Tigers are revered, loved and feared. Millions of people from all corners of the world adore them. They enthrall us with their majesty, power and grace, yet they are still endangered. Their very survival hangs in the balance as they are trapped and killed for body parts, which can fetch a fortune on the illegal medicine market, and their forest habitat is under threat. If they were to become extinct in the wild it would be an enormous loss. There is now a huge worldwide “save the tiger”campaign involving several key television personalities, wildlife photographers, books and even strip for tigers becoming a yearly event. Yet many other species are also at risk. The planet’s red list grows bigger every day and tigers, charismatic as they may be, are only one species in a giant network of what makes our planet so unique – its biodiversity. So what of the other species?
Take the humble Bumble Bee for example. Albert Einstein once predicted that if bees disappeared then man would only have four years of life left. Bees pollinate plants. In fact, they are responsible for pollinating more than 30% of all food eaten in the United States as well as the rest of the world. Because many trees and flowering plants depend on bees for their reproductive cycle, they would become highly stressed and would either have to adapt to life without bees or become extinct themselves. This would then have a knock on effect along the food chain effecting herbivores, carnivores and also humans. Recent studies have shown that 90% of the wild bee population in the United States has died out and recent studies in European countries have shown an 80% decrease in bee diversity. So given a choice of investing precious time and valuable funds, what would you save first: the proud tiger or the lowly bee?
A keystone in an arch’s crown secures the other stones in place. Keystone species play the same role in many ecological communities by maintaining the structure and integrity of the whole community. If the keystone species disappears the entire community collapses.
Social network analysis is a widely used approach in psychology, social sciences and economics. It focuses not on individuals or social units but the relationships between them. It can be used to model interactions between individual people in a group thus revealing who the “key players” in the community are: i.e., who has the most important interaction structure. This also leads to the “six degrees of separation” theory that in the modern world everyone and everything is six or fewer steps away, by way of introduction, from any other person in the world. Thus a chain of “friend of a friend” statements can be made to connect any two people in a maximum of six steps.
Hue (from red=0 to blue=max) indicates each node’s centrality.
We are now living in the age of the sixth mass extinction, with extinction rates forecasted to reach one to three species per hour. It will be impossible to save all species so it is important to identify which species, areas and ecosystems have the richest interaction structures. If we concentrate on saving them it may then be possible to outline a conservation policy to prevent a cascade of further extinctions occurring.
Ferenc Jordan’s paper, “Keystone Species and Food Webs,” analyzes a network diagram of the Kuosheng Bay food web and attempts to quantify the positional importance of each species. Using network analysis theory he tries to determine a method for locating the keystone species in ecological food chains, the important species being the major interactors i.e. those with many links to others. By looking at the number of direct partners and the indirect in the neighbourhood (neighbours of neighbours) he develops a mathematical formula identifying the “key players” reflecting both the importance and uniqueness of their network. He suggests future developments could focus on the relationship between web structure, and dynamics such as population time series. Would a young “Bayesian” genius be interested?
Other examples of keystone species include beavers and ivory tree coral. Beavers are habitat engineers – by building dams they form areas of still water in which many species flourish. Ivory tree coral is home to more than 300 species of invertebrate. Here fish live, breed and become food for larger fish.
Jordan concludes that it could be the case that a mundane species such as the earthworm could actually be functionally more important than rare “sexy” species such as tigers and rhinos:
“Future conservation biology should focus on the little things that run the world – if they are in a special network position.”
Joe recently helped develop the British Woodlands food webs educational simulation for Newbyte and is donating his share of The Last Tiger (available Amazon kindle) children’s fantasy novel profits to the Animals on the Edge conservation project.