Geography Reference
In-Depth Information
carefully worked out by my colleagues Tessa Francis and Daniel Schindler.
These limnologists and i sh fanatics assessed more than i fty lakes, about half
of which were in the Pacii c Northwest. They observed that the density of
houses ringing lakeshores closely predicted the abundance of dead trees,
branches, and other decaying plant growth—what the scientists call “coarse
woody debris”—that was found along the shore and in the lake shallows.
When the number of dwellings per mile exceeded about six, the coarse woody
debris disappeared from the lakes because residents cleared it away for an
unimpeded view of the lake and access to its water. Fish growth suf ered from
the reduced cover and especially from reduced food in the form of insects
from the land.
In urban streams, food from the land is also af ected by light pollution.
Lights on city streets, yards, commercial buildings, and elsewhere attract and
kill many urban insects and reduce the emergence of aquatic insects from
streams. This double whammy means that insectivorous i sh in urban streams
have less food and may be stunted in size or outcompeted by species with
more general diets. Changes in food as well as increased sewage, silt, nonna-
tive species, and i shing pressure together determine the community of i shes
that live among us.
A quick look in the dark corners of one's house will coni rm that not all
urban invertebrates are i sh food. The four million Americans who live in Phoe-
nix, Arizona, know this all too well. Despite a general decline in arthropod
diversity—the variety of insects, spiders, and crustaceans—inside the city rela-
tive to the surrounding desert, some species are seemingly everywhere. Water
is a key feature; it is diverted from the few nearby rivers into the city and put
to work. Plants that support arthropods also benei t from the moisture. Wolf
