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Climate Change Sends Species on the Move, Giving Invasives a Leg Up

Warmer temperatures and rising sea levels are already forcing migrations of animals and plants, and invasive species may be some of biggest winners as habitat are disrupted by climatic changes.

Whether species survive new conditions brought by a changing climate will depend on their ability to move with those changes, says a study in the current issue of the journal Nature. Plants and animals, on average, will have to be able to migrate at a rate of about a quarter mile (0.42 km) a year in order to stay within the ecological "envelope" to which they are adapted, it says.

But as some species' envelopes shrink, others' are expanding, particularly those of invasive species and often at significant economic and ecological cost.

The Nature study focuses on the velocity at which species will need to migrate. It deliberately steers clear of looking at the effects on specific species, says Scott Loarie, a co-author of the report. But he agrees that the disturbances in ecosystems pointed out in the study could open the door to expanded ranges for invasive species.

"We know invasive species can capitalize on these disturbances," Loarie says.

As ecosystems are transformed, he says, "weedy-type species might be able to adapt and expand better than the original species."

"In Australia, temperatures have risen the most at the highest altitudes, and these are the places where invasive species have multiplied the most," says Tim Low of the Australia-based Invasive Species Council. "In the Australian Alps, introduced foxes, rabbits, hares, house mice, horses and weeds have all increased either in numbers or in range."

"The foxes are a real concern," Low adds, explaining that the Bogong moths that used to be a major food source for foxes are migrating to the mountains later in the season due to changing temperatures. This means foxes are preying on other species, such as the endangered mountain pygmy possum (top photo), which also rely on the moths for food and are now forced to spend more time in the open searching for food.

"Often it will be the combination of climate change and [invasive] pests operating together that will wipe species out," says Low.

It is not just invasive species that are benefiting from a changing climate at the expense of humans and other species. Another recent study has found what many have predicted and seen elsewhere — temperatures have increased 2 degrees Celsius in the Kenyan Central Highlands over the last 20 years, allowing malaria-causing parasites to spread to higher altitudes on the slopes of Mount Kenya.

In the oceans, changing oxygen and temperature levels are forcing — or allowing — species to move into new waters. Giant Nomura's jellyfish in the Eastern Pacific, for instance, have expanded their range, spoiling fishing boats' hauls off Japan.

Humboldt squid (right), a large mollusk normally found off the coast of Baja California first moved north over a decade ago, but now appear to have taken up permanent residence in the traditionally colder waters off California and Oregon. Fishermen worry the squid will cut into fish stocks, though others welcome the calamari windfall.

Oceans and waterways are thought to be likely the first to experience the dramatic effects of climate change on their biological populations, and this contention is supported by another recent study.

Researchers at NASA's Jet Propulsion Laboratory, in attempting to quantify warming trends in six Northern California and Nevada lakes, found that lake surface temperature is warming faster than that of the surrounding air. Their 18 years' worth of data from satellite sensors indicates that, on average, surface water has warmed at twice the rate of the air in the region.

One potential fallout of this trend is a more hospitable environment for invasive species, like the Asian clam that first appeared in California's Lake Tahoe at the beginning of this decade but which is now prevalent enough that its waste has caused algae blooms in the lake's tourist-drawing crystal waters.

On the other side of the globe, river flows are decreasing in West Africa due to less precipitation at their sources, a result of climate change. This has allowed the South American native water hyacinth to prosper. The hyacinth clogs rivers and water intakes, blocks sunlight, and crowds out native species.

Plants like serrated tussock have invaded grazing land in Australia and elsewhere, pushing out the native grasses livestock depend on with devastating speed.

And the mountain pine beetle, aided by milder winter temperatures, is devastating British Columbia forests. Changing temperatures have also allowed the beetle to move to higher latitudes. It is expected to kill almost 80 percent of pine in the province by 2015.

The list goes on.

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