ScienceDaily (Oct. 27, 2011) — The mere presence of a predator causes enough stress to kill a dragonfly, even when the predator cannot actually get at its prey to eat it, say biologists at the University of Toronto.
"How prey respond to the fear of being eaten is an important topic in ecology, and we've learned a great deal about how these responses affect predator and prey interactions," says Professor Locke Rowe, chair of the Department of Ecology and Evolutionary Biology (EEB) and co-principal investigator of a study conducted at U of T's Koffler Scientific Reserve.
"As we learn more about how animals respond to stressful conditions -- whether it's the presence of predators or stresses from other natural or human-caused disruptions -- we increasingly find that stress brings a greater risk of death, presumably from things such as infections that normally wouldn't kill them," says Rowe.
Shannon McCauley, a post-doctoral fellow, and EEB professors Marie-Josée Fortin and Rowe raised juvenile dragonfly larvae (Leucorrhinia intacta) in aquariums or tanks along with their predators. The two groups were separated so that while the dragonflies could see and smell their predators, the predators could not actually eat them.
"What we found was unexpected -- more of the dragonflies died when predators shared their habitat," says Rowe. Larvae exposed to predatory fish or aquatic insects had survival rates 2.5 to 4.3 times less than those not exposed.
In a second experiment, 11 per cent of larvae exposed to fish died as they attempted to metamorphose into their adult stage, compared to only two per cent of those growing in a fish-free environment. "We allowed the juvenile dragonflies to go through metamorphosis to become adult dragonflies, and found those that had grown up around predators were more likely to fail to complete metamorphosis successfully, more often dying in the process," says Rowe.
The scientists suggest that their findings could apply to all organisms facing any amount of stress, and that the experiment could be used as a model for future studies on the lethal effects of stress.
The research is described in a paper titled "The deadly effects of 'nonlethal' predators," published in Ecology and highlighted in Nature this week. It was supported by grants to Fortin and Rowe from the Canada Research Chairs program and the Natural Sciences and Engineering Research Council of Canada, and a post-doctoral fellowship awarded to McCauley.
http://www.sciencedaily.com/releases/2011/10/111027125241.htm
Showing posts with label naural predators. Show all posts
Showing posts with label naural predators. Show all posts
Sunday, October 30, 2011
Monday, October 10, 2011
Trust turns to eels in war against US crayfish
THE battle against invading American signal crayfish is being stepped up in one of Scotland's biggest lochs.
Millions of crayfish have infested picturesque Loch Ken, north of Castle Douglas in Dumfries and Galloway, and efforts to control their numbers have failed.
Now thousands of European eels, which eat crayfish, are being introduced into a river that runs into the loch in the hope that they will reduce the population.
Fishing in the loch, the biggest in the south of Scotland, has been badly hit by the infestation of the American crayfish, costing the region tens of thousands of pounds.
The Galloway Fisheries Trust, which is behind the project to introduce the baby eels, believes that once they are fully grown the eels will leave the River Dee for the loch, where they are expected to devour large numbers of crayfish.
Rownan Armstrong, a biologist with the Galloway Fisheries Trust, said: "The eels are still young and it will take time for them to grow."
The loch and the River Dee used to be home to a healthy population of the eels, but following the construction of Tongland Dam, near Kirkcudbright, the numbers fell dramatically.
But now eels are being trapped below the dam and are being transported above it and placed in small burns in the lower river.
A Scottish Government-backed cull of the invading crayfish resulted in the deaths of two million two years ago, but it has made little impression on the fast-growing American species, which was introduced to the United Kingdom 20 years ago.
http://scotlandonsunday.scotsman.com/nature/Trust-turns-to-eels-in.6850154.jp
Now thousands of European eels, which eat crayfish, are being introduced into a river that runs into the loch in the hope that they will reduce the population.
Fishing in the loch, the biggest in the south of Scotland, has been badly hit by the infestation of the American crayfish, costing the region tens of thousands of pounds.
The Galloway Fisheries Trust, which is behind the project to introduce the baby eels, believes that once they are fully grown the eels will leave the River Dee for the loch, where they are expected to devour large numbers of crayfish.
Rownan Armstrong, a biologist with the Galloway Fisheries Trust, said: "The eels are still young and it will take time for them to grow."
The loch and the River Dee used to be home to a healthy population of the eels, but following the construction of Tongland Dam, near Kirkcudbright, the numbers fell dramatically.
But now eels are being trapped below the dam and are being transported above it and placed in small burns in the lower river.
A Scottish Government-backed cull of the invading crayfish resulted in the deaths of two million two years ago, but it has made little impression on the fast-growing American species, which was introduced to the United Kingdom 20 years ago.
http://scotlandonsunday.scotsman.com/nature/Trust-turns-to-eels-in.6850154.jp
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