[LEPS-L:8016] Extincted vs extirpated

[Michael Gochfeld]

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.

However, we shouldn't ignore direct exploitation which eliminated
Passenger Pigeon and Carolina Parakeet as well as a whole fauna on New
Zealand. 

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.  


Mike Gochfeld

 
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