|MadSci Network: Evolution|
You asked about the effects on animal evolution of human activities, a very broad question indeed.
The big picture, as you put it, is very hard to see. For example, although humans undoubtedly helped to cause the total extinction of the passenger pigeon in the early years of the 20th century, there is no good evidence that this affected anything else. http://www.ris.net/~tony/ppige on.html
In other cases, there does seem to be an effect. You asked about the dodo, a large, flightless bird related to pigeons. It lived on the island of Mauritius, and was hunted to extinction by sailors who ate all the dodos they could catch. The last one was apparently killed in 1681. Recently, scientists noticed that a tree called Calvaria major also seemed to be going extinct on Mauritius. Most of the trees seemed to be about 300 years old, and there were no new seedlings. Experiments showed that the seeds of Calvaria needed to have their tough coat removed before they could germinate. Dodos probably ate the seeds of Calvaria, which were then damaged by the stones in the birdís crop and by passing through the digestive system. Without dodos, the trees were on the way to extinction. Scientists fed Calvaria seeds to turkeys, which are a little like dodos, and those seeds germinated. So now there are young Calvaria trees on Mauritius again. http://www.baghee ra.com/inthewild/ext_dodobird.htm
In this case the extinction of the dodo, caused by people, was having an effect. But other people, with the help of turkeys, are making sure the Calvaria trees survive, at least for now.
There are other examples where the extinction of an animal has changed the survival of other animals and plants, but none as clear as the story of the dodo and Calvaria.
I hope that helps.
Science Writer, International Plant Genetic Resources Institute.
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