Geography Reference
In-Depth Information
spiders, spitting spiders, and poisonous black widow spiders rule the city
along with small ground beetles, Argentine ants, fruit l ies, European cab-
bage butterl ies, roaches, and termites. Reduced numbers of native scorpions,
pseudoscorpions, tarantulas, and large predatory ground beetles are of little
relief to most Phoenix residents, whose homes support thirty times the den-
sity of black widows found in the native desert. And even though urban female
widows lay about one hundred fewer eggs than their desert sisters do, each
still produces a brood of nearly two hundred. The shiny black beauties with
beguiling red hourglass markings are in Phoenix to stay. In the sunny, warm
niches of Swiss cities, it is the diversity rather than the density of arthropods
that impresses. There, biologists have identii ed 163 species of spiders and 139
species of bees (though most bees were just traveling through the city on their
way to or from the hive and nectar-rich plantings).
The loss of large predatory insects from urban ecosystems is similar to
the loss of large predatory birds, mammals, and herps, as is the increase in
some particularly destructive invaders. In Phoenix, Argentine ants outcom-
pete many other native ground-dwelling arthropods, leading to lower overall
diversity in places where the ants are abundant. Changes in arthropod diver-
sity ripple up the food chain as herbivory, decomposition, seed dispersal, and
pollination are af ected.
Despite the abundance of native bees in some Swiss cities, fostering them
in urban areas is challenging. In Boston, for instance, bumblebee declines
have been linked to excessive road mortality. (Checking your windshield
or car grill may give you a i rsthand look at this problem.) In Phoenix, bee
numbers are also low, raising concerns that the essential pollination ser-
vices our gardens and crops require may be compromised by the city and its
surroundings.
Rot is not something about which many of us worry. But this essential
service is provided in large part by invertebrates, and, as a result, it too is
 
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