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.

18 Mar 2022 0

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).

18 Mar 2022 0

Sea otters, sea urchins and algae

When Europeans settled the Alaskan coast in the 19th century, they created a trade in sea otter pelts that led to the disappearance of the species in the region. In the absence of the otters, the sea urchins they love swarmed. They have eaten up all the kelp, the large brown seaweed that can grow to tens of metres in length and line the coasts of the North Pacific. The kelp forests have disappeared, leaving small fish unprotected and the coastline bare to the ocean waves. This “ecological cascade” is an emblematic example of the massive impact of the extermination of a single species on an entire seascape.

Fortunately, the transformation is reversible: as soon as otters were reintroduced to Alaska in the late 1960s, they went back to fishing for sea urchins. Where they thrive, the kelp forests are less ferociously browsed, and gradually recover. All’s well that ends well? Not completely, because, apart from sea urchins, otters love to eat shells. They bring them to the surface and, floating comfortably on their backs, they smash them with pebbles. From the shore, otters can easily be seen treating themselves to a platter of seafood, then grooming themselves vigorously with their offspring. Even the most hardened of scientists describe the sight as “wonderfully adorable”. The First Peoples of southern Alaska, whose livelihoods include shellfish harvesting, are not entirely enchanted. Local communities see the otters as competitors, and have obtained hunting licences, greatly reducing the populations of the small marine mammals near the village of Sitka in the Alexander Archipelago.

Is it impossible for fishermen and otters to live together? Researchers from the University of California at Santa Cruz have been looking into this question (1) . For three decades, they have studied otters, sea urchins and kelp near Sitka and in Torch Bay, an uninhabited area in southern Alaska. They have traced the ups and downs of the ecological cascade associated with otters: with them come kelp forests. However, beyond these major trends, they identified a mosaic of coastal micro-habitats, within which otters have very restricted territories: females spend their entire lives within a 10-25 km radius, and the animals avoid areas where they are likely to encounter their predators, killer whales and great white sharks.

In the infinite landscapes of Alaska, an ecological balance is therefore likely to be established naturally; local communities do not necessarily have to choose between otters and shellfish, ecotourism and fisheries. As the authors of the study note, this hypothesis is reinforced by “archaeological evidence that indigenous people in the Pacific Northwest had access to distinct areas where shellfish and sea otters were abundant”.
(1) Gorra et al. (2022) Southeast Alaskan kelp forests: inferences of process from large-scale patterns of variation in space and time. Proc. R. Soc. B 289: 20211697. https://doi.org/10.1098/rspb.2021.1697

7 Feb 2022 0

The flycatcher and COP26

As COP26 draws to a close, with little hope for a real transformation of our ways of doing things, let’s take a look at past climates and their impacts on wildlife. We are living in the Quaternary Era, which began 2.58 million years ago; a straw in the history of the Earth, but a period with a particularly tormented climate: no less than 50 climatic oscillations of varying magnitude and duration, and between 8 and 10 ice ages in the last 800 000 years alone. Many of the species we see, including the smallest birds, existed millions of years ago. I find it absolutely fascinating that they have come through all these crises, adapting to dramatically changed temperatures and landscapes.

This is what colleagues have shown in a recent study led by Vera Warmuth from the University of Munich (1). The scientists looked at the genetics of the black flycatcher, a passerine bird weighing about ten grams and smaller than my hand, which nests in forests, parks and gardens in Eurasia, feeding on insects. The research team determined the DNA mutations in different flycatcher populations from Spain to Norway. The frequency of these mutations allowed them to date the exact moment when these populations split from each other. They found that these divergences correspond closely to major climatic events, including global temperature fluctuations sometimes exceeding ten degrees.

This was the case approximately 130,000 years ago, with an abrupt period of cooling that turned European forests into tundra and damaged flycatcher populations. At the end of this episode, around 110,000 years ago, flycatchers recolonised the spaces that were once again habitable, with distinct populations in the Iberian Peninsula compared to the rest of Europe. This early differentiation of Iberian flycatchers is surprising, as it was previously thought that it only appeared after the very last ice age, some ten thousand years ago. As Jacques Blondel, a specialist in the evolution of birds at the CNRS, confirms, “today’s biodiversity is a legacy of the climatic oscillations that have punctuated the last two million years. The study by Warmuth and colleagues has the great merit of specifying the tempo and mode of this differentiation with the help of a precise example.

The flycatchers in my area are currently wintering in sub-Saharan Africa and I cannot ask them about the posturing of COP26. It is highly likely that the ongoing warming will again transform their ranges and affect their population sizes. Recent studies show that it is already disrupting their migration, forcing them to return to Europe about ten days earlier (2). In their nesting areas, they will find landscapes devastated by intensive agriculture and modern forestry, where the insects essential to their survival are becoming rare.

(1) Warmuth, Vera M., et al. (2021) “Major population splits coincide with episodes of rapid climate change in a forest-dependent bird”. Proceedings of the Royal Society B. 288.1962: 20211066.

(2) Helm, Barbara, et al. (2019) “Evolutionary response to climate change in migratory pied flycatchers”. Current Biology 29.21: 3714-3719.

22 Nov 2021 0

In Brittany, gannets are on the decline

September 2021: There are plans for a marine extension to the natural reserve of the Sept-Iles archipelago in Brittany. This marine extension may include a quiet zone, closed to marine traffic between April and August each year. The quiet zone will be essential for rafts of northern gannets and other seabirds, the Sept-Iles being the most important seabird breeding area in metropolitan France. Unfortunately, this plan for a quiet zone is meeting the fierce opposition of local recreational sailors, who see the plan for a marine extension to the Sept-Iles terrestrial reserve as an attempt to their “freedom”. I wrote a tribune in Libération, explaining why this marine extension and the quiet zone are essential for seabird conservation: En Bretagne, les fous de Bassan battent de l’aile.

2 Sep 2021 0