It is difficult to estimate the time to extinction of a species or a population. This is partly due to a time lag between degradation of a habitat to the point that it no longer supports a species to the actual death of the last member of the population or species. The species would be doomed to extinction but may be decades away from a total loss. Secondarily wild habitats are quite resilient and will recover if by chance or intent humans lose interest in their exploitation. This may give us a little bit more time to act.
Some species are very sensitive to elements in their environment such as light and heat or depend on other species that are so sensitive. Slight changes in these elements just wipe them out if they cannot move to find another similar habitat elsewhere. A species that needs to migrate to keep up with the rising temperatures but is trapped in a forest fragment, no matter how large, is not likely to make it. As we tear through the wild habitats with the roads, cities, agriculture, pipelines, dams, clear-cuts, we not only decimate populations of wildlife and plants but make it all but impossible for the survivors to move across the human barriers.
The biosphere is made up of incalculable interactions between the many millions of species and their habitat. The survival of species, including the human species, depends on the constancy of those interactions. The process needs to repeat itself so that it continues to create the results that produce the life sustaining environment, the air, the water, the food, weather and temperature. Our activity on this planet has interfered and radically changed so many of the interactions in the biosphere that the planetary ecosystems may be already compromised. In other words the die may already have been cast and we may already be on death row.
The incredibly rich biodiversity we have on Earth is the result of the inbuilt propensity to move, adapt and change coupled with the ‘limited’ ability to disperse. The emphasis here is on the word ‘limited’. Each species had its place of origin and could only disperse by walking, running, slithering, swimming, crawling or casting its seed upon the wind. In pre-human days dispersal was slow and sometimes impeded by rivers, mountain ranges or the oceans. This is the reason why different species evolved in the different parts of the world although the terrain and climate were similar. As human travelling around the world became more and more efficient and widespread all this changed. As we moved around the globe, by design or accident, we took with us over centuries tens of thousands of species, what we call invasive species. This resulting disruption in the eco system that received the new species caused and continues to cause substantial biodiversity loss. This is bad news as biodiversity is the reason for most of our cures to illness and is necessary for our mental health and wellbeing. Biodiversity is what makes the Earth so interesting for us, it is what makes life worth living.
There are important lessons for human society in this. Cultural and geographically dispersed diversity within humanity is not only important but essential for our survival. We should not become as one but should learn to respect our differences, keep within our boundaries. We should celebrate and cultivate all things local and all that makes our community different to others. In nature the boundaries that impede the dispersal of a species are hard and unforgiving to the individuals that try to cross them. We humans have the ability to easily go where we please. As we invade the territory of other human communities as tourists, as economic or war mongering invaders, as migrants we neglect to value our own community back home and we reduce human diversity. This is not a value judgement. It is simply a statement of fact.
The Anthropocene, or age of humans, has undone millions of years of geographic separation. The process of reshuffling the Earth’s flora and fauna began along the routes of human migration. It has now accelerated to such an extent that in a number of places the invasive species outnumber the indigenous ones. In any given twenty four hour period ten thousand species are being moved around the globe in ships’ ballast water alone. In his 2007 research published on the US National Centre for Biotechnology Information journal, Anthony Ricciardi calls this a “mass invasion event”.
Conservationists see non-human invasive species as intruders and there are many laudable initiatives around the world to remove them in an effort to protect the native species. In his 1997 book, The Song of the Dodo, David Quammen warns against demonising invasive species when he says of invasive species that they “are not evil, they are amoral and in the wrong place”. The principal and most pervasive invasive species of all is, without a doubt, people – humanity. We are also the deadliest as wherever we go we leave devastation in our wake. This is an indictment of human values if there ever was one.
The human invasion of the planet started one hundred and twenty thousand years ago when modern humans first migrated out of Africa. Humans arrived in North America thirteen thousand years ago. This gives some idea of the speed of migration at that time as opposed to the speed humanity moves around the planet today. Other species accompanied humans in their travel such as domesticated dogs, rats and pigs just to mention a few. Some species were deliberately introduced such as rabbits in Australia and starlings in the North America.
Charles Elton, a British biologist, is credited to have initiated the studies on invasive species with his 1958 book ‘The Ecology of Invasions by Animals and Plants’. Elton concludes that the shuffling of species around the globe caused by humans is disrupting ecosystems and the whole Earth system. He states that “It might take a long time before the whole system came into equilibrium” and he issues this warning that comes to us prophetically from sixty years ago “If we look far enough ahead, the eventual state of the biological world will become not more complex, but simpler – and poorer.”
Main source: Book ‘The sixth Extinction – An Unnatural History’ by Elizabeth Kolbert