A landscape of fear

A landscape of fear

The Cape gannet saw the seal coming, but too late. In smooth undulations, it glided at three meters per second, a brown and shiny shadow on the surface of the Southern Ocean. The bird frantically tried to take off, flapping its wings and legs, but the mammal grabbed it in the abdomen. The agony that followed is sometimes brief, sometimes slow if the seal is in a playful mood. Some rare crazies escape and come to give their last breath on land, between the nests of imperturbable congeners. Most often, the corpse of bones and feathers sinks, or washes up on a nearby beach.

Off the coast of South Africa, penguins, cormorants and gannets fear seals, but have to live with their presence. Indeed, they all share the same resource: schools of sardines and anchovies historically abundant and largely decimated by industrial fishing. During the day, electronic tracking of the movements of seals and Cape gannets[1] show that they visit the same coastal areas to feed. At night, a quarter of the birds prefer to go ashore to sleep in safety. The others, who have to interrupt their fishing trips because they are hunting on sight, choose to stay close to the schools of fish. At night, they cork the surface of the water with their heads under their wings. The gannets are then particularly vulnerable to seal attacks; with their huge eyeballs, the seals keep a good vision and remain active in the dark. In response, the gannets that remain at sea move their nautical dormitories 15 km offshore, into waters that are less full of fish but also less frequented by seals. The maneuver takes them a quarter of an hour, whereas a return to land would require a flight of more than an hour.

In this little game of “who eats whom”, the seals exclude the birds from certain areas by their mere presence. They thus create a landscape of fear, well known in terrestrial environments: Encounters with lions shape the movements of zebras[2]. At sea, this constraint is little studied, but off the coast of South Africa, it becomes a textbook example. Indeed, the bird-eating seals are themselves the prey of great white sharks. Close to the city of Cape Town, they avoided resting on the surface of the water around the small islands where they breed. On guard against regular shark attacks, these seals had high levels of stress hormones[3].

However, since 2016 everything has changed: the great white sharks have deserted the area; the seals have become indolent and sunbathe while floating around their colonies. Our South African colleagues wonder about the causes of the sudden transformation of a landscape of fear established for decades, but they have a strong hypothesis: a group of orcas moved into the area, killing some great white sharks. Maybe the others preferred to go elsewhere.

A whole hierarchy of fear, which affects even super-predators like sharks, shapes the use of marine spaces by its inhabitants. This constraint is rarely taken into account by management strategies: If coastal marine protected areas are set up to save the last penguins in South Africa and the sardines on which they depend, what happens if hungry seals colonize these areas? Ideally, this is not a confetti, but an entire marine region that should be preserved.

[1] Courbin, N., Pichegru, L., Seakamela, M., Makhado, A., Meÿer, M., Kotze, P.G.H., Mc Cue, S.A., Péron, C. & Grémillet, D. (2022) Seascapes of fear and competition shape regional seabird movement ecology. Communications Biology 5:208.

[2]Courbin, N., Loveridge, A. J., Fritz, H., Macdonald, D. W., Patin, R., Valeix, M., & Chamaillé‐Jammes, S. (2019). Zebra diel migrations reduce encounter risk with lions at night. Journal of Animal Ecology, 88(1), 92-101.

[3] Hammerschlag, N., Fallows, C., Meÿer, M., Seakamela, S. M., Orndorff, S., Kirkman, S., … & Creel, S. (2022). Loss of an apex predator in the wild induces physiological and behavioural changes in prey. Biology Letters, 18(1), 20210476.

Coffee, machete and biodiversity

Photo : Près de 95% des productions éthiopiennes de café n’utilisent pas de pesticides selon la Banque mondiale. (Michael Tewelde /Xinhua. AFP)

Coffee, machete and biodiversity

Early night; this working day will once again hang on my coffee pot. Where would I be without this beverage, in a less globalised world? My daily life depends on a multitude of other imported products, but it is probably coffee that would be the most difficult to give up. Debates about local supply chains carefully avoid questioning the import of teas, coffees and chocolates, which are always available in our organic shops in their multi-certified forms. In the tropical world, the trade in these products is essential to the survival of small producers, who would be plunged into poverty if international transport was to slow down.

But what are the links between coffee growing and biodiversity? Beyene Zewdie and his colleagues from Addis Ababa and Stockholm Universities studied this essential question in the Ethiopian highlands[1], the multi-millennial source of the energising potion. Coffee trees grow there naturally under the forest canopy, between 1000 and 2000 metres above sea level. Villagers harvest their berries and the primary forests also provide firewood, honey and spices. In the shade, coffee yields are low and farmers often thin the canopy to provide sunny clearings. In some areas, the forest almost completely disappears in favour of coffee plantations. This intensification is strongly encouraged by development programmes and the World Bank.

Three years during the rainy season, when plant identification is best, the researchers visited 60 coffee-growing plots, dividing their efforts between those located in the forest and others that were more or less deforested. They expected to find fewer woody species (trees and shrubs) where coffee trees produce the most fruit in full sunlight, but were surprised by the strong impact of even minor agricultural practices on biodiversity: As soon as farmers prune the primary forest to favour coffee trees, half of the woody species disappear, and it can be assumed that this disadvantages resident animals in these landscapes. Subsequently, even if coffee cultivation is intensified, the number of wild woody species present in the plantations remains stable.

According to the authors, these results argue for a strict separation of areas dedicated to coffee cultivation from those left untouched. These latter areas favour regional biodiversity and natural genetic resources of coffee trees. Around them, coffee plantations dotted with large trees remain ecologically much richer than our western monocultures, and they form buffer zones between the villagers’ livestock and the large predators that roam the forest.

Olivier Dangles, a tropical ecologist at IRD, emphasises the interest of these results in a little-studied region, but puts their significance into perspective: “As the authors acknowledge, it is perfectly logical to observe a strong loss of diversity in wild woody plants as soon as a few coffee plants are introduced. What I find more surprising, however, is that satisfactory levels of biodiversity can be maintained with high coffee yields. It would be interesting to understand what kind of management is carried out in these systems, in order to apply it more widely.”

[1] Zewdie, B., Tack, A. J., Ayalew, B., Wondafrash, M., Nemomissa, S., & Hylander, K. Plant biodiversity declines with increasing coffee yield in Ethiopia’s coffee agroforests. Journal of Applied Ecology (in press).

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