What on earth does ‘trophic’ mean? And ‘downgrading of planet earth’ sounds pretty serious!
Well it all concerns something that is very important both for man and for all living creatures, because all living creatures, including ourselves, belong to food chains. To give you an example of a food chain. An antelope feeds on vegetation, then a lion feeds on antelopes. And this is where ‘trophic’ comes in. This word is derived from a Greek word that means food or feeding.
In a food chain, each organism belongs to a trophic layer. We usually call vegetation trophic layer one, herbivores (meaning animals that feed on herbs, but it can be any sort of vegetation) is trophic layer two, and carnivores (animals like the lion eating other animals) make up trophic level three. There is one other word the meaning of which you should understand, that is ‘ecosystems’. Put simply, an ecosystem is the collection of organisms and a particular physical environment in which they live, occurring in a particular place or places; for example, a tropical rain forest, or sub-tropical grassland, or a pond or an ‘artificial’ ecosystem like a forestry plantation.

And what has all this to do with ‘downgrading of planet earth’? To answer this we need to read a new paper by James Estes and colleagues published this year in the journal Science volume 333. that has the title “Trophic Downgrading of Planet Earth”.
As the human population of the planet grew, and new techniques for killing carnivores were developed, the pace of predator killing accelerated, so that most predators like lions are now much rarer than they were say a hundred years ago or even 50 years ago. For example, you will probably have heard stories of the vast ‘pods’(herds) of whales seen in the past in the southern oceans.

Now what these researchers have found is that this removal of most big predators has produced a veritable cascade of usually harmful effects across the planet. For example, in only the last three decades, the number of lions in Africa has declined by nearly 50 per cent. This loss of lions allowed an explosion of the baboon populations. Bu these animals carried diseases that began to infect people.
To take another example from Africa. Wildebeest, an animal that belongs to the same family as antelopes and cattle, is an animal of grassland-shrubland areas in Africa. Man accidentally introduced the disease rinderpest, and this almost wiped out the wildebeest in parts of Africa. This allowed a build up of areas of (often dense) woody vegetation, and this in turn led to devastating wildfires caused by man or by lightning.

From our point of view, this whole story provides evidence for the harmful effect of the massive growth in the human population that has occurred in the last three centuries.