SURVIVAL OF THE CRUCIAL

A few animals shoulder our planet’s future, as without them, our civilisation could collapse. However, the true heroes of nature rarely get the credit they deserve.

From the rocks high above the stony coast of Tatoosh Island, a man is throwing starfish into deep water after spending hours using a crowbar to loosen the creatures from their habitat on the small island off Washington State in the US.

It is 1963, and the man on the rocks is American zoologist Robert Paine. He is studying what happens to an ecosystem, when he removes the top of the food chain. In the small ecosystem, which he has chosen, the Pisaster ochraceus starfish is the ultimate top predator. The starfish consumes mussels, snails, and small crustaceans, which make up the rest of the food chain along with algae, sea anemones, and sea sponges. Much to Paine's surprise, the disappearance of the starfish cut the number of species of the small ecosystem in half in the course of only one year.

SOME SPECIES ARE MORE IMPORTANT

The rooting out of the top layer of the food chain proved to have a much greater effect on the entire ecosystem’s structure and make-up than scientists had previously believed. Top predators such as the starfish had not been considered vital for ecosystems, because no other species depended on them as food. Not until they were dead, and their dead bodies had released nutrients to the surroundings, would the predators give something back to the system. In comparison with what plants offer, the predators’ contribution seemed less important.

While the role of the predators had been underestimated, scientists agreed that a high number of species is very important to ecosystems as a whole.

Biodiversity in the system means that one single organism’s role can more easily be filled by others, should the species go extinct due to disease, etc. Many different species prepare eco-systems for overcoming epidemics and natural disasters, whereas ecosystems with only a few species are more vulnerable.

However, Paine’s observations provided scientists with a better understanding of how ecosystems function. Some species cannot be replaced. Paine removed one single species, and the entire system changed. Without starfish, mussels were able to take over the rocks, so other species were driven out. The ground-breaking discovery made Paine invent a concept, which changed biologists’ view of nature: keystone species. Some species are more important than others.

KEYSTONE SPECIES HAVE MANY ROLES

Top predators such as starfish are not the only keystone species. Other animals, which play very different roles than those of predators, can be at least as important to their ecosystems.

The base of the food chain, which might consist of algae and plants, is totally indispen- sable. The same goes for the animals which pollinate plants, spread plant seeds, or fertilise the ground with their nutritious faeces.

Other animals such as beavers literally contribute to shaping their habitats. By building dams in rivers, the beavers create new lakes, redirecting the flow of nutrients to the benefit of a long series of plants and animals.

ECOSYSTEMS LOSE ENERGY

In order to learn more about an ecosystem, biologists must map out all the interaction going on between each organism and between organisms and their surroundings such as soil, rock, and water. The scientists study how energy and materials are distributed and flow through the system, and they

try to find the driving forces behind nature’s complex networks.

Robert Paine’s studies made him divide ecosystems into trophic levels – an update of the food chain concept. The first trophic level corresponds to the base of the food chain, primarily including plants and other organisms, which get their energy from sunlight. The plants convert solar energy into chemical energy, which the next trophic level, herbivores, benefit from. At the next levels, you will find most predators, and the final level consists of top predators, which are not consumed by others.

The energy transfer between individual levels is incredibly inefficient. Averagely, only about 10 % of the energy is sent on to the next level, because the majority of the energy absorbed by an organism is used to power the metabolism and is hence not available to the next level of the food chain. The continuous loss means that the third trophic level only has access to 1% of the original solar energy, and consequently, there will be ever

fewer organisms per level of the chain. There will always be more plants than herbivores and more herbivores than predators in an ecosystem. Due to the major energy loss, there are rarely more than six trophic levels in a system.

EARTH IS ONE LARGE ECOSYSTEM

One single food chain can be simple, but an ecosystem consists of a long series of interwoven food chains, so the integral whole is very complex. Large ecosystems with high species diversity are so complex that scientists have difficulties forming a general view of them, but they are trying. Just like Paine did in the 1960s, they study small, predictable ecosystems to find patters which they can subsequently use in connection with larger systems.

It becomes much more complex, when scientists take a look at the interaction between all the ecosystems of the world. Every ecosystem on Earth is linked with several others. Nutrients pass between areas, and animals pass back and forth between habitats. In spite of the boundless confusion, Robert Paine’s theory still holds water. Even on a global scale, the disappearance of one single group of animals could have fatal consequences.

Over millions of years of evolution, the majority of plants in the world have entered into unbreakable cooperation with pollinating insects such as bees. Without bees, the plants would not be able to reproduce, and the base of the global food chain would collapse. Other insects are a nuisance to plants, eating their leaves or stems, but insectivores such as bats prevent disasters.

Other creatures sustain global ecosystems by contributing vital nutrients. Algae, which form the basis of most ocean life, are highly dependent on whales, which bring tonnes of nutrition from their lengthy dives deep below the ocean surface.

KEYSTONE SPECIES THREATENED

Although Robert Paine’s experiment focused on a limited ecosystem, he contributd to revealing a global keystone species: humans. Using of a crowbar, he was able to affect the balance of an entire ecosystem. Our global reach and intervening activities have greatly affected the biological state of the world. Without us, it would be highly different. We affect species in everything from the deep sea to rain forests, but unlike that of starfish, our influence is not stabilizing, but rather destructive.

Particularly farming and forestry have meant that many plants and animals struggle to survive. In 2014, a team of British scientists concluded that more than half of the world’s animal population has disappeared in only 40 years. And the keystone species have not been spared. The numbers of predatory fish which, like Paine’s starfish, reign at the top of their ecosystems, have been reduced by some 90 % over the past century, whereas the population of tigers has fallen by 96 % during the same period of time.

WE CAN TURN THINGS AROUND

Our role as a global keystone species also means that we are in a position to correct ecosystems throughout the world. And we are already in full swing. Thousands of projects are helping endangered species gain a new foothold, and several have already produced promising results such as the number of white rhinos in Southern Africa having doubled since the beginning of the millennium.

Moreover, scientists are learning more about the interaction between keystone species and other organisms to the benefit of ecosystems as a whole, and the entire world supports the promising development, establishing ever more natural reserves, where keystone species and their neighbours can regain their strength.