climate refugees from the distant past?


Imagine the view from the western coastline of southern Africa during the Last Glacial Maximum (LGM) more than twenty thousand years ago: in the distance you will see at least fifteen large islands – the largest being 300 square kilometers – filled with hundreds of millions of seabird colonies and penguins.

Imagine the view from the western coastline of southern Africa during the Last Glacial Maximum (LGM) more than twenty thousand years ago: in the distance you will see at least fifteen large islands – the largest being 300 square kilometers – filled with hundreds of millions of seabird colonies and penguins.

Now imagine sea level rising by up to a hundred meters between fifteen to seven thousand years ago, gradually covering these large islands until only small hilltops and outcrops remain above the water. The past 22,000 years have resulted in a tenfold reduction in suitable nesting habitat for African penguins, causing their population numbers to plummet.

This is a paleo-historical depiction of the geographic range of the African penguin, made by scientists in the evolutionary genomics research group at the Department of Botany and Zoology and the School of Climate Studies at Stellenbosch University (SU). With this effort, they hope to provide new insights into the vulnerability of Africa’s last remaining penguin species.

The study entitled “Pleistocene natural terminal African penguin population decline increases risk of anthropogenic extinction” was published in Journal of African Marine Sciences on April 20, 2023.

Dr Heath Beckett, first author of the article and postdoctoral fellow in SU’s School for Climate Studies, said this paleo-historical picture of millions of people stands in stark contrast to the current reality of the post-1900 African penguin population collapse.

In 1910, Dassen Island (an island off the West Coast, with an area of ​​about three square kilometers) was teeming with about 1.45 million penguins. However, in 2011 the entire population of African penguins in South Africa fell to 21,000 pairs, and in 2019 they have decreased further to just 13,600. About 97% of the current population in South Africa is supported by only seven breeding colonies.

In May 2005, the International Union for Conservation of Nature classified the African penguin as endangered.

Paleo-historical estimate of penguin population size

So how were the southern and western coastlines of southern Africa during the last Ice Age? And what can that tell about the penguin population numbers?

Because penguins prefer to breed on islands to escape mainland predators, the researchers used topographic maps of the seafloor off the coast of southern Africa to identify potential historic islands that lie ten to 130 meters below current sea level.

For islands to qualify as suitable for penguins, they need to offer protection from land predators and must be surrounded by suitable foraging grounds for sardines and anchovies within a 20 kilometer radius.

Assuming that sea levels were much lower during the last Ice Age, they identified 15 large islands off the West Coast, the largest being 300 km wide.2 island located 130 meters below sea level. Then taking into account sea level rise over the last 15,000 to 7,000 years, they identified 220 islands that would provide suitable nesting conditions for penguins, of which 216 were less than one km (0.1 km) across.2 in area, while some are as small as 30 m2barely more than a rock.

Currently the five largest islands off the West Coast of South Africa are Robben Island (~5 km2), Dassen Island (~3 km2), Ownership Island (~ 1.8 km2) and Seal Island and Penguin Island (both under 1 km2). Possession, Seal, and Penguin Island are all off the coast of Namibia.

Based on the earliest available population density estimates, they then calculated the penguin population estimates based on available island area, assuming that penguins typically nest 500 meters from the coast at most.

Following this approach, they estimated that between 6.4 million and 18.8 million individuals could have occupied waters south of the Cape during the Last Glacial Maximum. However, due to rising sea levels, 15,000 to 7,000 years ago, nesting habitats for African penguins, declined sharply.

According to Dr Beckett, the main aim of the study was to demonstrate that there have been major changes in habitat availability over the last 22,000 years: “This can have a large impact on penguin populations. This population is now experiencing additional human pressure on top of this in the form of climate change, habitat destruction and competition for food,” he explained.

Implications for conservation management

While this finding raises great concern, the researchers argue that it also highlights the potential reserves of African penguin resilience that could be leveraged for their conservation and management in the uncertain future.

Dr Beckett explained: “Sea-level changes will entail the need for multiple relocations of African penguin breeding colonies on centuries-old timescales, if not shorter timescales, and intense competition for breeding space as island habitats become greatly reduced in size. The flexibility of this historical response gives conservation managers some leeway to provide suitable breeding spaces, even on land, as long as suitable nesting sites are available.”

According to Prof. Guy Midgley, interim director of SU’s School for Climate Studies and co-author, this millennial-scale series of selection pressures will support strong colonization capabilities in species: “These do survive and given half a chance, they will survive. Island hopping saved it in the past, they know how to do this,” he emphasized.

But even given the opportunity to relocate, how much more will it take to survive given the increasing pressures of modern humans? When competing with the commercial fishing industry and humanity in general for the same food resources, penguins – and other marine life – may not stand a chance.

Therefore, “for any relocation measures to be successful,” they warned, “adequate access to marine food sources remains a critical element of a coordinated response to prevent species extinction”.


Source link

Related Articles

Back to top button