Geography Reference
In-Depth Information
sued governments and industries bent on applying it. Even the i sh we eat are
evolving. Gillnets and sport i shing target large salmon and grayling; small
ones squeeze through the mesh of nets and rarely end up on the walls of tro-
phy seekers. As a result, the size of wild pink salmon—an abundant Pacii c
species—has declined by 30 percent in just four decades. Grayling in Scandi-
navia have likewise shrunk, closely matching their girth at maturity to the
legal net mesh size.
It is easy to see natural selection at work when we are the direct selective
agent. We i sh; i sh evolve. We poison; insects and bacteria evolve. But for ev-
ery species af ected directly, many others respond to a changed community.
Removing or adding predators, competitors, or facilitators stretches and
warps subirdia's web of life. Sometimes the web responds with splendor, but
often it does not.
Hawaii's suburbs contain at best one or two of the spectacular array of
native birds that evolved in the absence of humans. Our intended and unin-
tended introductions of predators such as cats and mongooses; competitors
such as rats, mynas, and i nches; and diseases such as malaria and pox have
shredded Hawaii's web. Seventy-i ve percent of the 125 or so native Hawaiian
birds present four thousand years ago when humans i rst colonized the is-
lands are now extinct. The few that survive will need to evolve disease resis-
tance and the ability to exploit a new diet heavy on exotic fruits. Evolution
may not happen fast enough to forestall extinction in the face of such exten-
sive change.
In subirdia, birds not only adjust their genes to the novel environment but
also their culture. Birds pit their innovative and l exible behavior against the
opportunities (such as new foods) and challenges (such as trai c noise) that
are omnipresent in cities. Culture evolves in urban birds if l ock mates copy
 
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