TOEFL Listening Lecture | Ecosystems – YouTube Dictation Transcript & Vocabulary

1.[Music] nature's ecosystems are delicate and the species that inhabit them are closely interrelated while we can learn valuable lessons by studying natural processes man's careless intervention can have negative consequences for the environment gary jenkins reports macquarie island is located about halfway between australia and antarctica it was once an uninhabited island with a unique ecosystem but the arrival of europeans resulted in widespread destruction to the flora and fauna of this designated world heritage site ecologist dr stella burnham is here to tell us about how this ecological disaster came about to understand the scale of the disaster we must first look at the history of macquarie island it was discovered in 1810 when traders came on sailing ships to hunt seals there when rodents on the ship started eating up the crew's food supplies the sailors introduced cats as a predator unfortunately they escaped the ships and reached the island later with rodents eating the ship's supplies rabbits were introduced and released onto the island by the sailors as an alternative food source for the crew over time the rabbit population expanded dramatically eventually they fell prey to the cats that helped to keep their numbers down but not before causing significant damage to the island's plant life why because rabbits are herbivores in 1968 as a means of protecting the island's remaining flora scientists introduced nyximatosis a disease fatal to rabbits as a result the rabbit population plummeted from 130 000 in 1978 to less than 20 000 within a decade and the island's vegetation recovered the problem is though that species are interdependent so as the rabbit population declined cats looked for new prey and this had major repercussions for the island's ecosystem yes it did because the cats began hunting the island's native birds that nest in the ground eventually measures were taken to save the native species of birds a cat eradication program began in 1985 and the last cat was killed in the year 2000 however mixomatosis had failed to keep the numbers of rabbits in check and now with its major predator the cat eliminated the rabbit population soared satellite images show that rabbits have reduced large areas of complex vegetation to short grazed lawns or bare ground by 2007 the threat to some protected valleys and slopes was serious our estimations indicate nearly 40 percent of the island area has undergone a change so you can see that invasive species in this case the cat and the rabbit including extinction in extreme cases there is ecosystem meltdown or total collapse that's why we sometimes have to eliminate an alien species what happened here is an example of trophic cascades the domino effect on the food chain caused by changes in the numbers of species when one species becomes abundant it can eat another's food supply feed on another species plant or animal or devastate local flora which in turn affects more species in the chain our studies show there is also a link between trophic cascades and the removal of an invasive species you see removing the cat for example also adversely affected other ecosystems the birds recovered but the rabbit population soared and then vegetation suffered so the advantages gained by removing the invader may be lost because another species can thrive on macquarie island ecosystems have been destroyed and years of conservation work to save its vegetation are threatened so what do we learn from the events on macquarie island clearly human intervention in ecosystems must be viable and comprehensive this implies that we must evaluate not only the benefits but also the potential risks of human interference so as to avoid repeating past mistakes that can cost millions of dollars to put right if they can be corrected at all number one why does dr burnham discuss the case of macquarie island number two why was mixomatosis introduced by scientists number three what was the effect of wiping out the cats number four why is the removal of an alien species dangerous number five what do we learn from the research on macquarie island [Music] it was once an uninhabited island with a unique ecosystem but the arrival of europeans resulted in widespread destruction to the flora and fauna of this designated world heritage site in 1968 as a means of protecting the island's remaining flora scientists introduced nyximatosis a disease fatal to rabbits as a result the rabbit population plummeted from 130 000 in 1978 to less than 20 000 within a decade and the island's vegetation recovered however mixomatosis had failed to keep the numbers of rabbits in check and now with its major predator the cat eliminated the rabbit population soared what happened here is an example of trophic cascades the domino effect on the food chain caused by changes in the numbers of species our studies show there is also a link between trophic cascades and the removal of an invasive species clearly human intervention in ecosystems must be viable and comprehensive this implies that we must evaluate not only the benefits but also the potential risks of human [Music] interference [Music] [Applause] [Music] [Music] [Music] [Music] [Music] [Applause] [Music] you