NATURE'S SCIENCE NURTURE

HIPPOS in South America are filling a huge hole.

When the Colombian drug kingpin Pablo Escobar died in 1993, his four African Hippos were forgotten. But field and ponds along the the Magdalena River, in a landscape that never had real before, suited them.

Their population as many as 80 animals now, could reach 5,000 by 2050.

Other herbivores are showing up in unexpected places, In Australia, feral camels roam the outback. Antelope are common sight in rangelands from Texas to Patagonia. And feral hogs are everywhere.

Conventional wisdom holds that these animals are causing new, and damaging, problems for ecosystems. But a new study argues that the lifestyles of these creatures may be restoring the ecological functions of species lost to extinction during the last ice age.

Beginning 100,000 years ago, extinctions claimed many large animals. Researchers suspected the loss these megafauna may have left holes in the food webs and other cycles of the ecosystems where they lived, particularly the Americas and Australia.

''We found that, amazingly, the world is more similar to the pre-extinction past when introduced species are included,'' said the ecologist Erik Lundgren, the study's lead author. [Asher Elbein]

VAMPIRES : Sharing The Feast.
At the dinner table, vampire bats make sure their friends don't go hungry.

Vampire bats don't have the best reputation. And despite the value of hats and their great variety - they make up about a quarter of all mammal species - not everyone loves them.

But bats are not like Dracula, nor any of his fellow blood friends. Vampire bats are, in fact, the soul of cooperation. Like good toddlers, they have learned to share. For the bats their lives depend on it.

IF a vampire bat drinks from a cow's ankle one night, it is likely to share that meal with another bat.

Vampire bats usually share what they've drunk with other members of their female-led families. But they also extend the blood-sharing habit no other bats that they create close bonds with, even though they have nothing common genetically.

Gerald Carter, a behavioral ecologist at Ohio State University who studied cooperation in vampire bats, reported in Current Biology that an experiment in his lab showed that bats build friendships gradually, as other bats show they are reliable. [James Gorman]

The honor and serving of the latest research on Tipping Ecological Scales, continues. The World Students Society thanks the authors.