Geography Reference
In-Depth Information
Seattle's suburbs we regularly document a community with i ve facilitators,
three foreign invaders, seven predators, and dozens of potential competitors.
I wonder how house i nches will af ect purple i nches, how white-crowned
sparrows will af ect song sparrows, and how Anna's hummingbirds and ru-
fous hummingbirds will get along. As long as our plantings continue to pro-
duce nectar-rich l owers and fruits, our bird feeders remain well stocked, and
our city streets aren't too tidy, I suspect that abundant food and generally
mild urban climates will keep competition's inl uence subdued.
The diversity that subirdia contains may seem redundant, but each piece
helps maintain the whole. A diverse ecosystem performs better than does a
simple one. Collectively, the many species in a wide ecological web capture
more energy from the sun's nourishing rays and convert it into the vegetation
that ultimately supports us all. A greater number of species is better able to
recycle the plant-derived nutrients that move through the ecosystem, espe-
cially its decomposers. In variable and changing conditions, diversity has
both a stabilizing and a performance-enhancing ef ect. In a diverse commu-
nity, as some species decline in response to change, others increase. Chal-
lenges posed by aggressive nonnative invaders, many of which are devastating
to human economies, are more likely stil ed by the collective actions of a di-
verse rather than a simple ecosystem. Species diversity can be thought of as an
insurance policy against today's environmental change and tomorrow's new
evolutionary challenges.
For subirdia's insurance policy to pay its full dividend, diversity must not
only be assembled, it must be sustained. The mere presence of a species is not
always indicative of its staying power. To gauge the ability of birds to persist
in subirdia, we must track the life trajectories of individuals. Their stories are
powerful.
On a July day in 2009, a small, darkly streaked, plump song sparrow sings
from a subdivision midway between the urban and wild ends of the Seattle
