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The University of Roehampton study that the seeds of some trees on Madagascar could be dispersed only through the droppings of a species of lemur (Campus round-up, 8 September) reminded me of an observation many years ago that the extinction of the dodo on Mauritius almost led to the loss of a particular tree (Calvaria major) as its seeds were apparently fertile only after passing through the animal.

Not only do such observations amuse my students, they also serve as excellent examples of how fragile ecosystems can be.

Peter Baker, London