Newsgroups: sci.environment

Robert Patrick Thille writes:

>Johan Ivar Kval| writes
>> 
>>          
>>          My question is as follows :
>> 
>>          Why do we need to protect species from extermination that aren't
>>   vital for the ecosystem?
>> 
>>          Examples of "unnecessary" animals :
>>    
>
>_All_ life is UNNECESSARY.
>
>Something to think about.
>

This is a major point, which perhaps should be unpacked a little for the
benefit of those who have been taught that only the fundamental limits
and requirements of physics are worthy of being deemed "scientific" when
thinking about nature. 

*None* of the species inventory of any ecosystem is "necessary" in the 
sense that it *has* to exist. All of these things are products of 
contingency -- of the *history* of life.  We too are products of that 
contingency. 

Nevertheless, the functioning of ecosystems results from all of the species
that make them up, and in turn places selection pressures on each species. 
Over time, the functioning becomes more efficient as a result of the 
*coevolution* of the species in the ecosystem -- as a result of evolutionary 
feedbacks among them. The more efficient the functioning, the more 
opportunities arise and the more different kinds of species there can be 
-- and the more species that arise.  A kind of spiral occurs, in which 
diversity, refined by coevolution, breeds more diversity, until a saturation
is arrived at in which the resource pie is so finely divided that each species
has the minimum amount it needs to continue to exist. At this point, further 
subdivision is impossible. 

This results in a delicate balance, one with the property that it is fairly
easily disrupted, and fairly good at repairing itself given enough time. 
Disruptions cause the balance to shed species. Repair occurs either on the 
timescales of succession and community assembly -- decades to many millennia 
-- or, in the case of global extinctions, on the time scales for the 
appearance of new species followed by their subsequent "fine tuning" by 
coevolution -- millions of years.

But the time scales that are meaningful to humans and human societies are
not those of community assembly and coevolution -- millennia and millions
of years. Damage to ecosystems which can only be repaired on these time
scales is, for us, effectively irreversible damage. Even damage which
takes a century to repair potentially represents a huge societal loss. Our
time scales are those of the day-to-day and year-in year-out functioning
of ecosystems, and to a lesser extent decadal processes. I.e. our time scales
are roughly those of the other organisms in ecosystems (surprised?). It is 
crucial to remember that when discussing whether ecosystems are "robust", 
"fragile" etc. -- time resolution has a big influence on the answer. 

On a human time resolution, removing species from ecosystems impairs them.
Some species, particularly predators and large-bodied grazers, have
so much influence over community structure that major disruption can
result when they are removed. Such major disruptions almost invariably
result in further extinctions as the entire food web rearranges itself.

For example, sea otters are predators of many kinds of shellfish along the 
California coast. One might think that removing sea otters would therefore 
increase the abundance of shellfish, but this is not what happens. When sea
otters are removed from the coast, sea urchins outcompete most other littoral
species, resulting in low-diversity communities called urchin barrens. These
sorts of complex interactions are typical of keystone species such as sea
otters. Moreover, such interactions are virtually impossible to predict in
detail in advance -- most of them that we know about, we know about because
the keystone species was in fact removed; i.e. through hindsight.

Species that are not keystones are not unimportant -- removing *enough* 
of them can also cause rearrangements of community structure. It is not 
possible to predict exactly how many is "enough", and it may depend
too on what sorts of future disturbances the ecosystem may encounter. 
As Edward O. Wilson has put it [in _The Diversity of Life_, Harvard Belknap
1992] we have to preserve each scrap of biological diversity -- at both
species and population levels -- while we learn to understand it, appreciate
it, and use it sustainably. In this light, further damaging ecosystems is 
simply unconscionable.

One final word. It is sometimes asserted that even if we do disrupt a 
community by removing species from it, since we can't predict exactly
what will shake out as a result, how do we know that the community will
not be "improved" by the disruption? This is a bit like hoping to improve
a delicate mechanical watch by banging it around. Removing species from
an ecosystem removes bits of functioning that help to support other 
species. Even though the functions may be redundant it is unwise to remove
them: the cells of an organ are redundant, too, but only so many of them
can be killed before the organ no longer does enough of what the organism
needs it to do. Preserving the health of ecosystems -- preventive medicine 
-- is a better approach than waiting until they are near collapse and then
taking heroic measures. And preventive medicine means protecting every bit
of biological diversity. This is best done by protecting ecosystems as
whole systems.

That's what's necessary.

------------
Alan McGowen