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| Many
birds on this continent are migrating an average of 9 days earlier
and breeding sooner than they did 30 years ago! (Photo:
Fran Ludwig) |
How
Can a Changing Climate Affect Plants and Animals?
In the distant past, most climate changes occurred slowly, over many
thousands of years. Plant and animal species adapted to new environments
or moved elsewhere. But as Earth's climate changes more quickly, some
species may not be able to react quickly enough to thrive or survive.
Some
animals — and even plants — can shift their ranges as
temperatures continue to warm. They may move further north or into
higher elevations where it’s cooler. Some can also tolerate
a wider range of conditions (e.g., temperatures) than others. Those
that can't are at greater risk.
But
there's a catch. First, a species may not find another suitable
habitat to move to. Why? Competition for resources, new predators,
and physical barriers (e.g., roads) are just a few of the problems
they could face. Also, all components of an ecosystem don’t
respond in the same way to a warming climate. Because living things
are interdependent with one another and their environment, a changing
climate can have a ripple effect. (See box,
below.)
Next:
What Do Scientists Know About Climate Change? >>
The
Challenge of Change for Living Things
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| Imagine
these scenarios, which are based on actual scientific research.
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A species of butterfly is adapted to emerge from its
chrysalis just as the wildflower it depends on for
nectar blooms. But as the climate warms, the
flower may bloom long before the adult emerges.
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Wintering
monarch butterflies need dry wings in order to withstand
cold temperatures. But
the rainfall and storms in the region where they overwinter
are predicted to increase as the climate continues
to change. This, combined with other risks related
to a warming climate, could affect the survival of
the entire Eastern Monarch population.
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The
climate warms in some low-elevation regions where robins
winter.
Come spring, the robins start arriving in their mountainous
breeding grounds an average of two weeks earlier than
in the past. But there they find loads of snow remaining,
and so they risk starvation.
- Some
birds migrate short distances each year as temperatures
warm and food sources are abundant. As
the climate warms, those species arrive on breeding grounds
even earlier. But other birds use day length as a trigger
to migrate. They fly long-distances to breeding grounds
only to encounter heavy competition for food and nesting
sites from the "early birds."
- Many
insect-eating songbirds migrate north from the neotropics
in the spring.
Their cue to migrate is day length. Their migration coincides
with the leafing out of trees. Why? The migrating birds
rely on caterpillars that eat the trees' young leaves. But
trees leaf out in response to warm temperatures, so if they
leaf out early, songbirds could arrive too late to feast
on a main food source.
- Gray
whales are staying longer in the Arctic feeding grounds.
The
expanding ice cover is their cue to migrate, but with less
ice and more open water, they stay to feed. As a result,
many pregnant females do not reach the safe, warm birthing
lagoons of Mexico before their babies are born. Gray whale
babies born in the open sea have difficulty surviving and
the gray whale population, once endangered, suffers a decline.
- Caterpillars
of a type of moth feed mainly on leaves from one tree species.
With warmer springs, the caterpillars now hatch 2 to 3 weeks
before the leaves emerge. The caterpillars can't survive
more than a few days without food. What's more, a bird species
that depends on the caterpillars to feed its young also
loses its food source . . . and so on, up the food chain.
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