Investigating the vulnerability of an African savanna tree (Sclerocarya birrea ssp. caffra) to fire and herbivory

Sclerocarya birrea ssp. caffra (marula), a typical savanna tree, is vulnerable to the effects of fire, herbivory and their combination. This paper investigated the relative importance of these agents of disturbance, at the level of the individual stem, by specifically focusing on the following questions: (i) What is the greatest cause of mortality in adult marula stems in conservation areas with both elephants and fire? (ii) Does fire interact with bark stripping to cause adult stem mortality and if so what is the dominant mechanism? (iii) At what stem diameter are marulas resistant to fire? Field surveys quantified the extent of damage in marula individuals in the Kruger National Park, South Africa, highlighting the high levels of extreme herbivory such as toppling (7%) and pollarding (8%), relative to bark stripping (only 6% with more than 50% of the circumference stripped). In addition to extreme herbivory, the progression from bark stripping through to invasion of the soft, exposed heartwood by wood borers, often facilitated by fire, through to toppling of the weakened stem after successive fires, appears to be the dominant mechanism by which fire interacts with herbivory to cause adult stem death. Bark stripping and fire manipulation experiments indicated that bark stripping failed to increase the vulnerability of stems to fire directly through transport tissue damage. However, the combination of bark stripping and fire reduced the ability of the stem to regrow bark, increasing the vulnerability of the exposed stem to boring insects and future fires. Fire manipulation experiments were used to identify the minimum stem diameter of resistance to fire. Marula resisted stem death when greater than 3.4 cm in basal diameter. This paper emphasizes the importance of both fire and herbivory in the development of woody plant population structure and by extension, the relative proportion of trees and grasses in savanna landscapes.     

Antelope ingestion enhances germination of the marula (Sclerocarya birrea), an important African savannah tree

The marula (Sclerocarya birrea Hochst.) is an important forage and fruit tree in African savannahs. This study compared germination rate (days to germination) and success (percentage of stones that produced seedlings) among an intact control and four treatments, where fruits were (i) ingested by antelope (Cephalophinae and Neotragini), (ii) manually depulped, (iii) manually depulped and burnt and (iv) burnt intact. Measurements on three unrelated trees showed that whilst stone size differed significantly, germination success was comparable. Antelope regurgitated and expelled stones during rumination, within 16 h of ingestion. Seedling emergence commenced approximately 6 months after fruit drop when ambient temperature increased. Removal of fruit pulp increased germination rate and germination success, but moderate exposure to fire inhibited germination, especially following depulping. Germinated seeds were from significantly smaller stones than ungerminated seeds, suggesting that thicker‐walled endocarps inhibited seedling emergence. However, germination of the second seed in a stone was from larger stones in the germinated subset, possibly due to larger seed size. That antelope ingestion significantly enhanced germination over other treatments suggests that endozoochory is an important mode of seed dispersal in marulas. Appropriate fire management is therefore required in savannahs, as high‐intensity fires may limit germination and recruitment of marulas.     

Myth, marula, and elephant: an assessment of voluntary ethanol intoxication of the African elephant (Loxodonta africana) following feeding on the fruit of the marula tree (Sclerocarya birrea)

Africa can stir wild and fanciful notions in the casual visitor; one of these is the tale of inebriated wild elephants. The suggestion that the African elephant (Loxodonta africana) becomes intoxicated from eating the fruit of the marula tree (Sclerocarya birrea) is an attractive, established, and persistent tale. This idea now permeates the African tourist industry, historical travelogues, the popular press, and even scholastic works. Accounts of ethanol inebriation in animals under natural conditions appear mired in folklore. Elephants are attracted to alcohol, but there is no clear evidence of inebriation in the field. Extrapolating from human physiology, a 3,000-kg elephant would require the ingestion of between 10 and 27 L of 7% ethanol in a short period to overtly affect behavior, which is unlikely in the wild. Interpolating from ecological circumstances and assuming rather unrealistically that marula fruit contain 3% ethanol, an elephant feeding normally might attain an ethanol dose of 0.3 g kg(-1), about half that required. Physiological issues to resolve include alcohol dehydrogenase activity and ethanol clearance rates in elephants, as well as values for marula fruit alcohol content. These models were highly biased in favor of inebriation but even so failed to show that elephants can ordinarily become drunk. Such tales, it seems, may result from "humanizing" elephant behavior.     

Continuing decline of a keystone tree species in the Kruger National Park,South Africa

Sclerocarya birrea subsp. caffra (marula), a keystone large tree species in southern Africa and heavily utilized by people and herbivores, is declining at an unprecedented rate in the Kruger National Park (KNP), South Africa. Due to increasing concerns over large tree declines in the KNP, mirroring those in eastern Africa over the last 50 years, and local extinctions of marula populations in the north‐western KNP, adult trees in the southern KNP were monitored between 2001 and 2010. Annual mortality rates across all adult size classes ranged between 3.2 and 4.6%. Loss of adult marula trees in some areas over the last decade exceeded 25%. Rainfall had a strong influence on mortality rates temporally and spatially, but the distance to the nearest perennial river had little influence. Overall, marula populations continue to decline and further local extinctions are possible. Given the clearly unacceptable trends of decline, the next step is to utilize this information (i) to develop predictive models for the future dynamics of marula populations incorporating all drivers; (ii) to advocate active management of refugia within the park where marula populations are protected from elephant impacts; and in combination with (iii) continued monitoring.     

The influence of tree canopies and elephants on sub-canopy vegetation in a savannah

The apparent influence of elephants on the structure of savannahs in Africa may be enhanced by management activities, fire and other herbivores. We separated the effect elephants have on grasses, woody seedlings (<0.5 m) and saplings (0.5–2 m) from the effect of tree canopies (canopy effect), and herbivory (park effect). We defined the canopy effect as the differences between plant abundances and diversity indices under tree canopies and 20 m away from these. Our testing of the park effect relied on the differences in the sub-canopy plant indices inside and outside a protected area that supported a range of herbivores. We based our assessment of the elephant effect on sub-canopy vegetation indices associated with elephant induced reductions in tree canopies. The park and canopy effects were more pronounced than the elephant effect. The park effect suppressed the development of woody seedlings into saplings. Conditions associated with tree canopies benefited woody plants, but not the grasses, as their indices were lower under trees. Elephants reducing canopies facilitated grass species tolerant of direct solar radiation. We concluded that management should consider other agents operating in the system when deciding on reducing the impact that elephants may have on vegetation.     

The impact of ecological variability on the reproductive endocrinology of wild female African elephants

Non-invasive endocrine methods enable investigation of the relationship between ecological variation and ovarian activity and how this impacts on demographic processes. The underlying physiological factors driving high variation in inter-calving intervals among multi-parous African elephants offer an interesting system for such an investigation. This study investigates the relationship between Normalized Differential Vegetation Index (NDVI), an ecosystem surrogate measure of primary productivity, and fecal progestin concentrations among wild female elephants. Matched fecal samples and behavioral data on reproductive activity were collected from 37 focal individuals during the two-year study. Linear mixed models were used to explore the relationship between fecal 5alpha-pregnane-3-ol-20-one concentrations and the independent variables of NDVI, calf sex, female age, gestation day, and time since last parturition. Among both non-pregnant and pregnant females, fecal 5alpha-pregnane-3-ol-20-one concentrations were significantly correlated with time-specific NDVI indicating a strong relationship between ecological conditions and endocrine activity regulating reproduction. In addition, the age of a female and time since her last parturition impacted hormone concentrations. These results indicate that the identification of an individual's reproductive status from a single hormone sample is possible, but difficult to achieve in practice since numerous independent factors, particularly season, impact fecal hormone concentrations. Regardless of season, however, fecal 5alpha-pregnane-3-ol-20-one concentrations below 1 microg/g were exclusively collected from non-pregnant females, which could be used as a threshold value to identify non-pregnant individuals. Collectively the information generated contributes to a better understanding of environmental regulation of reproductive endocrinology in wild elephant populations, information salient to the management and manipulation of population dynamics in this species.     

The movement of African elephants in a human-dominated land-use mosaic

Land outside of gazetted protected areas is increasingly seen as important to the future of elephant persistence in Africa. However, other than inferential studies on crop raiding, very little is understood about how elephants Loxodonta africana use and are affected by human-occupied landscapes. This is largely a result of restrictions in technology, which made detailed assessments of elephant movement outside of protected areas challenging. Recent advances in radio telemetry have changed this, enabling researchers to establish over a 24-h period where tagged animals spend their time. We assessed the movement of 13 elephants outside of gazetted protected areas across a range of land-use types on the Laikipia plateau in north-central Kenya. The elephants monitored spent more time at night than during the day in areas under land use that presented a risk of mortality associated with human occupants. The opposite pattern was found on large-scale ranches where elephants were tolerated. Furthermore, speed of movement was found to be higher where elephants were at risk. These results demonstrate that elephants facultatively alter their behaviour to avoid risk in human-dominated landscapes. This helps them to maintain connectivity between habitat refugia in fragmented land-use mosaics, possibly alleviating some of the potential negative impacts of fragmentation. At the same time, however, it allows elephants to penetrate smallholder farmland to raid crops. The greater the amount of smallholder land within an elephant's range, the more it was utilized, with consequent implications for conflict. These findings underscore the importance of (1) land-use planning to maintain refugia; (2) incentives to prevent further habitat fragmentation; (3) the testing and application of conflict mitigation measures where fragmentation has already taken place.     

Kamala tree as an indicator of the presence of Asian elephants during the dry season in the Shivalik landscape of northwestern India

The availability of forage resources during the dry season is often a critical factor in determining the distribution and movement of large herbivores. It has long been suspected that the Kamala tree (Mallotus philippinensis) can serve as an indicator of the distribution for Asian elephants during the dry season in northwestern India. However, there is little direct evidence in support of this speculation, especially at a large landscape scale. Here, we predicted the distribution of Kamala trees in the Shivalik landscape of northwestern India based on topographic and bioclimatic variables, as well as satellite-derived vegetation indices and forest canopy height data using a presence-only ecological niche model. We used the area under the receiver operating characteristic curve (AUC) and true skill statistic (TSS) to validate the model. We then examined the relationship between the occurrence probability of Kamala trees and the presence of Asian elephants with data collected during dry seasons between 2010 and 2014 using logistic regression models. Our results showed that the probability of occurrence of Kamala trees was predicted with good accuracy (AUC = 0.88 and TSS = 0.51). The logistic regression models showed that the presence of Asian elephants can be adequately predicted by the occurrence probability of Kamala trees. This result suggests that the distribution of Kamala trees is a good indicator of the presence of Asian elephants during the dry season in the Shivalik landscape. These findings may have major implications for the conservation of Asian elephants, especially in designing wildlife corridors and mitigating human-elephant conflicts.     

象科动物对当地森林生态系统的影响

现存的象科动物(Elephantidae)分为非洲草原象(Loxodonta africana)、非洲森林象(Loxodonta cyclotis)和亚洲象(Elephas maximus)3 种,作为森林生态系统的关键物种,它们对当地森林生态系统的影响非常复杂,在一定环境条件下,既可能是积极的作用,也可能是消极的作用。积极的作用包括:帮助植物传播种子;促进种子萌发;创造断层,维持群落多样性;为其他动物增加食物资源;为其他动物创造栖息地。消极的作用包括:使一些物种的种群数量减小;使森林变成灌木丛和草原等。而由于活动受限导致的种群密度过高是象科动物对森林生态系统产生消极作用的主要原因。当前象科动物的3 个物种均面临种群数量锐减和生存空间不断缩小的危机,为此迫切需要针对其对生物多样性和生态平衡的影响开展深入和全面的研究,并且应根据实际情况因地制宜地制定管理措施。     

Influencing factors on the foot health of captive Asian elephants (Elephas maximus) in European zoos

Pathological lesions of feet occur frequently in captive elephant populations. To improve foot health, it is important to identify risk factors associated with such pathologies. Several previous studies have analyzed potentially influencing factors but were limited, for example, by small sample sizes. This study analyzed the relationship between 87 independent variables and the foot health score of 204 Asian elephants (Elephas maximus) in European zoos using bivariate correlation, multivariable regression models, and principal component analysis (PCA). Correlation and regression tests revealed significant results for 30 different variables, mainly with small effect sizes. Only three variables were significant in more than one test: sex, time spent indoors, and time spent on hard ground, with lower scores (i.e. less or less severe pathological lesions) in females, and when less time is spent indoors or on hard ground. Due to small effect sizes and differing results of the statistical tests, it is difficult to determine which risk factors are most important. Instead, a holistic consideration appears more appropriate. A biplot of the PCA shows that factors representing more advanced husbandry conditions (e.g. large areas, high proportions of sand flooring) were associated with each other and with decreased foot scores, whereas indicators of more limited conditions (e.g. high proportions of hard ground, much time spent indoors) were also associated with each other but increased the foot score. In conclusion, instead of resulting from just one or two factors, reduced foot health might be an indicator of a generally poorer husbandry system.     

Home range, association and related aspects of elephants in the eastern Transvaal Lowveld

Home range and association patterns of elephants Loxodonta africana in private nature reserves adjacent to the Kruger National Park, South Africa, were determined over a period of six years by using radio telemetry. The minimum convex polygon (MCP) and harmonic mean (HM) methods were used for data processing. The minimum and maximum range areas required by females were estimated at 115 and 465 km², respectively, whilst those of males varied between 157 and 342 km². Core areas of females comprised on average 10·1% of the range areas as calculated by the MCP method. Range areas between females in the Klaserie and Timbavati Private Nature Reserves differed significantly. A significant difference in range size was also found between the male population (pooled data) and the females of the Klaserie Private Nature Reserve. Range areas increased from the wet to the dry season. Three male elephant categories were established, namely males utilizing the same area during the study period, those who shifted their range areas and individuals with very large range areas which frequented the area on an irregular basis. A loose relationship existed between males. Association between females can be attributed to kinship and not to the overlapping of range areas. Results indicated avoidance behaviour between females in their core areas, which might partially explain the ability of elephants to tolerate high densities. It is concluded that male elephant hunting should be approached with caution.     

Enzyme‐immunoassay for the measurement of luteinizing hormone in the serum of African elephants (Loxodonta africana)

Circulating patterns of progesterone and luteinizing hormone (LH) in the elephant have been well characterized, and routine monitoring of these hormones is now viewed as a valuable tool for making informed decisions about the reproductive management of elephants in captivity. Currently, LH monitoring in elephants is done with radio‐immunoassays (RIAs); unfortunately, the use of radioactive materials in RIAs limits their application to institutions with laboratory facilities equipped for the storage and disposal of radioactive waste. Enzyme‐immunoassays (EIAs) offer an inexpensive and more zoo‐friendly alternative to RIA. This work reports on an EIA capable of quantifying circulating LH in African elephants. The EIA employs a biotin label and microtiter plates coated with goat anti‐mouse gamma globulin. LH surges in African elephants (n=3) increased fivefold over baseline concentrations (1.00±0.1 ng/ml vs. 0.2±0.1 ng/ml) and occurred 19.3±0.2 days apart. Ovulatory LH surges were associated with an increase in serum progestogens from 4.8±0.4 ng/ml to 11.7±0.4 ng/ml. The ability to quantify reproductive hormones in elephants via EIA is an important step in the process of making endocrine monitoring more accessible to zoos housing these species. Zoo Biol 21:403–408, 2002. © 2002 Wiley‐Liss, Inc.     

Demographic status of elephants in the Samburu and Buffalo Springs National Reserves, Kenya

Individual based demographic records of the elephants utilizing Samburu and Buffalo Springs National Reserves were collected from 1998 through 2003 and indicate that this elephant population was increasing at an average rate of 4.6% per year. Although the majority of carcasses were not found, known sources of mortality include disease, injury, and predation by lions and humans. Poaching did occur during the study period, however the population is increasing and thus our findings indicate ivory poaching has limited impact on the demographic status of these elephants. This population is part of the Samburu/Laikipia MIKE Site and thus its status is relevant to CITES ligislation.     

社群压力对圈养雌性亚洲象动情的影响

亚洲象是中国一级濒危保护动物,改善圈养亚洲象的繁殖状况是亚洲象保护工作的重要内容之一。本研究旨在通过分析社群压力对圈养雌性亚洲象应激和动情状况的影响,从而探究圈养雌性亚洲象长期不动情的原因。通过放射性免疫法检测雌性亚洲象尿液中皮质醇、孕酮和雌二醇水平以及粪便中皮质醇和雌二醇水平,以雌激素水平反映亚洲象的动情状况,以皮质醇水平反映亚洲象的应激状态,以争斗行为和友好行为的发生情况反映圈养群体的社群压力。研究发现：(1)处于优势地位的个体表现出更多的斗争行为,处于从属地位的个体受到更多的攻击行为;(2)优势个体的皮质醇水平显著高于处于从属地位个体的皮质醇水平;(3)优势个体的雌二醇和孕酮具有小幅周期性波动,而从属个体的雌二醇和孕酮水平没有表现出明显的波动。从本研究结果可以看出圈养亚洲象群体中优势个体对从属个体的行为抑制可能是导致从属个体雌激素水平低,长期不能参与繁殖的原因。     

The influence of lunar cycles on crop‐raiding elephants; evidence for risk avoidance

Long‐term solutions to crop raiding by elephants (Loxodonta africana) should be based on an understanding of their behaviour and ecology. The real and perceived risks from humans have been shown to affect elephant behaviour. This is evidenced by elephants predominantly raiding crops at night, avoiding the height of human activity. If such human avoidance behaviours are apparent, it might also be expected that elephants avoid risks associated with higher visibility and increased human activity as may occur during the full moon. However, elephant nocturnal crop‐raiding behaviour in relation to lunar cycles has largely been a neglected factor in studies of human–elephant interactions. In this study around Mikumi National Park, Tanzania, we apply circular statistics in this context for the first time to show a significant decrease in crop raiding during the full moon and apply this method retrospectively to data from another site in West Africa with similar results. Additionally, a greater proportion of farms raided was guarded during the full moon than any other moon phase. Our results indicate that variations in crop raiding with lunar phase could be a general feature of elephant behaviour and thus could be used to design and time mitigation efforts.     

From left to right all through the night: Characteristics of lying rest in zoo elephants

Despite increased research during the past years, many characteristics of resting behavior in elephants are still unknown. For example, there is only limited data suggesting elephants express longer lying bouts and increased total nightly lying durations on soft substrates as compared to hard surfaces. Additionally, it has not been investigated how frequently elephants change body sides between lying bouts. Here we present these characteristics based on observations of nighttime lying behavior in 10 zoo elephants (5 African Loxodonta africana and 5 Asian Elephas maximus elephants) living in five different European facilities. We found that elephants housed on soft substrates have significantly increased total lying durations per night and longer average lying bouts. Furthermore, at 70%−85% of all bouts, a consistently higher frequency of side change between lying bouts occurred on soft substrates, leading to an overall equal laterality in resting behavior. Deviations from this pattern became evident in elephants living on nonsand flooring or/and in nondominant individuals of nonfamily groups, respectively. Based on our findings, we consider elephants to normally have several lying bouts per night with frequent side changes, given an appropriate substrate and healthy social environment. We encourage elephant-keeping facilities to monitor these characteristics in their elephants' nighttime behavior to determine opportunities for further improvements and detect alterations putatively indicating social or health problems in individual elephants at an early stage.     

Seed dispersal of Acacia erioloba by African bush elephants in Hwange National Park, Zimbabwe

Approximately two-thirds (64%) of all dry season samples of elephant dung analysed during a 3-year study in the Main Camp subregion of Hwange National Park, Zimbabwe, contained seed and/or pod materials from Acacia erioloba . Most seeds were recovered intact and actively germinating seeds were not uncommon. Very little pod mass relative to seed mass was recovered in most instances, with pod fragments recorded from only 56% of all exhaustively sampled elephant dung piles containing A. erioloba fruit materials. Nonetheless, large pod fragments and even entire intact pods were recovered occasionally from elephant dung. Seeds and pods of A. erioloba may comprise 12% or more of total wet-weight dung mass; individual dung piles were found which contained > 5000 A. erioloba seeds. Birds and smaller mammals search out and consume A. erioloba seeds present within elephant dung piles. The findings of this study indicate that potential digestibility of A. erioloba seeds for bush elephants ( Loxodonta africana africana ) may be much higher than expected from previous studies. In controlled feeding trials with captive bush elephants (age 11–15 years old) maintained on predominantly free-range dry season diets, the estimated efficiency of digestion for A. erioloba seeds consumed in pods was 81% to 96%, with a gut-transit time of between 24.5 and 36.0 h. On the basis of throughput times determined in experimental feeding trials, potential elephant-dispersal distances of 20–50 km are predicted for A. erioloba in the Kalahari Sands landscapes of southern central Africa.