Invasive predators more harmful to biodiversity than native predators
March 20, 2007
Analyzing prey response across dozens of field experiments in New Zealand, Australia, and island ecosystems, an international team of researchers led by Pälvi Salo of the University of Turku in Finland found that alien predators have twice the impact as native predators on prey populations. Surprisingly, the research also showed that alien predators in mainland areas had a greater impact than in island environments, though the researchers say this finding may be biased by a large amount of data from Australia.
The authors cite a number of possible factors for the difference in effectiveness between indigenous and alien predators.
A lemur's potential response to predators. Photo by Rhett A. Butler.
While not a subject in the Salo study, lemurs have been significantly impacted by the invasion of alien predators: most notably humans, but also Indian civet, mongoose, cats, and dogs. Dozens of species of lemurs have gone extinct since mankind first set foot on the island.
The authors look specifically at Australia, where many of their experimental studies were based.
"Recent research shows that Australia has also possessed a rich assemblage of marsupial carnivores from Miocene to recent times... and that the native fauna may not be as predator naive as previously thought," they write. "However, Australia never had placental carnivores until they were introduced by humans, and it may be that these novel predators use tracking and hunting tactics that differ from those of their marsupial counterparts, to which native prey have little or no defence."
The researchers say that while "alien predators have long been presumed to have greater impacts in island ecosystems when compared with the mainland ecosystems... [they] found no support for such phenomena."
"In these analyses, Australia was considered mainland; but despite its large size, Australia's island-like characteristics, such as geographical isolation and diversity of endemic species, may also have contributed to the profound impacts of alien predators there," they explain.
Wallaby in Australia. Photo by Nancy Butler.
Overall the results bolster the contention that invasive species can have a detrimental impact on biodiversity. Biologists elsewhere argue that alien invasives are among the greatest threats to global biodiversity.
CITATION: Pälvi Salo, Erkki Korpimäki, Peter B. Banks, Mikael Nordström, and Chris R. Dickman (2007). Alien predators are more dangerous than native predators to prey populations. Proceedings of the Royal Society B: Biological Sciences. March 20, 2007. DOI: 10.1098/rspb.2006.0444
Biodiversity extinction crisis looms says renowned biologist. Few people know more about extinction than Dr. Peter Raven, director of the Missouri Botanical Garden. He is the author of hundreds of scientific papers and books, and has an encyclopedic list of achievements and accolades from a lifetime of biological research. These make him one of the world's preeminent biodiversity experts. He is also extremely worried about the present biodiversity crisis, one that has been termed the sixth great extinction, following the earlier events caused variously by catastrophic climate change, extraterrestrial collisions, atmospheric poisoning, and hyperactive volcanism. Unlike these older episodes, the current extinction event is one of our own making, fueled mainly by habitat destruction and exploitation of certain species. Further, as Raven points out, because the planet has more species now than at any time in the past, a mass extinction today could well involve more species than ever before.
Feral beasts threaten lemurs in Madagascar. The lemurs of Madagascar are among the world's most threatened primates. Extensive habitat destruction, hunting, and the introduction of alien species have doomed dozens of species to extinction since humans first arrived on the island within the past 2000 years. Most of the casualties were Madagascar's largest lemurs -- today the biggest lemur is but a fraction of the gorilla-sized giants that once ruled the island.