Magazine article Ecos

Quokka Defence. (Journal Extracts)

Magazine article Ecos

Quokka Defence. (Journal Extracts)

Article excerpt

MANY animals form groups and, Like humans, their behaviour tends to change as group size increases. Typically, individuals in a group of animals forage more and become less vigilant as group size increases. This is usually attributed to a reduction in the per capita risk of predation in larger groups. But what happens when a population becomes isolated from predators? Does their inherited behaviour in relation to group size change?

Dr Daniel Blumstein of the University of California Los Angeles and the Marsupial CRC, Sydney, and his colleagues, have been studying the evolution of group-size effects in macropodids (kangaroos, wallabies and rat kangaroos). They were interested in the quokkas of Rottnest Island, off Western Australia, because these small, wallaby-like marsupials have been virtually free of predation for about 7000 years. Mainland quokkas also occur, but are endangered.

The researchers were keen to find out how the toss of predators has influenced the benefit to individuals of forming groups.

They found that, despite tong isolation from predators and therefore relaxed natural selection, quokkas showed typical group-size effects. They foraged more and looked around less as group size increased. The scientists think that the observed group-size effects must, at least partly, result from factors other than anti-predator benefits.

The quokkas did retain some anti-predator behaviour in that they remained sensitive to the distance from cover and to the time of day when foraging. …

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