[LEPS-L:8024] Re: Extincted vs extirpated

[Chris J. Durden]

At 04:41  28/11/00 -0500, you wrote:
>I was impressed recently with someones wise words that we spend a lot of
>time focusing on endangered species that have slipped into critically
>low population numbers, while ignoring the much more tractable risk
>factors that propel a population to that state. Particularly we ignore
>the numerous local extinctions which don't seem to matter since the
>species is still fairly common somewhere else.  Moreover, we seem to
>have focused a lot of attention on forest fragmentation while ignoring
>the consequences of grassland fragmentation. The accompanying local
>extirpations eventually coalesce into an endangered species. This is
>much better documented in birds than in butterflies. Each of the
>extinctions has its own explanation which encourages people to think
>that there isn't one root cause. But ultimately expanding human
>populations put pressure on resources and habitats.
- - - - -
I agree completely. We should address restriction of habitat, extirpation
of local population, and extinction of genetic lineage as three different
issues.   The first involves communities, what benefits one species may
threaten another in the same community, so species management is very
risky. Here we have the oxymoron: wildlife management. Managed life is not
wild! 
  The second may involve some of the genetic diversity of a species,
especially at the edge of its geographic or altitudinal range. It may even
involve unrecognized subspecies or cryptic species. All populations are
valuable, but some will be lost while others may be gained in the course of
habitat modification through natural causes.
  The third involves species, and this is what we should be most concerned
with as it is final.
- - - -C
>
>However, we shouldn't ignore direct exploitation which eliminated
>Passenger Pigeon and Carolina Parakeet as well as a whole fauna on New
>Zealand. 
>- - - -
  The Passenger Pigeon was a peculiar nomadic species that followed mast
events of the different oak species in Eastern North America. As such it
was naturally very vulnerable to weather or disease that interfered with
these mast events. The human hunts were secondary and may or may not have
been the deciding factor in its extinction. More likely oak pathogens
acting in conjunction with agricultural disturbance were the primary cause.
  The Carolina Parakeet had the misfortune to be attracted to corn patches
and was eradicated as a pest. The Monk Parakeet seems to be filling some of
the vacant niche without being such an obvious pest.
  The New Zealand Faunal decimation by swamping by exotic species is the
story of our American earthworms and terrestrial isopods. This was a direct
result of importation of seed, stock and agricultural material and
continues unabated.
- - - - -C
>An interesting pressure which may mean more for butterflies than we
>think is the invasion of aggressive exotic plants (or animals for that
>matter) which dramatically change habitats.  We are witnessing in the
>1990's and now the rapid spread of Garlic Mustard which within a few
>years can achieve 100% ground cover in disturbed forests. Don't expect
>Toothwort-feeding species to appreciate this change.  
- - - - -
  I agree. Old *Pieris virginiensis* had better watch out. It is our
disturbing of the forests however that is the real cause of any decline in
*Dentaria* species.
- - - - -Chris Durden
>
>
>Mike Gochfeld
>


 
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