Heres how ants became the most successful invasive species

December 19th, 2007 - 2:18 pm ICT by admin  

Washington, December 19 (ANI): A consortium of researchers from the University of Illinois and the University of California at San Diego has shed light on how the Argentine ant Linepithema humile became one of the most successful invasive species in the world, and colonized parts of five continents besides its native range in South America.

The researchers say that the Argentine ants traits like being tiny, aggressive, and adaptable have helped it in its transit around the world.

Once seen only in South America, the ant is now found in parts of Asia, Australia, Europe, North America and South Africa. According to the researchers, it most likely made its way to these destinations on ships carrying soil or agricultural products.

They also say that under the right conditions, the Argentine ant marches through a new territory, wipes out most of the native ants and many other insects by eating and out-competing them, and thereby radically alters the ecology of its new home.

University of Illinois entomology professor Andrew Suarez, principal investigator on the study, says that the Argentine ant thrives in a warm climate with abundant water and is often found on agricultural lands or near cities, but it also invades natural areas.

In previous research, Suarez has shown that the ant is highly social, and sometimes forms immense super-colonies made up of millions workers spread over vast territories. That time he identified a super-colony in California that stretched from San Diego to San Francisco.

In the new study, Suarezs team followed an invasion wave of Argentine ants across Rice Canyon, in southern California. They tracked the invasion for eight years, collecting data on conditions before and during the invasion.

Rather than comparing an invaded to a non-invaded community, which may be different for all sorts of other reasons, we try to follow an invasion front in real time to document what this invader is doing, Suarez said.

The researchers used a technique called stable isotope analysis to determine what the ants were eating. Measuring the ratio of heavy to light isotopes (molecular weights) of nitrogen in all members of an ecological community enabled them to determine whether a particular organism was primarily a carnivore or herbivore.

As a matter of surprise, the Argentine ants behaved much as they did in their own home ranges in the early stages of invasionbeing carnivores, aggressively attacking and probably eating most of the other ants they encountered. However, as they displaced the native species, they began foraging lower on the food chain.

The researchers also discovered that the ants were taking over an important food sourcethe honeydew excretions of aphids and scale insects that feed on plants.

These are really important, often fixed resources, from which ants can get a huge amount of their carbohydrate fuel, the energy to fuel their worker force. As the native ants are displaced, the Argentine ants start monopolizing these resources, Suarez said.

He further said that the impact on the natives was disastrous, as over a period of eight years, the number of native ant species in the study area decreased from 23 to two.

Suarez stressed the need for more long-term studies of native and non-native species, instead of the more common and short-term studies that see only a fragment of the bigger puzzle.

The way the invasive species are interacting with the environment might actually be changing over time, Suarez said.

He said that only by following an invasion over time, the researchers could begin to understand the dynamics that allowed alien species to win out over the natives.

The study has been reported in the Proceedings of the National Academy of Sciences. (ANI)

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