Forest or the trees: At what scale do elephants make foraging decisions?

The deterrent effects of individual monoterpene odours on the dietary decisions of African elephants

African savanna elephants use pre-ingestive olfactory cues when making dietary choices, and previous research has observed that elephant diet choice is negatively correlated with vegetation species that contain high concentrations of monoterpenes. However, the frequency and concentration of monoterpenes can vary dramatically across plant species. Thus, we aimed to explore the effects that the odours of individual monoterpenes have on elephant diet choice and how these effects vary with concentration. To do this, we conducted three odour-based choice experiments focusing on eight common monoterpenes found in the woody plants in Southern African savannas. In the first experiment, we tested whether elephant diet choice for a frequently consumed plant (Euclea crispa) was influenced by the addition of the odour of an individual monoterpene at a set concentration. In the second experiment, we explored the relative deterrence of each monoterpene. Lastly, we tested how elephant diet choice varied as a function of the addition of individual monoterpene odours at 5%, 10%, and 20% concentrations. We found that the elephants avoided most individual monoterpenes at high concentrations, with the exception being α-pinene. Furthermore, we found that the odours of some individual monoterpenes were, in fact, more deterrent than others. In the third experiment, we found that the elephants avoided β-pinene, limonene, ocimene, γ-terpinene, and terpinolene across all concentrations, but only avoided sabinene and linalool at high concentrations. Ultimately, our results show that the odour of individual monoterpenes may deter elephant consumption, but that this deterrent effect depends on both the monoterpene and its concentration.

Trunk picking from a truncating menu: Dry season forage selection by Asian elephant in a multi-use landscape

Elephants show a strong selection towards areas with high foraging opportunities at the landscape level making top-down decisions by first selecting patch types within landscapes and finally species within them. Understanding forage selection in a multi-use landscape is critical for prioritising patches for habitat management, ensuring availability of selected forage, helping in minimizing pressure on food crops and subsequent negative interactions with people. We assessed dry season forage selection in a multi-use landscape of West Bengal state, India. Relative forage use and relative plant species availability ratio were calculated to assess forage selection in a multi-use landscape comprising of the forest, tea estates, agricultural land, and human settlement. Forage use was assessed using the opportunistic feeding trail observation method (150.01 km). Stratified random sampling was used to assess plant species availability using the quadrat method (123 plots of 0.1 ha each). Among 286 plant species recorded, 132 plant species were consumed by elephants. A majority (80.21%) of plant species were consumed more than the proportional availability thereby showing selective foraging during the dry season in the study area. From forest to semi-open forest and open forest, canopy layer tree density and the total number of species decreased whereas invasive species density increased. This indicates the high impact on the forage species availability for elephants and the requirement of appropriate habitat management strategies. The presence of 32.14% of the selected forage species in human-use landscape alone demands the development of conservation interventions. This is the first study to assess forage selection by elephants in a multi-use landscape and used to prioritise conservation and management strategies at a landscape level.

Short duration overnight cattle kraaling in natural rangelands leads to increased tree damage by elephants

Elephants are attracted to nutrient hotspots created through short duration overnight cattle corralling (hereafter kraaling) in natural rangelands at Debshan, a mixed cattle-wildlife private ranch in central Zimbabwe, causing severe tree damage. We determined the effect of age of nutrient hotspot (i.e., time after kraal use) on elephant use and the extent of tree damage. Elephant use and tree damage were assessed in nutrient hotspots of varying ages (6, 12, 24, 36 and 48 months after kraal use) and in surrounding landscape. We also compared Acacia karroo bark nutrient and soil nutrient concentration between nutrient hotspots (24 months after kraal use) and the surrounding landscape. Elephant use of nutrient hotspots was highest at 12 and 24 months after kraaling. The most severely damaged trees were in the 12-, 24- and 36-month-old nutrient hotspots. Acacia karroo bark nutrient concentrations (nitrogen, potassium, calcium, magnesium and iron) were higher in nutrient hotspots than surrounding vegetation, while soil nutrients (nitrogen, phosphorus, calcium and potassium) were higher in nutrient hotspots than surrounding landscape. We concluded that elephants mostly used nutrient hotspots 12 and 24 months after kraaling, while severe tree damage occurred 12, 24 and 36 months after kraal use.

The Chemical Ecology of Elephants: 21st Century Additions to Our Understanding and Future Outlooks

Chemical signals are the oldest and most ubiquitous means of mediating intra- and interspecific interactions. The three extant species of elephants, the Asian elephant and the two African species, savanna and forest share sociobiological patterns in which chemical signals play a vital role. Elephants emit secretions and excretions and display behaviors that reveal the importance of odors in their interactions. In this review, we begin with a brief introduction of research in elephant chemical ecology leading up to the 21st century, and then we summarize the body of work that has built upon it and occurred in the last c. 20 years. The 21st century has expanded our understanding on elephant chemical ecology, revealing their use of odors to detect potential threats and make dietary choices. Furthermore, complementary in situ and ex situ studies have allowed the careful observations of captive elephants to be extended to fieldwork involving their wild counterparts. While important advances have been made in the 21st century, further work should investigate the roles of chemical signaling in elephants and how these signals interact with other sensory modalities. All three elephant species are threatened with extinction, and we suggest that chemical ecology can be applied for targeted conservation efforts.

Nutritional influences on enzyme activities in saliva of Asian and African elephants

Asian and African elephants show morphological adaptations to their ecological niche including the oral cavity. Variety and preferences of forage plants differ between both herbivorous elephant species. Diet can affect salivary enzymes. Asian elephants were shown to have a higher salivary amylase activity than African elephants. Species-specific differences were presumed to be influenced by feeding during collection procedure. This study aimed to determine the influence of feeding on enzyme activities in saliva of both elephant species to differentiate from species-specific effects. Additionally, season and housing conditions on salivary enzyme activities in non-fed elephants of both species were investigated. Salivary amylase (sAA), lysozyme (sLYS) and peroxidase (sPOD) activity were measured photometrically or fluorometrically. Results of this study reinforce previous observations of higher basic sAA activity in Asian elephants compared to African elephants. Salivary LYS and sPOD activity showed neither species-specific nor housing-specific differences. Independent from season, most elephants of both species revealed a lack of or low sPOD activity. Feeding caused a temporary decrease of sAA, sLYS and sPOD activity in both elephant species kept in four of eight tested zoos. Furthermore, sAA activity in Asian elephants was higher and sLYS activity lower in Spring than in Autumn. This study summarizes that sAA and sLYS are components of Asian and African elephant saliva in an active conformation in contrast to sPOD. Diet varying between season and zoos might influence sAA and sLYS activities primarily in Asian elephants but temporary low effects suggest sufficient buffer capacity of elephant saliva of both species.

Heterogeneity in African savanna elephant distributions and their impacts on trees in Kruger National Park, South Africa

Though elephants are a major cause of savanna tree mortality and threaten vulnerable tree species, managing their impact remains difficult, in part because relatively little is known about how elephant impacts are distributed throughout space.This is exacerbated by uncertainty about what determines the distribution of elephants themselves, as well as whether the distribution of elephants is even informative for understanding the distribution of their impacts.To better understand the factors that underlie elephant impacts, we modeled elephant distributions and their damage to trees with respect to soil properties, water availability, and vegetation in Kruger National Park, South Africa, using structural equation modeling.We found that bull elephants and mixed herds differed markedly in their distributions, with bull elephants concentrating in sparsely treed basaltic sites close to artificial waterholes and mixed herds aggregating around permanent rivers, particularly in areas with little grass.Surprisingly, we also found that the distribution of elephant impacts, while highly heterogeneous, was largely unrelated to the distribution of elephants themselves, with damage concentrated instead in densely treed areas and particularly on basaltic soils.Results underscore the importance of surface water for elephants but suggest that elephant water dependence operates together with other landscape factors, particularly vegetation community composition and historical management interventions, to influence elephant distributions.

Megaherbivore browsers vs. tannins: is being big enough?

Megaherbivores have been of particular interest to scientists because of the physiological and ecological challenges associated with their extreme body size. Yet, one question that has seldom been explored is how browsing megaherbivores cope with plant secondary metabolites (PSMs), such as tannins, found in their food. It is possible that the sheer body size of these megaherbivores allows them to ingest tannins with no deleterious effects. However, it is plausible that megaherbivores must rely on other mechanisms to cope with PSMs, such as the production of salivary tannin-binding proteins. Thus, we aimed to determine whether megaherbivore browsers produce tannin-binding proteins to further reduce the consequences of ingesting a tannin-rich diet. Using a series of laboratory assays, we explored whether elephants, black rhinoceros, and giraffe had tannin-binding proteins in their saliva. We tested for the presence of proline-rich proteins in the saliva using two different approaches: (1) SDS-PAGE using Laemmli's (Laemmli, Nature 227:680-685, 1970) destaining method, and (2) comparative SDS-PAGE gels using Beeley et al.'s (Beeley et al. Electrophoresis 12:493-499, 1991) method for staining and destaining to probe for proline-rich proteins. Then, to test for the tannin-binding affinity of their saliva, we performed an inhibition assay. We did not observe proline-rich proteins in any of the megaherbivore species, but they did have other protein(s) in their saliva that have a high tannin-binding affinity. Our results highlight that, despite their large body sizes, and their abilities to tolerate low-quality food, browsing megaherbivores have likely evolved tannin-binding proteins as a way of coping with the negative effects of tannins.

Are there phylogenetic differences in salivary tannin-binding proteins between browsers and grazers, and ruminants and hindgut fermenters?

While feeding, mammalian browsers (primarily eat woody plants) encounter secondary metabolites such as tannins. Browsers may bind these tannins using salivary proteins, whereas mammalian grazers (primarily eat grasses that generally lack tannins) likely would not. Ruminant browsers rechew their food (ruminate) to increase the effectiveness of digestion, which may make them more effective at binding tannins than nonruminants. Few studies have included a sufficient number of species to consider possible scaling with body mass or phylogenetic effects on salivary proteins. Controlling for phylogeny, we ran inhibition radial diffusion assays of the saliva of 28 species of African herbivores that varied in size, feeding strategy, and digestive system. We could not detect the presence of salivary proline-rich proteins that bind tannins in any of these species. However, using the inhibition radial diffusion assay, we found considerable abilities to cope with tannins in all species, albeit to varying degrees. We found no differences between browsers and grazers in the effectiveness of their salivary proteins to bind to and precipitate tannins, nor between ruminants and nonruminants, or scaling with body mass. Three species bound all tannins, but their feeding niches included one browser (gray duiker), one mixed feeder (bush pig), and one grazer (red hartebeest). Five closely related species of small ruminant browsers were very effective in binding tannins. Megaherbivores, considered generalists on account of their large body size, were capable of binding tannins. However, the grazing white rhinoceros was almost as effective at binding tannins as the megaherbivore browsers. We conclude, contrary to earlier predictions, that there were no differences in the relative salivary tannin-binding capability that was related to common ancestry (phylogeny) or to differences in body size.

'Remote' behavioural ecology: do megaherbivores consume vegetation in proportion to its presence in the landscape?

Examination of the feeding habits of mammalian species such as the African elephant (Loxodonta africana) that range over large seasonally dynamic areas is exceptionally challenging using field-based methods alone. Although much is known of their feeding preferences from field studies, conclusions, especially in relation to differing habits in wet and dry seasons, are often contradictory. Here, two remote approaches, stable carbon isotope analysis and remote sensing, were combined to investigate dietary changes in relation to tree and grass abundances to better understand elephant dietary choice in the Kruger National Park, South Africa. A composited pair of Landsat Enhanced Thematic Mapper satellite images characterising flushed and senescent vegetation states, typical of wet and dry seasons respectively, were used to generate land-cover maps focusing on the forest to grassland gradient. Stable carbon isotope analysis of elephant faecal samples identified the proportion of C₃ (typically browse)/C₄ (typically grass) in elephant diets in the 1–2 days prior to faecal deposition. The proportion of surrounding C₄ land-cover was extracted using concentric buffers centred on faecal sample locations, and related to the faecal %C₄ content. Results indicate that elephants consume C₄ vegetation in proportion to its availability in the surrounding area during the dry season, but during the rainy season there was less of a relationship between C₄ intake and availability, as elephants targeted grasses in these periods. This study illustrates the utility of coupling isotope and cost-free remote sensing data to conduct complementary landscape analysis at highly-detailed, biologically meaningful resolutions, offering an improved ability to monitor animal behavioural patterns at broad geographical scales. This is increasingly important due to potential impacts of climate change and woody encroachment on broad-scale landscape habitat composition, allowing the tracking of shifts in species utilisation of these changing landscapes in a way impractical using field based methods alone.

Multiproxy evidence for leaf-browsing and closed habitats in extinct proboscideans (Mammalia, Proboscidea) from Central Chile

The multiproxy approach represents a novel methodology and a unique opportunity to obtain a more detailed view of ancient resource use. Our multiproxy study, carried out on gomphotheres from Chile, widens potential occupied habitats to closed-canopy forests. This habitat variability supports the hypothesis that the diet of gomphotheres appears to be more constrained by resource availability than by the potential dietary range. We strongly recommend the use of a multiproxy approach, where morphology analyses are complemented by other sources of information. This approach prevents misleading conclusions about the origin of the proxy’s signal from arising, such as a leaf-browsing diet inferred from the dental calculus and microwear not necessarily being indicative of humidity.

Proboscideans are so-called ecosystem engineers and are considered key players in hypotheses about Late Pleistocene megafaunal extinctions. However, knowledge about the autoecology and chronology of the proboscideans in South America is still open to debate and raises controversial views. Here, we used a range of multiproxy approaches and new radiocarbon datings to study the autoecology of Chilean gomphotheres, the only group of proboscideans to reach South America during the Great American Biotic Interchange (∼3.1 to 2.7 million years before present). As part of this study, we analyzed stable isotopes, dental microwear, and dental calculus microfossils on gomphothere molars from 30 Late Pleistocene sites (31° to 42°S). These proxies provided different scales of temporal resolution, which were then combined to assess the dietary and habitat patterns of these proboscideans. The multiproxy study suggests that most foraging took place in relatively closed environments. In Central Chile, there is a positive correlation between lower δ¹³C values and an increasing consumption of arboreal/scrub elements. Analyses of dental microwear and calculus microfossils have verified these leaf-browsing feeding habits. From a comparative perspective, the dietary pattern of South American gomphotheres appears to be constrained more by resource availability than by the potential dietary range of the individual taxa. This multiproxy study is aimed at increasing knowledge of the life history of gomphotheres and thus follows an issue considered one of the greatest challenges for paleontology in South America, recently pointed out by the need to thoroughly understand the role of ecological engineers before making predictions about the consequences of ecosystem defaunation.

Defence strategies in African savanna trees

Southern African savannas are commonly polarised into two broad types based on plant functional types and defences; infertile savannas dominated by broad-leaved trees typically defended by nitrogen-free secondary compounds and fertile savannas dominated by fine-leaved trees defended by structural defences. In this study, we use trait and other data from 15 wooded savanna sites in Southern Africa and ask if broad-leaved and fine-leaved species dominate on nutrient-poor and nutrient-rich soils, respectively. We then test if there is there any evidence for trade-offs in chemical (i.e., condensed tannins and total polyphenols) vs. structural defences on different soil types. We did not find strong evidence for a general divide in fine- vs. broad-leaved savannas according to soil fertility, nor for a simple trade-off between chemical and structural defences. Instead, we found savanna species to cluster into three broad defence strategies: species were high in leaf N and either (A) highly defended by spines and chemicals or (B) only structurally defended, or (C) low in leaf N and chemically defended. Finally, we tested for differences in browser utilisation between soil types and among plant defence strategies and found that browsing by meso-herbivores was higher on nutrient-rich soils and targeted species from groups A and B and avoided C, while browsing by elephants was mostly not affected by soil type or defence strategy. We propose a framework that can be used as a basis for asking strategic questions that will help improve our understanding of plant defences in savannas.

Harvesting and chewing as constraints to forage consumption by the African savanna elephant (Loxodonta africana)

As a foundation for understanding the diet of African savanna elephants (Loxodonta africana), adult bulls and cows were observed over an annual cycle to determine whether harvesting (P_t), chewing (C_t) and handling times (H_t) differed across food types and harvesting methods (handling time is defined as the time to harvest, chew and swallow a trunkload of food). Bulls and cows were observed 105 and 26 times, respectively (94 and 26 individuals), with a total of 64 h of feeding recorded across 32 vegetation types. Some food types took longer to harvest and chew than others, which may influence intake rate and affect choice of diet. The method used to gather a trunkload of food had a significant effect on harvesting time, with simple foraging actions being comparatively rapid and more difficult tasks taking longer. Handling time was constrained by chewing for bulls, except for the processing of roots from woody plants, which was limited by harvesting. Time to gather a trunkload had a greater influence on handling time for cows compared to bulls. Harvesting and handling times were longer for bulls than cows, with the sexes adopting foraging behaviors that best suited their energy requirements.

Habitat Heterogeneity Variably Influences Habitat Selection by Wild Herbivores in a Semi-Arid Tropical Savanna Ecosystem

An understanding of the habitat selection patterns by wild herbivores is critical for adaptive management, particularly towards ecosystem management and wildlife conservation in semi arid savanna ecosystems. We tested the following predictions: (i) surface water availability, habitat quality and human presence have a strong influence on the spatial distribution of wild herbivores in the dry season, (ii) habitat suitability for large herbivores would be higher compared to medium-sized herbivores in the dry season, and (iii) spatial extent of suitable habitats for wild herbivores will be different between years, i.e., 2006 and 2010, in Matetsi Safari Area, Zimbabwe. MaxEnt modeling was done to determine the habitat suitability of large herbivores and medium-sized herbivores. MaxEnt modeling of habitat suitability for large herbivores using the environmental variables was successful for the selected species in 2006 and 2010, except for elephant (Loxodonta africana) for the year 2010. Overall, large herbivores probability of occurrence was mostly influenced by distance from rivers. Distance from roads influenced much of the variability in the probability of occurrence of medium-sized herbivores. The overall predicted area for large and medium-sized herbivores was not different. Large herbivores may not necessarily utilize larger habitat patches over medium-sized herbivores due to the habitat homogenizing effect of water provisioning. Effect of surface water availability, proximity to riverine ecosystems and roads on habitat suitability of large and medium-sized herbivores in the dry season was highly variable thus could change from one year to another. We recommend adaptive management initiatives aimed at ensuring dynamic water supply in protected areas through temporal closure and or opening of water points to promote heterogeneity of wildlife habitats.

Effects of plant defenses and water availability on seasonal foraging preferences of the Nubian Ibex (Capra nubiana)

The study of herbivore patch use has implications for herbivore habitat quality assessment, foraging behaviors, species interactions, and coexistence in patchy environments. This research focuses on the comparison of the effects of two qualitatively different plant defenses, mechanical (thorns) and chemical (tannins), on ibex foraging preferences during different seasons of the year. The occurrence of both chemical and mechanical plant defenses were experimentally manipulated in artificial resource patches, in addition to water availability. Ibex foraging preferences were quantified using giving-up densities during four separate fieldwork sessions in each of the seasons of the year at cliff sites overlooking the Zin Valley of the Negev Highlands. Both mechanical and chemical plant defenses significantly hindered ibex food intake overall. Mechanical and chemical defenses acted as substitutable defenses, meaning that their combined effects were not greater than additive. There were strong seasonal patterns of the amount of food consumed by ibex, further corroborated by comparison to rainfall levels. Seasonality also interacted with the effectiveness of plant defenses. Thorns were especially ineffective in summer, whereas tannins were most effective in spring. Decreases in seasonal food availability and increased marginal value of energy for ibex may have resulted in thorn ineffectiveness, while seasonal changes in the emergence of young foliage may have resulted in the greater springtime tannin effectiveness. Water was not found to mitigate the detrimental effects of tannins through dilution. The implications for decreased constraints on selective pressures on ibex due to the substitutability of plant defenses are discussed.

Data-driven discovery of the spatial scales of habitat choice by elephants

Setting conservation goals and management objectives relies on understanding animal habitat preferences. Models that predict preferences combine location data from tracked animals with environmental information, usually at a spatial resolution determined by the available data. This resolution may be biologically irrelevant for the species in question. Individuals likely integrate environmental characteristics over varying distances when evaluating their surroundings; we call this the scale of selection. Even a single characteristic might be viewed differently at different scales; for example, a preference for sheltering under trees does not necessarily imply a fondness for continuous forest. Multi-scale preference is likely to be particularly evident for animals that occupy coarsely heterogeneous landscapes like savannahs. We designed a method to identify scales at which species respond to resources and used these scales to build preference models. We represented different scales of selection by locally averaging, or smoothing, the environmental data using kernels of increasing radii. First, we examined each environmental variable separately across a spectrum of selection scales and found peaks of fit. These 'candidate' scales then determined the environmental data layers entering a multivariable conditional logistic model. We used model selection via AIC to determine the important predictors out of this set. We demonstrate this method using savannah elephants (Loxodonta africana) inhabiting two parks in southern Africa. The multi-scale models were more parsimonious than models using environmental data at only the source resolution. Maps describing habitat preferences also improved when multiple scales were included, as elephants were more often in places predicted to have high neighborhood quality. We conclude that elephants select habitat based on environmental qualities at multiple scales. For them, and likely many other species, biologists should include multiple scales in models of habitat selection. Species environmental preferences and their geospatial projections will be more accurately represented, improving management decisions and conservation planning.

Plant selection and avoidance by the Bornean elephant (Elephas maximus borneensis) in tropical forest: does plant recovery rate after herbivory influence food choices?

The plant vigour hypothesis proposes that herbivores should favour feeding on more vigorously growing plants or plant modules. Similarly, we would expect herbivores to favour plants that regrow vigorously after herbivory. Larger animals, like elephants, may also select plant species relative to their availability and prefer species with larger growth forms in order to meet their intake requirements. The food preferences of the Bornean elephant (Elephas maximus borneensis) in the Lower Kinabatangan Wildlife Sanctuary, Sabah, Malaysia, were investigated along 12 transects in areas where elephants were recently sighted feeding. One hundred and eighty-two plants were eaten and 185 plants were measured for species availability along transects. Species vigour was determined by the monthly regrowth in new shoot length after elephant feeding and the number of new shoots produced on each plant. Measurements were carried out on each plant for 9 mo or until the new shoot was eaten. Plant sizes were determined from their basal diameter. The Bornean elephant did not prefer more vigorous species or species with larger growth forms. New shoots did not grow longer on preferred than avoided species. Additionally, unlike other elephants that live in a forest environment, the Bornean elephant preferred species from the Poaceae (specifically Phragmites karka and Dinochloa scabrida) over other plant types including gingers, palms, lianas and woody trees.

Herbivores shape woody plant communities in the Kruger National Park: Lessons from three long-term exclosures

The role of grazers in determining vegetation community compositions and structuring plant communities is well recognised in grassy systems. The role of browsers in affecting savanna woody plant communities is less clear. We used three long-term exclosures in the Kruger National Park to determine the effect of browsers on species compositions and population structures of woody communities. Species assemblages, plant traits relating to browsing and soil nutrients were compared inside and outside of the exclosures. Our results showed that browsers directly impact plant species distributions, densities and population structures by actively selecting for species with traits which make them desirable to browsers. Species with high leaf nitrogen, low total phenolic content and low acid detergent lignin appeared to be favoured by herbivores and therefore tend to be rare outside of the exclosures. This study also suggested that browsers have important indirect effects on savanna functioning, as the reduction of woody cover can result in less litter of lower quality, which in turn can result in lower soil fertility. However, the magnitude of browser effects appeared to depend on inherent soil fertility and climate.Conservation implications: Browsers were shown to have significant impacts on plant communities. They have noticeable effects on local species diversity and population structure, as well as soil nutrients. These impacts are shown to be related to the underlying geology and climate. The effects of browsers on woody communities were shown to be greater in low rainfall, fertile areas compared to high rainfall, infertile soils.