south-central Burkina Faso, West Africa, were studied. The ranch covers 940 km2 of tallgrass Combretum/Terminalia woodland. The density of tree and shrub stems abobe 1 m tall averaged approximately 800/ha, and remained relatively unchanged at densities from 0 to 0·6 elephants/km2. At higher elephant densities, woody-stem density was sharply reduced. At low elephant densities (less than 0·6 elephants/km2), the size distribution of woody stems had on increased proportion of larger trees compared with the stratum containing no elephants. The highest density of elephants (2·5/km2) showed no further changes in the size-class distribution of trees and shrubs, but a change in species composition was apparent with increasing proportions of species of low palatability for elephants. An elephant density between 0·5 and 0·6/km2 is suggested to keep major short-term vegetation changes to a minimum.

Links between terrain characteristics and forage patterns of elephants (Loxodonta africana) in northern Botswana

Article

Nov 2002
J TROP ECOL

Spatial vegetation utilization of elephants was investigated within mixed woodland savanna along the Chobe River in northern Botswana in the dry season of 1998. Using multiple linear regression, accumulated stem breakage by elephants was predicted by a terrain index, distance to water, stand density, number of trees > 4 m tall, tree height, density of Combretum apiculatum, C. elaeagnoides, C. mossambicense and the density of other (accumulated) tree species. Within mixed woodland at 2–7 km distance from the river fine-grained terrain ruggedness was the most important factor contributing to 55% of observed differences in use by elephants, while distance to water and the density of C. apiculatum contributed an additional 20% and 4%, respectively to the multiple linear regression model. Stem breakage was, on average, almost twice as high in rugged terrain compared with flat terrain at similar distance to water within the same vegetation type. Rugged terrain had 2–3-fold higher proportion of plots with very high Combretum shrub densities. These results suggest that the terrain index may be useful in management, predicting the areas most sensitive to vegetation change in a woodland system with increasing elephant densities.

Herd‐switching and long‐distance dispersal in female African buffalo Syncerus caffer

Article

Feb 2002
AFR J ECOL

Utilization by elephants of the Brachystegia woodlands of the Kasungu National Park, Malawi

Article

Apr 2008
AFR J ECOL

Utilization by elephants of the trees of the Brachystegia woodlands of Kasungu National Park, Malawi, was investigated. Of forty-one common species thirtyfive species were eaten, of which thirteen species were selected by elephants. The chemical composition of the leaf material was analysed and a significant correlation was found between the utilization of certain species and the protein and sodium content, whereas the crude fibre content showed no significant correlation but in general appeared to be relatively low in highly favoured species. The pushing over and uprooting of trees by elephants appear to be part of a feeding strategy which improves the availability of food for elephants during the dry season. The number of trees browsed increased with an increasing tree density up to 300 trees ha-1, where browsing intensity remained constant for both selected and non-selected species. The reasons why the species composition of Brachystegia woodlands is hardly affected by elephant use are briefly discussed.

The elephant problem - An alternative hypothesis

Article

Apr 2008
AFR J ECOL

GRAEME CAUGHLEY

Published hypotheses to account for habitat changes wrought by elephants begin from the assumption that elephant-forest systems possess a stable equilibrium point. The ‘elephant problem’ is conceived as a displacement of this equilibrium by man. Controversy centres around which human activities caused the dislocation of equilibrium and by which mechanisms these activities resulted in local high densities of the elephant Loxodonta africana. A study on elephant-forest relationships in the Luangwa Valley of Zambia casts doubt upon the basic assumption of these hypotheses and an alternative hypothesis is therefore offered. It begins from the opposite assumption–that there is no attainable natural equilibrium between elephants and forests in eastern and southern Africa. The relationship is viewed instead as a stable limit cycle in which elephants increase while thinning the forest and decline until reaching a low density that allows resurgence of the forest. This in turn triggers an increase of elephants and the cycle repeats. The period of the cycle, if the hypothesis is correct, is in the order of 200 years in the Luangwa Valley. The activities of man can impose an artificial equilibrium on the system such that trees and elephants are trapped at the low density phase of the cycle. When interference is relaxed, as with the conversion of an area to a national park, the cyclic relationship reasserts. The parameters of a system possessing a stable limit cycle need not differ in kind or interrelationship from those of a system with a stable equilibrium. Whether one or other outcome manifests may depend only on the numerical values of the parameters. If the elephant-forest system is characterized by a stable limit cycle the period and amplitude should change along a climatic gradient and may contract to a stable equilibrium in some climatic zones. A set of predictions is offered to facilitate rejection of the hypothesis.

Effects of woodland modification by African elephant Loxodonta africana on bird diversity in Northern Botswana

Article

Jun 2006
ECOGRAPHY

Marc Herremans

Bird diversity was assessed by point-transect-count sampling during the dry and the wet season in riverine gallery woodland and in Colophospermum mopane woodland with different levels of elephant impact Dramatic woodland degradation did not result in a dramatic overall reduction m bird diversity, but resulted in substantial changes in bird species composition and capacity for migrant birds Less affected, more dense woodlands functioned as dry season refuges for‘resident’Afrotropical species, but this function was lost in degraded woodlands In contrast, secondanzed habitat had a much higher capacity for long distance migrants in the wet season Species endemic to the sub-region and subspecies with restricted ranges centred in the area were not negatively affected by woodland degradation The cumulative interference of past and current elephant numbers with the conservation of bird diversity appears to be insignificant in northern Botswana

The Impacts of Elephant, Giraffe and Fire upon the Acacia tortilis Woodlands of the Serengeti

Article

Mar 1983
AFR J ECOL

R. A. P. PELLEW

The reduction in canopy cover of the Seronera woodlands since the mid‐ 1960s can be largely attributed to the destruction of mature Acacia tortilis trees by elephants. The development of the tree regeneration that has colonized the gaps in the mature canopy is being suppressed by giraffe browsing and periodic burning. A simple model is presented which simulates these impacts upon the dynamics of the A. tortilis population. Height‐specific impact rates of these three agents are quantified. Between 1968 and 1977, mature trees were lost at a mean annual rate of some 6%, although this figure showed considerable annual variation (13.5‐2%). Combinations of impact rates, simulating possible natural developments within the Serengeti woodlands, are programmed into the model to assess their effects upon the tree population structure. The results suggest that measures to promote regeneration development (fire protection and/or giraffe culling) are more effective in the long‐term to encourage mature canopy recovery than are measures to reduce mature tree mortality (elephant culling). The management implications of these results are considered, and their extrapolation to other wildlife conservation areas experiencing similar declines in mature canopy woodland is discussed. It is suggested that the effects of the combination of low elephant densities and high giraffe densities prevalent in the Serengeti produce a dynamic system in which the woodland structure oscillates between mature canopy and open regeneration‐grassland phases. The woodland structure desired by Park management to ensure continuity of mature tree canopy represents an unstable transitional stage between these two phases. Résumé La réduction du couvert végétal dans les forêts de Seronera depuis les années 1965–1970 peut être largement attribuée ai la destruction des Acacia tortilis par les éléphants. Le développement de la régénération des arbres ayant colonisé les espaces libres du couvert végétal est anihilé par le broutage des girafes et les incendies saisonniers. On présente un modeile simple qui simule ces impacts sur la dynamique de population de Acacia tortilis . Pour ces trois facteurs, les taux d'impact spécifique de la hauteur sont quantifiés. Entre 1968 et 1977, le taux de perte

Woodland dynamics under the influence of elephants and fire in Northern Botswana

Article

Apr 1996

Raphael Ben-Shahar

Sustained elephant browsing and intense burning could result in the loss of woodlands under conditions where elephant densities are high, such as in northern Botswana. Three woodland types dominated by Acacia erioloba, Baikiaea plurijuga and Colophospermum mopane were monitored in plots and contemporary recruitment rates of woody plants were compared with the associated local elephant densities and fire occurrences. Woodland types differed with respect to structure, extent of elephant damage and the occurrence of fire. Canonical correlations indicated that high extent of fire damage and high elephant densities did not covary within the woodland types investigated. Low tree densities in some woodland types were associated with high elephant densities and new elephant damage to plants increased with high elephant densities during the dry season. Plots with an apparent high fire frequency had lower tree densities and higher cover abundance of shrubs and seedlings. The annual rates of tree recruitment/loss in each woodland type were estimated through a model based on observed seedling recruitment, mortality and reversal to lower height classes due to combinations of fire occurrence and elephant browsing. The model suggested that elephants induce tree loss in woodlands dominated by plant species which are principal food sources. Fire however, seems to have a widespread effect across woodlands which could result in extensive tree loss.

Realistic parameter assessment for a well known elephant–tree ecosystem model reveals that limit cycles are unlikely

Article

Sep 1999
ECOL MODEL

In 1976 Caughley proposed a simple predator–prey model for elephant–tree dynamics. To our knowledge no-one has attempted to assess this model against real data. The significance of Caughley’s model was to show that limit cycle behavior is possible for the elephant-tree system. Using realistic parameter estimates the paper emphasizes that, in fact, limit cycles are highly unlikely. For a wide range of realistic parameter estimates the model predicts a fixed point equilibrium between elephant and trees. Equilibrium model results are compared to real data for systems where there is a strong dependence between elephant and a dominant tree species. These results compare well giving added confidence in the biological premises of the model. Reasonable variations in parameter values change the equilibrium points in explainable ways. The conclusion is that this model, while crude, is realistic for certain ecological situations and can provide useful insights into such ecosystems.

Effect of plant species on nutrient cycling. Trends Ecol Evol 7:336-339

Article

Oct 1992
TRENDS ECOL EVOL

Sarah E. Hobbie

Plant species create positive feedbacks to patterns of nutrient cycling in natural ecosystems. For example, in nutrient-poor ecosystems, plants grow slowly, use nutrients efficiently and produce poor-quality litter that decomposes slowly and deters herbivores. /n contrast, plant species from nutrient-rich ecosystems grow rapidly, produce readily degradable litter and sustain high rates of herbivory, further enhancing rates of nutrient cycling. Plants may also create positive feedbacks to nutrient cycling because of species' differences in carbon deposition and competition with microbes for nutrients in the rhizosphere. New research is showing that species' effects can be as or more important than abiotic factors, such as climate, in controlling ecosystem fertility.

The importance of herbivore interactions for the dynamics of African savanna woodlands: a hypothesis

Article

Jan 1999

Herbivore Population Crashes and Woodland Structure in East Africa

Article

Jun 1993

1) Between 1985 and 1991, bush encroachment was serious in Lake Manyara National Park, northern Tanzania. Shrub cover increased by ~20%. The increase was independent of initial(1985) shrub cover. 2) Since 1987 there hasa been a steep decline in teh number of African elephant in the Park due to poaching. Elephant density decreased from about 6/km2 to1/km2. However, shrub establishment, as determined from counting tree-rings, preceded poaching. 3) Shrub establishment in two areas of the Park coincided with anthrax epidemics that drastically reduced the impala population. In the northern section of the Park, this was in 1984, in the southern section in 1977. 4) The diameter increment of Acacia tortilis was 5.24mm/year, irrespective of the size of trees. Size measurements indicated an even-aged stand of Acacia established in 1961, which coincided with another anthrax outbreak among impala. 5) Size measurements of old A.tortilis trees indicated another even-aged established at the end of the 1880s. The size of the trees of this stand was not significantly different from a stand in Tarangire National Park, nor from a stand near Ndutu(on the boundary between Serengeti National Park and Ngorongoro Conservation Area), also northern Tanzania. All three stands are likely to have originated from bush establishment caused by the rinderpest pandemic at the end of teh 1880s. 6) It is suggested that seedling establishment of Acacia is a rare event under the prevailing conditions of high browsing pressure by ungulates such as impala. Punctuated disturbances by epidemics among these ungulates create narrow windows for seedling establishment, which may explain the occurrence of even-aged stands

Elephants & fire as causes of multiple stable states in the Serengeti-Mara woodlands

Article

Jan 1990

Sinclair Dublin

Ecology and Behaviour of the African Buffalo: Social Inequality and Decision-making

Article

Mar 1997

Herbert H T Prins

Ecology of the Zambezi Valley Bushbuck Tragelaphus scriptus ornatus Pocock

Article

Jan 1974

Christopher David. Simpson

Thesis (Ph. D. in Wildlife Science)--Texas A & M University.

CD8 + Lymphocytes Can Control HIV Infection in Vitro by Suppressing Virus Replication

Article

Jan 1987

Lymphocytes bearing the CD8 marker were shown to suppress replication of human immunodeficiency virus (HIV) in peripheral blood mononuclear cells. The effect was dose-dependent and most apparent with autologous lymphocytes; it did not appear to be mediated by a cytotoxic response. This suppression of HIV replication could be demonstrated by the addition of CD8+ cells at the initiation of virus production as well as after several weeks of virus replication by cultured cells. The observations suggest a potential approach to therapy in which autologous CD8 lymphocytes could be administered to individuals to inhibit HIV replication and perhaps progression of disease.

History of elephants in Botswana In: The Future of Botswana's © Royal Swedish Academy of Sciences 2004 http://www.ambio.kva.se 282 Ambio Vol distance dispersal in female African buffalo Syncerus caffer

97-99

A C Campbell

Campbell, A.C. 1990. History of elephants in Botswana. In: The Future of Botswana's © Royal Swedish Academy of Sciences 2004 http://www.ambio.kva.se 282 Ambio Vol. 33 No. 6, August 2004 distance dispersal in female African buffalo Syncerus caffer. Afr. J. Ecol. 40, 97-99.

Population Structure, Group Dynamics, Home Ranges and Habitat Use of Lions (Panthera leo) in North East Chobe National Park

G Neo

Neo, G. 2001. Population Structure, Group Dynamics, Home Ranges and Habitat Use of Lions (Panthera leo) in North East Chobe National Park, Botswana. MSc Thesis, Agricultural University of Norway.

Rainfall changes over South Africa during the period of meteorological record Junk, the Hague

55-69

P D Tyson

Tyson, P.D. 1978. Rainfall changes over South Africa during the period of meteorological record. In: Biogeography and Ecology of Southern Africa. Werger, M.J.A. (ed.). Junk, the Hague. pp. 55-69.

An Ecological Survey of North-eastern Botswana. FAO, TA 2563

G Child

Child, G. 1968. An Ecological Survey of North-eastern Botswana. FAO, TA 2563. Report to the Government of Botswana, 133 pp.

The Future of Botswana's Elephants Workshop organised by The Kalahari Conservation Society in conjunction with The Department of Wildlife and National Parks

P Hancock
M Cantrell
S Hughes

Kalahari Conservation Society 1990. The Future of Botswana's Elephants. Hancock, P., Cantrell, M. and Hughes, S. (eds). Proc. Workshop organised by The Kalahari Conservation Society in conjunction with The Department of Wildlife and National Parks. Gaborone, 96 pp.

A Survey of Elephant Populations in Northeast Botswana

M W L Sommerlatte

Sommerlatte, M.W.L. 1976. A Survey of Elephant Populations in Northeast Botswana. DWNP. Gaborone.

Elephants -Habitat Relationships in Northern Botswana

D N Moroka

Moroka, D.N. 1984. Elephants -Habitat Relationships in Northern Botswana. DWNP Gaborone, Botswana.

Botswana's problem elephants

15-19

C A Spinage

Spinage, C.A. 1990. Botswana's problem elephants. Pachyderm 13, 15-19.

Effects of Fire, Elephants and other Herbivores on the Chobe Riverfront Ecosystem

M Vanderwalle

Vanderwalle, M. (ed.) 2003. Effects of Fire, Elephants and other Herbivores on the Chobe Riverfront Ecosystem. Proc. Conference organised by the Botswana-Norway institutional Cooperation and Capacity Building Project (BONIC). Governement Printer, Gaborone.

The Potential of the Soil Seed Bank in Regenerating Riparian Woodland along Chobe River

I Mathumo

Mathumo, I. 2003. The Potential of the Soil Seed Bank in Regenerating Riparian Woodland along Chobe River, Botswana. MSc Thesis, Agricultural University of Norway.

The Return of the Giants: Ecological Effects of an Increasing Elephant Population

Abstract

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