Geography Reference
In-Depth Information
the city to a low in the city center. Much of this variable response can be
explained by the occurrence of sugary nectar that butterl ies crave. Where
nectar-producing plants are abundant and of many types, especially if night
lighting is low and trai c slow, butterl y diversity in the city—and probably
bee and nectivorous bird diversity as well—will be high.
Evolutionary responses to urbanization are not the sole province of birds and
mammals. Insects and amphibians also evolve strategies to urban life. Color
changes in response to urban pollution are well documented, as we saw with the
case of industrial melanism that darkened much of England's fauna, including
many insects, during the coal age (Chapter 7). Moor frogs in urban Russia are
also changing their appearance, but not in response to pollution. These hand-
sized frogs come in two basic morphs: one with a broad, creamy stripe promi-
nently etched down the center of their backs, and one plain-backed without a
stripe. Those with stripes mature quickly and therefore survive the ephemeral
nature of pond life in hot, dry, and high-elevation environments better than do
the plain, slow-growing variety. The ability to quickly metamorphose and hop
away from the natal pool is also advantageous in the unpredictable urban land-
scape. As a result, Russian cities harbor mostly striped frogs.
Road noise is a factor in the evolution of insect and frog calls, just as it is
with birdsongs. Grasshoppers that live along Germany's autobahn overcome
the low-frequency background hum of vehicles by chirping at a higher pitch
than country hoppers do. In southern Australia, southern brown tree frogs and
common eastern froglets croak at higher frequencies near roads than away
from them. For frogs, the shift to a higher voice is costly; big frogs with deep
voices are more intimidating to their rivals and more attractive to potential
mates. The balance between being heard and not being perceived as a wimp
