March 7, 2000

Warming the Food Web

migrating birds Records show that 1998 and 1999 were the hottest summers of the century. How did you adjust to the heat? Did you change your diet? Did you change your style of clothing? Did you spend more time indoors or by water? People have the ability to control their immediate climate by going inside and turning up the air-conditioning. How do you think animals cope with climate change?

The list of phenomena being attributed to global warming is growing: record heat waves, extremely severe storms (hurricanes, tornadoes, etc.), extreme trends in precipitation (dry areas getting drier, wet areas getting wetter), and the rise of diseases spread by fleas and mosquitoes (encephalitis, malaria, yellow fever, etc). A study issued last month by the National Academy of Sciences claims that global warming is also disrupting the hibernation and migration patterns of animals and birds.

The study notes that while there is a trend toward warmer spring temperatures, the average snowmelt in high altitudes has remained the same and the snow may actually be getting deeper due to increased precipitation. Birds that migrate to high-altitude summer breeding grounds may have to wait for the snow to melt before they can eat and breed. For example, American robins are migrating about two weeks earlier than they did two decades ago, so they may be faced with short food supplies until spring foliage appears.

Another recent study showed that the increasingly snowy winters in the Isle Royale National Park in Michigan are changing wolf behavior, with far-reaching effects. The wolves are hunting in larger packs, enabling them to triple the number of moose they kill for food. The declining moose population has in turn led to an increase in balsam fir saplings, which are usually eaten by the moose.

Other studies have been conducted showing the effect of global warming on different animal species:

Learn about the Problem

Think about the Problem

There are several major differences in the food chains described by the first two studies: robins starving and wolves thriving, both due to increased snow in their habitats. Contrast the situations, and answer the following questions.

  • In which of the two food chains is the producer directly affected by climate change?
  • In which of the two food chains is the consumer directly affected by climate change?
  • In the food chain with the wolves, how does the predatorsí changed behavior affect the herbivores and the lowest trophic level? Draw a rough graph containing the general growth curves of the wolves, moose, and fir saplings.

For the Teacher: Extending the Problem

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