Beginning in the 1990's, the Northern
Spotted Owl became the center of controversy when biologists called
for listing these owls as an endangered species[#](US Fish and Wildlife Service 1990). The biologists
claimed that the species was threatened because its habitatThe place and conditions in which an organism lives. (old growth forest) was being lost due to logging. They said that without
this critical habitat - if the cutting of old growth forest continued
unabated - the species was doomed.
Opponents of the listing were skeptical,
and soon found a problem with the biologists’ argument when
it was reported that a pair of owls had been found nesting atop
a department store sign. (The veracity of this story is questionable,
but we’ll assume it’s accurate). How, they asked,
could biologists claim that the birds need old growth forest,
when here was this pair happily nesting in a parking lot? Intuitively,
it certainly makes sense to conclude that a species is found in
an area because the habitat is suitable.
Before we accept what common sense tells us, we should also be
skeptical of conclusions based on
intuitionA quick and ready insight, akin to “common sense.”.
Habitats can differ in many ways, including the amount, kind
and distribution of resources (such as food or nesting sites),
competing species, or predators. Some habitats may be ideal, while
others are less suitable, even though populations may be found
in each. Differences in resources among habitats can lead to drastic
differences in survival and reproductive
success among individuals.
The only way to know if a habitat can sustain a species is to
study the birth and death rates of individuals in the habitat[#](Van Horne 1983).
If birth rates are not sufficient to replace individuals that
die, then the population will go extinct unless other individuals
move in from elsewhere[#](Pulliam 1988).
When suitable habitat is reduced or destroyed, many inhabitants
and/or their offspring are displaced and must move elsewhere.
And the remaining habitat will support fewer individuals, so offspring
are less likely to find suitable habitat, forcing them to settle
anywhere they can, perhaps even a store sign.
A thorough search to corroborate the story of the sign-nester
failed, so we don’t know if the pair fledged any young.
But the point is that despite our intuition, concluding that the
story shows this species can survive without old growth forest
is a potentially huge mistake.
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