Nobody would dispute the fact that the destruction of the Earth’s biodiversity is accelerating. The culprit? Homo sapiens. Or, more precisely, homo industrialis, as some scientists prefer to call him, no doubt judging his technological prowess to have outstripped his wisdom. The key question is whether the current erosion of life is indeed unprecedented and occurring on an altogether different scale to past crises. The only way to provide an answer is to study the ecosystems of the past.
Decoding an ecosystem, even a living one, is a painstaking job. It involves taking a census of, quantifying (even approximately), and understanding the interrelations between the elements of which it is composed. The number of recorded species currently stands at around 1.7 million (most of them invertebrates) and there is no doubt that ten times that number remains to be discovered.
When an ecosystem disappeared thousands of years ago, the task of studying it becomes even more complicated. Scientists then have to focus their investigations on rare fossil evidence. The natural fate of a dead organism is to be broken down by carrion eaters and decomposing micro-organisms, the molecules of which it is composed rapidly being recycled in the process with all trace of the organism disappearing. It is only in very particular circumstances, notably the absence of oxygen or an acid environment, that some tissue is preserved. The fossilisation often only concerns the hardest parts (seeds, shells, teeth, bones) on the basis of which the complete organism must be inferred. As for DNA, this is extremely fragile and any fragments of this molecule that remain through the ages are generally unsuitable for use.
Five major extinctions Scientists have nevertheless succeeded in mapping a rough history of biodiversity. It seems it exploded 530 million years ago, at the start of what is known as the Cambrian geological age. We then see a rapid increase in the families of living elements – it being difficult to speak in terms of species at this distant point in time. However, on five occasions the diversity of the biosphere suffered a major setback, during disasters that brought the extinction of a large number of species in a relatively short space of time. The cause of these mass extinctions remains one of evolution’s great mysteries. Cataclysmic volcanic eruptions, sudden changes in sea levels, the impact of asteroids or a combination of these and other factors are all possibilities. Whatever the truth, between these natural disasters, biodiversity tends to recover globally as new species ‘compensate’ for those that were wiped out.
Pollinating history For comparatively more recent periods, such as the Quaternary age that covers the last 2 million years, the history of ecosystems becomes easier to trace, especially in Europe, by analysing pollen grains. Particularly abundant and well preserved in Europe, pollen has much to tell us about the environments of the past. Many plants are anemophilous, meaning they depend on the wind for pollination,(1) which requires the production of vast amounts of pollen able to cover a vast area. Europe also has a remarkable system of peat bogs, waterlogged areas in which plant matter is well conserved over long periods of time.
Ancient pollen grains found in Europe, especially in peat bogs, shed light on the history of ecosystems dating back 2 million years.
More than 900 000 years ago the glacial and interglacial cycles alternated at a frequency of about 40 000 years and were quite moderate in amplitude without an extremely cold phase. “At that time, the forests contained many so-called tertiary species that require humidity and mild winters. A progressive change then set in and we entered a very regular periodicity of 100 000 years, with some periods of very intense cold. This spelled extinction for many of these tertiary species and a total reordering of the dominant trees,” explains the palynologist Jacques Louis de Beaulieu, the coordinator of the European Fossilva project that is studying the history of the European forests. “Starting700 000 years ago, we find forest systems that are very similar to those we find in western Europe today, with oaks, ash, beech, and relatively few species.”
This change, that is perceptible in terms of large trees, certainly affected the rest of the flora and fauna. It is also important to note that during the most recent glaciations some of those living organisms that were ill-adapted to the cold managed to survive in the extreme south of Europe, notably in the Balkans and on the Iberian peninsula. These were zones of sanctuary from which, when the next interglacial period arrived, animals and plants were able to set out in conquest of the land they had been forced to abandon.
European research is also interested in the biodiversity of the past when viewed from another angle. A number of programmes are studying environments that are genuine museums of life, handed down to us virtually intact over thousands of years. The Oasis project, for example, is exploring undersea mountains or ‘seamounts’ off the coast of Madeira and the Azores. These sub-aquatic islands, isolated from the coast, are teeming with life and are usually home to many animal, plant and planktonic communities.
“Teams from eight European universities are working on this project, as well as the WWF (Worldwide Fund for Nature),” explains Oasis’s coordinator Bernd Christiansen of Hamburg University (DE). “One of our objectives is to make decision-makers aware of the damage caused to these environments by fishing and to propose plans for the sustainable management and exploitation of these ecosystems.”
Another project, known as Aces, is devoted to the extraordinary coral reefs in the depths of the Atlantic Ocean that just a decade ago we did not even know existed. Present at various latitudes, from Galicia in Spain to Norway, and at depths of between 150m and over 1 000m, these structures are home to a varied and original fauna of a wealth comparable to that of the coral reefs found in tropical waters.
“These environments to which access is difficult were discovered because the oil industry and fisheries started to show an interest in them,” points out André Freiwald of Erlangen University (DE), the project coordinator. “But today they are the focus of a genuine international scientific effort, for which Europe paved the way in a sense. We are in discussion with teams of Canadian, Australian and New Zealand researchers who intend to use our experience to develop their own studies of deep water coral ecosystems.”
As to the future of biodiversity, that is the concern of researchers from the European Biota cluster, a grouping of some 40 projects. Biodiversity is currently disappearing at a speed comparable to that of the five extinctions of the past and it is important to study and above all reduce the impact of this sixth upheaval. Not so much for life itself as it has always – in the course of a few million years – managed to overcome even the very worst catastrophes, but for us and our descendants who will not be able to wait that long!
(1) Europe’s moderate or even cold climate does not guarantee permanent insect activity, which is why the wind is used as an ally. By contrast, most tropical plants are entomophilous, meaning pollinated by insects that are able to carry the precious seed straight to its destination.
Biodiversities The diversity of species is reduced when extinction occurs.
Intraspecific diversity represents diversity within a given species (example: the 3 000 European bison alive today, all originating from about 50 individuals, are less diversified than their population a few centuries ago).
The diversity of ecosystems is due to the fact that species combine between themselves in different ways, depending on the environment, developing specific characteristics on each occasion.