As reported today in the journal Science, the investigators discovered that the incursion of big-headed ants at Kenya’s Ol Pejeta Conservancy reduces lions’ efficiency in hunting zebras, their primary prey. This is due to the invasive ants eliminating native acacia ants that safeguard the whistling-thorn tree from elephants and other herbivores, resulting in diminished tree cover for lions to ambush zebras.

“We demonstrate that a minuscule invader has reshaped predator-prey interactions among emblematic species,” stated the researchers, led by UW Ph.D. student Douglas Kamaru, affiliated with Professor Jacob Goheen’s research group in the UW Department of Zoology and Physiology.

Encouragingly, the lion population hasn’t dwindled post-insect invasion, likely because lions have adapted their diets from zebras to African buffalo, equally vulnerable to lion predation in affected areas.

The research team comprises members from The Nature Conservancy, the University of British Columbia, the University of Florida, the University of Nairobi, Duke University, the University of Glasgow, Karatina University, the University of Nevada-Reno, and the U.S. Geological Survey.

Symbiosis

Whistling-thorn trees, the predominant species in much of East Africa, offer nectar and shelter for native ants. In return, the ants shield the trees against browsers by biting them and emitting formic acid. The native ants are particularly adept at defending the trees against elephants, thereby stabilizing savanna tree cover across vast landscapes, noted the researchers.

Over the past two decades, the invasion of big-headed ants—thought to originate from an island in the Indian Ocean—has disrupted the mutualistic bond between whistling-thorn trees and native ants. While big-headed ants exterminate the native ants, they fail to shield the trees from elephants, enabling the colossal herbivores to browse and break trees at a rate five to seven times higher than uninvaded areas.

The researchers postulated that the dwindling tree cover would impact interactions between lions and their primary prey, zebras. Through observation of zebra and lion activity across several study plots—some invaded by big-headed ants, some not—the scientists confirmed that the big-headed ant invasion diminishes zebra kills by lions by augmenting openness across the landscape.

Ecological cascade

“We elucidate that the expansion of the big-headed ant, one of the planet’s most pervasive and ecologically impactful invaders, has triggered an ecological cascade that diminishes lions’ proficiency in hunting their primary prey,” the researchers wrote.

The scientists speculate that lions at the Ol Pejeta Conservancy have sustained their numbers by preying more on African buffalo, which are larger and more challenging to kill than zebras. In other parts of East Africa, larger lion groups are needed to hunt buffalo, potentially leading to alterations in the size and composition of lion prides at the Ol Pejeta Conservancy.

“Despite the big-headed ants’ influence on the spatial distribution of zebra kills, and the declining frequency of such kills over time, lions’ shift to more formidable prey has thus far averted any consequential effects on lion numbers,” concluded the researchers. “The significance of behavioral adaptations in upholding lion population stability, along with the extent to which such stability can endure as big-headed ants encroach upon the landscape, remain unresolved questions warranting future exploration.”

Source: University of Wyoming
Photo: Joey Zhou / Unsplash

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The lioness was captured by a remote camera in February, and according to the Wildlife Conservation Society, it was a “beautiful lioness, in her prime and clearly in great health”. The image has been described as an “incredible conservation story” and is proof that the efforts to conserve wildlife populations in the region are bearing fruit.

The border region between Chad and Cameroon has suffered from poaching and habitat loss, which have contributed to the decline of the lion population. However, the governments of Chad and Cameroon have taken strong steps to protect the national parks and wildlife populations in the area, resulting in the gradual recovery of the lion population.

The lion is categorized as “Vulnerable” by the International Union for the Conservation of Nature, and their populations are especially “small and fragmented” in west and central Africa. The loss of their prey, habitat loss, and killing by humans have all contributed to the population decline. Lions have fared better than some other big cats such as tigers in recent decades, but their numbers have declined by two-thirds over the past three decades in Africa. Some of their populations are now facing extinction.

The return of the lioness to Chad’s Sena Oura National Park is a positive step forward for the conservation of lions in the region. The sighting is a testament to the concerted efforts by the governments of Chad and Cameroon to protect wildlife populations, and it is hoped that more lions will return to the park in the future. As the lion population continues to decline globally, it is crucial that we take steps to protect these magnificent creatures and their habitats.

Source: WCS and government of Chad

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Most such studies have concentrated on the impacts of either just one large carnivore, or all as a whole, rather than the varied impacts that large carnivore species may have in intact multi-predator-prey ecosystems. Experimentally testing the behavioural responses of ungulates to different large carnivores is a necessary first step in understanding these likely differing impacts.

In the Greater Kruger National Park in South Africa, the research team examined the fearfulness that ungulates displayed in response to playbacks of lion, African wild dog, cheetah, or non-predator control (bird) vocalizations.

The researchers initially gathered audio recordings of lions, cheetahs, and African wild dogs as well as bird calls to use as a control treatment in order to examine ungulates’ reactions to various sounds. Instead of roaring, they used only short-range sounds like snarls and growls to imitate the proximity of a predator. Then, they used a speaker attached to a video trap to broadcast these scary sounds to wild animals. The speaker was activated to broadcast a predator sound when the camera sensed an animal moving in the area and began recording a video.

Ungulates reacted most fearfully to lions, then wild dogs, and last cheetahs, showing a highly distinct hierarchy of fear. Lion sounds caught the attention of ungulates the most. Notably, the patterns found were not predicted by the death rates (hunting success rates) of the prey species for each predator.

This “hierarchy of fear” is crucial, according to Liana Zanette, a wildlife ecologist at Western University in Canada and a coauthor of the study. Fear influences every element of a prey animal’s behaviour and can have a ripple impact on the environment.

These findings show that various large carnivores cause ungulate prey to exhibit varying degrees of anxiety, resulting in various community-level effects, which ultimately has an impact on vegetation development and landscape features – and potentially even climate. This shows the importance of halting the ongoing global decline and extinction of large carnivores.

Source: Behavioral Ecology
Photo: Brianna R./Unsplash

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While current approaches tend to focus on separating livestock from wild carnivores, for instance through fencing or lethal control, this is not always possible or desirable. Alternative and effective non-lethal tools that protect both large carnivores and livelihoods are urgently needed.

In a new study we describe how painting eyes on the backsides of livestock can protect them from attack.

Many big cats – including lions, leopards, and tigers – are ambush predators. This means that they rely on stalking their prey and retaining the element of surprise. In some cases, being seen by their prey can lead them to abandon the hunt. We tested whether we could hack into this response to reduce livestock losses to lions and leopards in Botswana’s Okavango delta region.

This delta, in north-west Botswana, has permanent marshlands and seasonally flooded plains which host a wide variety of wildlife. It’s a Unesco world heritage site and parts of the delta are protected. However, though livestock are excluded, the cordon fence is primarily intended to prevent contact and disease transmission between cattle and Cape buffalo. Large carnivores, and other wildlife including elephants, are able to move freely across it, and livestock losses to large carnivores are common in the area. In response, lethal control through shooting and poisoning can occur.

While the initial focus of the study was ambush predators generally, it soon became clear that lions were responsible for most of it. During the study, for instance, lions killed 18 cattle, a leopard killed one beast, and spotted hyaenas killed three.

Ultimately, our study found that lions were less likely to attack cattle if they had eyes painted on their rumps. This suggests that this simple and cost-effective technique can be added to the coexistence toolbox, where ambush predators are involved.

Eye-catching solution

Conflict between farmers and wildlife can be intense along the borders of protected areas, with many communities bearing significant costs of coexisting with wildlife. The edge of the Okavango delta in Botswana is no exception, where farmers operate small non-commercial livestock enterprises.

Livestock rub shoulders with lions, leopards, spotted hyaenas, cheetahs, and African wild dogs. To protect the cattle, herds (anything between about six and 100 individual cattle) are kept within predator-proof enclosures overnight. However, they generally graze unattended for most of the day, when the vast majority of predation occurs.

Working with Botswana Predator Conservation and local herders, we painted cattle from 14 herds that had recently suffered lion attacks. Over four years, a total of 2,061 cattle were involved in the study.

Before release from their overnight enclosure, we painted about one-third of each herd with an artificial eye-spot design on the rump, one-third with simple cross-marks, and left the remaining third of the herd unmarked. We carried out 49 painting sessions and each of these lasted for 24 days.

The cattle were also collared and all foraged in the same area and moved similarly, suggesting they were exposed to similar risk. However the individuals painted with artificial eye-spots were significantly more likely to survive than unpainted or cross-painted control cattle within the same herd.

In fact, none of the 683 painted “eye-cows” were killed by ambush predators during the four-year study, while 15 (of 835) unpainted, and 4 (of 543) cross-painted cattle were killed.

These results supported our initial hunch that creating the perception that the predator had been seen by the prey would lead it to abandon the hunt.

But there were also some surprises.

Cattle marked with simple crosses were significantly more likely to survive than unmarked cattle from the same herd. This suggests that cross-marks were better than no marks at all, which was unexpected.

From a theoretical perspective, these results are interesting. Although eye patterns are common in many animal groups, notably butterflies, fishes, amphibians, and birds, no mammals are known to have natural eye-shaped patterns that deter predation. In fact, to our knowledge, our research is the first time that eye-spots have been shown to deter large mammalian predators.

Previous work on human responses to eye patterns however do generally support the detection hypothesis, perhaps suggesting the presence of an inherent response to eyes that could be exploited to modify behaviour in practical situations, such as to prevent human-wildlife conflicts, and reduce criminal activity in humans.

Possible limitations

First, it is important to realise that, in our experimental design, there were always unmarked cattle in the herd. Consequently, it is unclear whether painting would still be effective if these proverbial “sacrificial lambs” were not still on the menu. Further research could uncover this, but in the meantime applying artificial marks to the highest-value individuals within the herd may be most pragmatic.

Second, it is important to consider habituation, meaning that predators may get used to and eventually ignore the deterrent. This is a fundamental issue for nearly all non-lethal approaches. Whether the technique remains effective in the longer term is not yet known in this case.

Protecting livestock from wild carnivores – while conserving carnivores themselves – is an important and complex issue that requires the application of a suite of tools, including practical and social interventions. While adding the eye-cow technique to the carnivore-livestock conflict prevention toolbox, we note that no single tool is likely to be a silver bullet. Indeed, we must do better than a silver bullet if we are to ensure the successful coexistence of livestock and large carnivores. Nevertheless, as part of an expanding non-lethal toolkit, we hope that this simple, low-cost approach could reduce the costs of coexistence for some farmers.

Dr J Weldon McNutt (Director, Botswana Predator Conservation) and Tshepo Ditlhabang (Coexistence Officer, Botswana Predator Conservation) contributed to this article.

Neil R Jordan, Lecturer, UNSW; Cameron Radford, PhD Candidate, UNSW, and Tracey Rogers, Associate Professor Evolution & Ecology, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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The research, a collaboration involving University of Queensland and Griffith University, published in Frontiers in Ecology & Evolution,and Ecological Solutions and Evidence, found that current lion counting methods for research/conservation purposes may be overestimating lion numbers and densities.

Lead author Alexander Braczkowski, formerly at University of Queensland, now a research associate at the Environmental Futures Research Institute

“African lions are one of the world’s most loved animal species and for that reason they garner both conservation attention and funding,” Mr Braczkowski said.

“Yet some experts believe their populations have experienced a 50% decline since 1994 when, coincidentally, Disney’s The Lion King was released.

“Current calculations indicate between 20,000 and 30,000 remain in the wild, scattered across 102 populations in Africa, however, our research suggests these numbers may be substantially lower.

“Most African lion abundance and density estimates are based upon track counts, audio lure surveys and expert solicitation – which are simply not informative enough to understand how lion populations are doing over time.”

According to Mr Braczkowski, as outlined in Frontiers in Ecology & Evolution, the methods being used to calculate lion abundance and density is lagging behind those adopted for other big cats, such as tigers, leopards and jaguars.

“Only by using long-term surveys using photographic methods to identify individual lions can you accurately track changes in population size, survival, density and sex-specific movements.

“Monitoring these parameters over time provides important insights into population health, that current methods like audio surveys or track counts, can’t. For example, our study demonstrated that large home ranges and skewed sex-ratios, can signal prey depletion and imminent population collapse.

“This technique, developed in the Maasai Mara by co-authors Dr Nic Elliot and Dr Arjun Gopalaswamy, compiles data on lion identities and their location, and subsequently uses power computers to determine the changes in lion density across the landscape.”

In their second research paper, Mr Braczkowski and colleagues assessed the ability of this technique to better understand the status of lions in Queen Elizabeth National Park, Uganda.

“This was the perfect place to use this approach since lions in Queen Elizabeth National Park spend a lot of their time up in trees, and it is relatively straightforward to get good pictures of them,” Mr Braczkowski.

“This lion population also carries great local tourism value, with each lion estimated to raise about USD$14,000 annually.

“Queen Elizabeth National Park is an unusual site where lions, owing to their unique tree-climbing behaviour are frequently seen by managers and tourists.”

“It is alarming to note that many continent-wide figures on African lion numbers are not backed by rigorous on-ground surveys,” said Dr Duan Biggs, a co-author on the studies from Griffith University.

“Accurate site-based estimates of lion population size are crucial to assess the effectiveness of conservation interventions.”

Mr Braczkowski and colleagues found lions in Queen Elizabeth National Park were now moving more and have larger home range sizes compared to the previous study conducted about a decade ago.

“Since larger home range sizes in big cats are often associated with lower animal densities due to less available prey, this is a concerning trend,” said Dr Arjun Gopalaswamy, a co-author and science advisor to the Wildlife Conservation Society’s Global Programs.

“There’s great value in using methods that keep track of lion populations directly and we urge conservation and research communities to cease using ad hoc, indirect methods and shift to more reliable and direct methods.”

“In light of the conservation threat due to the collapse in tourism in Africa it is now more urgent than ever to have accurate, reliable monitoring of lion numbers on the continent,” said Mr Braczkowski.

“It appears this is starting to happen, with the method being adopted by the Kenya Wildlife Service and partners to survey lions and other carnivores across Kenya.”

Source: Griffith University

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