Welcome to Subirdia by John M. Marzluff

Author:John M. Marzluff [Marzluff, John M.]
Language: eng
Format: epub
Publisher: Yale University Press
Published: 2014-05-22T04:00:00+00:00

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 prominently 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 landscape. 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 must be fine. At present, getting the message out is winning, and pitches are on the rise, just as they are in urban birds, such as great tits, that also balance bravado and clarity. In frogs, however, the change in pitch proceeds much more slowly than it does in birds because while big frogs may be able to raise their voices above the traffic din, this ability is ultimately constrained by size. Big frogs have deep voices because their bodies resonate at lower frequencies while croaking. Change is also slow in roadside grasshopper populations, because it requires either evolution of the nervous system or the toothed comblike structure on the insects’ hind legs that are raked against the forewing to “sing.” Evolution of physical characteristics, such as body size or leg form, proceeds slowly across generations, but birdsong can evolve culturally through social learning within a generation. Big birds learn to sing soprano much more quickly than big frogs or leggy grasshoppers can evolve new instruments.

Possessing the cultural wherewithal to quickly and persistently adjust behavior to new environmental challenges is one reason that many birds have adapted to cities. An inability to do so is part of the reason why other animals have succeeded less well. Flexibility benefits birds, but much of their success is deeply rooted in their DNA, essentially preadapting them to the fast-paced, urban life.

Wings allow birds to avoid massive road mortality that culls the urban herd of mammals and herps.

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