Monday, June 27, 2011

Evolutionary cascade

Extinctions always happen, and many if not most species either disappear entirely or change to become something different.  We say many if not most, because as we've posted before, there is the curious phenomenon of species staying morphologically (as seen in fossils) static for tens or hundreds of millions of years, while nonetheless accumulating genetic distance from related species in amounts corresponding to their fossil-based times.

Humans will become extinct, too, and probably to the great relief of whatever else is left.  And that raises today's point.  Because normally, extinctions (species lifespans) have a kind of regular, probabilistic distribution. But times of rapid large-scale extinctions lead to much less stable change for the survivors.  The onset of humans has led to an acceleration of species changes:  demise of many prey, pathogen, and other species (small pox, passenger pigeons, buffalo), and the growth of others (cows, chickens, poodles, parakeets).

We know that our impact on the world is non-trivial, but a recent report by the International Programme on the State of the Ocean, reported on the BBC website, suggests that as far as the oceans are concerned, it's much worse than even global-warming catastrophists have feared.  As the report summary says:
The current inadequate approaches to management of activities that impact the ocean have lead to intense multiple stressors acting together in many marine ecosystems. 
The impact of such stressors  is often negatively synergistic meaning that the combination of the two magnifies the negative impacts of each one occurring alone. This is already resulting in large--‐scale changes in the ocean at an increasing rate and in some regions has resulted in ecosystem collapse. The continued expansion in global population exerts ever increasing pressures on scarcer ocean resources and tackling this issue needs to be a part of the solution to current concerns. 
The changes in the ocean that are coming about as a result of human CO2 emissions are perhaps the most significant to the Earth system particularly as they involve many feedbacks that will accelerate climate change. 
The resilience of many marine ecosystems has been eroded as a result of existing stressors, leading to increased vulnerability to climate change impacts and a decreased capacity for recovery. An example is coral reefs, the most biodiverse marine ecosystem and one of the most valuable in socioeconomic terms to humankind.
The depletion of ocean species diversity from pollution, climate change, and over-fishing will be serious because even if we are not tree-huggers we depend on the ocean for many things--food not being the only one.  Politics is never far away from these kinds of assessments, and the BBC stories' use of words like 'shocking' decline of ocean life ("The findings are shocking," said Alex Rogers, IPSO's scientific director and professor of conservation biology at Oxford University) are emotive forms of lobbying, whether we agree with the writers or not.  If everything announced by scientists were really 'shocking' we would all be wandering through life as stunned zombies.  But let's try to go beyond manipulative rhetoric...

Evolutionary change usually involves proliferating consequences.  This is because ecosystems are built up over eons, as countless species become adapted to food-chains, niche specialization, and so on.  Removing one or another species may have little effect, because someone else already existing will adapt to the vacated niche (or may have been responsible for it having been vacated).  The system is usually robust enough to tolerate such things---because they are always happening and always have been.

But if the system suffers major eco-quakes, the result can be chaos or oscillations of species relationships that swing way out of control.  Even 'rapid' settling down may take an infinite amount of time as far as humans are concerned: say, hundreds of thousands of generations.  So this is serious.

Maybe the consequences of current oceanic changes will take generations to materialize, and we simply can enjoy the luxury of not having to worry about it all that much ourselves (although having to do without swordfish or squid or whales).

But if the cascade of implications of one species going, leading to starving out of other species, and on ad infinitum, is serious, we or our children may live to regret all those international vacations, high thermostat settings, and drives to the mall that neither we, nor the Earth, needed.

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