"Extinction Vortex"

I read an interesting paper in a biology journal last week, on the processes of extinction of biological species. First, couple of definitions. A "species", using an intuitive working definition that should suffice for this post, is one that does not naturally interbreed with other species. (There are rare exceptions: CNN News reported last week the discovery of a hybrid bear born from a polar mother and a grizzly father.) The "extinction" of a species usually means the death of the last known individual of that species on the earth. This is also known as a "global extinction", which signifies the permanent and irreversible loss of a species from the planet. Biologists use another and more easily tractable definition, the so called "local extinction", which implies the disappearance of a population of the species in a certain region, while it may still persist elsewhere.

Now, back to the paper, which appeared January this year in the acclaimed journal Ecology Letters (a subscription is required to read it). The main objective of the paper is to validate an important theoretical prediction: as a population - defined as a collection of individuals of a particular species within a region - declines in numbers and approaches (local) extinction, the factors causing the decline intensify, driving the population faster and faster towards extinction. This is known as the "extinction vortex". (Mathematically, the rate of population decline increases with decreasing population size.) The paper offers the first empirical verification of this prediction for a wide array of species, from mammals to birds, turtles and even one fish population. Such empirical success of fundamental theoretical precepts is rare in biology, and is a source of excitement for praciticing scientists.

Let the biologists gloat over their success: what has it got to do with the general public? Extinction, be it an inconsequential insect population from the backyard or the gorgeous ivory-billed woodpecker (see the picture above) from the entire planet, is first and foremost a loss, and not merely from moral or aesthetic point of view (even though they are significant). Scientists are still figuring out the intricate ways each and every species contributes to sustaining the balance of the ecosystem around us, which itself provides important services to humankind. The loss of the insect population in the backyard can trigger a precipitous decline of the still larger insects that eat them, which in turn can starve the local bird population that feeds on these larger insects. The depletion of the birds, either by death or emigration, deprives the plant specices of an important mode of dispersal - the seeds and pollen carried along by the birds to far away places. This is not a mere theoretical construct, examples of such keystone species are many in nature. While a global extinction cannot be reversed after it happens, extinction can be prevented from happening in the first place. Scientists and non-scientists alike have a role to play in this endeavor, and the first step is to develop an awareness of the key processes involved as a species hurtles towards fateful oblivion.