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Elephant Populations (elephant + population)

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Life Sciences	86%

Kinds of Elephant Populations

african elephant population

Selected Abstracts

Resource variability, aggregation and direct density dependence in an open context: the local regulation of an African elephant population

JOURNAL OF ANIMAL ECOLOGY, Issue 1 2008
Simon Chamaillé-Jammes
Summary 1An emerging perspective in the study of density dependence is the importance of the spatial and temporal heterogeneity of resources. Although this is well understood in temperate ungulates, few studies have been conducted in tropical environments where both food and water are limiting resources. 2We studied the regulation of one of the world's largest elephant populations in Hwange National Park, Zimbabwe. The study period started in 1986 when the population was released from culling. Using census data we investigated changes in elephant abundance with respect to rainfall and density across the entire park and across waterholes. 3The population more than doubled since culling stopped. The population increased continuously during the first 6 years, and then fluctuated widely at about 30 000 individuals. Immigration processes must have been involved in the increase of the population size. 4Population growth rates were negatively related to previous population density by a convex relationship, and negatively related to the ratio of previous population density on annual rainfall by a linear relationship. However, only this latter model (i.e. assuming a fluctuating carrying capacity related to annual rainfall) produced realistic dynamics. Overall, population decreased during dry years when the elephant density was high. 5During dry years there were fewer waterholes retaining water during the dry season and consequently elephant numbers at waterholes increased, while their aggregation level across waterholes decreased. On the long-run elephant numbers increased only at the less crowded waterholes. 6We suggest that the interaction between population size and the available foraging range determined by the number of active waterholes during the dry season controls the park population. 7Our results emphasize the need to understand how key-resource areas cause resource-based aggregation, which ultimately influences the strength of density dependence. More specifically, this study suggests that climate variability strongly affects local elephant population dynamics through changes in surface-water availability. Finally, as dispersal is likely to be an important driver of the dynamics of this population, our results support views that a metapopulation framework should be endorsed for elephant management in open contexts. [source]

Managing heterogeneity in elephant distribution: interactions between elephant population density and surface-water availability

JOURNAL OF APPLIED ECOLOGY, Issue 3 2007
SIMON CHAMAILLÉ-JAMMES
Summary 1Concerns over the ecological impacts of high African elephant Loxodonta africana densities suggest that it may be necessary to control their numbers locally, although the best management approach is still widely debated. Artificial water supply is believed to be a major cause of local overabundance, and could be used as a potential tool to regulate elephant distribution and impact across landscapes, but its effect on elephants at the population scale has never been studied. 2We assessed how dry-season surface-water availability constrained the distribution of an entire elephant population, using aerial and waterhole census data from Hwange National Park, Zimbabwe. The study was initiated in 1986, when the population was released from culling. We studied how artificial waterholes, holding water throughout the dry season, and vegetation production, estimated from a normalized difference vegetation index (NDVI), influenced the long-term distribution of elephant densities. We also investigated how the elephant distribution responded to changes in population density and annual rainfall, a driver of surface-water availability. 3Long-term dry-season elephant densities across the park tended to increase with vegetation production, and increased asymptotically with the density of artificial waterholes. 4Since the culling stopped, dry-season elephant densities have increased in most areas of the park, except in areas of low vegetation production and low water availability. Interannual fluctuations in elephant distribution are linked to rainfall variability through its effect on surface-water availability. During dry years elephants concentrated in areas where artificial pumping maintained surface-water availability during the dry season. 5During dry years elephant numbers at waterholes increased because of reduced surface-water availability, and elephants were distributed more evenly across waterholes, although active waterholes were unevenly distributed across the park. 6Synthesis and applications. Surface-water availability drives the distribution and abundance of elephants within Hwange National Park, and therefore appears to be at the heart of the trade-off between elephant conservation and the extent of their impact on ecosystems. Artificial manipulation of surface water is one of the tools available for the management of elephant populations and should not be overlooked when considering options for controlling elephant numbers in places where they are considered to be overabundant. [source]

Predicting time-specific changes in demographic processes using remote-sensing data

JOURNAL OF APPLIED ECOLOGY, Issue 2 2006
HENRIK B. RASMUSSEN
Summary 1Models of wildlife population dynamics are crucial for sustainable utilization and management strategies. Fluctuating ecological conditions are often key factors influencing both carrying capacity, mortality and reproductive rates in ungulates. To be reliable, demographic models should preferably rely on easily obtainable variables that are directly linked to the ecological processes regulating a population. 2We compared the explanatory power of rainfall, a commonly used proxy for variability in ecological conditions, with normalized differential vegetation index (NDVI), a remote-sensing index value that is a more direct measure of vegetation productivity, to predict time-specific conception rates of an elephant population in northern Kenya. Season-specific conception rates were correlated with both quality measures. However, generalized linear logistic models compared using Akaike's information criteria showed that a model based on the NDVI measure outperformed models based on rainfall measures. 3A predictive model based on coarse demographic data and the maximum seasonal NDVI value was able to trace the large variation in observed season-specific conception rates (Range 0,0·4), with a low median deviation from observed values of 0·07. 4By combining the model of season-specific conception rates with the average seasonal distribution of conception dates, the monthly number of conceptions (range 0,22) could be predicted within ±3 with 80% confidence. 5Synthesis and applications. The strong predictive power of the normalized differential vegetation index on time-specific variation in a demographic variable is likely to be generally applicable to resource-limited ungulate species occurring in ecologically variable ecosystems, and could potentially be a powerful factor in demographic population modelling. [source]

Heard but not seen: an acoustic survey of the African forest elephant population at Kakum Conservation Area, Ghana

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2010
Mya E. Thompson
Abstract This study, designed to survey forest elephants (Loxodonta africana cyclotis) at Kakum Conservation Area, Ghana, is the first to apply acoustic methods to elephant abundance estimation and to compare results with independent survey estimates. Nine acoustic sensors gathered sound continuously for 38 days. Low-frequency calling rates have been established as useful elephant abundance indices at a Namibian watering hole and a central African forest clearing. In this study, we estimated elephant population size by applying an abundance index model and detection function developed in central Africa to data from simultaneous sampling periods on Kakum sensors. The sensor array recorded an average of 1.81 calls per 20-min sampling period from an effective detection area averaging 10.27 km2. The resulting estimate of 294 elephants (95% CI: 259,329) falls within confidence bounds of recent dung-based surveys. An extended acoustic model, estimating the frequency with which elephants are silent when present, yields an estimate of 350 elephants (95% CI: 315,384). Acoustic survey confidence intervals are at least half as wide as those from dung-based surveys. This study demonstrates that acoustic surveying is a valuable tool for estimating elephant abundance, as well as for detecting other vocal species and anthropogenic noises that may be associated with poaching. Résumé Cette étude, conçue pour étudier les éléphants de forêt (Loxodonta africana cyclotis) de l'Aire de conservation de Kakum, au Ghana, est la première qui applique des méthodes acoustiques pour l'estimation de l'abondance des éléphants et qui compare les résultats avec des estimations indépendantes. Pendant 38 jours, neuf senseurs acoustiques ont récolté les sons en continu. Le rythme des appels à basse fréquence est un indice utile de l'abondance des éléphants que l'on a pu établir à un point d'eau en Namibie et dans une clairière d'une forêt d'Afrique centrale. Ici, nous estimons la taille d'une population d'éléphants en appliquant un modèle d'indice d'abondance et une fonction de détection mis au point en Afrique centrale à des données provenant des senseurs de Kakum pour des périodes d'échantillonnage simultanées. La batterie de senseurs a enregistré une moyenne de 1.81 appel par 20 min, pour une superficie de détection réelle de 10.27 km² en moyenne. L'estimation qui en résulte, qui est de 294 éléphants (95% IC 259,329), tombe dans les limites de confiance de récentes études basées sur les crottes. Un modèle acoustique étendu, qui estime aussi la fréquence à laquelle les éléphants sont silencieux pendant leur présence, donne une estimation de 350 éléphants (95% IC 315,384). Les intervalles de confiance d'une étude acoustique sont au moins la moitié de ceux des études par les crottes. Cette étude montre que l'étude acoustique est un outil intéressant pour estimer l'abondance des éléphants et aussi pour détecter d'autres espèces bruyantes et les bruits d'origine anthropique qui pourraient être associés au braconnage. [source]

Growth response of woody species to elephant foraging in Mwea National Reserve, Kenya

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
Robert M. Chira
Abstract The African elephant (Loxodonta africana) is known to greatly affect the structure and dynamics of vegetation. In Mwea National Reserve, elephants foraged mainly on Acacia ataxacantha and Grewia bicolor out of the five most preferred woody species. However, out of the five preferred woody species, only Grewia virosa and G. bicolor showed a positive association between their fresh use and past elephant use. All the five selected woody species showed high coppicing response after foraging, with the highest coppice growth rates recorded for Acacia brevispica and lowest for Grewia tembensis. The mean heights of woody species utilized by elephants were highest for A. brevispica and lowest for G. bicolor. The mean heights of coppices emerging after utilization by elephants were not significantly different for A. ataxacantha but were significantly shorter in the rest of the foraged species. Elephants avoided the coppices of many other woody species notably C. africana, A. tortilis, A. mellifera, Combretum aculeatum among others in the reserve. The objective of this study was to understand the capacity of woody species to recover after utilization by elephants and feeding response of elephants to new woody species re-growth; a cycle that would define the dynamics of food resources and elephant population within the reserve. Résumé On sait que l'éléphant africain Loxodonta africana affecte beaucoup la structure et la dynamique de la végétation. Dans la Réserve Nationale de Mwea, les éléphants consommaient principalement de l'Acacia ataxacantha et du Grewia bicolor parmi les cinq espèces ligneuses préférées. Cependant, parmi ces cinq espèces, seuls Grewia virosa et .G. bicolor présentaient une association positive entre leur utilisation récente et ancienne par les éléphants. Les cinq espèces ligneuses sélectionnées manifestaient une forte repousse en réponse à la consommation des éléphants, et le taux de repousse était le plus élevé a été enregistré chez Acacia brevispica et le plus faible chez Grewia tembensis. La hauteur moyenne des espèces ligneuses consommées par les éléphants était plus grande chez A. brevispica et plus petite chez G. bicolor. La hauteur moyenne des tiges qui avaient repoussé après consommation des éléphants n'était pas significativement différente chez A. ataxacantha, mais elle était significativement plus courte pour les autres espèces consommées. Les éléphants évitaient les taillis de nombreuses autres espèces ligneuses telles que, particulièrement, C. africana, A. tortilis, A. mellifera, Combretum aculeatum, entre autres, dans la réserve. L'objectif de cette étude était de comprendre la capacité des espèces ligneuses de se régénérer après le passage des éléphants, et la réponse alimentaire des éléphants à la nouvelle repousse de différentes espèces ligneuses et d'esquisser ainsi un cycle qui définirait la dynamique des ressources alimentaires et de la population des éléphants de la réserve. [source]

African elephants: the effect of property rights and political stability

CONTEMPORARY ECONOMIC POLICY, Issue 1 2000
MA. McPherson
African elephant populations have declined by more than 50% over the past 20 years. International outrage over the slaughter led to a worldwide ban on ivory sales beginning in 1989, despite the objections of many economists and scientists, and of several southern African countries that have established systems of property rights over elephants. Far from declining, elephant populations in many of these countries have increased to levels at or above the carrying capacity of the ecosystem. This article estimates the determinants of changes in elephant populations in 35 African countries over several time periods. The authors find that, controlling for other factors, countries with property rights systems of community wildlife programs have more rapid elephant population growth rates than do those countries that do not. Political instability and the absence of representative governments significantly lower elephant growth rates. [source]

African elephants Loxodonta africana and human-elephant interactions: implications for conservation

INTERNATIONAL ZOO YEARBOOK, Issue 1 2006
P. C. LEE
African elephants face an uncertain future. Politics, war, sustained media campaigns, corrupt, weak or absent institutions supporting conservation, land-use planning or general governance, and greed are all bringing elephants into direct conflict with humans. Although elephant populations have declined considerably relative to their historical size and range, human populations have expanded to occupy and intensively use remaining elephant areas. Strategies to minimize perceptions of conflict and the implementation of land-use planning with biodiversity protection as its goal could help to sustain at least some populations of elephants. Here, we review threats to elephants, with an emphasis on those resulting from human perceptions of conflict, and suggest some mechanisms for grappling with these threats. [source]

Resource variability, aggregation and direct density dependence in an open context: the local regulation of an African elephant population

Managing heterogeneity in elephant distribution: interactions between elephant population density and surface-water availability

METHODOLOGICAL INSIGHTS: Using seismic sensors to detect elephants and other large mammals: a potential census technique

JOURNAL OF APPLIED ECOLOGY, Issue 3 2005
JASON D. WOOD
Summary 1Large mammal populations are difficult to census and monitor in remote areas. In particular, elephant populations in Central Africa are difficult to census due to dense forest, making aerial surveys impractical. Conservation management would be improved by a census technique that was accurate and precise, did not require large efforts in the field, and could record numbers of animals over a period of time. 2We report a new detection technique that relies on sensing the footfalls of large mammals. A single geophone was used to record the footfalls of elephants and other large mammal species at a waterhole in Etosha National Park, Namibia. 3Temporal patterning of footfalls is evident for some species, but this pattern is lost when there is more than one individual present. 4We were able to discriminate between species using the spectral content of their footfalls with an 82% accuracy rate. 5An estimate of the energy created by passing elephants (the area under the amplitude envelope) can be used to estimate the number of elephants passing the geophone. Our best regression line explained 55% of the variance in the data. This could be improved upon by using an array of geophones. 6Synthesis and applications. This technique, when calibrated to specific sites, could be used to census elephants and other large terrestrial species that are difficult to count. It could also be used to monitor the temporal use of restricted resources, such as remote waterholes, by large terrestrial species. [source]

Effects of water dependence on the utilization pattern of woody vegetation by elephants in the Tembe Elephant Park, Maputaland, South Africa

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2010
Jerome Y. Gaugris
Abstract The utilization of vegetation and particularly trees in enclosed small reserves where elephant populations are confined is a contentious conservation issue. In Tembe Elephant Park in Maputaland, the diverse Sand Forest is considered the most valuable feature to conserve; yet it is considered at risk from increasing elephant utilization of the park's vegetation in general. The mean canopy removal by elephants across the park was studied over two periods: a recent period including the twelve months before the study and an older period >12 months earlier. Age of utilization was determined from the degree of decay observed on woody fibres. The relationships between intensity of utilization, vegetation unit selection and distance to water were evaluated. Results show that utilization patterns have shifted in the recent drier period, during which elephants used vegetation communities closer to permanent water. Concurringly, a significant decrease in utilization intensity was correlated to an increasing distance from water points in the park during that period, while this effect was not observed during the wetter old period. We debate that active water availability management may be a way to limit elephant utilization in small fenced reserves. Résumé L'utilisation de la végétation, et particulièrement des arbres, dans de petites réserves clôturées où sont confinées des populations d'éléphants est un problème de conservation controversé. Dans le Tembe Elephant Park, au Maputaland, la Sand Forest, très variée, est considérée comme la caractéristique la plus intéressante à préserver; pourtant, on estime qu'elle est en danger en raison de l'utilisation croissante que font les éléphants de la végétation du parc en général. Pendant deux périodes de temps, on a étudié l'enlèvement moyen de la canopée par les éléphants dans tout le parc : une période récente qui incluait les 12 mois qui ont précédé cette étude et une période plus ancienne, plus de 12 mois auparavant. La date de l'utilisation fut déterminée à partir du degré de décomposition observé sur les fibres ligneuses. Les relations entre l'intensité de l'utilisation, la sélection du type de végétation et la distance par rapport à l'eau ont étéévaluées. Les résultats montrent que les schémas d'utilisation se sont modifiés lors de la période sèche récente, au cours de laquelle les éléphants ont fréquenté des communautés végétales plus proches des points d'eau permanents. Dans le même temps, une réduction significative de l'intensité d'utilisation était corrélée à l'éloignement croissant par rapport aux points d'eau dans le parc, alors que cet effet ne fut pas constaté au cours de la première période, plus humide. Nous discutons du fait que la gestion de la disponibilité en eau pourrait être un moyen de limiter la fréquentation des petites réserves clôturées par les éléphants. [source]

Modelling the effectiveness of contraception for controlling introduced populations of elephant in South Africa

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
Robin L. Mackey
Abstract Re-introduced African elephant (Loxodonta africana Blumenbach) populations are growing at very high rates in many of southern Africa's reserves, have attained densities higher than previously thought possible and may be exhibiting irruptive growth. Active management of such populations is necessary to prevent the potentially negative effects on habitat and biodiversity that are associated with elephant overpopulation. One potentially feasible method of elephant management is immunocontraception, but very little is known about the long-term effectiveness of this method. Using demographic data from three South African elephant populations, we made model projections of the effects of contraception on population growth rates to determine whether contraception may be a feasible management tool for elephant. In comparison with noncontracepted populations, realistic reductions in population growth rate after 20 years of contraception were projected to be up to c. 64%, with 50% being a very feasible target. Through its ability to reduce population growth rates, immunocontraception should be an effective tool for preventing or minimizing irruption in elephants and, perhaps, other introduced ungulate species. Résumé Le taux de croissance des populations réintroduites d'éléphants d'Afrique (Loxodonta africana Blumenbach) est très élevé dans les réserves d'Afrique australe; elles ont atteint des densités plus élevées qu'on ne l'avait cru possible et elles pourraient présenter une croissance irruptive. La gestion active de telles populations est nécessaire pour empêcher les effets potentiellement négatifs liés à une surpopulation d'éléphants. Une méthode éventuellement possible pour la gestion des éléphants est l'immuno-contraception, mais on sait très peu de choses sur l'efficacitéà long terme de cette méthode. En utilisant les données démographiques portant sur trois populations d'éléphants d'Afrique du Sud, nous avons modélisé des projections des effets de la contraception sur le taux de croissance des populations pour déterminer si la contraception peut constituer un outil de gestion envisageable pour les éléphants. En comparaison avec les populations sans contraception, des projections réalistes de la réduction du taux de croissance de populations après 20 ans de contraception se chiffraient à environ 64%,50% représentant un objectif tout à fait réaliste. Par sa capacité de réduire le taux de croissance de la population, l'immuno-contraception devrait être un outil efficace pour empêcher ou pour réduire au minimum l'irruption des éléphants et, peut-être, celle d'autres espèces ongulés introduits. [source]

Changes in miombo woodland cover in and around Sengwa Wildlife Research Area, Zimbabwe, in relation to elephants and fire

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2002
Isaac N. Mapaure
Abstract One of the consequences of impacts of elephants and fire on woodlands is a change in woody cover, which often results in major challenges for wildlife managers. Changes in miombo woodland cover in and around Sengwa Wildlife Research Area (SWRA) between 1958 and 1996 were quantified by analyzing aerial photographs. Woody cover in SWRA decreazed from 95.2% in 1958 to 68.2% in 1996, with a lowest mean of 62.9% in 1983. The annual absolute rate of woody cover change in SWRA increazed from ,1.1% per annum between 1958 and 1964 to a recovery of 1.6% per annum between 1993 and 1996, while the annual relative rate increazed from ,1.1% per annum between 1958 and 1964 to 3.3% per annum between 1993 and 1996. There was a strong negative correlation between elephant densities and woody cover in SWRA, suggesting that loss of woody cover was mainly due to elephants. Woodland recovery after 1983 was due to reductions in elephant populations through legal and illegal off-take and reductions in fire frequency. Surrounding areas experienced less woody cover losses than SWRA, mainly due to tree removal by locals whose densities increazed after the eradication of tsetse fly in the 1970s. Résumé Une des conséquences de l'impact des éléphants et des feux sur les forêts s'exprime par un changement du couvert ligneux qui pose souvent de fameux défis pour les gestionnaires de la faune. Les changements du couvert forestier à Miombo, qui sont survenus à l'intérieur et aux alentours de l'Aire de Recherche sur la Faune de Sengwa (SWRA) entre 1956 et 1996, ont été quantifiés grâce à l'analyse de photos aériennes. Le couvert forestier de la SWRA a diminué de 95.2% en 1958 à 68.2% en 1996, la moyenne la plus basse étant observée en 1983, avec 62.9%. Le taux annuel absolu de changement du couvert forestier dans la SWRA est passé de , 1.1% par an entre 1958 et 1964 à une restauration de 1.6% par an entre 1993 et 1996, tandis que le taux annuel relatif augmentait de , 1.1% par an entre 1958 et 1964 à 3.3% par an entre 1993 et 1996. Il existait une forte corrélation négative entre la densité des éléphants et le couvert forestier de la SWRA, ce qui laisse supposer que la perte de couvert forestier était due principalement aux éléphants. La restauration de la forêt après 1983 était due à des réductions des populations d'éléphants suite à des prélèvements, légaux ou non, et à une baisse de la fréquence des feux. Les zones adjacentes ont subi de moins fortes pertes du couvert forestier que la SWRA, et celles-ci étaient principalement dues à des coupes faites par les locaux dont la densité a augmenté suite à l'éradication de la mouche tsé-tsé dans les années 1970. [source]

Characterization of tetranucleotide microsatellite loci in the African Savannah Elephant (Loxodonta africana africana)

MOLECULAR ECOLOGY RESOURCES, Issue 2 2003
E. A. Archie
Abstract Most African elephant (Loxodonta africana africana) populations are isolated and thus threatened by a loss of genetic diversity. As a consequence, genetic analysis of African elephant populations will play an increasing role in their conservation, and microsatellite loci will be an important tool in these analyses. Previously published sets of polymorphic microsatellites developed for African elephants are all dinucleotide repeats, which are prone to typing error. Here, we characterize 11 tetranucleotide microsatellite loci in the African elephant. All loci were polymorphic in 32 faecal samples and two tissue samples from 33 individual African savannah elephants. [source]