How Warming Is Changing The Wild Kingdom

The planet is warming, humans are mostly to blame and plants and animals are going to dramatic lengths to cope. That's the consensus of a number of recent studies that used wildlife to gauge the extent of global warming and its effects.

While the topic of climate change is contentious -- including whether the planet is actually heating up -- a growing number of documented shifts in traits and behaviors in the wild kingdom is leading many scientists to conclude the world is changing in unnatural ways.

Among the changes:

Marmots end their hibernations about three weeks earlier now compared to 30 years ago. Polar bears today are thinner and less healthy than those of 20 years ago. Many fish species are moving northward in search of cooler waters. A fruitfly gene normally associated with hot, dry conditions has spread to populations living in traditionally cooler southern regions.

While we argue ...
Over the past century, Earth's average temperature has risen by about 1 degree Fahrenheit and many scientists believe greenhouse gases and carbon dioxide emissions from human activities are to blame. Left unattended, they warn, temperatures may rise by an additional 2-10 degrees by the end of the century. In the leading computer models, it follows that polar ice will melt and seas would rise drastically, threatening coastal communities around the globe.

A handful of scientists dispute the data. Others say humans aren't to blame.

Terry Root, an environmental science and policy professor at Stanford University, says that as humans argue about thermometer readings, animals are providing evidence that should be figured in to scientific and political decisions.

Animals are "just reacting to what's going on out there," Root says. "And if their behavior is very similar to what we expect with what's going on with global warming -- if they're shifting and they're moving, if they're changing their breeding time by 5 days in 10 years -- we can use that information to support what the thermometers are also showing."

Climate change can occur naturally, but what worries many scientists the most -- and the reason why they don't think this is part of a natural cycle -- is the rapid rate at which the current changes are happening -- changes that are being reflected in the responses of wildlife.

In a 2003 study published in the journal Nature, Root and her colleagues analyzed numerous studies involving wild plant and animals for changes due to global warming. Out of the nearly 1,500 species examined, the researchers found that about 1,200 exhibited temperature-related changes consistent with what scientists would expect if they were being affected by global warming.

The authors highlighted four possible ways that species might respond to rising temperatures, all of which have been documented by other studies and researchers.

Divide and destroy
The first is for species to migrate northward or move to higher elevations. The ubiquitous presence of humans, however, is making this option difficult for some species.

"The thing that is very, very different from prehistoric times is that there are now K-Mart parking lots these species have to cross as they try to move north to get away from the heat down south," Root told LiveScience.

As a result, species that can't adapt to urban or agricultural environments become isolated, their lines of retreat cut off.

In a study published last year in the journal PLoS Biology, Elizabeth Hadly, a biologist at Stanford University, examined fossil records from past warming periods and concluded that global warming can reduce genetic diversity by affecting the connections between species populations.

The best way to ensure species survival is to have large, interconnected populations that are genetically diverse, Hadly explained in an email interview.

This means that even if the genetic diversity of a species as a whole is high, if the individuals are scattered and prevented from interbreeding, they can become just as vulnerable to disease and external threats as a species with a small population and low genetic diversity. Like the military strategy of divide-and-conquer, a group that together might have had the resources to withstand an assault can be picked off one by one if split up.

Connections among individuals within a species aren't the only things that can be disrupted: global warming can also threaten the ties that bind members of different species to one another.

Many biologists, including Darwin, once believed that species responded to temperature changes as a group, thus preserving their relationships to one another. But scientists are finding that this is often not the case.

Instead, different species respond to environmental stressors in different ways, and this can lead to what Root calls the "tearing apart of communities."